***Useful Information for Apprentices***

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“ General Health and Safety at Work “

Question 1.1
What do the letters CDM stand for ?
A: Control of Demolition and Management Regulations
B: Control of Dangerous Materials Regulations
C: Construction (Demolition Management) Regulations
D: Construction (Design and Management Regulations ) Answer: D )
Question 1.2
Identify one method of enforcing regulations that are
available to the Health and Safety Executive:
A: Health Notice
B: Improvement Notice
C: Obstruction Notice
D: Increasing insurance premiums
Answer: B Improvement notices require action to achieve standards which meet health and safety law :
Question 1.3
What happens if a Prohibition Notice is issued by an
Inspector of the local authority or the HSE ?
A: The work in hand can be completed, but no new work started
B: The work can continue if adequate safety precautions are put in place
C: The work that is subject to the notice must cease
D: The work can continue, provided a risk assessment is carried out,
Answer: C The work covered by a prohibition notice must cease until the identified danger is removed.
Question 1.4
Health and Safety Executive Inspector can ?
A: Only visit if they have made an appointment
B: Visit at any time
C: Only visit if accompanied by the principal contractor
D: Only visit to interview the site manager
Answer: B Inspectors have a range of powers, including the right to visit premises at any time.
Question 1.5
A Prohibition Notice means:
A: When you finish the work you must not start again
B: The work must stop immediately
C: Work is to stop for that day only
D: Work may continue until the end of the day
Answer: B The work activity covered by the prohibition notice must cease, until the identified danger is removed ,
Question 1.6
In what circumstances can an HSE Improvement Notice be issued ?
A: If there is a breach of legal requirements
B: By warrant through the police
C: Only between Monday and Friday on site
Answer: A Improvement notices require action to achieve standards which meet health and safety law .
Question 1.7
What is an “Improvement Notice”?
A: A notice issued by the site principal contractor to tidy up the site
B: A notice from the client to the principal contractor to speed up the work
C: A notice issued by a Building Control Officer to deepen foundations
D: A notice issued by an HSE/local authority Inspector to enforce compliance with health
Answer: D Improvement notices require action to achieve standards which meet health and safety law .
Question 1.8
If a Health and Safety Executive Inspector issues a“ Prohibition Notice”, this means that:
A: the Site Manager can choose whether or not to ignore the notice
B: specific work activities, highlighted on the notice, must stop
C: the HSE must supervise the work covered by the notice
D: the HSE must supervise all work from then on
Answer: B Prohibition notices are intended to Stop activities which can cause serious injury.
Question 1.9
Which one of the following items of information will you find on the Approved Health and Safety Law poster?
A: Details of emergency escape routes
B: The location of the local HSE office
C: The location of all fire extinguishers
D: The identity of the first aiders
Answer: B The poster also lists the persons with health and safety responsibilities, but not first aiders.
Question 1.10
Who is responsible for signing a Company Safety Policy ?
A: Site Manager
B: Company Safety Officer
C: Company Secretary
D: Managing Director
Answer: D The Health and Safety at Work Act requires the most senior member of management to sign the health and safety policy
statement.

Question 1.11
Which one of the following must be in a company’s written Health and Safety Policy:
A: Aims and objectives of the company
B: Organisation and arrangements in force for carrying out the health and safety policy
C: Name of the Health and Safety Adviser
D: Company Director’s home address
Answer: B This requirement appears in the Health and Safety at Work Act.
Question 1.12
Employers have to produce a written Health and Safety Policy statement when:
A: A contract commences
B: They employ five people or more
C: The safety representative requests it
D: The HSE notifies them
Answer: B This is a specific requirement of the Health and Safety at Work Act.
Question 1.13
Companies employing five or more people must have a written Health and Safety Policy because:
A: The principal contractor gives them work on site
B: The HSAWA 1974 requires it
C: The Social Security Act requires it
D: The trade unions require it
Answer: B
Question 1.14
What do the letters HSC stand for ?
A: Health and Safety Contract
B: Health and Safety Consultant
C: Health and Safety Conditions
D: Health and Safety Commission Answer: D
Question 1.15
Which ONE of the following statements is correct ? The Health and Safety Executive is:
A: a prosecuting authority
B: an enforcing authority
C: a statutory provisions authority
Answer: B The Health and Safety Executive enforces health and safety legislation.
Question 1.16
The Health and Safety at Work Act requires employers to provide what for their employees?
A: Adequate rest periods
B: Payment for work done
C: A safe place of work
D: Suitable transport to work
Answer: C This is a specific requirement of Section 2 of the Health and Safety at Work Act.
Question 1.17
The Health and Safety at Work Act 1974 and any regulations made under the Act are:
A: Not compulsory, but should be complied with if convenient
B: Advisory to companies and individuals
C: Practical advice for the employer to follow
D: Legally binding Answer: D
Question 1.18
Under the Health and Safety at Work Act 1974, which of the following have a duty to work safely?
A: Employees only
B: The general public
C: Employers only
D: All people at work
Answer: D Employers, employees and the self-employed all have a duty to work safely under the Act.
Question 1.19
What is the MAXIMUM penalty that a Higher Court, can currently impose for a breach of the Health and Safety at Work Act?
A: £20,000 fine and two years imprisonment
B: £15,000 fine and three years imprisonment
C: £1,000 fine and six months imprisonment
D: Unlimited fine and two years imprisonment
Answer: D A Lower Court can impose a fine of up to £20,000 and/or up to six months imprisonment for certain offences. The potential fine in a Higher Court, however, is unlimited and the term of imprisonment can be up to 2 years.
Question 1.20
What do the letters ACoP stand for ?
A: Accepted Code of Provisions
B: Approved Condition of Practice
C: Approved Code of Practice
D: Accepted Code of Practice
Answer: C An ACOP is a code of practice approved by the Health and Safety Commission.

Question 1.21
Where should you look for Official advice on health and safety matters?
A: A set of health and safety guidelines provided by suppliers
B: The health and safety rules as laid down by the employer
C: Guidance issued by the Health and Safety Executive
D: A professionally approved guide book on regulations
Answer: C The HSE is the UK enforcing body and its guidance can be regarded as ‘official’
Question 1.22
Regulations that govern health and safety on construction sites:
A: apply only to inexperienced workers
B: do not apply during ’out of hours’ working
C: apply only to large companies
D: are mandatory ( that is, compulsory )
Answer: D The requirements of health and safety law are mandatory, and failure to follow them can lead to prosecutions.
Question 1.23
Which of the following statements is correct ?
A: The duty for health and safety falls only on the employer
B: All employees must take reasonable care, not only to protect themselves but also their colleagues
C: Employees have no responsibility for Health and Safety on site
D: Only the client is responsible for safety on site
Answer: B The responsibility for management of Health and Safety Act at Work rests with the employer
Question 1.25
Which of the following is correct for risk assessment?
A: It is a good idea but not essential
B: Only required to be done for hazardous work
C: Must always be done
D: Only required on major jobs
Answer: C There is a legal requirement for all work to be suitably risk assessed.
Question 1.26
In the context of a risk assessment, what do you understand by the term risk?
A: An unsafe act or condition
B: Something with the potential to cause injury
C: Any work activity that can be described as dangerous
D: The likelihood that harm from a particular hazard will occur
Answer: D Hazard and risk are not the same. Risk reflects the chance of being harmed by a hazard
Question 1.27
Who would you expect to carry out a risk assessment on your working site?
A: The site planning supervisor
B: A visiting HSE Inspector
C: The construction project designer
D: A competent person
Answer: D A risk assessment must be conducted by a 'competent person’.
Question 1.28
What is a HAZARD ?
A: Where an accident is likely to happen
B: An accident waiting to happen
C: Something with the potential to cause harm
D: The likelihood of something going wrong
Answer: C Examples of hazards include: a drum of acid, breeze blocks on an elevated plank; cables running across a floor.
Question 1.29
What must be done before any work begins ?
A: Emergency plan
B: Assessment of risk
C: Soil assessment
D: Geological survey
Answer: B This is a legal requirement of the Management of Health and Safety at Work Regulations.
Question 1.30
Complete the following sentence: A risk assessment
A: is a piece of paper required by law
B: prevents accidents
C: is a means of analysing what might go wrong
D: isn’t particularly useful
Answer: C Risk assessment involves a careful review of what can cause harm and the practical measures to be taken to reduce the risk of harm.

 

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method when installing cable on insulation ?

Reference methods 100 and 101 refer to twin & earth (T/E) cable installed within various thickness of insulation. What reference method should I use when cable is installed on top of any insulation ?

Regulation 523.7 of BS-7671 requires that, where a cable is to be run in a space to which thermal insulation is likely to be provided, the cable is - wherever practicable - to be fixed in a position where it will not be covered by the thermal insulation.

the cable would appear to be in contact with thermal insulation on one side only. Therefore, if there is free air on the remaining sides of the cable, reference method 'C' for either Table 4D2A or Table 4D5 would be appropriate.

BS5803-5:1985
Thermal insulation for use in pitched roof spaces in dwellings. Specification for installation of man-made mineral fibre and cellulose fibre insulation

Thermal insulating materials, Roof spaces, Pitched roofs, Domestic facilities, Man-made fibres, Mineral fibres, Cellulose, Fibres, Installation, Sheet materials, Pellets, Beads, Particulate materials, Thermal insulation, Water storage cisterns, Pipes, Ven
Cross references :
BS 874, BS 3533, BS 3589, BS 5250, BS 5422, BS 5803art 1, BS 5803art 2, BS 5803art 3, BS 7671, PD 6501art 1

Loft Insulating Materials
Mineral fibre or fibreglass matting is usually available in rolls 400mm (16in) wide. Thicknesses range from 100mm (4 in) to 200mm (8 in). In the UK, the total thickness of insulation should be at least 200mm (8in), the thinner insulation material available allow for old, thinner loft insulation to be overlaid to achieve the 200mm. Roll insulation

Sheep’s Wool insulation is a general purpose natural wool fibre product designed for use in loft, rafter, internal wall and inter-floor applications. It is specifically constructed to match and surpass the Part L Building Standards with reference to Thermal, Fire, Mould Resistance and Structural performance.

 

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COLD BENDING 20-25MM CONDUIT

This may be carried out on all conduit sizes up to25mm in diameter using the correct size and gauge of bending spring. It should be noted that the heavy gauge spring is colour banded green and the light gauge spring colour banded white near the tip of the spring. These springs are not interchangeable under any circumstances. Make sure they are not damaged in any way as this can cause the conduit to kink and fracture making removal of the spring difficult.(In cold weather the Conduit should be warmed by rubbing with a rag or some other suitable means before bending.)

To bend the conduit insert the spring to the desired position, grip the conduit on either side of the
bend and bring slowly together to form the bend. The bend should be made more acute than necessary because of the tendency of the PVC-U to ‘recover’ after bending. To remove the spring twist in an anti-clockwise direction which will reduce its in an anti-clockwise direction which will reduce its diameter. At the same time turn the conduit in a
clockwise direction gently pulling the spring and conduit apart. If the spring fails to release during this operation do not pull too hard otherwise damage to the spring may occur. Repeat the removal procedure turning the spring again in an
anti-clockwise direction and rotating the conduit clockwise slowly pulling them apart. The conduit
should then be fastened into position to prevent further ‘recovering’ of the bend.

HOT BENDING

This should be carried out on all conduit above25mm diameter using the correct size and gauge of
bending spring. Insert the bending spring into the conduit as previously described, gently heating the
conduit with a hot air torch, hot water or by other suitable means, with care being taken to avoid the
direct application of a flame to the conduit. When the conduit is in a pliable state, slowly bend around a suitable former, holding in position for about one minute until set when the bending spring may then be removed by twisting in an anticlockwise direction and gently withdrawing from the conduit. If the conduit is bent too fast or, particularly in the
case of light gauge across the knee, there is a risk of damage to both the conduit and spring. Similarly
once the bend has been made it should not be forced backwards but allowed to recover naturally.

JOINTS AND COUPLERS

To accommodate for thermal movement due to temperature change (Materials Data) on surface installations, it is recommended that expansion
couplings be used at a maximum distance of 6m intervals. Where high ambient temperatures or frequent variations in temperature are likely to occur this distance should be reduced. Expansion couplers are installed with the →→ short side coated with solvent cement ←← and the coupler pushed firmly over the conduit down to the shoulder. The slip side coated inside with lubricant sealant receives the conduit to a midpoint to the nib. This will then permit expansion or contraction providing the conduit is free to move in the saddles.

Conduit fittings are installed in the system using solvent cement (MSC20) for permanent installations and lubricant sealant (MSC1) where the installation is subject to frequent changes.

Straight runs exceeding 3 metres, or runs of any
length incorporating bends or sets. The term ‘bend’ signifies a British Standard 90º bend and one double set is equivalent to one bend.

Conduit / Following cable factors :

O.S.G ( table 5C ) 16 for 1mm2 , 30 for 2.5mm2 & 58 for 6mm2
Cf : ( 8 x 16 ) + ( 4 x 30 ) + ( 2 x 58 ) = 128 + 120 + 116 = 364

the term “ bend “ means a right angle bend or left angle or double set ,

O.S.G ( table 5D ) gives a conduit factor for 20mm conduit 6m long with double set as 233 ,
Which is less than 364 and thus to small . The next size has a conduit factor of 422 which will be acceptable since it is larger than 364 .

The correct conduit size is 25mm diameter ,

O.S.G ( table 5D ) 10m long Straight 25mm conduit has a factor of 442 . This is too small , so the next size , with a factor of 783 must be used ,
The correct conduit size is 32mm diameter ,

Example :
1.5mm2 Straight length of conduit from a Consumers Unit encloses ten 1.5mm2 & four 2.5mm2 Solid ↔ Conductor P.v.c
Insulated cables , Calculate a suitable Conduit size ,

From O.S.G ( table 5A ) which is for short straight runs of conduit ) total cable factor will be :
1.5mm2 ↔ 10 x 27 + 2.5mm2 ↔ 4 x 39 = 426

From O.S.G ( table 5B ) 20mm diameter conduit with a factor of 460 will be necessary ,

Example :

A length of trunking is to carry eighteen 10mm2 , sixteen 6mm2 , twelve 4mm2 , and ten 2.5mm2 Stranded single P.v.c
Insulated cables , Calculate a suitable trunking size , O.S.G ( table 5E )
18 x 10mm2 at 36.3 = 18 x 36.3 = 653.4
16 x 6mm2 at 22.9 = 16 x 22.9 = 366.4
12 x 4mm2 at 15.2 =12 x 15.2 = 182.4
10 x 2.5mm2 at 11.4 = 10 x 11.4 = 114.0
Total cable factor = 1316.2

From the trunking factor O.S.G ( table 5F )
Two stranded trunking sizes have factors slightly greater than the cable factor , and either could be used ,
They are ( 75mm x 50mm at 1555 ) & ( 100mm x 38mm at 1542 )

CAPACITY EXAMPLE : 5C

Number of cables for a 3.0 metre run with three bends
CONDUIT 20mm dia.
CABLE SOLID 2.5mm2 ( 3 qty )
CABLE STRANDED 4.0mm2 (2 qty )
Term total – ( 30+30+30 )+( 43+43 ) = 176

Note-: It is recommended that a 32 TPI hacksaw blade be used for cutting steel trunking.

Earthing of Steel Trunking

A trunking installation must be earthed. Earth continuity is ensured by the proper tightening of all bolts used throughout the system. Some manufactures recommend that earth continuity be completed by fixing a copper or aluminium strap across all joints. It is more important that all the bolts involved in the system are tightened. It is not unusual to find that copper or aluminium straps are used, but are left loose, resulting in poor earth continuity.

Eddy Currents in Steel Conduit

Metal conduits in which a.c. circuit wiring is installed MUST contain all the current carrying conductors of each circuit in the same conduit, to eliminate the possibility of induced eddy currents. Eddy currents could result in the metal conduit and cables becoming hot.

Some Advantages of Steel Conduit
• Affords cables good mechanical protection
• Permits easy rewiring
• Minimises fire risks.
• Can be utilized as the Circuit Protective Conductor. ( CPC )

Cable Capacity of Steel Conduit ( Space Factor )

Having determined the correct number and cross-sectional area of cables for a given load it is necessary to select the size of conduit that will accomodate them.
If a greater number of cables are installed in the conduit, over-heating, insulation damage and fire may result. As a general rule the number of cables drawn into a conduit should not be such as to cause damage to either the cables or the conduit during the installation.

Termination of Steel Conduit to Enclosures

Two methods of terminating steel conduit are commonly used.
• The coupling and male bush method, (Usually used and preferred)
• The locknut and female bush method, (Used where space is tight)

Jointing Steel Conduit

Where two lengths of conduit are to be joined a plain coupling is used. To ensure good electrical continuity and maximum mechanical strength the tube ends must tighten inside the coupling (Max gap 2 mm) Care must be exercised to do this without leaving threads outside the coupling.
Where neither tube can be turned it is necessary to resort to the technique known as the “running coupling” , After tightening up the lockring the exposed thread must be painted to prevent corrosion.
Expansion of PVC Conduit
Expansion couplings should be used for surface installations at a recommended maximum of 4 metre intervals.
Where frequent variations in ambient temperature are likely to occur this distance must be greatly reduced.

Advantages of PVC Conduit
• Lightweight and easy to handle
• Easy to cut and deburr
• Simple to form and bend
• Does not require painting
• Minimal condensation due to low thermal conductivity in wall of conduit.
• Speed of installation
• Excellent electrical and fire resistant properties

Disadvantages of PVC Conduit

• Care must be taken when glueing joints to avoid forming a barrier across the inside of the conduit.
• If insufficent adhesive is used the joints may not be waterproof.
• PVC expands about 5 times as much as steel and this expansion must be allowed for.
• PVC does not offer the same level of mechanical protection as steel.
• A separate Circuit Protective Conductor must be run inside the conduit.

 

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Ways of assessing Knowledge Evidence:
Questioning
Both verbal and written questioning gives the teacher/tutor the opportunity to gauge the learner’s understanding and allows them to demonstrate their underpinning knowledge. Questioning can be done during feedback sessions and can be used to check whether learners can understand their mistakes when errors are pointed out or to explore in greater depth a situation which has arisen.
• Oral questions
Oral questioning is used to check a learner’s underpinning knowledge of the subject. The learner can be asked questions about a subject which has just taken place or more general questions to check on their knowledge about other topics in which they are involved. If the answers to the oral questioning are to provide final portfolio evidence, concise but clear notes should be made at the time by the assessor. These notes should be signed and dated by the learner and by the assessor for verification purposes.
• Written questions
Written questions could be set in the contexts of task sheets, short tests or homework and can take several forms from short to extended answers. They are a valuable assessment tool to check a learner’s underpinning knowledge as it gives the teacher/tutor the opportunity to ask more searching questions and the learner the opportunity to think about their answers and to do some research if necessary. Once the answers have been assessed, the learner and their assessor have some tangible evidence which can form a basis for discussion and there will be a record of the answers in the portfolio.
• Pre-set questions
These could be set by the assessor as homework, or given under test conditions. In some circumstances, they could also be examination questions set by the Awarding Body. In this case, all learners doing the qualification are being given the same sets of questions in the interests of fairness and standardising assessment practices. A bank of questions may be produced which are used for assessment purposes by all assessors for a standard approach.
• Assessor devised questions
These would generally be set by the teacher/tutor. Some sets of questions may need to be specifically devised to test certain required skills. Other questions can be devised to be used as a learning tool for the learner and an assessment tool for the teacher/tutor. They are valuable in that they allow the teacher/tutor to be responsive to the particular conditions under which the learner is working.

An ammeter inserted in the circuit will record a PLUS and MINUS READING. Which means the current is flowing in the opposite direction.

In most cases many cycles of the waveform occur in one second and the number of
cycles which occur per second is known as the FREQUENCY – Symbol ( f ). Frequency is measured in HERTZ - (Hz).

Time ( mS ) : there are five cycles occurring in one second and hence :- Frequency ( f ) = 5 Hz
Relationship between frequency and period (time):-
( a ) f = 1 – T Hz or ( b ) T – 1 – f sec

Where T is the PERIOD (i.e. the time taken to complete one waveform )

Examples :
1. A waveform has a frequency of 5 Hz, calculate the period of the waveform.
T = 1 – f = 1 – 5 = 0.2 sec
(This means 1 waveform will be traced every 0.2 seconds)
2. If the period of an AC waveform is 5milli seconds , find the frequency
5 milli seconds = 0.0005 seconds
f = 1 – T = 1 ÷ 0.0005 = 200Hz

Exercise :
1. Given the following frequencies, calculate the period of the waveform.
(a) f = 100Hz
(b) f = 5Hz
(c) f = 20Hz
(d) f = 100Hz
(e) f = 1Hz

2. Given the following periods of each cycle calculate the frequency of the waveforms.
(a) T = 0.05 seconds
(b) T = 2 seconds
(c) T = 25 milliseconds
(d) T = 125 milliseconds
(e) T = 5 milliseconds

Power Dissipation :

All components have resistance so when a current flows through them power is dissipated in most cases in the form of heat. It is something to be aware of in the selection of components to be used in a circuit that the power ratings are not exceeded, examples are bulbs and resistors.

Example 1
Find the power dissipated by the bulb ( Resistance of bulb = 100 ohms )
To find the power dissipated in the bulb which has a resistance of 100Ω
If the formula Power = I x V watts is to be used the following data must be known: current flowing through the bulb and voltage across the bulb.
As the 200 Ohms resistor and the lamp are in series then :
R t = 200 + 100 = 300Ω
So now having one voltage and one resistance the current flowing in the circuit can be calculated :
I = V – Rt = 9v ÷ 300 = 0.03 Amps
The voltage across the bulb can be found:
V (bulb) = I x R where R = the resistance bulb and I is the current
Vd = 0.03 x 100 = 3volts
We now have values for both the current through the bulb and the voltage across it.
P = I x V = 0 .03 x 3 = 0 .09W or 90mW.
The power could also be calculated using the formula : Power = V2 – R = 9 ÷ 100 = 0.09 watts

Example 2
In the circuit shown calculate the power dissipated in the 3Ω resistor.
18V / R1 = 4Ω R2 = 6Ω R3 = 3Ω
The first step is to find the total résistance of the circuit.
R2 and R3 are in parallel and this parallel arrangement is in series with R1
To calculate the parallel pair R2 // R3 ( let equivalent resistance = Rv )
Rv = R2 x R3 = 6 x 3 = 18
…….R2 + R3 ….. 6 + 3 ….. 9 = 2 Ω

Circuit now reads R1 and R2 in series.
18V / R1 = 4Ω Rv = 2Ω : R total = R1 + Rv = 4 + 2 = 6Ω

From having one voltage and one resistance the current flowing in the circuit can be found:
18V R total = 6Ω ( I = V – R total = 18 ÷ 6 = 3 Amps

Knowing there is 3Amps flowing in the circuit we can now calculate the voltage across the two resistors in parallel. Remember that their effective resistance is 2Ω

Voltage across parallel block: I x Rv = 2 x 3 = 6volts 18V R1 =4 Ω R2 = 6 Ω R3 = 3Ω V = 6V : Voltage = 6V Résistance = 3 Ω Power dissipated by the resistor : Power = V2 – R = 6 x 6 – 3 = 12 Watts

Exercises :
(a) In the circuit shown the motor has an internal resistance of 10Ω Find the power developed by the motor. ( 20V )
(b) Calculate the power dissipated in the 12Ω resistor. ( 54V / 6Ω 120Ω )
(c) The bulb shown has a filament resistance of 12 ohms. Calculate the output power. ( 45V / 6Ω 120Ω ulb )
(d) In the circuit shown all the bulbs have a resistance of 10Ω. Find the output power B3 : ( 30V / B1 / B2 / B3 )

 

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Ohms Law :

Power = V2 – R or R x I2 or V x I
Voltage = P – I or R x I or √ P x R
Resistance = V – I or V2 – P or P – I2
Current = P – V or V – R or √ P – R

1a) Three resistors are connected in series to a 240 V power supply. One of the resistors is rated at 10 Ω, one at 15 Ω, and the third is unknown. If the current in the circuit is measured to be 4 A, what is the total resistance of the circuit ? ( 60 Ω )

1b) What is the rating of the unknown resistor ? ( 35 Ω )

1c) What is the voltage drop across the unknown resistor ? ( 140 V )


2 ) Four resistors are hooked up in series to unknown power supply. The resistors are rated as follows; 5 Ω, 10 Ω, 20 Ω, and 25 Ω. If the voltage drop across the 10 Ω resistor is measured to be 60 V, what is the rating of the power supply ? ( hint: first find the current in the circuit )( 360 V )

V . R1.R2.R3 ,

V/1 . 120 V. R1 5 Ω . I1 24 A
V/2 . 120 V. R2 10 Ω . I2 12 A
V/3. 120 V. R3 25 Ω . I3 4. 8 A
V total 120V . R total 2.94 Ω . I total 40.8 A
Fill in the rest of the blanks if V total = 120V, R1 = 5 Ω, R2 = 10 Ω, and R3 = 25 Ω

* Ohm’s Law V I R =
(Voltage drop equals current times resistance.)
This is the main equation for electric circuits but it is often misused. In order to
calculate the voltage drop across a light bulb use the formula: V light bulb = I light bulb R light bulb
For the total current flowing out of the power source, you need the total resistance of the circuit and the total
Current : V . total = I total , R total ,

Power is the rate that energy is released. The units for power are Watts (W), which
equal Joules per second [W] = [J]/. Therefore, a 60 W light bulb releases 60 Joules energy every second

The equations used to calculate the power dissipated in a circuit is P. I V =

As with Ohm’s Law,
one must be careful not to mix apples with oranges. If you want the power of the entire circuit, then you multiply the total voltage of the power source by the total current coming out of the power source. If you want the power dissipated (i.e. released) by a light bulb, then you multiply
the voltage drop across the light bulb by the current going through that light bulb

 

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Why measure earth loop impedance ?

Earth loop impedance testing is essential since if a live conductor is accidentally connected to an earth conductor in a faulty appliance or circuit, the resulting short-circuit current to earth can easily be high enough to cause electric shock or generate enough heat to start a fire. Normally, the fuse will blow or another circuit protection device will trip, but a
situation may arise where the actual short-circuit current in a faulty installation is of insufficient level and the protection device would thus take too long to activate. The delay can be disastrous for life and property. It is therefore necessary to know if the impedance of the path that any fault current would take is low enough to allow sufficient current to flow in the event of a fault and that any installed protective device will operate within a safe time limit.

Verifying protection by automatic supply disconnection :

fault loop testing falls under the category of ‘Verifying protection by automatic supply disconnection’.
This covers verification of the effectiveness of protective measures, and the test methods applied depend on the type of system. TT systems, for example, require measurement of the earth electrode resistance for exposed conductive- parts of the installation,
whereas IT systems use calculation or measurement of the first fault current. This application note looks specifically at TN systems, which require measurement of the fault loop impedance and verification of the characteristics of the associated protective device ( i.e. visual inspection of the nominal current setting for circuit-breakers, the current ratings and blow characteristics
for fuses and the correct functioning of RCDs ).

The earth loop impedance of each individual circuit from the point of use back to the incoming supply connection point should be measured.

A separate measurement of the external loop impedance of the installation can also be made at the incoming supply point or main distribution panel and this value will form part of the overall loop impedance from any part of the final circuit installation. Knowing the earth loop impedance, it is possible to calculate the value of the prospective fault current (PFC) at any point in an installation and to ensure that all installed protective devices are of an adequate rating to clear the potential fault current level.

Measuring earth loop impedance :

Since the AC impedance of a circuit may be different from its DC resistance particularly for circuits rated at over
100 A – the fault loop impedance is measured using the same frequency as the nominal mains frequency (50 Hz).
The earth loop impedance test measures the resistance of the path that a fault current would take between line and protective earth. This must be low enough to allow sufficient current to flow to trip a circuit protection device such as a fuse or miniature circuit breaker.

testers can be
used to carry out the test at a distribution board using the three separate test leads supplied, and at appliance
outlets using a dedicated lead fitted with a mains plug. A plug of the appropriate national standard is also

Determining the PFC is important to ensure that the capability of fuses and over-current circuit breakers are not exceeded.

Interpreting results and taking remedial action :

Remember that it is not sufficient just to carry out tests and record the results. Knowledge of Regulations– and of how to interpret results – is also required to ensure the installation’s safety characteristics are within the prescribed limits. An excessive earth loop impedance value should, for example, prompt an investigation into its cause. Remedial be carried out, and the installation action should then retested.

Multifunction Installation Testers have a loop impedance test function in addition to being able to measure
prospective short circuit current (PSC) and fault current (PFC).

Proper use of clamp meters in commercial and residential environments ?

Clamp meters in residential applications;

For residential electricians, clamps are a necessity to measure loads on individual branch circuits at the distribution panel.
While a spot check of current is often sufficient, sometimes it doesn’t provide the full picture as loads are switching on and off, going through cycles, etc. Voltage should be stable in an electrical system, but current can be very dynamic. peak or worst-case loading on To check the a circuit, use a clamp with a min/max function which is designed to catch high currents that exist for longer than 100 ms, or about eight cycles. These currents lead to intermittent overload conditions which can cause nuisance tripping of circuit breakers.
Take measurements on the load side of the circuit breaker load side of the circuit breaker or fuse. The breaker will open the circuit in the event of an accidental short circuit. This is especially important with any kind of direct-contact voltage measurement. Even though
clamp jaws are insulated and therefore have a level of protection that doesn’t exist with direct-contact voltage measurement, it’s still a good idea to be cautious. A common problem in residential electrical work is mapping outlets to breakers.
A clamp can be useful in identifying which circuit a particular outlet is on. First take a baseline reading, at the distribution panel, of the existing current on the circuit. Then put the clamp in min/max mode. Go to the outlet in question, plug in a load—a hair dryer is ideal—and turn it on for a second or two. Check the clamp to see if the max current reading has changed. A hair dryer will typically draw 5 A, so there should be a noticeable difference. If the reading is the same, you’ve got the wrong breaker.

Clamp meters in commercial environments :

Clamp meters are used at the panelboard to measure circuit loading on feeders as well as on branch circuits. Measurements on branch circuits should always be made at the load side of the breaker or fuse.
• Feeder cables should be checked for balance as well as loading: current on all three phases should be more
or less the same, to minimize the return current on the neutral.
• The neutral should also be checked for overloading. With harmonic loads, it’s possible for the neutral to be
carrying more current than a feeder—even if the feeders are balanced.
• Each branch circuit should also be checked for possible overloading.
• Finally the earth circuit should be checked. Ideally there should be no current on the earth,

Testing for leakage currents :

To check if there is leakage current on a branch circuit, put both the live and neutral wires in the jaws of the clamp. Any
current that is measured is leakage current, i.e., current returning on the earth circuit The supply and return currents
generate opposing magnetic fields. The currents should be equal (and opposite) and the opposing fields should cancel
each other out. If they don’t, that means that some current, called leakage current, is returning on another path, and
the only other available path is the earth. If you do detect a net current between the supply and return, consider the nature of the load and the circuit. A mis-wired circuit can have up to half of the total load current straying through the earth system. If the measured current is very high, you probably have a wiring problem. Leakage current may also be caused by leaky loads or poor insulation. Motors with worn windings or moisture in fixtures are common culprits. If you
suspect excessive leakage, a de-energized test using a megohm -meter will help evaluate the integrity of the circuit’s insulation and help identity if and where a problem exists.

Continuity :

Testing the continuity of protective conductors is normally carried out with an instrument being able to generate a no-load voltage in the
range 4 to 24 V (DC or AC) with a minimum current of 0.2 A. The most common continuity test is measuring the resistance of protective
conductors, which involves first confirming the continuity of all protective conductors in the installation, and then testing the main and supplementary equipotential bonding conductors. All circuit conductors in the final circuit are also tested. ( 612.2.1 ) ↔

As Continuity Testing Measures very Low Résistances ,
the resistance of the test leads must be compensated for. a time-saving Auto-Null feature that, by simply touching the test leads together and
pressing the zero button, measures and stores the test lead resistance,

 

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Verifying protection by automatic supply disconnection :

Verification of the effectiveness of the measures for protection against indirect contact by automatic disconnection of supply depends on
the type of system. In summary, it is as follows:

• For TN systems: measurement of the fault loop impedance; and verification of the characteristics of the associated protective device
the associated protective device nominal current setting for circuit breakers, the current ratings for fuses and testing RCDs).

• For TT systems: measurement of the earth electrode resistance for exposed-conductive-parts of the installation; and verification of the
characteristics of the associated protective device (i.e. RCDs by visual inspection and by test).

• For IT systems: Calculation or measurement of the fault current.

Measurement of fault loop impedance :

Measurement of the fault loop impedance is carried out using the same frequency as the nominal frequency of the circuit (50 Hz). The
earth-loop impedance test measures the resistance of the path that a fault current would take between line and protective earth, which must be low
enough to allow sufficient current to flow to trip a circuit protection device such as a MCB (Miniature Circuit Breaker).

Functional test :

All assemblies, such as switchgear and control gear assemblies, drives, controls and interlocks, should be functionally tested to show that they
are properly mounted, adjusted and installed in accordance with the relevant requirements of the standard. Protective devices must be
functionally tested to check whether they are properly installed and adjusted.

Polarity test :

Where regulations forbid the installation of single-pole switching devices in the neutral conductor, a test of polarity must be made to
verify that all such devices are connected in the phase only. Incorrect polarity results in parts of an installation remaining connected
to a live phase conductor even when a single-pole switch is off, or an over-current protection device has tripped.

 

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Where metal conduit is used as a protective conductor, its cross-sectional area shall be determined either by application of the formula of 543.1.4 , or Table 54.7

* AC motor :
A type of electric motor that runs on alternating current. AC motors are more commonly used in industry than DC motors but do not operate well at low speeds.
* alternating current :
Current that regularly reverses the direction of its flow in a repeating, cyclical pattern.
* armature :
The part of a motor or generator in which a current is induced by a magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.
* bearing :
A friction-reducing device that allows one moving part to glide past or rotate within another moving part.
* brush :
A device found inside a generator that is used only in pairs to transfer power from a rotating object. Brushes rest on the commutator of a DC motor.
* capacitor :
An electrical device that stores energy and releases it when needed. A capacitor gives a single-phase motor more torque but has a limited life.
* capacitor motor :
A single-phase motor with a running winding, starting winding, and a capacitor. Capacitor motors have more torque than other single-phase motors.
* capacitor start-and-run motor :
A type of capacitor motor that uses two capacitors, one for starting the motor, and one that remains in the circuit while the motor is running.
* capacitor-run motor :
A type of capacitor motor that has a capacitor and starting winding connected in series at all times.
* capacitor-start motor :
A single-phase motor with a capacitor. The capacitor gives the motor more starting torque.
* centrifugal switch :
A type of switch that operates using the centrifugal force created from the rotating shaft. The centrifugal switch activates and de-activates depending on the speed of the motor.
* direct current :
A current formed when electrons flow in one continuous direction.
* dual voltage motor :
A type of three-phase motor that operates on two voltage levels. Dual voltage motors allow the same motor to be used with two different power line voltages.
* electric motor :
A machine that converts electricity into mechanical energy or motion. An electric motor is a common power source for a mechanical system.
* efficiency losses :
A measure of the energy output versus the amount of input energy. The output energy is typically less than the input energy.
* electromagnetic induction :
The process in which current is induced in a magnetic field using a current-carrying coil. An AC generator produces a current through electromagnetic induction.
* field winding :
The conducting wire connected to the armature that energizes the pole pieces. Field windings are connected in series or parallel.
* generator :
A device that converts mechanical energy into electrical energy by magnetic induction.
* induction motor :
A type of AC motor that uses electrical current to induce rotation in the coils.
* magnet :
A device or object that attracts iron and produces a magnetic field.
* magnetic flux :
The area in and around a magnet that exhibits the powers of attraction and repulsion. Rotating an armature through lines of magnetic flux induces AC.
* motor nameplate :
A plate attached to a motor that displays all of the motor's information
* output shaft :
The rotating part on the AC motor that holds the rotor and allows it to turn.
* phase displacement :
The separation of the three phases in a three-phase motor. The windings are spaced 120º apart.
* reactance :
The resistance to the flow of alternating current due to inductance.
* resistance :
The opposition to current flow. Electricity flows in the path of least resistance.
* rotor :
The rotating part of a motor.
* running winding :
Heavy, insulated copper wire in a single-phase motor that receives the current for running the motor. The running winding remains connected when the starting winding is disconnected.
* secondary winding :
The second winding that current passes through in a transformer. The secondary winding contains fewer, but thicker wires that are wrapped into a coil.
* shaded-pole motor :
A single-phase motor that is 1/20 HP or less and is used in devices requiring low torque.

* sine wave :
The most common type of AC waveform. A sine wave consists of 360 electrical degrees and is produced by rotating machines.
* single voltage motor :
A type of three-phase motor that operates on only one voltage level. Single voltage motors are limited to having the same voltage as the power source.
* single-phase motor :
A type of motor with low horsepower that operates on 120 or 240 volts. Single-phase motors are often used in residential appliances like washing machines and air conditioners.
* slip :
The difference between a motor's synchronous speed and its speed at full load. Percent slip is a way to measure the speed performance of an induction motor.
* slip ring :
A conductive device attached to the end of a generator rotor that conducts current to the brushes. Slips rings are also used in AC wound rotor motors.
* split-phase motor :
A single-phase motor that consists of a running winding, starting winding, and centrifugal switch. The reactance difference in the windings creates separate phases, which produce the rotating magnetic field that starts the rotor.
: squirrel cage rotor :
A type of three-phase AC rotor that is constructed by connecting metal bars together at each end. It is the most common AC rotor type.
* starting winding :
Fine, insulated copper wire in a single-phase motor that receives current in the motor at start-up. When the motor reaches 60-80% of the full load, the starting winding is disconnected and the running winding remains in the circuit.
* stator :
The stationary part of a motor.
* stepped down :
In electricity, a phrase used to describe voltage adjustment. To step down voltage means to decrease voltage.
* stepped up :
In electricity, a phrase used to describe voltage adjustment. To step up voltage means to increase voltage.
* synchronous motor :
A constant-speed AC motor that does not use induction to operate. A synchronous motor needs DC excitation to operate.
* thermal switch :
A type of switch often found in split-phase motors that signals that the motor may overheat
* three-phase motor :
A motor with a continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large AC motors and is the standard power supply that enters homes and factories.
* torque :
A force that produces rotation.
* transform :
To increase or decrease the voltage in a circuit
* wound rotor :
A type of three phase rotor that contains windings and slip rings. This motor type permits control of rotor current by connecting external resistance in series with the rotor windings.

 

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How to Test & Troubleshoot Electric Motors :

Step (1) Place safety glasses over your eyes. Any time you are repairing an electrical device, safety glasses should be your number one tool. Shut off all electric power to the motor, whether this is turning off a circuit breaker or removing fuses from the disconnect switch.

Step (2) Remove the wiring cover on the motor and set aside the screws so you do not lose them. Read the motor's nameplate data to confirm whether this is a low voltage 115 volt motor, a 230 volt motor, or a 3-phase 230 volt or high voltage 480 volt motor. This will determine the number of power leads the motor has. All single phase 115 volt and 230 volt motors have two wire leads that connect to the power supply. All 3-phase 230 volt and 480 volt motors have three wire leads that connect to the 3-phase power supply.

Step (3) Remove the plastic wire connectors that are connecting to the power supply. You may have to identify the power leads to the wires on the motor if it is a 3-phase motor. This will ensure the rotation will be correct when re-terminating the motor. Turn your volt ohm meter to the ohm setting. The meter should read OL (open lead) or zero ohms. Take one lead and touch it to the case of the motor and test each motor lead. The ohm meter should read OL or zero ohms. If a reading of any ohms is observed you may have a direct short in the motor windings; the motor may be bad. Some motors, especially the 3-phase type, may have a very large resistance reading--in the 20 megaohms range or larger. This may be fine, or this may be a sign that the bearings are going bad as the motor may have deteriorating windings due to excessive heat.

Step (4) Testing single phase motors, whether they are 115 volt or 230 volt, with a capacitor is a little trickier but can still be accomplished. Remove the capacitor from its housing, being careful no to touch the exposed leads. The capacitor is like a battery and stores a high voltage charge. Turn your volt ohm meter to volts and carefully touch to the bare leads of the capacitor. If voltage is read, the capacitor still contains a charge. Holding the leads of the meter to the capacitor should show it discharging, Continue until zero voltage is observed on the meter. Most modern volt ohm meters have a capacitor testing switch on them and it is a simple matter to determine the status of the capacitor. In most cases the capacitor only needs to be replaced on these type of single phase motors.

* Check for blown line fuses or tripped breakers first, if your motor won't start at all. If it has failed while running, allow the motor to cool and then try to reset it.

Heavy duty electrical motors most often consist of split-phase induction motors designed for heavy duty assignments. As split-phase motors use a separate starter winding, these require a capacitor in the starting circuit to provide increased starting power. Failure of split-phase induction motors is often corrected by troubleshooting the capacitor function as described.

Diagnosing Capacitor Malfunction

Step (1) Attempt to start the induction motor. In there is a malfunction, the motor hums but does not start.
Step (2) Rule out malfunction of the centrifugal starter switch by spinning the rotor shaft by hand. If the shaft is frozen the problem is in the switch, and it most be replaced.
Step (3) If the rotor shaft rotates freely by hand, attempt to start the motor. If it starts the switch is either defective or stuck in the closed position, and the motor will stop running. Use electrical contact cleaner to clean the switch. Replace the switch if cleaning fails to correct problem.
Step (4) Rule out a malfunctioning centrifugal switch as above before assuming a failed capacitor function.
Once the switch has been ruled out, a motor that continues to hum ( has current ) but is too weak or otherwise fails to start may be the result of a short or open circuit in the capacitor.
Troubleshooting the Capacitor :
Step (1) Locate the capacitor, which is usually mounted on the side of the induction engine.
Step (2) Remove electrical wires from the two male contacts on the front of the capacitor.
Step (3) Set the volt ohmmeter to the 100 scale and connect the positive and negative leads from the volt ohmmeter to the two contacts of the capacitor.
Step (4) Observe the meter reading. If the needle jumps immediately to zero ohms and gradually drifts back to a high ohm reading, the capacitor is functional and is not the problem.
Step (5) A meter reading that registers steady zero ohms or steady high ohms indicates the capacitor is malfunctioning and should be replaced.
Step (6) Double check meter results by reversing meter leads to the capacitor and re-checking the readings.

Tips : One indicator of an open circuit in a faulty capacitor is high frequency interference in nearby radios when the motor is use.

 

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Flickering fluorescent tubes can cause the ballast to overheat and fail prematurely! They can even cause a starter to burn out! Don't wait too long to fix the problem or you may end up with a bigger repair!

look at the tube! If either tube appears to be very dark near either end the tube is defective or close to failure.

* An electrical short is often called a short circuit. It is a path for electrical current to flow that is the result of a defect or a breakdown of the electrical circuit. Because it's a clear path for electrical current, electrical shorts can be found by using an ohmmeter, which measures resistance, which is measured in units called ohms, to electrical current. A typical electrical short will have a very low resistance, usually less than a few ohms. By using an ohmmeter and a few simple troubleshooting techniques, you can identify electrical shorts.

 

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Electric Wiring :

If we connect a voltmeter between a live part ( e.g. the Line Conductor of a socket outlet ) and earth , we read 230V ;
The conductor is at 230V and the earth at Zero . The Earth provides a path to complete the circuit , We would measure nothing at all if we connected our voltmeter , say the positive 12v terminal of a car battery and Earth , as in this case the Earth plays no part in any circuit ,

Colours of indicator lights and their meanings

Colour : RED : Emergency Explanation : Warning of potential danger or a situation which requires immediate action
Typical application : • Failure of pressure in the lubricating system , • Temperature outside specified (safe) limits , • Essential equipment stopped by action of a protective device ,
Colour : Yellow : Meaning Abnormal condition , Explanation Impending critical condition , • Temperature (or pressure) different from normal level , • Overload, which is permissible for a limited time ,
• Reset ,
Colour : Green : Meaning : Normal Explanation : Indication of safe operating conditions or authorization to proceed, clear way Typical application : • Cooling liquid circulating • Automatic tank control switched on • Machine ready to be started
Colour : Blue : Meaning : Enforced action : Explanation : Operator action essential Typical application : • Remove obstacle • Switch over to Advance ,
Colour : White : Meaning : No specific meaning , Explanation : Every meaning: may be used whenever doubt exists about the applicability of the colours RED, YELLOW or GREEN; or as confirmation

Crimp terminals :

Crimp terminals are used for connecting wire by means of a screw joint to: bus-bar, switchgear housing, electric device and apparatus, etc. Terminals with rated sizes up to 0,5 - 6 mm² are designed in principle for a particular wire cross-sections, e.g. 6 mm² terminal can be used for the wires with a cross-section of 4 to 6 [mm²]. Terminal with a cross-section over 6 mm² can be used only for defined wire cross-section. Crimp terminals can only be used on stranded wire and cannot be used on solid cable.←←

Here are some of the more popular crimp terminals : Ring terminals , Fork terminals , Blade terminals , Fully insulated Female push-ons , Butt connectors , Butt connectors are used to join two wires together. You can also find terminals such as pins, male tabs, piggy back, male and female bullets.
Do not forget that the color is also important. Each color represents a different size of crimp terminal. Red ones should be used for the wires with a cross-section of 0,75mm2 to 1,5mm2. Blue ones for the wires from 1,5mm2 to 2,5mm2, and yellow terminals are for the wires with a cross-section of 4mm2 to 6mm2.

RED : wire size : 0,5 - 1,5mm BLUE : wire size 1,5 - 2,5mm YELLOW : 4 - 6mm

Colours of push-buttons and their meanings :
Colour RED : Meaning : Emergency ,
Typical application : * Emergency stop * Fire fighting

Colour YELLOW :
Meaning : abnormal conditions
Typical application : Intervention, to suppress abnormal conditions or to avoid unwanted changes

Colour GREEN :
Meaning : Normal ,
Typical application : Start from safe condition

Colour BLUE :
Meaning : Enforced action ,
Typical application : Resetting function

Colour WHITE :
Meaning : No specific meaning ,
Typical application : * Start/ON * Stop/OFF

Colour Gray :
Meaning : No specific meaning ,
Typical application : * Start/ON * Stop/OFF


Colour BLACK :
Meaning : No specific meaning ,
Typical application : * Start/ON * Stop/OFF

Insulation resistance : Pat ;
Insulation resistance is normally checked by applying 500V dc between both live conductors (line and neutral) connected together and protective earth when testing a Class I appliance

Competence of the inspector
A final consideration when carrying out inspection and tests is the competence of the inspector. Any person undertaking these duties must be skilled and experienced and have sufficient knowledge of the type of installation. It is the responsibility of the inspector to:

* ensure no danger occurs to people, property and livestock
* confirm that test and inspection results comply with the requirements of BS 7671 and the designer’s requirements
* express an opinion as to the condition of the installation and recommend remedial works
* make immediate recommendations, in the event of a dangerous situation, to the client to isolate the defective part.

The inspection process

In new installations, inspection should be carried out progressively as the installation is installed and must be done before it is energised. As far as is reasonably practicable, an initial inspection should be carried out to verify that:

* all equipment and material is of the correct type and complies with applicable British Standards or acceptable equivalents
* all parts of the fixed installation are correctly selected and erected no part of the fixed installation is visibly damaged or otherwise defective
* the equipment and materials used are suitable for the installation relative to the environmental conditions.

 

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EXTENT AND FREQUENCY OF INSPECTION & TESTING

WHAT IS REQUIRED TO BE INSPECTED AND TESTED ? All types of mains powered electrical portable, moveable, hand-held, stationary, fixed, equipment for 'building-in', I.T. equipment and extension leads are required to be regularly inspected and tested.

It should be noted that provision of new appliance does not exempt the need for formal Inspection and Testing. Manufacturer's warranties only provide for repair or replacement of a faulty device, they do not guarantee that a new device is electrically safe.
Equipment Types :

* Portable Appliance
An appliance of less than 18gm in mass that is intended to be moved while in operation or an appliance which can easily be moved from one place to another, e.g.;- Toaster, Food Mixer, Vacuum Cleaner, Fan Heater

* Movable Equipment (sometimes called transportable)
This is equipment that is either:
18Kg or less in mass and not fixed, e.g. Electric Fire, or equipment with wheels, castors or other means to facilitate movement by the operator as required to perform its intended use, e.g. Air Conditioning Unit.
* Hand-Held Appliances or Equipment
This is portable equipment intended to be held in the hand during normal use e.g.
Hair Dryer, Power Drill, Soldering Iron, Angle Grinder

* Stationary Equipment or Appliances
This equipment has a mass exceeding 18Kg and is not provided with a carrying handle e.g. Refrigerator, Washing Machine, Dishwasher

* Fixed Equipment/Appliances
This is equipment or an appliance which is fastened to a support or otherwise secured in a specified location e.g. Convector Heater, Water Heater, Heated Towel Rail, Production Machinery, Fixed Tools

* Appliances/Equipment for Building-In
This equipment is intended to be installed in a prepared recess such as a cupboard or similar. In general, equipment for building-in does not does not have an enclosure on all sides because on one or more of the sides additional protection against electric shock is provided by the surroundings e.g. Built-In Cooker, Built-In Dishwasher

* Information Technology Equipment (Business Equipment)
Information technology equipment includes electrical business equipment such as computers and mains powered telecommunications equipment and other equipment for general business use e.g. Mail Processing Machines, Electric Plotters, Trimmers, PCs, VDUs, Data Terminal Equipment, Telephones, Printers, Photo-Copiers, Power Packs

* Extension Leads, RCD Extension Leads & RCD Adaptors
The use of extension leads other than for temporary power supplies should be avoided were possible. RCDs are required to be checked for operation.

* The Environment - equipment installed in a benign environment will suffer less damage than equipment used in an arduous environment.

* The Equipment's Construction - Class 1 equipment is dependant upon the connection with earth of the fixed installation.

* The Equipment Type - Hand-held appliances are more likely to be damaged than fixed appliances. If they are Class I appliances then the risk of danger is increased as safety is dependant upon the continuity of the protective (earth) conductor from the plug to the appliance. The initial frequency of inspection and testing should comply with the Institution of Electrical Engineer’s Code of Practice for the In-Service Inspection and Testing of Electrical equipment.

Insulation resistance test

insulation resistance test being conducted on a twin and earth cable between the line and cpc at the distribution board end of the cable.
The reading obtained should be greater than 100 MΩ, indicating that the insulation resistance is satisfactory and that the supply is safe to put on. But what would the instrument indicate in the situation ?

In the situation an insulation resistance test is again being conducted between line and cpc. However, this time a nail has penetrated the sheath of the cable, breaking the cpc and touching the line conductor .When the test is done the instrument may read greater than 100 MΩ, indicating that the insulation resistance is acceptable and that it is safe to connect the supply. However, we can clearly see that it is not. Beyond the break in the cpc, the line and cpc are connected. If the supply was now connected to the cable we would have a potentially lethal situation, as all the metal work connected to the cpc will become live. Automatic disconnection will not take place as the break in the cpc means there is no longer a return path. The metalwork will remain live until someone touches it – which could result in a fatal electric shock In this case,
** if we had conducted a Continuity Test of the cpc before the insulation resistance test, we would have identified that the cpc was broken. Action could then have been taken to remedy the situation

Electrical Terms :

CCT - Circuit
CCU - Cooker Control Unit
CPC - Circuit Protective Conductor
CU - Consumer Unit
The CNE conductor (combined neutral and earth) PEN
EEBAD - Earthed Equipotential Bonding And Automatic Disconnection Of Supply ( Old ) must be replace now ,
ELV - Extra Low Voltage = Below 50V AC \ 120V Ripple Free DC
FCU - Fused Connection Unit
FELV - Functional Extra Low Voltage
HBC - High Breaking Capacity
HRC - High Rupturing Capacity
HV - High Voltage
LV - Low Voltage = 50V - 1000V AC \ 1500V Ripple Free DC
MCB - Miniature Circuit Breaker
MCCB - Moulded Case Circuit Breaker
MD - Maximum Demand
MICC - Mineral Insulated Copper Cable aka Pyro
PAT - Portable Appliance Testing
PELV - Protected Extra Low Voltage
PEN - Protective Earthed Neutral
PFC - Prospective Fault Current
PME - Protective Multiple Earthing
PSCC - Prospective Short Circuit Current
PVC - Poly Vinyl Chloride
RCBO - Residual Current Breaker With Integral Overload Protection
RCCB - Residual Current Circuit Breaker
RCD - Residual Current Device
SELV - Separated Extra Low Voltage
SRCBO's - Socket Outlet Incorporating RCBO's
SWA - Steel Wire Armour (Cable)
UPS - Uninterruptible Power Supply
VD - Voltage Drop

A - Amp
W - Watt
V - Volt
R - Resistance
Z - Impedance
mA - milliampere
mV - millivolt
kW - Kilowatt
kV – Kilovolt

 

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Alternating current circuit calculations :

Impedance ,

In DC, circuits ,the current is limited by résistance . In AC ,circuits , the current is limited by Impedance ( Z ) Résistance & Impedance are measured in Ohms ,

For this calculation , Ohms law is used and ( Z ) is substituted for ( R ) U – Z = I or voltage ( U ) ÷ impedance ( Ohms ) = Current ( Amperes )
* the voltage applied to a circuit with an impedance of 6Ω , is 200 volts , calculate the current in the circuit ,
U – Z = I ( 200 ÷ 6 = 33.33A )
* the current in a 230V single–phase motor is 7.6A calculate the impedance of the circuit , U – I = Z ( 230 ÷ 7.6 = 30.26Ω )
* a discharge lamp has an impedance of 265Ω and the current drawn by the lamp is 0.4A , calculate the voltage
Z x I = U ( 265 x 0.4 = 106 volts )
* the current through an impedance of 32Ω is 8A , calculate the voltage drop across the impedance U = I x Z = 8 x 32 = 256v
* the current through an electric motor is 6.8A at 230V , calculate the impedance of the motor , U = I x Z
( transpose for Z ) Z = U – I ( 230 ÷ 6.8 = 33.82Ω )
* an AC . coil has an impedance of 430Ω calculate the voltage if the coil draws a current of 0.93A
U = I x Z ( U = I x Z 0.93 x 430 = 400V )

* a mercury vapour lamp take 2.34A when the mains voltage is 237V calculate the impedance of the lamp circuit ?
* an inductor has an impedance of 365Ω how much current will flow when it is connected to a 400V ac supply ?
* a coil of wire passes a current of 55A when connected to a 120V dc supply but only 24.5A when connected to a 110V ac supply calculate (a) the résistance of the coil (b) its impedance ,

Test to measure the impedance of an earth fault loop were made in accordance with BS-7671 and the results for five different installations are given below , for each case calculate the value of the loop impedance ,

(a) test voltage ac ( V ) 9.25 : Current ( A ) 19.6 (b) test voltage ac ( V ) 12.6 : Current ( A ) 3.29
(c) test voltage ac ( V ) 7.65 : Current ( A ) 23.8 (d) test voltage ac ( V ) 14.2 : Current ( A ) 1.09 (e) test voltage ac ( V ) 8.72 : Current ( A ) 21.1

* the choke in a certain fluorescent-fitting causes a voltage drop of 150V when the current through it is 1.78A , calculate the impedance of the choke ,
* the alternating voltage applied to a circuit is 230V and the current flowing is 0.125A , the impedance of the circuit is ,
(a) 5.4Ω (b) 1840Ω (c) 3.5Ω (d) 184Ω ,
* an alternating current of 2.4A flowing in a circuit of impedance 0.18Ω produces a voltage drop of
(a) 0.075V (b) 13.3V (c) 0.432V (d) 4.32V ,
* when an alternating e.m.f of 150V is applied to a circuit of impedance 265Ω , the current is ,
(a) 39 750A (b) 1.77A (c) 5.66A (d) 0.566A

We will assume that the résistance of the circuits is so low that it may be ignored and that the only opposition to the flow of current is that caused by the inductive reactance ,
The formula for inductive reactance , ( is XL = 2nfL ( answer in ohms )
Where L is the inductance of the circuit or coil of wire and is stated in henrys ( H ) f is the frequency of the supply in hertz (Hz )
* calculate the inductive reactance of a coil which has an inductance of 0.03 henrys when connected to a 50Hz supply
( XL = 2nfL ( 2 x 3 . 142 x 50 x 0.03 = 9.42Ω
* calculate the inductive reactance of a coil when connected to a 60Hz supply , XL 2nfL ( = 2 x 3. 142 x 60 x 0.03 = 11.31Ω )
It can be seen from this calculation that the frequency increases the inductive reactance will also increase ,

 

[amberleaf]

Working knowledge :

What we call "Electricity" is actually made up of three parts.

Real Power (Kw, Mw),
Apparent Power (Kva),
Reactive Power (Kvar).
These 3 parts form the "Power Triangle"

Real Power (Kw) is the part of the triangle which results in real work done, in the form of heat energy.

Apparent Power is that portion of the power triangle that we actually measure.

And then....there is Reactive Power....which serves no real function at all.

The phase angle between Real Power and Apparent Power in the power triangle is identified as the angle "q" which is the Greek letter "THETA". The size, in degrees, of that angle determines the size of the Reactive Power leg of the triangle. The cosine of that angle is called Power factor or pf and the value of the pf is inversely proportional to the amount of reactive power you are generating. What this means is that the smaller the angle q, the less Reactive Power you are making and the greater your Power Factor is.

Electrical

A = Ampere
V = Volt
W = Watt
Ω = Ohm
F = Farad

Power / Energy

HP = horsepower
W = watt
kW = kilowatt
kWh = kilowatt-hours

I = Current (ampere)
U = Voltage (volt)
R = Resistance (ohm)

Electrical power

P = U x I x PF / 1000
P =Power in kW (1-phase)
PF = Power factor

P = U x I x PF x √2 / 1000
P =Power in kW (2-phase)

P = U x I x PF x √3 / 1000
P =Power in kW (3-phase)

Conversion factors

Power
1 hp = 0,736 kW 1 kW = 1,36 hp
1 hp = 0,746 kW (UK,US) 1 kW = 1,34 hp (UK;US)
1 kcal/h = 1,16 W 1 W = 0,860 kcal/h

Energy
1 kpm = 9,80665 J 1 J = 0,102 kpm
1 cal = 4,1868 J 1 J = 0,239 cal
1 kWh = 3,6 MJ 1 MJ = 0,278 kWh

Mass
1 lb = 0,454 kg 1 kg = 2,20 lb
Area
1 acre = 0,405 ha 1 ha = 2,471 acre

Length
1 mile = 1,609344 km 1 km = 0,621 mile
1 yd = 0,9144 m 1 m = 1,09 yd
1 ft = 0,3048 m 1 m = 3,28 ft
1 in = 25,4 mm 1 mm = 0,039 in

 

[amberleaf]

Insulation Résistance Test :

Insulation résistance is normally checked by applying 500V dc
Between both Live Conductors ( Line & Neutral ) and Protective Earth when Testing a Class 1 Appliance .

Mathematical :

˂ Less than .
≤ Less than or Equal to .
˃ More than .
≥ More than or Equal to .

Inspection checklists :

To ensure that all the requirements of the Regulations have been met, inspection checklists should be drawn up and used as appropriate to the type of installation being inspected. Examples of suitable checklists are given in which follows.

Switchgear ( tick if satisfactory )

All switchgear is suitable for the purpose intended .
Meets requirements of the appropriate BS EN standards .
Securely fixed and suitably labelled .
Suitable glands and gland plates used (526.1) .
Correctly earthed .
Conditions likely to be encountered taken account of, i.e. suitable for the environment .
Correct IP rating .
Suitable as means of isolation .
Complies with the requirements for locations containing a bath or shower .
Need for isolation, mechanical maintenance, emergency and functional switching met .
Fireman switch provided, where required .
Switchgear suitably coloured, where necessary .

Lighting controls ( tick if satisfactory )

Light switches comply with appropriate British Standard .
Switches suitably located .
Single-pole switches connected in phase conductor only .
Correct colour-coding of conductors .
Correct earthing of metal switch plates .
Switches out of reach of a person using bath or shower .
Switches for inductive circuits (discharge lamps) de-rated as necessary .
Switches labelled to indicate purpose where this is not obvious .
All switches of adequate current rating .
All controls suitable for their associated luminaire .

Lighting points ( tick if satisfactory )

All lighting points correctly terminated in suitable accessory or fitting .
Ceiling roses comply with appropriate British Standard .
No more than one flexible cord unless designed for multiple pendants .
Devices provided for supporting flex used correctly .
All switch wires identified .
Holes in ceiling above ceiling rose made good to prevent spread of fire .
Ceiling roses not connected to supply exceeding 230V .
Flexible cords suitable for the mass suspended .
Lamp holders comply with appropriate British Standard .
Luminaire couplers comply with appropriate British Standard .

Conduits ( general ) ( tick if satisfactory )

All inspection fittings accessible .
Maximum number of cables not exceeded .
Solid elbows used only as permitted .
Conduit ends reamed and bushed .
Adequate number of boxes .
All unused entries blanked off .
Lowest point provided with drainage holes where required .
Correct radius of bends to prevent damage to cables .
Joints and scratches in metal conduit protected by painting .
Securely fixed covers in place adequate protection against mechanical damage .

Wiring accessories ( general requirements) (tick if satisfactory )

All accessories comply with the appropriate British Standard
Boxes and other enclosures securely fastened
Metal boxes and enclosures correctly earthed
Flush boxes not projecting above surface of wall
No sharp edges which could cause damage to cable insulation
Non-sheathed cables not exposed outside box or enclosure
Conductors correctly identified
Bare protective conductors sleeved green and yellow
All terminals tight and contain all strands of stranded conductor
Cord grips correctly used to prevent strain on terminals
All accessories of adequate current rating
Accessories suitable for all conditions likely to be encountered
Complies with the requirements for locations containing a bath or shower
Cooker control unit sited to one side and low enough for accessibility and to prevent trailing flexes
across the radiant plates
Cable to cooker fixed to prevent strain on connections

Socket outlet ( tick if satisfactory )

Complies with appropriate British Standard and is shuttered for household and similar installations
Mounting height above floor or working surface is suitable
All sockets have correct polarity
Sockets not installed in bath or shower zones unless they are shaver-type socket or SELV
Sockets not within 3m of zone 1
Sockets controlled by a switch if the supply is direct current
Sockets protected where floor mounted
Circuit protective conductor connected directly to the earthing terminal of the socket outlet on a sheathed wiring installation
Earthing tail provided from the earthed metal box to the earthing terminal of the socket outlet
Socket outlets not used to supply a water heater with uninsulated elements

Rigid metal conduits (tick if satisfactory)
Complies to the appropriate British standard
Connected to the main earth terminal
Line and neutral cables contained within the same conduit
Conduits suitable for damp and corrosive situations
Maximum span between buildings without intermediate support

Rigid non-metallic conduits (tick if satisfactory)
Complies with the appropriate British Standard
Ambient and working temperature within permitted limits
Provision for expansion and contraction
Boxes and fixings suitable for mass of luminaire suspended at expected temperatures

Flexible metal conduit (tick if satisfactory)
Complies with the appropriate British Standard
Separate protective conductor provided
Adequately supported and terminated

Trunking (tick if satisfactory)
Complies to the appropriate British Standard
Securely fixed and adequately protected against mechanical damage
Selected, erected and rooted so that no damage is caused by ingress of water
Proximity to non-electrical services
Internal sealing provided where necessary
Hole surrounding trunking made good
Band 1 circuits partitioned from band 2 circuits, or insulated for the highest voltage present .
Circuits partitioned from band one circuits, or wired in mineral-insulated and sheathed cable .
Common outlets for band 1 and band 2 circuits provided with screens, barriers or partitions .
Cables supported for vertical runs

Metal trunking (tick if satisfactory )
Line and neutral cables contained in the same metal trunking
Protected against damp corrosion
Earthed
Joints mechanically sound, and of adequate earth continuity with links fitted

Plant , Equipment & component failure :

It is said that nothing lasts forever and this is certainly true of electrical equipment there will be some faults that you will attend that will be the result of a breakdown simply caused by wear & tear , although it must be said that planned maintenenance systems and regular testing and inspections can extend the life of equipment , some common failures on installations and plant are :
* switches not operating – due to age .
* motors not running – new brushes required .
* lighting not working – lamps life expired .
* fluorescent luminaire not working – new lamp or starter needed .
* outside PIR not switching – ingress of water causing failure.
* corridor socket outlet not working due to poor contacts created by excessive use / age .

The intention of the measure is to phase out less efficient lamps in favour of products with greater energy efficiency. A brief description of the lamps affected by the measure follows below along with a summary of main characteristics

A. Incandescent lamps (General Lighting Service (GLS))
These lamps are the traditional filament lamps which have been in domestic use for decades and provide a bright light source when made with transparent glass. They are very low efficiency lamps compared with other lamps (CFLs in particular) but are generally available in good quality, and provide good performance.

B. Conventional halogen lamps (Halo conv)
Standard halogen lamps consume at best, 15% less energy than GLS lamps for the same light output. Many of these lamps are low voltage lamps which are more efficient that mains voltageones but which require a transformer either in the luminaire or in the lamp itself. They provide good quality light.

C. Halogen lamps with xenon filling (C-class)
These are recent technology lamps with xenon filling and will use approximately 25% less energy for the same light output as GLS lamps. These lamps come in two types, one which is placed in glass bulbs, shaped like incandescent lamps, which are compatible with existing luminaries (retro C), and halogen socket c type lamps which can only be used in special halogen sockets (halosocket C). Lamps provide good quality light and performance.

D. Halogen lamps with infrared coating (B-class)
These lamps are new technology, with an application of infrared coating to the wall of the halogen lamp capsule making the lamp considerably more efficient. However, this is only possible with low voltage lamps and therefore a transformer is required. Currently only one manufacturer produces these lamps with a fitting so that they can fit traditional sockets. Due to heat issues, these are only available up to the equivalent of 60W GLS bulbs. They provide a bright light source and good performance and are estimated to provide 45% energy savings over GLS lamps

E. Compact fluorescent lamps (CFLs)
These include an integrated ballast, fit into existing GLS sockets, and are produced with both bare tubes and also with a traditional bulb-shaped cover. They have a long lifetime and vary in their energy efficiency, being estimated to use between 20-35% of energy of that needed for GLS lamps. CFLs are sometimes criticised by consumers resulting from lingering perceptions over poor light quality and it is recognised that long periods of close-up use can have adverse effects on those with pre-existing photo-sensitive conditions.

 

[pipster1973]

thanks very much this has helped me no endl

 

[amberleaf]

On and Off – load devices :

Not all devices are designed to switch circuits “ on or off “ it is important to know that when a current is flowing in a circuit , the operation of a switch ( or disconnector ) to break the circuit will result in a discharge of energy across the switch terminals ,

You may well have had this happen when entering a dark room and switching on the light ,
Where for an instant you may see a blue flash from behind the switch plate . this is actually the arcing of the current as it dissipates and makes contact across the switch terminals . a similar arcing takes place when circuits are switched off or when protective devices operate thus breaking fault current levels .

Fundamentally , an isolator is designed as an off-load device and is usually only operated after the supply has been made dead and there is no load current to break . an on-load device can be operated when current is normally flowing and is designed to make or break load current .

An example : of an on-load device could be a circuit breaker , which is not only designed to make and break load current
But has been designed to withstand make and break high levels of fault current ,

* all portable appliances should be fitted with the “ Simplest form of Isolator “. a fused plug . this , when unplugged from the socket-outlet . provides complete isolation of the appliance from the supply ,

* Meltdown of plastic connector due to overcurrent : ( Fire ) ←
* Meltdown of insulation due to Overcurrent ,

When insulation of conductors and cables fail . it is usually due to one or more of the following ,
* poor installation methods .
* poor maintenance .
* excessive ambient temperatures .
* high fault current levels .
* damage by third party .

When a protective device has been operated correctly and this device was the nearest device to the fault ( Discrimination ) is said to have occurred

Luminaires :
The most common fault with luminaires is expiry of lamp life . which obviously only requires replacement .
Discharge lighting systems employ control gear which on failure will need replacement as they cannot be repaired , discharge type lighting may have problems with the control circuit ,
Common items of equipment in the luminaire control circuit are :
* the capacitor used for power factor correction . if this has been broken down it would not stop the lamp operating but would prevent the luminaire operating efficiently ,
* the choke or ballast used to create high p.d to assist in the lamp starting . a common item which could break down and need replacement ,
* the starter , which is used to assist the discharge across the lamp when switched on at the start , this is the usual part to replace when the lamp fails to light .

Many fluorescent luminaires have starter – less electronic control gear , which is not only quick-start with increased efficiency , but requires less maintenance . they have a longer lamp life but when the quick-start unit fails it will need replacement ,

Risk of high frequency on high capacitive circuits :

Capacitive circuits could be circuits with capacitors connected to them or some long runs of circuits wiring which may have a capacitive effect .
This is usual on long runs of mineral-insulated cables . when working on such circuits no work should commence until the capacitive effect has been discharged . in some cases it would be practical to discharge capacitors manually by shorting out the capacitor ,

MULTIPLE CHOICE :

Choose the one alternative that best completes the statement or answers the question.

1) Electrons are made to flow in a wire when there is
A) an imbalance of charges in the wire.
B) more potential energy at one end of the wire than the other.
C) a potential difference across its ends. **

2) An ampere is a unit of electrical
A) pressure.
B) current. **
C) resistance.
D) all of these.
E) none of these.

3) A wire that carries an electric current
A) is electrically charged.
B) may be electrically charged. **
C) is never electrically charged.

4) A coulomb of charge that passes through a 6-volt battery is given
**A) 6 joules. B) 6 amperes. C) 6 ohms. D) 6 watts. E) 6 Newton’s.

5) Which statement is correct?
A) Charge flows in a circuit. **
B) Voltage flows through a circuit.
C) Resistance is established across a circuit.
D) Current causes voltage.

6) Electrons move in an electrical circuit
A) by being bumped by other electrons.
B) by colliding with molecules.
C) by interacting with an established electric field. **
D) because the wires are so thin.
E) none of these.

7) Heat a copper wire and its electric resistance
A) decreases. B) remains unchanged. C) increases. **

8) Stretch a copper wire so that it is thinner and the resistance between its ends
A) decreases. B) remains unchanged. C) increases. **

9) A wire carrying a current is normally charged
A) negatively. B) positively. C) not at all. **

10) In an ac circuit, the electric field
A) increases via the inverse square law.
B) changes magnitude and direction with time. **
C) is everywhere the same.
D) is non-existent.
E) none of these.

11) The current through a 10-ohm resistor connected to a 120-V power supply is
A) 1 A.
B) 10 A.
C) 12 A. **
D) 120 A.
E) none of these.

12) A 10-ohm resistor has a 5-A current in it. What is the voltage across the resistor?
A) 5 V
B) 10 V
C) 15 V
D) 20 V
E) more than 20 V **

13) When a 10-V battery is connected to a resistor, the current in the resistor is 2 A. What is the resistor's value?
A) 2 ohms
B) 5 ohms **
C) 10 ohms
D) 20 ohms
E) more than 20 ohms

14) The source of electrons in an ordinary electrical circuit is
A) a dry cell, wet cell or battery.
B) the back emf of motors.
C) the power station generator.
D) the electrical conductor itself. **
E) none of these.

15) The source of electrons lighting an incandescent ac light bulb is
A) the power company.
B) electrical outlet.
C) atoms in the light bulb filament. **
D) the wire leading to the lamp.
E) the source voltage.

16) A woman experiences an electrical shock. The electrons making the shock come from the
A) woman's body. **
B) ground.
C) power plant.
D) hairdryer.
E) electric field in the air.

17) In a common dc circuit, electrons move at speeds of
A) a fraction of a centimeter per second. **
B) many centimeters per second.
C) the speed of a sound wave.
D) the speed of light.
E) none of these.

18) When a light switch is turned on in a dc circuit, the average speed of electrons in the lamp is
A) the speed of sound waves in metal.
B) the speed of light.
C) 1000 cm/s.
D) less than 1 cm/s. **
E) dependent on how quickly each electron bumps into the next electron.

19) Alternating current is normally produced by a
A) battery. B) generator. **
C) both of these. D) neither of these.

20) The electric power of a lamp that carries 2 A at 120 V is
A) 1/6 watts. B) 2 watts. C) 60 watts. D) 20 watts. E) 240 watts. **

 

[pipster1973]

are all these mock or gola and where do you get them

 

[amberleaf]

Power Dissipation :
All components have résistance so when a current flows through them power is dissipated in most cases in the form of heat. It is something to be aware of in the selection of components to be used in a circuit that the power ratings are not exceeded, examples are bulbs and resistors

Find the power dissipated by the bulb (Résistance ) of bulb = 100 ohms)
To find the power dissipated in the bulb which has a résistance of 100Ω.
If the formula Power = I x V watts is to be used the following data must be known: current flowing
through the bulb and voltage across the bulb
As the 200ohm resistor and the lamp are in series
then: Rt = 200 + 100 = 300Ω

mock learning curve

• Type AAA is the smallest of the above batteries and also produces the smallest amount of current (somewhere in the region of ˃10 milliamps over an extended period). Used in musical IPODS, and infra red controllers for televisions etc.

• Type AA one of the most used batteries, can be found in small radios, torches, toys, cassette players etc. This type can readily supply current of ˃ ˃ 40 milliamps over long periods.

• Types C, D can provide a much larger current region of ˃ 100 milliamps over extended periods and are used in power torches and large portable musical centres. Note the above batteries can provide much larger current over shorter periods.

• The PP3 battery has an output voltage of 9V. It is used extensively in small radios and also in smoke alarms. It can provide a continuous current output of 20 milliamps. ˂

The magnetic field is produced in two ways :

Permanent magnets (this method used only in the cheaper type of motors) Field coils which are wound around soft iron cores known as the FIELD
POLES.
Thus when current is passed through the field coil the soft iron core is magnetised. Motors must have a least two field poles to have a north/south pole arrangement

1µF = 1 microFarad = 1x10-6 Farads = 1 millionth of a Farad

1nF = 1 nanoFarad = 1x10-9 Farads = 1 billionth of a Farad

1pF = 1 picoFarad = 1 x 10-12 Farads = 1 trillionth of a Farad

if you have a Transformer: 28 VA / 12 volts rating and you're testing the power pack would have 2.33 amps available ( 28 ÷ 12 = 2.33 ).

Tell me and I forget, show me and I remember, involve me and I understand.

* When an initial inspection and test should be carried out ? During and on completion, before being put into service
The precautions to be taken during an inspection and test ? Avoid danger to persons, livestock and damage to property

a) Within the code IP2X what is represented by: ( i) 2 : ii) X )
b) State the level of protection offered by IP4X
a) i) standard finger 80mm long x 12mm diameter and no penetration by 12.5mm diameter sphere
ii) unspecified regarding the protection provided
b) Protection against small items 1.0mm diameter

State the three general requirements to which the installed equipment must conform when carrying out an initial inspection
* The equipment is in compliance with standards i.e. To the correct BS or BSEN
* Correctly selected and erected in accordance with BS7671
* It is not visibly damaged

State three requirements of the Electricity at Work Regulations regarding test instruments ?
* Equipment must be:
* Constructed,
* Maintained and Used in a way to prevent danger

State three human senses that could be used during an inspection of an installation ?
All of the senses could be used:-
* Sight,
* Smell,
* Hearing,
* Touch (give examples) Some smells taste

Conduit
* Fixings (correct number and type of saddle)
* Couplings tightened
* Running couplings locknuts tightened
* Box lids fitted complete with screws
* Vice marks removed
* Damaged finishes restored
* External protective conductors installed

Use of Class II equipment or equivalent insulation
* Non-conducting locations absence of protective conductors
* Earth free-local equipotential bonding presence of earth-free equipotential bonding conductors
* Electrical separation

Inspection
Inspection shall precede testing and shall normally be done with that part of the installation under inspection disconnected from the supply

HSE Guidance Note GS-38 Approved Voltage Tester← this will come up -&-

* Adequate insulation
* Have coloured leads to distinguish one lead from the other
* Have finger barriers
* Maximum of 2mm / 4mm exposed probe
* Flexible and Robust
* Sheathed leads to prevent damage
* Long enough for their purpose
* No accessible parts even if the lead is loose
* Have fused leads

Avoid Damage to Property

* Is there an RCD in the circuit
* Are there computers on line
* Is there electronic equipment in the circuit
* Could gaskets be damaged when removing covers
* Are all the loads disconnected
* Is there any equipment or processes which may be damaged if disconnected for long periods of time
* Is there any essential equipment which cannot be turned off

Avoid Danger to Persons
* Have you checked to see if any essential services are supplied from the board e.g emergency lighting, fire alarms, life-support equipment, UPS systems, gas monitoring systems, etc.
* Have you isolated the circuit correctly
* Have you discharged any capacitors
* Is the test equipment appropriate for the environment e.g. intrinsically safe
* Are you using long test leads that could cause people to trip over
* Have you informed people of the dangers

Initial Verification ← this will come up -&-

Every installation shall, during erection and on completion before being put into service be inspected and tested to verify , so far as is reasonably practicable that the requirements of the Regulations have been met.
Precautions shall be taken to avoid danger to persons and damage to property and installed equipment during the inspection and testing

Suppose we need to find out how many cables of overall diameter 3 mm we can install in a 50mm x 50mm steel trunking ,

Total area of trunking : ( 50 x 50 = 2500mm2 )

Space available for cables ( 45% )

( 2500 x 45 ÷ 100 = 1125mm2 )
This leaves 2500 – 1125 = 1375mm2 of air space within the trunking
Space occupied by one cable : ) π d2 / 4 = π x 3;2 / 4 = 7.07mm2
The maximum number of cables we can install ,
= space available for cables ---------------- space occupied by 1 cable
= 1125 ÷ 7.07 = 159.1
the maximum number of these cables we could install in a 50mm x 50mm trunking is ( 159 )

Remember that we always round down to the nearest whole number , never round up ←

Example :
A 75mm x 25mm trunking is installed and contains 26 x 2.5mm2 stranded cables and 20 x 4mm2 cables ,
We are to install some extra circuits which will total 12 x 1.5mm2 solid copper cables , does the trunking have enough capacity for these extra cables ?
Factors we require are :
75mm x 25mm = 738 ……… ( On-Site Guide table 5F .. p/122 )
2.5mm2 stranded cable = 12.6 ( On-Site Guide table 5F .. p/121)
4mm2 stranded cable = 16.6
1.5mm2 stranded cable = 8.0
Total factor for 2.5mm2 stranded cables ( 26 x factor = 26 x 12.6 = 327.6 ) 26 time 12.6 = 327.6
Total factor for 4.0mm2 cables ( 20 x factor = 20 x 16.6 = 332 )
Total factor for installed cables ( 327.6 + 332 = 659.6
Trunking factor for 75mm x 25mm = 738 ( 5F o/s/g
Factor available for extra cables :
Trunking factor – total factor for installed cables ( 738 sub 659.6 = 78.4 )
Factor for 1.5mm2 solid copper cable = 8.0
Number of extra cables we could install ( 78.4 ÷ 8.0 = 9.8 )
So we could install 9 extra cables ,
Therefore our trunking has got sufficient capacity to allow us to install 12 more , 1.5mm2 solid cables

↔ The provision of spare space is advisable , however , any circuits added at a later date must take into account grouping , Regulation 523.5 p- 103 regs

Live conductors: should be either insulated and protected against mechanical damage or placed and safeguarded, for example inside an earthed metal enclosure. This is to ensure that persons do not have access to them, when they are live or energised. Where necessary to prevent danger, the access door should be interlocked with the supply so that conductors are isolated and earthed before access is permitted.

Fuses: should be selected to be the minimum rating (but having taken into account the likelihood of them failing on,
for example, the surge current on starting up a motor)

Capacitors • Used to store electricity

 

[amberleaf]

Volts (V) A water dam with pipes coming out at different heights. The lower the pipe along the dam wall, the larger the water pressure, thus the higher the voltage :
Amps (A) A river of water. Objects connected in series are all on the same river, thus receive the same current. Objects . Connected in parallel make the main river branch into smaller rivers. These guys all have different currents.
Résistance : Ohm (Ω)
If current is analogous to a river, then resistance is the amount of rocks in the river. The bigger the resistance the less current that flows

Resistors in Series: All resistors are connected end to end. There is only one river, so they all receive the same current .
But since there is a voltage drop across each resistor , they may all have different voltages across them. The more resistors in series the more rocks in the river, so the less current that flows

Resistors in Parallel: All resistors are connected together at both ends. There are many rivers (i.e. The main river branches off into many other rivers), so all resistors receive different amounts of current .But since they are all connected to the same point at both ends they all receive the same voltage.

In alternating current (AC, also ac) the movement (or flow) of electric charge periodically reverses direction. An electric charge would for instance move forward, then backward, then forward, then backward, over and over again. In direct current (DC), the movement (or flow) of electric charge is only in one direction.

• Kilovolt: kV; One thousand volts.
• Kilovolt amperes: Kva; One thousand volt amps.
• Kilowatt: Kw; One thousand watts.
• Kilowatt Hour: Kwh; One thousand watt-hours.

DEFINITIONS & TERMINOLOGY

* Alternating Current: (AC); Electrical current that changes (or alternates) in magnitude and direction of the current at regular intervals.
* Amp: (ampere)The basic unit of current in an electrical circuit. One ampere is the rate of flow of electric current when one coulomb of charge flows past a point in the circuit in one second. Symbolically characterized by the letter "I" and sometimes "A" when used in formulas.
* Amplifier: An electrical circuit that increases the power, voltage or current of an applied signal.
* Anode: A positive (+) electrode. The point where electrons exit from a device to the external electric circuit.
* Break: The act of the opening of an electrical circuit.
* Bridge Rectifier: A full-wave rectifier where the diodes are connected in a bridge circuit. This allows the current to the load during both the positive and negative alternating of the supply voltage.
* Capacitor: A device used to store electrical energy in an electrostatic field until discharge.
* Cathode: A negative (-) electrode. The point of entry of electrons into a device from an external circuit. The negative electrode of a semiconductor diode.
* Celsiuses: A temperature scale. Also known as centigrade. Sea level water will freeze at 0°C and will boil at 100°C.
* Charge: The measured amount of electrical energy that represents the electrostatic forces between atomic particles. The nucleus of an atom has a positive charge (+) and the electrons have a negative charge(-).
* Circuit: A full path of electrical current from a voltage source that passes completely from one terminal of the voltage source to another.
* Conductance: The measure of the ability of a material or substance to carry electrical current.
* Conduction: The moving of electricity or heat through a conductor.
* Conductor: A material used to conduct electricity or heat.
* Coulomb: A unit of electric charge. The amount of charge conveyed in one second by one ampere.
* Current: The rate at which electricity flows, measured in amperes, 1 ampere = 1 coulomb per second.
* Cycle: or Hertz; The measurement of the time period of one alternating electric current. In the UK this is commonly 50 cycles per second, or 50 Hertz.
* Cycle Time: The time it takes for a controller to complete one on/off cycle.
* Delta: In a three phase connection all three phases are connected in series thus forming a closed circuit.
* Dilectric: Non-conducting material used to isolate and/or insulate energized electrical components.
* Diode: A device having two terminals and has a low resistance to electrical current in one direction and a high resistance in the other direction.
* Direct Current: (DC); Electrical current that flows consistently in one direction only.

• Efficiency: Output power divided by input power, (work performed in ratio to energy used to produce it).
• Electric circuit: An arrangement of any of various conductors through which electric current can flow from a supply current.
• Electricity: A form of energy produced by the flow of particles of matter and consists of commonly attractive positively (protons (+) and negatively (electrons (-) charged atomic particles. A stream of electrons, or an electric current.
• Electrochemistry: Chemical changes and energy produced by electric currents.
• Electrode: An anode (+) or cathode (-) conductor on a device through which an electric current passes.
• Electrodynamic: The interaction of magnetism and electrical current.
• Electrokinetics: The behaviour of charged particles and the steady motion of charge in magnetic and electric fields.
• Electrolysis: Electric current passing through an electrolyte which produces chemical changes in it.
• Electromagnet: A coil of wire wound about a magnetic material, such as iron, that produces a magnetic field when current flows through the wire.
• Electromagnetic field: Electric and magnetic force field that surrounds a moving electric charge.
• Electron: A fundamental negatively (-) charged atomic particle that rotates around a positively (+) charged nucleus of the atom.

• Farad: The unit for capacitance. A capacitor that stored one coulomb of charge with one volt across it will have a value of one farad.
• Field cell: Commonly used in generators and motors, it is an electromagnet formed from a coil of insulated wire that is wound around a soft iron core.
• Field-Effect Transistor (FET): A three terminal semiconductor device. In a "FET" the current is from source to drain because a conducting channel is formed by a voltage field between the gate and the source.
• Filament: The element inside a vacuum tube, incandescent lamp or other similar device.
• Filter: A circuit element or components that allows signals of certain frequencies to pass and blocks signals of other frequencies.
• Fluorescent: The quality of having the ability to emit light when struck by electrons or another form of radiation.
• Flux: The rate of transfer of energy.
• Frequency: Also known as Hertz, it is the number of complete cycles of periodic waveform that occur during a time period of one second.
• Ground: A reference point at zero potential with respect to the earth. In an electronic circuit it is the common return path for electric current. A conducting connection between the earth and an electrical circuit or electrical equipment. Also, the negative side of DC power supply.
• Hard Wired: That part of a circuit which is physically interconnected.
• Hazardous Location: An area in which combustible or flammable mixtures are or could be present.
• I: Intensity. The commonly used symbol used to represent Amperes when used in formulas. I = Intensity = Current = Amps = Amperes.
• Impedance: The opposition to electrical flow.
• Infrared: The form of radiation used to make non-contact temperature measurements. In the electromagnetic spectrum it is the area beyond red light from 760 nanometers to 1000 microns.
• Interface: The method by which two devices or systems are connected and interact with each other.
• Joule: The basic of thermal energy. The work done by the force of one newton acting through a distance of one meter.
• Lag: The time delay between the output signal and the response time of the receiver of the signal.
• Leakage current: A small current leaking from an output device in the off state caused by semiconductor characteristics.
• Light Emitting Diode: LED; A solid state light source component that emits light or invisible infrared radiation.
• Load: The electrical demand of a process. Load can be expressed or calculated as amps (current), ohms (resistance) or watts (power).

 

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• Farad: The unit for capacitance. A capacitor that stored one coulomb of charge with one volt across it will have a value of one farad.
• Field cell: Commonly used in generators and motors, it is an electromagnet formed from a coil of insulated wire that is wound around a soft iron core.
• M: Symbol for Mega, one million.
• Magnetic Field: A region of space that surrounds a moving electrical charge or a magnetic pole, in which the electrical charge or magnetic pole experiences a force that is above the electrostatic ones associated with particles at rest.
• Magnetic Flux: Expressed in webers, it is the product of the average normal component of the magnetic intensity over a surface and the area of that surface.
• Make: To close an electrical circuit. To establish an electrical circuit through the closing of a contact, switch or other related device.
• Manual Reset Switch: A switch in a controller that manually resets after exceeding the controllers limit.
• Maximum Load Current: see; "Maximum Power Rating".
• Maximum Operating Temperature: The maximum temperature at which a device can be safely operated.
• Maximum Power Rating: The maximum watts that a device can safely handle.
• Mean Temperature: The average temperature of a process.
• Microamp: One millionth of an amp.
• Micron: One millionth of a meter.
• Microvolt: One millionth of a volt.
• Mil: One thousandth of an inch.
• Milliamp: mA; One thousandth of an amp.
• Millimeter: mm; One thousandth of a meter.
• Millivolt: mV; One thousandth of a volt. The difference in potential needed to cause a current of one milliampere flow through a resistance of one ohm.
• Momentary switch: A switch with contacts that are made with actuating force and released when that force is removed.

• N.C.: Normally Closed.
• N.O.: Normally Open.
• Ohm: The unit by which electrical resistance is measured. One ohm is equal to the current of one ampere which will flow when a voltage of one volt is applied
• Ohmeter: A meter used to measure electrical resistance in units of ohms.
• On/Off Controller: A controller whose action is either fully on or off.
• Open Circuit: An electrical circuit that is not "made". Contacts, switches or similar devices are open and preventing the flow of current.
• Operating Temperature: The range of temperature over which a device may be safely used. The temperature range which the device has been designed to operate.
• Output: The energy delivered by a circuit or device. The electrical signal produced by the input to the transducer.
• Phase: The time based relationship between a reference and a periodic function.
• Polarity: Magnetically, opposite poles, north and south. In electricity, oppositely charged poles, positive and negative.
• Power Dissipation: The amount of power that is consumed and converted to heat.
• Power Supply: The part of a circuit that supplies power to the entire circuit or part of the circuit. Usually a separate unit that supplies power to a specific part of the circuit in a system.
• Pulse: A rise and fall of voltage, current, or other faction that would be constant under normal conditions. A pulse that is intentionally induced will have a finite duration time.
• Quantum: One of the very small discrete packets into which many forms of energy are subdivided.
• Quartz: A form of silicone dioxide. Commonly used in the making of radio transmitters and heat resistant products.
• Rectifier: A device that converts AC voltage to pulsating DC voltage.
• Relay: A Solid State relay is a switching device that completes or interrupts a circuit electrically and has no moving parts. A Mechanical relay is an electromechanical device that closes contacts to complete a circuit or opens contacts to interrupt a circuit.
• Resistance: The resistance to electrical current. Resistance is measured in ohms.
• Response Time: The amount of time it takes for a device to react to an input signal.
• Rheostat: A variable resistor.
• Ripple: A fluctuation in the intensity of a steady current.
• Root Mean Square: RMS; AC voltage that equals DC voltage that will do the same amount of work. For an AC sine wave it is 0.707 x peak voltage.

• SCR: Silicone Controlled Rectifier.
• Series Circuit: A circuit which may have one or many resistors and/or other various devices connected in a series so that the current has only one path to follow.
• Supply Current: Current Consumption. The amount of amps or milliamps needed to maintain operation of a control or device.
• Supply Voltage: The range of voltage needed to maintain operation of a control or device.
• System International: SI; The standard metric system of units.
• Transducer: A device that transfers power or energy from one system to another, such as taking a physical quality and changing it to an electrical signal.
• Transient: A sudden and unwanted increase or decrease of supply voltage or current.
• Thermistor: An electrical resistor composed of semiconductor material, whose resistance is a known rapidly varying function of temperature.
• Transient: A sudden and unwanted increase or decrease of supply voltage or current.

• Triac: A solid-state switching device used in switching AC wave forms.

• UHF: Ultra High Frequency

• Vacuum: Pressure that is less than atmospheric pressure.
• VF: Variable Frequency.
• VHF: Very High Frequency.
• Volt: Voltage; The unit of electromotive force (EMF) that causes current to flow. One volt causes a current of one amp through a resistance of one ohm.
• Voltage Drop: The difference in potential measured between two points caused by resistance or impedance.
• Voltmeter: A meter used to measure units of volts.
• Watt: The unit of power. One watt equals one joule per second, 1/746th horsepower.
• Watt-hour: The power of one watt operating for one hour, and equal to 3,600 joules.
• Weber: The standard unit of magnetic flux.

• Zener Diode: A silicone semiconductor that maintains a fixed voltage in a circuit.

 

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What is a Portable Appliance?

Generally, portable appliances can be thought of as electrical goods that can be plugged into a power socket. This includes such items as FAX machines, toasters, drills etc. Testing incorporates 110 volt and 400 volt (3 phase) appliances , not just mains powered equipment (230 volt).

When is testing required?
•Testing is a requirement whenever:
•Employees use electrical appliances
•Customers (ie non-employees) use electrical appliances
•When electrical goods are re-sold or hired
•When appliances have been repaired

What has to be done?
Under the Electricity at Work Regulations 1989 in particular, and other Health & Safety requirements,
it is generally agreed that a planned regime of testing is the only way to
show that a proper ‘duty of care’ has been taken to protect users from electrical shock and the hazard of fire.
Unless the equipment is to be tested every time it is to be used, you will need to keep records to show when testing has been carried out, test results and who did the testing.

Equipment that has passed its testing should be marked on the outside to show the date when re-testing is due.
The equipment should not be used after this date. Showing the test date will have little value to the average user who will not have the knowledge to decide Test intervals are determined by considering the nature of use, frequency of use and
Test intervals are determined by considering the nature of use, frequency of use and working environment. Equipment used in an office where it is not moved eg a FAX machine will not require testing as often as the kitchen kettle, which in turn may not require testing as often as an extension cable that is being used outdoors on a building site.

A principle of electrical safety is that there should be 2 levels of protection. Earth + insulation
(an earthed appliance) are known as Class 1 appliances. Class 2 appliances are
protected using insulation + insulation (a double insulated appliance).
Nearly all of the equipment we meet falls into either Class 1 or Class 2. We will
concentrate on these here, but seek specialist advice if you feel that you have equipment that falls outside these classes.

All test equipment should be calibrated at intervals determined by the Test House.
Without using calibrated test equipment the tests are all but meaningless. It is easiest to conduct the tests using equipment especially designed for such testing, but separate items of equipment can be used where the Inspector has sufficient knowledge. Many PAT testers are designed to store and then download the test results to a PC, although manual testers can be used where results are recorded by the Inspector.

TESTING PROCEDURES :

Before undertaking any electrical tests you should always conduct a visual inspection, looking for damage exposing live parts, missing insulation, damage to the earth conductor, loose cable grips, checking for correctly rated fuses etc. Only when you feel that the equipment has passed all visual checks should you move on to conduct the appropriate
electrical tests. Please remember to switch on the item before conducting further tests. Where possible, always use an RCD (Residual Current Device), with a trip value of no greater than 30mA, in the supply to the test equipment. This precaution should prevent any shocks sustained by the Inspector from proving fatal.

Class 1 Protection :

This is the class of protection we meet most frequently. There are 2 tests that must be carried out, once a careful visual inspection has been conducted, and the equipment has been deemed fit for electrical testing.

EARTH BOND TEST : Must be completed with a successful test result before commencing the Insulation Test. ,

A substantial current is passed down the earth conductor, to the external metalwork and returns via the probe or crocodile
clip which is connected to the test equipment. The value of the resistance is shown on the tester. When selecting a test point
on the case, bear in mind than many decorative finishes are also poor conductors. We are looking for a low value (< 0.1Ω). In the case of a failure, the earth return should present a lower resistance path to earth than that offered by the human body. Where long cables are being tested, the Inspector will need to make an adjustment to the value returned by the test to allow for the resistance in the cable itself, before they can be sure that the nett resistance value is low enough to be considered safe. How this adjustment is calculated is outside the scope of this document.
A high test current is used so that should an earth conductor be too flimsy to provide protection under fault conditions, it
will fail (melt) under test. This will allow the fault to be remedied before re-testing, and its eventual return to service.

Do not touch the equipment while conducting the test. ←←←

INSULATION TEST :
A test voltage is applied, usually 500V DC, between the Earth conductor and Live & Neutral linked together.
We are looking for a high value (>1MΩ), and results showing infinity (∞) are common.

Do not touch the equipment while conducting the test.←←←

PAT Testing and Portable Appliance Testing information

Fuse Ratings
For the convenience of users, appliance manufacturers have standardised on two plug fuse ratings- 3A & 13A and adopted appropriate flex sizes. For appliances up to 700W a 3A fuse is used, for those over 700W a 13A fuse is used.
A variety of fuse ratings (1A, 2A, 3A, 5A, 7A, 10A 13A common ratings in bold) are available.
The fuse in the plug is not fitted to protect the appliance, although in practice it often does this. Appliances are generally designed to European standards for use throughout Europe. In most countries the plug is unfused. If an appliance needs a fuse to comply with the standard it must be fitted within the appliance. The fuse in the plug protects against faults in the flex and can allow the use of a reduced csa flexible cable. This is advantageous for such appliances as electric blankets, soldering irons and Christmas tree lights, where the flexibility of a small flexible cable is desirable.
With some loads it is normal to use a slightly higher rated fuse than the normal operating current. For example on 500 W halogen floodlights it is normal to use a 5 A fuse even though a 3 A would carry the normal operating current. This is because halogen lights draw a significant surge of current at switch on as their cold resistance is far lower than their resistance at operating temperature.

The Regulations implement an EC Directive aimed at the protection of workers and the "general duties" will require the need to:

a) Make sure that equipment is suitable for the use that will be made of it.
b) Take into account the working conditions and hazards in the workplace.
c) Ensure equipment is used only for operations for which, and under conditions for which, it is suitable.
d) Ensure that equipment is maintained in an efficient state, in efficient working order and in good repair.
e) Provide equipment that conforms to EC product safety directives.
f) Plus certain other general duties and specific requirements etc.

VISUAL INSPECTION

In practice approximately 90% of all equipment defects are found during a preliminary visual inspection.

(1) The exterior of the equipment will be inspected for:
(i) physical damage.
(ii) signs of overheating
(iii) signs of ingress of liquid or foreign materials.

Particular attention will be paid to possible physical damage at accessible mains components such as switches, fuses and appliance couplers.

(2) All mains and power cords, including interconnecting cords, will be checked for physical damage. All flexible cords showing any sign of damage will be replaced

(3) Where re-wireable plugs or appliance couplers are used, their covers will be removed, and (i) terminations and cord grips will be checked for tightness.
(ii) terminations will be checked for correct polarity.
(iii) conductors will be checked for damage or loose strands.

(4) Operator accessible fuses on the outside of the equipment will be checked for correct type and rating. If the equipment manufacturer has specified a particular rating for the plug fuse, this will also be checked. If the manufacturer has not specified a fuse rating for the plug the preferred fuse size will be determined and the correct size fitted, and check that properly manufactured cartridge fuses to British Standards are used.

5) Plugs with none insulated pins will be replaced with British Standards approved Insulated ones.

 

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Class 2 Protection :

How do you recognise Class 2 equipment ? It should be marked with the symbol below.
The double box - symbolising the 2 levels of insulation - should be found on the outside of the equipment. A test voltage is applied, usually 500V DC, between the Live & Neutral conductors linked together and the tip of a test probe. This probe is moved over the exterior of the case, paying
particular attention to any openings for cooling etc. We are looking for a high resistance value, and results showing infinity (∞) are common. There is just one test that must be carried out, once a careful visual inspection has been conducted, and the equipment has been deemed fit for electrical testing.

INSULATION TEST
Do not touch the equipment while conducting the test

Re-tests
Equipment should not be used once it has passed the “ DO NOT USE ” date marked on the outside. You need to develop a procedure for identifying such items so that they can be tested before next use. It is perfectly acceptable to have items ‘out of date’ and untested if they are not being used. Once they need to be used, however, they need to be tested.
Repair work that affects the power or protection arrangements e.g. dismantling part of a case on a Class 1 item, will require testing before use.

PVC-U CONDUIT CABLE CAPACITIES :

used to determine the size of conduit necessary to accommodate cables of the same size, or different sizes, and provides a means of compliance with
Regulations, which states ‘The number of cables drawn into conduit of a wiring system shall be such that no damage is caused to the cables or to the
conduit during their installation.’ The method employs a ‘unit system’ each cable size being allocated a factor. The sum of all factors for the cables intended to be run in the same conduit is compared against the factors given for conduit in order to determine the size of conduit necessary to accommodate those cables.

It has been found necessary, for conduit, to distinguish between – 1. Straight runs not exceeding 3 metres in length, and
2. Straight runs exceeding 3 metres, or runs of any length incorporating bends or sets. The term ‘bend’ signifies a British Standard 90º
bend and one double set is equivalent to one bend

For the case 1, each conduit size is represented by only one factor. For the case 2, each conduit size has a variable factor which is dependent on the
length of run and the number of bends or sets. For a particular size of cable the factor allocated to it for case 1 is not the same as for case 2.

Because of certain aspects, such as the assessment of reasonable care of pulling-in, acceptable utilisation of the space available and the
dimensional tolerance of cables and conduit, any method of standardising the cable capacities of such enclosures can only give guidance on the
number of cables which can be accommodated.

Thus the sizes of conduit determined by the method given in this appendix are those which can be reasonably expected to accommodate the
desired number of cables in a particular run using an acceptable pulling force and with the minimum probability of damage to cable insulation.

Only mechanical considerations have been taken into account in determining the factors given in the following tables.
o/s/g 5A – 5B – 5C – 5D ,

As the number of circuits in a conduit increases, the current-carrying capacities of the cables must be reduced according to the appropriate grouping
factors. It may therefore be more attractive economically to divide the circuits concerned between two or more enclosures.

Cable factors for long straight runs or runs incorporating bends ( 3 meters )
Cable factors for short straight runs 5A ( under 3 meters )
Conduit factors for short straight runs 5B
Conduit factors for runs incorporating bends 5D
Supertube increase cable factor by 15%.

SURFACE INSTALLATION
All horizontal runs of conduit should be secured at a maximum distance of 0.9m and vertical runs should be secured at a maximum of 1.2m. For high
ambient temperatures or where rapid changes in temperature are likely to be encountered this distance should be reduced. At fittings or where
directional changes takes place the conduit should be fastened approximately 150mm either side to maintain support. The fastenings should not be
over tightened to permit thermal movement of the conduit.

CHOICE CONDUIT/CHANNEL
The choice is dependent on the type of work being undertaken and the specification. Heavy gauge round conduit is normally used in surface work and
for casting in-situ. Light gauge round conduit is suitable for concealed work and in screeds. Oval conduit is normally chosen for use in plastered walls and can be used as switch drops in surface work. The channel sections are frequently used as an inexpensive method of installing cables in domestic installations beneath plaster.

General Guidelines
The following contains information on the placement of fiber optic cables in various indoor and outdoor environments. In general, fiber optic cable can be installed with many of the same techniques used with conventional copper cables. Basic guidelines that can be applied to any type of cable installation are as follows:
• Conduct a thorough site survey prior to cable placement.
• Develop a cable pulling plan.
• Follow proper procedures.
• Do not exceed cable minimum bend radius.
• Do not exceed cable maximum recommended load.
• Document the installation.

Testing

The Flashlight Test
A simple continuity test for short-to-medium length fiber optic links is to shine a flashlight into a cleaved or connectorized link and observe if light comes out of the other end. On short lengths, it may be necessary to cleave only the end where the flashlight injects light into the fiber.

This simple check can be made on cable lengths of up to a mile and more. If cable ends are outdoors, sunlight may be used. NOTE: on longer lengths, the light observed at the opposite end may appear red in colour. This is normal and is caused by the filtering of light within the fiber.

CAUTION: NEVER LOOK DIRECTLY INTO A FIBER CONNECTED TO LIGHT LAUNCHING EQUIPMENT. THIS CAN CAUSE PERMANENT EYE DAMAGE.

Magnifying Glasses and Microscopes:

Because the naked eye cannot detect scratches or defects in optical fibers, use of magnification equipment is required. For most routine inspections, and ordinary battery-powered illuminated microscope of 30x to 100x can produce satisfactory results.

Some microscopes are available with special adapters specifically designed for use with fiber optic connectors.

Bend radius
a) Do not exceed the cable bend radius. Fiber optic cable can be broken when kinked or bent too tightly, especially during pulling.
b) If no specific recommendations are available from the cable manufacturer, the cable should not be pulled over a bend radius smaller than twenty (20) times the cable diameter.
c) After completion of the pull, the cable should not have any bend radius smaller than ten (10) times the cable diameter.

Twisting cable
a) Do not twist the cable. Twisting the cable can stress the fibers. Tension on the cable and pulling ropes can cause twisting.
b) Use a swivel pulling eye to connect the pull rope to the cable to prevent pulling tension causing twisting forces on the cable.
c) Roll the cable off the spool instead of spinning it off the spool end to prevent putting a twist in the cable for every turn on the spool.
d) When laying cable out for a long pull, use a "figure 8" on the ground to prevent twisting. The figure 8 puts a half twist in on one side of the 8 and takes it out on the other, preventing twists.

Vertical cable runs
a) Drop vertical cables down rather than pulling them up whenever possible.
b) Support cables at frequent intervals to prevent excess stress on the jacket. Support can be provided by cable ties (tightened snugly, not tightly enough to deform the cable jacket) or Kellems grips.
c) Use service loops can to assist in gripping the cable for support and provide cable for future repairs or rerouting.

Use Of Cable Ties
Fiber optic cables, like all communications cables, are sensitive to compressive or crushing loads. Cable ties used with many cables, especially when tightened with an installation tool, are harmful to fiber optic cables, causing attenuation and potential fiber
breakage.
a) When used, cable ties should be hand tightened to be snug but loose enough to be moved along the cable by hand. Then the excess length of the tie should be cut off to prevent future tightening.

→→ Hook-and-loop fastener ties are preferred for fiber optic cables, as they cannot apply crush loads sufficient to harm the cable. ←←

Conduit : If bends are installed using a spring or former it is often good practice to place saddles close to the bend ,

 

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Steel Conduit
Where conduit is installed externally or in potentially damp locations, connections to accessory boxes shall be made with flanged couplings and long reach bushes, and all conduit boxes shall be fitted with gaskets.
• Conduit shall be free from all score marks. ( a must ) ←←←
• Conduit shall be screwed and butted solidly into all fittings so as to ensure a continuous electrical and mechanical installation.
• Conduit shall be installed with the minimum number of running couplings.
• Conduit shall have no more than two right angle bends without the provision of a draw-in box.
• All exposed threads shall be painted using a zinc rich paint.

PVC Trunking
Where trunking passes through the building structure, it shall be installed with a fixed section of lid. Such fixed sections shall be restricted to the absolute minimum length necessary. ( it could be 6ins fixed then fire barrier !! remember to screw it down ? small self tappers PS and with steel trunking

Relays :
Relays are switches that are turned on and off by a small electrical current.
Inside a relay is an electromagnet. When a small current energizes this electromagnet, it attracts an armature blade and closes contact points. Current that the relay is designed to switch on or off, can then flow across the points.
As long as the small switching current flows to the relay, the much larger current will flow through its contact points.
A relay is an electrical switch that opens and closes under control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered, in a broad sense, to be a form of electrical amplifier.
These contacts can be either normally-open, normally-closed, or change-over contacts.
• Normally-open contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive.
• Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive.
• Change-over contacts control two circuits: one normally-open contact and one normally-closed contact.

Rotating magnetic fields
A rotating magnetic field is a magnetic field which rotates in polarity at non-relativistic speeds. This is a key principle to the operation of alternating-current motor. A permanent magnet in such a field will rotate so as to maintain its alignment with the external field. This effect is utilised in alternating current electric motors. A good rotating magnetic field can be constructed using three phase alternating currents . Synchronous motors and induction motors use a stator's rotating magnetic fields to turn rotors.

* Changing magnetic fields, according to Faraday's law of induction, can induce an electric field and thus an electric current; similar currents can be induced by conductors moving in a fixed magnetic fields. These phenomena are the basis for many electric generators and electric motors.

Resistance & Area :

Resistance decreases if the cross-sectional area is increased. This sometimes confuses people,
The narrow wire has fewer paths available for the electrons to move through. Whilst the larger wire has
many more routes they could take. This makes conduction easier.

Think of the fat wire as being a 6-lane motorway. There is always somewhere to go, so going quickly is easy. The thin wire is like a narrow countryside lane. Movement is restricted, so you have to drive slowly!

AC/DC

Electrical current can transfer energy from an energy source to a device in two ways. We are used to a cell providing CURRENT in one direction , only. We call this direct current or DC. ←

However, it is possible to transfer energy using a current that changes direction all the time. By moving electrons one way, then back, then repeating, energy can be transferred. We call this alternating current or AC. ←

Alternating Current (AC)

Alternating Current is the movement of electrons in a wire backwards then forwards repeatedly. In Europe this change repeats 50 times per second (or 50 Hz). In the USA, the frequency is 60 Hz.
AC is remarkably useful because it allows us to change electricity very easily using transformers which cannot work with DC.

Atoms

The word "atom" is Greek and it means "cannot be split". But we now know that atoms can be split and that they split into protons, neutrons and electrons.
The protons and neutrons form the atom's nucleus. Protons have a “ + positive charge “ whereas neutrons are neutral. -
Electrons have a negative charge and they orbit the nucleus like the planets orbit the Sun:
Most atoms have the same number of protons and electrons and so have a neutral charge overall.
If an atom has more protons than electrons, it has more positive charge than negative charge, so the atom is positively charged.
If an atom has more electrons than protons, it has more negative charge than positive charge, so the atom is negatively charged.

P is for positive and proton.
N is for neutral and neutron.
To balance the charges, electrons must be negative.

* Think of an electric charge as an imbalance between protons and electrons. The more protons the more positive charge. The more electrons the more negative charge.

* Positively-charged atoms are called positive ions (or cations). Negatively-charged atoms are called negative ions (or anions).

Voltage & Current

In order for a current to flow, something has to make it flow. That something is measured by voltage; voltage measures the energy available to drive the flow of current.

Potential Difference or Electromotive Force

The energy available to drive a flow of current *is called potential difference or electromotive force (EMF). It is provided by an energy source such as a cell * or mains supply and is measured in volts by a voltmeter:

One volt is the energy required to drive a current of one amp * through a circuit * with a resistance of one Ohm *. Voltage is represented by the symbol, V. There is a direct relationship between voltage and current.

dimmers work ?

Typical light dimmers are built using thyristors and the exact time when the thyristor is triggered relative to the zero crossings of the AC power is used to determine the power level. When the the thyristor is triggered it keeps conducting until the current passing though it goes to zero (exactly at the next zero crossing if the load is purely resistive, like light bulb). By changing the phase at which you trigger the triac you change the duty cycle and therefore the brightness of the light.

Here is an example of normal AC power you get from the receptacle (the picture should look like sine wave):
... ...
. . . .
. . . .
------------------------------------ 0V
. . . .
. . . .
... ...

Sorry I cant down load the drawing sorry about that amberleaf

 

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* ELV - Extra low voltage- Voltage that is below 50 Volts AC
* FELV - Functional Extra low voltage-any other extra low voltage circuit that does not fulfil the requirements for an SELV or PELV circuit. Although the FELV part of a circuit uses an extra low voltage, it is not adequately protected from accidental contact with higher voltages in other parts of the circuit. Therefore the protection requirements for the higher voltage have to be applied to the entire circuit.
* KW- Kilowatt One thousand watts of electricity. Ten 100-watt light bulbs use one kilowatt of electrical power.
* KW/h- One kW of electrical power used for one hour. The most common measurement of electrical consumption, most grid connected electrical meters measure kW / h for billing purposes.
* MD - Maximum demand- is the largest current normally carried by circuits, switches and protective devices.
* PAT- Portable appliance testing - testing of portable appliances to ensure that they are electrically safe to use.
* PELV- Protected extra low voltage- In contrast to an SELV circuit, a Protected Extra Low Voltage (PELV) circuit has a protective earth (ground) connection. A PELV circuit, just as with SELV, requires a design that guarantees a low risk of accidental contact with a higher voltage. For a transformer, this can mean that the primary and secondary windings must be separated by an extra insulation barrier or by a conductive shield with a protective earth connection.
* SELV - Separated extra low voltage- This should be safely separated from other circuits that carry higher voltages and isolated from earth (ground) and from the protective earth conductors of other circuits.
* VD- Volt drop- a voltage drop in a circuit normally occurs when current is passed through a circuit. The greater the resistance of the circuit the greater the volt drop.
* VOLT- A unit of measure of the pressure in an electrical circuit. Volts are a measure of electric potential. Voltage is often explained using a liquid analogy -- comparing water pressure to voltage: a high pressure hose would be considered high voltage, while a slow-moving stream could be compared to low voltage.
* WATT HOUR- Electrical power measured in terms of time. One watt hour of electricity is equal to one watt of power being consumed for one hour. (A one-watt light operated for one hour would consume one watt hour of electricity.)
* IEE- INSTITUTE OF ELECTRICAL ENGINEERS- Founded in 1871, the IEE is the largest professional engineering society in Europe and has a worldwide membership of 140,000.
* BASEC- British Approvals Services for Cables. You will often see BASEC approved on the pvc covering of today's modern cable.
* NICEIC- National Inspection Council for Electrical Installation Contracting. The NICEIC is the UK's consumer safety organisation and independent regulatory body for the electrical industry.

 

[mikilianis]

Hi I wonder if I am posting in the correct forum ,if by chance I am not then would some- one please be kind and direct me to the correct forum my query being as follows
I have 3 clip on current meters ( tong testers ) and when a load is measured I get different readings now all is very well if one just wants to check if a circuit is drawing a load , but when one has to explain the reason for the different readings ,
Meter A is a analogue meter
Meter B is a digital “ R.M.S. “ meter
Meter C is a digital meter
On an inductive load the readings are
A = 43 amps B = 42 amps C = 45 amps
On an resistive load the readings are
A = 95 amps B = 87.5 amps C = 103 amps
What could the reason be for the different readings.
Thanks Mike.

 

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Total Load Rating of Transformer ( revision )

Load ratings for transformers are usually given as VA or kVA, these are obtained by multiplying the load current by the supply voltage: this gives the volt-ampere (VA) rating, where 1000 VA = 1 kVA. This is often loosely referred to as the "power" rating of the transformer. In actual practice the power which the transformer can deliver into a given load also depends on a quantity known as the power factor (p.f.), which is defined as the ratio of real power to apparent power, i.e. the absorbed power divided by the volt-ampere (VA) product. For a purely resisitive load the p.f. is unity and the transformer will be able to supply a load power equal to its VA rating. In practice the majority of loads are not purely resistive and have a small reactive (inductive or capacitive) component which should be taken into account. When a p.f. value is not known it is common practice to assume a value of 0.8.

Filament lamps and coiled heater elements may be assumed to have a power factor of approximately 0.95, which is often ignored when specifying a trasnsformer. Discharge lamps (which includes fluorescent lamps) present a lower power factor, which in industrial and commercial situations is normally adjusted by the connection of a p.f. correction capacitor to a value of 0.95. Uncorrected power factors for discharge lamps can be as low as 0.5, so it pays to correct.

Motors also have fairly low power factors. A single phase induction motor will typically have a p.f. in the range 0.6 - 0.85, cheaper motors being worse. Again, p.f. correction is advisable. The power factor is normally marked on the motor rating plate as a cos Ø value.

Induction motors are frequently marked with the shaft power rather than the input power which makes the situation more confusing. To obtain the actual input kVA for such a motor it may be possible to measure the input current (preferably with a clamp meter) whilst the motor is under full load. Multiplying the value obtained by the supply voltage will then give the kVA loading of the motor.

E.g. A particular 2 kW load has a p.f. of 0.8, what VA rating should be allowed for the transformer supplying this load ?

A. 2000 / 0.8 = 2 500 VA = 2.5 kVA This transformer should be specified with a minimum rating of 2.5 kVA.

Phases
Transformers are normally wound as either single or three phase units for connection to a single or three phase electrical supply respectively. A single phase transformer requires a single live (phase) connection and a neutral to the primary for operation. A three phase unit requires three lives (phases) and sometimes a neutral. The phase to phase voltage for a 3 phase plus neutral system is 1.732 x Phase to neutral voltage.

E.g. A 415 V 3 phase supply has a phase to neutral voltage of 415 V / 1.732 = 240 V
Note: 1.732 is the square root of 3, to 4 significant figures.

Winding Type
Transformers may be manufactured as either isolating or auto-wound.

An isolating transformer has primary and secondary windings which are not in any way electrically connected to one another, they are purely coupled by magnetic effects in the iron core. This has the benefit that the secondary windings may be electrically connected to a different ground system to the primary, or not grounded at all, simply left floating with respect to ground.

An auto-transformer has a point which is electrically common to the input and output of the unit. It does not, therefore, provide isolation between input and output, the circuits are electrically connected. The benefits of using an auto-winding are a reduction in the size and cost, as the transformer does not actually have to be large enough to handle the full load power, it merely has to provide the balance of the power. Hence, if the difference between the supply voltage and output voltage is small the transformer can be small.

e.g. A single phase supply voltage of 230 volts is available and it is desired to connect a 240 volt load rated
at 24 kW what part of the load is the auto-transformer required to handle ?

Ans. Calculate the load current, 24 000 W / 240 V = 100 A
Calculate the difference between supply voltage and load voltage, 240 V - 230 V = 10 V
Calculate the transformer loading, 100 A x 10 V = 1 000 W = 1 kW

The transformer has to handle 1 kVA (assuming a load power factor of unity.

how we can calculate the transformer size.

Answer ; Transformer size is depends upon the load.
Take one building having load of 630KW Now we can calculate the t/f size
KW=KVA*P.f
630=KVA * 0.8
KVA = 630/0.8 KVA = 787.5 KVA So the Transformer size is 800KVA

how we can calculate the transformer size.
* it depends on the load.
* depends on frequency of operation & operating power
* it depends upon flux density & kva rating

Calculating Transformer Rating
Load rating for transformers are usually given as VA or kVA. These power ratings are obtained by multiplying the load current by the supply voltage, this gives the volt-ampere rating, where 1000VA=1 kVA. This is referred to as the power rating of the transformer. The power which the transformer can deliver to a given load also depends on power factor, which is defined as the ratio of real power to apparent power - the absorbed power divided by the volt-ampere product. For a resistive load the power factor is unity and the transformer will be able to supply a load power equal to its VA rating. The majority of loads are resistive loads having a small reactive or inductive or a capacitive component which should be taken into account. When a power factor value is unknown, for simple calculation purposes it usually assumes a value of 0.8.

Transformer Rating of Secondary Voltage
Secondary rating on a transformer is the secondary voltage, which could be more than one on a transformer. The secondary transformer rating also has a maximum current or power which it can deliver to a load. The total VA rating of all the windings will normally equal the VA rating specified as the total load rating of the transformer. The secondary voltages for each set of secondary windings must be specified, along with the VA in each case. The only exception to this is when there is only one secondary winding; in this case it will have a rating equal to the total load rating for the transformer.

Transformer KVA is the load voltage times the load current. For example, a single phase transformer rated for 120 VAC and 20 Amperes would be rated for 120 X 20 = 2400 VA, or 2.4 KVA (thousand VA).

To calculate transformer KVA, there are only two formulas that you need:

Single Phase Transformers
Volts X Amps = Transformer KVA ,1000

Three-Phase Transformers
Volts X Amps X 1.732 = Transformer KVA ,1000

Transformer Sizing : Step 1 – Understanding the language.

Certain terminology is used when sizing the transformer. The terms are easy once you understand the abbreviations. V which stands for Voltage - A (or Amps) which is Amperage - K which stands for Kilo which is equal to 1000. If a transformer is rated at 120VA it means that it can handle 120 volts at 1-ampere or 1 amp of current. The VA is short for volt-ampere a designation of power. A transformer rated at 1.2 KVA is another way of say 1200 VA or 120 volts at 10 amps of current.

Calculating Transformers

Single Phase when KVA is known:
(kva x 1000) divided by (voltage) = amps

Three Phase when KVA is known:
(kva x 1000) divided by (voltage x 1.732) = amps

Single Phase:
(Volts) x (Load Amps) divided by (1000) = kva

Three Phase:
(Volts) x (Load Amps) x (1.732) divided by (1000) = kva

What is the main difference between small transformers 50W and larger transformers’ and what key specifications will normally decide the price for a transformer

Answer
There is no fundamental difference. The principal of the transformer is always the same. It uses the principal that a magnetic field can be formed by a coil. Like wise a changing magnetic field will generate a voltage in an electrical coil. The power of a transformer is defined by how much current the coil wires can carry. The thicker the wires the more current, and the lower the internal resistance. also the core of the transformer can be magnetically saturated which in return limits the power that can be transformed.

The difference is that to manufacture of a 50 watts WE can afford to be eneficient a bit . But for a 5000w efficiency becomes a factor. Dissipating 5w is not the same as dissipating 500w. THIS IS ASUMING A 10% EFFICIENCY.

 

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Some information that you might need a refresher on:

To convert mA to A (milliamps to amps) 1000mA = 1A
to convert µA to A (microamps to amps) 1000,000 µA = 1A
To converter µA to mA (microamps to amps) 1000µA = 1mA
To convert mW to W (milliwatts to watts) 1000mW = 1A
To converter µW to W (microwatts to watts) 1,000,000 µA = 1A

How to convert Watts to Amps

Basics
You cannot convert watts to amps, since watts are power and amps are coulombs per second (like converting gallons to miles). HOWEVER, if you have at least two of the following three: amps, volts and watts then the missing one can be calculated. Since watts are amps multiplied by volts, there is a simple relationship between them.
However, In some engineering disciplines the volts are more or less fixed, for example in house wiring, automotive wiring, or telephone wiring. In these limited fields technicians often have charts that relate amps to watts and this has caused some confusion. What these charts should be titled is "conversion of amps to watts at a fixed voltage of 110 volts" or "conversion of watts to amps at 13.8 volts," etc.
Converting Watts to Amps

The conversion of Watts to Amps is governed by the equation Amps = Watts/Volts

For example 12 watts/12 volts = 1 amp
Converting Amps to Watts

The conversion of Amps to Watts is governed by the equation Watts = Amps x Volts

For example 1 amp * 110 volts = 110 watts

Converting Watts to Volts

The conversion of Watts to Volts is governed by the equation Volts = Watts/Amps

For example 100 watts/10 amps = 10 volts

Converting Volts to Watts

The conversion of Volts to Watts is governed by the equation Watts = Amps x Volts

For example 1.5 amps * 12 volts = 18 watts

Converting Volts to Amps at fixed wattage

The conversion of Volts to Amps is governed by the equations Amps = Watts/Volts

For example 120 watts/110 volts = 1.09 amps

Converting Amps to Volts at fixed wattage

The conversion of Amps to Volts is governed by the equation Volts = Watts/Amps

For Example, 48 watts / 12 Amps = 4 Volts

Explanation

Amps are how many electrons flow past a certain point per second. Volts is a measure of how much force that each electron is under. Think of water in a hose. A gallon a minute (think amps) just dribbles out if it is under low pressure (think low voltage). But if you restrict the end of the hose, letting the pressure build up, the water can have more power (like watts), even though it is still only one gallon a minute. In fact the power can grow enormous as the pressure builds, to the point that a water knife can cut a sheet of glass. In the same manner as the voltage is increased a small amount of current can turn into a lot of watts.

How to convert VA to Watts and KVA to Kilowatts

Basics
Since watts is volts times amps, what is VA? VA (or volt-amps) is also volts times amps, the concept however has been extended to AC power. For DC current
VA = Watts (DC current).
In AC if the volts and amps are in phase (for example a resistive load) then the equation is also
VA=Watts (resistive load)
where V is the RMS voltage and A the RMS amperage.
In AC the volts and amps are not always in phase (meaning that the peak of the voltage curve is does not happen at the peak of the current curve). So in AC, if the volts and amps are not precisely in phase you have to calculate the watts by multiplying the volts times the amps at each moment in time and take the average over time. The ratio between the VA (i.e. rms volts time rms amps) and Watts is called the power factor PF.
VA•PF = Watts (any load, including inductive loads)

In other words, volt-amps x power factor = watts. Similarly, KVA*PF = KW,
Or kilovolt-amps times power factor equals kilowatts.
When you want to know how much the electricity is costing you, you use watts. When you are specifying equipment loads, fuses, and wiring sizes you use the VA, or the rms voltage and rms amperage. This is because VA considers the peak of both current and voltage, without taking into account if they happen at the same time or not

Finding the Power Factor
How do you find the power factor? This isn’t easy. For computer power supplies and other supplies that are power factor corrected the power factor is usually over 90%. For high power motors under heavy load the power factor can be as low as 35%.
Industry standard rule-of-thumb is that you plan for a power factor of 60%, which somebody came up with as a kind of average power factor.
Converting VA to Amps
How to convert VA to amps? Use the following formula:

Where A stands for the RMS amps, VA stands for volt-amps, V stands for RMS volts and PF stands for the power factor.
Converting VA to Volts
How to convert VA to volts? Use the following formula:

Where V stands for RMS volts, A stands for the RMS amps, VA stands for volt-amps, and PF stands for the power factor.
What is KVA?
KVA is just kilovolt-amps, or volts times amps divided by 1000:
KVA•PF = KW (any load, including inductive loads)
Where KVA stands for kilovolt-amps, KW stands for kilowatts, and PF stands for the power factor.

Keep the factor of 1000 straight when dealing with mixed units:
KVA•PF = W/1000 (any load, including inductive loads)
VA•PF = 1000•KW (Kilowatts to VA)

The Following equations can be used to convert between amps, volts, and VA. To convert between kilovolt-amps, kilowatts, and kiloamps, keep track of the factor of 1000.

Converting VA to Amps (voltage fixed)

The conversion of VA to Amps is governed by the equation Amps = VA•PF/Volts)

For example 12 VA•0.6/(12 volts) = 0.6 amp

Converting KVA to KW (Kilovolt-amps to Kilowatts)

The conversion of KVA to KW is governed by the equation KVA = KW/PF)

For example, if the power factor is 0.6
120 KVA•0.6 = 72 Kilowatts

Converting Watts to KVA (watts to kilovolt-amps)

The conversion of W to KVA is governed by the equation KVA=W/(1000*PF)

For example 1500W/(1000*0.83) = 1.8 kVA (assuming a power factor of 0.83)
F
Converting Amps to VA (voltage fixed)

The conversion of Amps to VA is governed by the equation VA = Amps • Volts/PF

For example 1 amp * 110 volts/0.6 = 183 VA

Converting Amps to KVA (voltage fixed)

The conversion of Amps to KVA is governed by the equation KVA = Amps • Volts/(1000•PF)

For example 100 amp * 110 volts/(1000*0.6) = 18.3 KVA

Converting VA to Volts (current fixed)

The conversion of VA to Volts is governed by the equation Volts = VA•PF/Amps

For example 100 VA • 0.6/10 amps = 6 volts

Converting Volts to VA (current fixed)

The conversion of Volts to VA is governed by the equation VA = Amps • Volts/PF

For example 1.5 amps * 12 volts/0.6 = 30 VA

Converting Volts to Amps at fixed VA

The conversion of Volts to Amps is governed by the equation Amps = VA•PF/Volts

For example 120 VA* 0.6 /110 volts = 0.65 amps

Converting Amps to Volts at fixed VA

The conversion of Amps to Volts is governed by the equation Volts = VA•PF/Amps

For Example, 48 VA • 0.6 / 12 Amps = 2.4 Volts

Explanation

Amps are how many electrons flow past a certain point per second. Volts is a measure of how much force that each electron is under. Think of water in a hose. A gallon a minute (think amps) just dribbles out if it is under low pressure (think voltage). But if you restrict the end of the hose, letting the pressure build up, the water can have more power (like watts), even though it is still only one gallon a minute. In fact the power can grow enormous as the pressure builds, to the point that a water knife can cut a sheet of glass. In the same manner as the voltage is increased a small amount of current can turn into a lot of watts.

Volt x amps, how to calculate volt-amps, kilovolt-amps, amps to KVA conversion, electrical KVA, KVA to KW, KVA calculations, what is kva ? Convert amps to VA. Convert VA to amps. Convert VA to volts, convert volts to VA, convert amps to volts at fixed wattage. How to convert VA to amps. How do I convert amps to VA? Amps converting va. Volt to VA conversion.

Convert VA to Amps (at a fixed voltage)
Convert KVA to KW (kilovolt-amps to kilowatts)
Convert KVA to Amps (at a fixed voltage)
Converting Watts to KVA (watts to kilovolt-amps)
Convert Amps to VA (at a fixed voltage)
Convert VA to Volts (at a fixed current)
Convert Volts to VA (at a fixed current)
Convert Volts to Amps (at a fixed VA)
Convert Amps to Volts (at a fixed VA)

Note: A kilowatt-hour is a 1000 watts times one hour = an energy unit.

associated conversions –

1 kilometre ( km ) = 1000 metre , 1 metre = 100 cm , 1 cm = 10 mm
1 mile = 5280 feet , 1 yard ( yd ) = 3 feet , 1 fathom = 6 feet ,
1 foot (ft.) = 12 inches (in.)

electromagnetic unit of capacitance : farad (F)
electromagnetic unit of charge : coulomb (C)
electromagnetic unit of current : ampere (A)
electromagnetic unit of inductance : Henry (H)
electromagnetic unit of potential : volt (V)
electromagnetic unit of resistance : ohm Ω
electronvolt : joule (J)
electrostatic unit of capacitance : farad
electrostatic unit of charge (Franklin) : coulomb
electrostatic unit of current : ampere
electrostatic unit of inductance : Henry
electrostatic unit of potential : volt
electrostatic unit of resistance : ohm

Paper Sizes
A0 :mm 841 x 1189 : inches 33.11 x 46.81
A1 :mm 594 x 841 : inches 23.39 x 33.1
A2 :mm 420 x 594 : inches 16.54 x 23.29
A3 :mm 297 x 420 : inches 11.69 x 16.54
A4 :mm 210 x 297 : inches 8.27 x 11.69
A5 :mm 148 x 210 : inches 5.83 x 8.27

 

[amberleaf]

- Watts = Amps x Volts

By dividing both sides of the formula by amps you get - Watts / Amps = Volts
... the amps / amps on the right hand side cancelling each other out to leave volts.
and by dividing both sides by volts you get - Watts / Volts = Amps
... the volts / volts on the right hand side cancelling each other out to leave amps.
Examples:-
q. What is the biggest electric fire that can be run on a 13 amp fused plug in the UK ?

a. Mains voltage in the UK is 230v so Watts = 13 x 230 = 2990 watts or just under 3kW
q. A 60 watt car spotlight is showing a drain of 5.5 amps on the ammeter.
What is the voltage?
a. 60 / 5.5 = 10.9 volts
q. A food mixer with a 400 watt motor runs in the US on 120 volt supply.
What fuse to fit?
a. 400 / 120 = 3.33 amps. A 5 amp fuse would be ok.
Ohms is a measure of resistance and Ohms = Volts / Amps

Formula 1 − Electrical (electric) power equation: power P = I × V = R × I2 = V2 ⁄ R
where power P is in watts, voltage V is in volts and current I is in amperes (DC).
If there is AC, look also at the power factor PF = cos φ and φ = power factor angle
(phase angle) between voltage and amperage.

Formula 2 − Mechanical (mechanic) power equation: Power P = E ⁄ t = W ⁄ t
where power P is in watts, Energy E is in joules, and time t is in seconds. 1 W = 1 J/s.
Power = force times displacement divided by time P = F • s / t or:
Power = force times speed (velocity) P = F • v.
Electric (electrical) Energy is E = P × t − measured in watthours, or also in kWh.

Calculate Amperage : Revision
When calculating the amperage on a branch circuit you must know if it is a single or a three-phase circuit In case of a 3-phase circuit, you will have a constant multiplier that you'll need to use in the formula. Calculating Amperage –single 1 Phase : I (Amperage - also known as Current) VA (Volt Amp - also known as Watt) V (Volt) Formula to Use: I = VA / V Example 1: Find the Amperage of an 2400 VA load on a 120 Volt, 1 phase branch circuit. Use the formula above, and substitute the given values. I = 2400 / 120 = 20 Amps ( 2400 ÷ 120 = 20 ) Example 2: Find the Amperage of an 5600 VA load on a 240 Volt, 1 phase branch circuit. Use the formula above, and substitute the given values. I = 5600 / 240 = 23.34 Amps ( 5600 ÷ 240 = 23.34 ) Calculating Amperage - 3 Phase : I (Amperage - also known as Current) VA (Volt Amp - also known as Watt) V (Volt) I = VA / (V * 1.732) Example 1: Find the Amperage of an 2400 VA load on a 240 Volt, 3 phase branch circuit. Use the formula above, and substitute the given values. I = 2400 / (240 * 1.732) = 5.78 Amps ( 2400 Va ÷ 240 V ÷ 1.732 = 5.78 A ) Example 2: Find the Amperage of an 7600 VA load on a 480 Volt, 3 phase branch circuit. Use the formula above, and substitute the given values. I = 7600 / (480 * 1.732) = 9.15 Amps ( 7600 ÷ 480 ÷ 1.732 = 9.141647421 amps ) round it up 9.15 amp For quick amperage calculation

Remember, the goal here is to pass your exam by studying relevant materials and not to get a PHD in Electrical Theory

* Micro--(U)
A metric prefix meaning one millionth of a unit or 10-6.
* Micron
A metric term meaning one millionth of a meter.
* Milli--(m)
A metric prefix meaning one thousandth of a unit or 10-3
* Motor, Shunt- Wound
This type of motor runs practically constant speed, regardless of the load. It is the type generally used in commercial practice and is usually recommended where starting conditions are not usually severe. Speed of the shunt-wound motors may be regulated in two ways: first, by inserting resistance in series with the armature, thus decreasing speed: and second, by inserting resistance in the field circuit, the speed will vary with each change in load: in the latter, the speeds is practically constant for any setting of the controller. This latter is the most generally used for adjustable-speed service, as in the case of machine tools.
* Motor, DC, Series- Wound
This type of motor speed varies automatically with the load, increasing as the load decreases. Use of series motor is generally limited to case where a heavy power demand is necessary to bring the machine up to speed, as in the case of certain elevator and hoist installations, for steelcars, etc. Series-wound motors should never be used where the motor can be started without load, since they will race to a dangerous degree.
* Motor, DC, Compound- Wound
A combination of the shunt wound and series wound type, which combines the characteristics of both. Varying the combination of the two windings may vary characteristics. These motors are generally used where severe starting conditions are met and constant speed is required at the same time.
Motor, Squirrel-Cage-Induction
The most simple and reliable of all electric motors. Essentially a constant speed machine, which is adaptable for users under all but the most severe starting conditions. Requires little attention as there is no commutator or slip rings, yet operates with good efficiency.
* Motor, Wound-Rotor (Slip Ring) Induction
Used for constant speed-service requiring a heavier starting torque than is obtainable with squirrel cage type. Because of its lower starting current, this type is frequently used instead of the squirrel-cage type in larger sizes. These motors are also used for varying-speed-service. Speed varies with this load, so that they should not be used where constant speed at each adjustment is required, as for machine tools.
* Motor, Single-Phase Induction
This motor is used mostly in small sizes, where polyphase current is not available. Characteristics are not as good as the polyphase motor and for size larger that 10 HP, the line disturbance is likely to be objectionable. These motors are commonly used for light starting and for running loads up to 1/3 HP Capacitor and repulsion types provide greater torque and are built in sizes up to 10 HP.
* Motor, Synchronous
Run at constant speed fixed by frequency of the system. Require direct current for excitation and have low starting torque. For large motor-generators sets, frequency changes, air compressors and similar apparatus which permits starting under a light load, for which they are generally used. These motors are used with considerable advantage, particularly on large power systems, because of their inherent ability to improve the power factor of the system.

 

[amberleaf]

* Horsepower The English unit of power, equal to work done at a rate of 550 foot-pounds per second. Equal to 746 watts of electrical power. * KVA (Kilovolt amperes) (volts times amperes) divided by 1000. 1 KVA=1000 VA. KVA is actual measured power (apparent power) and is used for circuit sizing. * KW (Kilowatts) watts divided by 1000. KW is real power and is important in sizing Uninterruptible Power Supplies, motor generators or other power conditioners. * KWH (Kilowatt hours) KW times hours. A measurement of power and time used by utilities for billing purposes. * Lagging Load An inductive load with current lagging voltage. Since inductors tend to resist changes in current, the current flow through an inductive circuit will lag behind the voltage. The number of electrical degrees between voltage and current is known as the "phase angle". The cosine of this angle is equal to the power factor (linear loads only). * Leading Load A capacitive load with current leading voltage. Since capacitors resist changes in voltage, the current flow in a capacitive circuit will lead the voltage.

*Null .Zero *Ohm The derived unit for electrical resistance or impedance; one ohm equals one volt per ampere. *Power Factor Watts divided by voltamps (VA), KW divided by KVA. Power factor: leading and lagging of voltage versus current caused by inductive or capacitive loads, and 2) harmonic power factor: from nonlinear current. *Transformer A static electrical device which , by electromagnetic induction, regenerates AC power from one circuit into another. Transformers are also used to change voltage from one level to another. This is accomplished by the ratio of turns on the primary to turns on the secondary (turns ratio). If the primary windings have twice the number of windings as the secondary, the secondary voltage will be half of the primary voltage.*Voltage DropThe loss of voltage between the input to a device and the output from a device due to the internal impedance or resistance of the device. In all electrical systems, the conductors should be sized so that the voltage drop never exceeds 3% for power, heating, and lighting loads or combinations of these. Furthermore, the maximum total voltage drop for conductors combined should never exceed 5%.

There are two types of transformer:
Step up transformer :
Step down transformer :

Step up transformer
A transformer in which Ns > Np is called a step up transformer. A step up transformer is a transformer which converts low alternatic voltage to high alternatic voltage.
Step down transformer :
A transformer in which Np> Ns is called a step down transformer. A step down transformer is a transformer which converts high alternatic voltage to low alternatic voltage.

Suppose an alternatic voltage source Vp is connected to primary coil. Current in primary will produce magnetic flux which is linked to secondary. When current in primary changes, flux in secondary also changes which results an EMF Vs in secondary. According to Faradays law EMF induced in a coil depends upon the rate of change of magnetic flux in the coil. If resistance of the coil is small then the induced EMF will be equal to voltage applied.

According to Faradays law
Vp=Np Δɸ/ Δt ------------ (1)
Where Np = Number of turns in primary coil.
Similarly, for secondary coil.
Vs = Ns Δɸ /Δ t ------------ (2)
Dividing equation (1) by equation (2)
Vp /Vs = Np /Ns
This expression shows that the magnitude of EMF depends upon the number of turns in the coil.

Under the 17th edition wiring regulations the following will apply to all domestic and residential installations.

*All socket outlets should be protected by 30mA RCD whether on the ground floor of a house or the top floor of a high rise apartment block*
*All circuits in a room with a fixed bath or shower should be protected by one or more 30mA RCDs**
*All cables buried beneath the plaster surface of a wall or partition (at less than 50mm) should be protected by 30mA RCDs***
*All cables concealed in metal stud partitions (common in new builds) should be protected by 30mA RCDs***
*Installations should be divided up into circuits so as to take account of danger and inconvenience caused by a single fault – e.g. such as a lighting circuit ****
*Installations should be designed and arranged so as to prevent unwanted tripping of RCDs****

411.3.3
Sockets up to 20A rating for general use by ordinary persons
701.411.3.3
All Circuits in a room with a fixed bath or shower
522.6.6 , 522.6.7 , & 522.6.8
All circuits buried in a wall or partition at less than 50mm and without mechanical protection

Note: Additional protection is provided as additional protection. It does not obviate the need for circuit protection by circuit
breakers or fuses.
* Regulation 411.3.3 socket outlets with a rated current not exceeding 20A that are for general use by ordinary persons (exceptions may be permitted).

** Regulation 701.411.3.3 Additional protection shall be provided for all circuits of the location by use of one or more 30mA RCD.
*** Regulations 522.6.6 522.6.7 522.6.8 cables concealed in a wall or partition at less than 50mm depth and without earthed mechanical protection e.g. conduit.
**** Regulation 314.1 Every installation shall be divided into circuits as necessary to avoid danger and inconvenience in the event of a fault,
take account of danger that may arise from the failure of a single circuit such as a lighting circuit, reduce the possibility of unwanted
tripping of RCDs etc.
**** Regulation 314.2 Separate circuits to be provided for parts of the installation that need to be separately controlled in such a way that those circuits are not affected by the failure of other circuits.

ADDITIONAL PROTECTION : 30mA RCD

Q / A
* What is the definition of adjustable frequency drive?
A device that converts incoming 60Hz AC power into other desired frequencies to allow for motor speed control.
* What is the definition of armature?
The part of a motor in which a current is induced by a magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.
* What is the definition of armature winding?
The conducting coils that are wound around the armature in which voltage is induced, causing it to rotate within a magnetic field. If the wires are damaged or broken, the armature will not rotate properly.
* What is the definition of commutator?
The rotating switch that contacts the brushes of a DC motor. The commutator maintains DC when the rotation of the armature switches the polarity of the conductor.
* What is the definition of copper loss?
A power loss due to current flowing through wire. The lost power is converted into heat.
* What is the definition of efficiency?
A measure of the work output of a system versus the total work supplied to it. An efficient system converts a greater percentage of input energy into useful work.
* What is the definition of electromagnet?
A powerful magnet that gains an attractive force only when current passes through it.
* What is the definition of electromotive force?
The force that pushes electrons through a conductor. Electromotive force is abbreviated "emf" and is measured in volts.
* What is the definition of energy?
The ability to do work. Energy is measured in watt hours and is expressed as the product of power and time.
* What is the definition of Faraday's Law?
A law that states an electric field is induced in any system in which a magnetic field is changing with time.
* What is the definition of frequency?
A measurement of the number of complete AC cycles that occurs in one second. Frequency is measured in Hertz (Hz).
* What is the definition of friction?
force that resists motion between two objects that are in contact with each other.
* What is the definition of generator?
A device that converts mechanical energy into electrical energy by magnetic induction.

 

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* What is the definition of horsepower?
A unit of power used to describe machine strength. One horsepower equals 33,000 ft-lbs of work per minute, or 746 watts.

* What is the definition of load?
The opposition to applied force, such as a weight, to be carried or moved.

* What is the definition of machine guard?
A shield or cover over hazardous areas on a machine to prevent accidental contact with body parts or to prevent debris, such as chips, from exiting the machine
* What is the definition of magnetic flux?
A measure of the strength of the field formed around a magnet. Flux is expressed in webers (Wb).
* What is the definition of magnetic induction?
The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.
* What is the definition of mechanical power variables?
The properties of mechanical energy that vary for specific machines and applications. Speed, torque, and horsepower are the three main mechanical power variables for motors.
* What is the definition of motor?
A machine that converts one form of energy, such as electricity, into mechanical energy or motion.
* What is the definition of percent slip?
The difference between a motor's synchronous speed and its speed at full load. Percent slip is a way to measure the speed performance of an induction motor * What is the definition of personal protective equipment?
Any example of various safety equipment that workers wear or use to prevent injury in the workplace. Safety glasses are common personal protective equipment (PPE).
* What is the definition of polarity?
Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.
* What is the definition of revolutions per minute?
A unit of measurement, abbreviated as rpm, that indicates the number of revolutions a machine component makes in one minute. Revolutions per minute is a measurement of speed.

* What is the definition of right-hand motor rule?
The relationship between the factors involved in determining the movement of a conductor in a magnetic field. This rule helps us understand how motors use magnetic flux to create motor torque.
* What is the definition of rotor? The rotating part of a motor.

between the poles from north to south. :
* What is the definition of shunt field?
A winding of small wire and many turns designed to be connected in parallel with the armature of a DC motor or generator.
* What is the definition of shunt motor?
A method of connecting field windings in parallel with the armature. The shunt DC motor is commonly used because of its excellent speed regulation.
* What is the definition of speed?
The amount of distance an object travels in a given period of time. Speed is used to measure both linear and rotational movement.
* What is the definition of speed control? the external means of varying the speed of a motor under any type of load.
* What is the definition of squirrel cage induction motor?
A type of three phase AC motor whose rotor is constructed by connecting metal bars together at each end. It is the most common AC motor type.
* What is the definition of stator? The stationary windings of a motor, usually inside an AC motor.
* What is the definition of speed?
The amount of distance an object travels in a given period of time. Speed is used to measure both linear and rotational movement.
* What is the definition of speed control?
The external means of varying the speed of a motor under any type of load.

* What is the definition of squirrel cage induction motor?
A type of three phase AC motor whose rotor is constructed by connecting metal bars together at each end. It is the most common AC motor type.
* What is the definition of stator? The stationary windings of a motor, usually inside an AC motor.
* What is the definition of synchronous motor?
A constant speed AC motor that does not use induction to operate. A synchronous motor needs DC excitation to operate.
* What is the definition of synchronous speed?
The speed of the rotating magnetic field of an AC induction motor.

* What is the definition of three-phase motor?
A motor with a continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large AC motors and is the standard power supply that enters homes and factories.
* What is the definition of torque?
A force that produces rotation. Torque is measured in pound-feet in the English system and Newton-meters in the metric system.

* What is the definition of watt?
A unit used to measure power. One horsepower is equal to 746 watts.
* What is the definition of weber?
A unit used to express flux density. One weber (Wb) is equal to 100 million lines of flux.
* What is the definition of wound rotor induction motor?
A three phase motor containing a rotor with windings and slip rings. This motor type permits control of rotor current by connecting external resistance in series with the rotor windings.