***Useful Information for Apprentices***

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[FONT=Arial+Black0]Resistivity [/FONT]
The basis of Ohms Law, of which the Ohmic Triangle we are all so familiar with is derived, is in part derived from these two simple rules…
The resistance of a conductor is Directly Proportional to it[FONT=Arial+Bold1252]’[/FONT]s length ...

i.e. If we double it[FONT=Arial+Bold1252]’[/FONT]s length we will double it[FONT=Arial+Bold1252]’[/FONT]s resistance.
If we half it[FONT=Arial+Bold1252]’[/FONT]s length we will half it[FONT=Arial+Bold1252]’[/FONT]s resistance.
And
The resistance of a conductor is inversely proportional to it[FONT=Arial+Bold1252]’[/FONT]s Cross- Sectional Area[FONT=Arial+Bold1252]…[/FONT].

i.e. If we double the C.S.A we will half the resistance.
If we half the C.S.A we will double the resistance

[FONT=Arial+Bold1252]…[/FONT]at a given temperature.

Note1 - Temperature:
This is an important factor when we consider resistance, as if the Temperature of a conductor increases the resistance increases quite dramatically. All Current Carrying Capacities of cables given in BS7671: 2008 are taken at 30°C. Reasons for an increase in temperature could include Thermal Insulation surrounding a conductor (Ci), Grouping of a number of cables together, all dissipating their heat against each other (Cg), and the Ambient Temperature they are installed in (Ca).

Note2 - Math’s:
Doubling the C.S.A is NOT the same thing as doubling the diameter. Since if the diameter of a cable is doubled it’s C.S.A will increase by a factor of 4 ! Similarly if we half the diameter of the cable it’s C.S.A will fall to a quarter of it’s original value.

Hence if we double the diameter (or radius) of a conductor it’s resistance will fall to one quarter (1/4) of its original value.

If we halve the diameter (or radius) of a conductor it’s resistance will increase by a factor of 4.

 

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Lighting Control (Automatic/Manual :-

The main lighting controls are:-
Switch (Manual)
Contactor (Manual or Automatic)
PIR (Automatic)
Photocell (Automatic)
Timer (Automatic)

Firstly it is important to consider the reason for your lighting & the amount of lighting required. The answers to those two main questions will effect the control equipment used, and is when possibly all aspects of the above could come into play. Remember, larger loads will nearly always require a contactor instead of a switch.

some installation methods are what could be described as ‘acknowledged cable management systems’
These could include :-

Domestic : PVC/PVC Twin
Outdoor Lighting & Power : SWA
Churches : MICC/MIMS
Small Industrial Workshop : Steel Trunking & Metal Conduit drops
Large Industrial Workshop : Bus-Bar Trunking and metal conduit drops
Industrial Kitchens : Galvanised Conduit
Medical Centres : Conduit Drops fixed with Hospital Saddles
Agricultural Buildings : High Impact PVC Conduit
High Explosive Areas : Seamless Conduit
Multi-Story Accommodation : Rising Main (Bus Bar) – or Rising Tray with SWA.

 

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Earth-Fault Loop Impedance :
Earth fault loop impedance is the impedance of the earth fault-current loop starting and ending at the point of earth fault. It comprises the following starting at the point of fault :-

(i) The Circuit Protective Conductor :
(ii) The Consumer’s Earthing Terminal & Earthing Conductor :
(iii) The Earth return Path ( for TT System ) :
(iv) The Path through the Earthed Neutral Point of the Transformer and the Transformer Winding :
(v) The Line Conductor from the Transformer to the Point of Fault :

Path for Earth Fault Current :
Earth Fault Loop Impedance > This is Only a EXAMPLE ‼
The significance of earth fault loop impedance is that a fast disconnection time of the protective device means that a ►high fault current ◄ is required to blow the fuse or to trip the circuit breaker. In order to allow sufficient fault current to flow in order to trip the protective device, the earth fault loop impedance must have a low value. ◄◄

If it exceeds the recommended figure, the circuit must be investigated to find out the underlying reason. The reading obtained should also be compared with the reading of the previous test ► (if this information is available) ◄ to see whether the Zs value is on the increase, which might indicate a potential dangerous condition appearing in the circuit. ► EXAMPLE , if the maximum ( Zs ) was ( 2Ω ) and the test reading was ( 1.2Ω ) on a previous test but is now ( 1.8Ω ) this indicates that the next would produce an unacceptable reading with the possibility that an earth fault occurring in the circuit would not produce enough fault current to operate the overcurrent protective device in either ( 0.4 ) second and ( 5 ) seconds, thus increasing the risk of electric shock to persons using the installation.

* the type of overcurrent protective device and its current rating : and
* whether the circuit feeding socket-outlets or equipment. :

 

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(1) The “ Line “ > Earth Loop Impedance' Tester is plugged into the 13A Socket Outlet :-
Press the Button. The Digital Meter , give a reading directly in Ohms. This is the Line/Earth Loop Impedance.
Repeat procedure (1) for the ( 4 ) number . 13A socket outlets. ► If the Digital Meter give a reading, record the results. ( each One )

If the Digital Meter does not read ‼ ( Houston we have a problem )

By measurement, the Earth Fault Loop Résistance = __________ Ωs

1st 13A S/O : Response of the Impedance Tester ( P-N LED ) ↔ (ON/OFF)↔ ( P-E LED ) Movement of Digital Meter ‼ Reading (Ω s)
2nd 13A S/O ?
3rd 13A S/O ?
4th 13A S/O ?

► Minimum values of the test results to be acceptable. ?
►What is the potential problem if the equipment/cable fails the insulation test ?
► Does all the earth fault loop impedance measured for the functional socket outlets : comply with the requirement as laid down ?

 

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Insulation resistance :
The object of the test is to verify that the quality of the insulation is satisfactory and has not deteriorated or short circuited.

In the event of any test indicating failure to comply, that test and those preceding, the results of which may have been influenced by the fault indicated, should be repeated after the fault has been rectified. ◄◄
Among these tests, items (iv) and (vi)

(iv) Insulation Résistance ,
(vi) Earth Fault Loop Impedance,
Principles of the Inspection & Testing of Electrical Installations.

 

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Q) The standard supply voltage in UK domestic premises is .. ? ( you will find . a lot of this comes under Pat / Testing ) CoP .
250V AC .
240V AC .
230V AC . ◄
115V AC .

A) The UK domestic supply has been 230V AC ( RMS ) since 1 January 1995. This has a tolerance of + 10% - 6% ( 216.2 – 253.0V
The old standard was 240V ± 6% / - 6% ( 225.6 – 254.4V ) ► Regs p/242

Q ) The Core Colours for the Phase, Neutral and Protective Conductors of a 3-Core Appliance cord are .. ?
Phase ( Line ) = Brown :
Neutral = Blue :
Earth = Green & Yellow :

Q) Electrical Current is Measured in .. ?
Amperes : ◄
Coulombs :
Volts :
Watts :
A) Electrical Current is Measured in Amperes, Usually shortened to Amps .

Q) Electrical Power is Measured in .. ?
Volts :
Ohms :
Coulombs :
Watts : ◄
A) Electrical Power is Measured in Watts . One Watt is Equivalent ( 1 ) Joule of Power Per-Second ,

Q) 100mA is the same as .. ?
10A :
1A ;
0.1A ◄
0.01A :
A) The Correct Answer is 0.1A : 1mA ( milliamp ) 0.001A , therefore 100mA is the same as ► 0.1A

2.5kW ( kilowatts ) is Equivalent to .. ?
25W :
250W :
2500W : ◄
25000W :
A) The Correct Answer is 2500W , 1kW is equivalent to 1,000W . Therefore 2.5kW = 2,500W

Q) A 230V Kettle rated at 2.3kW draws how much Current .. ?
1A :
10A : ◄
0.1A :
100A :
A) The Correct Answer is 10A ,
Power = Current x Voltage . in this case we know the Power is ( 2.3kW ) and the Voltage is ( 230V ) Therefore the Current = ( 2300W ) ÷ ( 230V ) = 10A

Q) How many 2.3kW heaters can be Safely Connected to a 230V Extension Lead rated at 13A .. ?
A) A 2.3kW heater draws 10A , Therefore Only ( 1 ) heater can be Connected to a 13A Socket .

Q) The Units Used to Measure Résistance are .. ?
Volts :
Ohms : ◄
Amps :
Watts :
A) Electrical Résistance is Measured in Ohms .

Q) When a Fuse is rated 13A , it Means .. ?
It will blow quicker than a 3A fuse if a Fault Occurs .
It can be Used in Any 13A plug .
It will Melt if the Current Exceeds 13A ◄ -&-s
It will blow if the Current falls Below 13A
A) it will Melt if the Current Exceeds 13A . ( The Wire in the Fuse is Designed to Melt if the Current Exceeds 13A )

 

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The Danger of Electrical Shock : ( Class 1 , must have an Earth )

Electric Power does a Tremendous Amount of Work . but because it,s such a Powerful Force , :-

1) Understanding how Electricity Works . ◄
2) Recognizing Potential Electrical Hazards . ◄
3) Learning about Safety Devices that Prevent Shock ◄

How Shocks Occur :
Electricity travels in closed circuits, normally through a conductor. Shock results when the body becomes part of the electrical circuit; current enters the body at one point and leaves at another. Typically, shock occurs when a person contacts:

1) Both wires of an energized circuit ,touching two ends of cables . 2) One wire of an energized circuit and to ground, touching one cable . 3) A metallic part in contact with an energized wire while the person is also in contact with the ground.

Metallic parts of electric tools and machines can become energized if there is a break in the insulation of their wiring. A low-resistance wire between the metallic case of the tool/machine and the ground – an equipment earthing conductor – provides a path for the unwanted current to pass directly to the ground. This greatly reduces the amount of current passing through the body of the person in contact with the tool or machine. Properly installed, the earthing conductor provides protection from electric shock.

 

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25 – when a four band resistor has only three band assumed tolerance will be ? a) 2% : b) 5% : c) 10% : d) 20% :
26 – H.R.C fuses can distinguish between ?
a) short circuit and starting currents .
b) high starting currents and short duration overload.
c) high fault currents and short term overloads.
d) starting currents and overloads.
27 – Exposed to radioactive material can lead to :
a) skin burns.
b) respiratory problems.
c) carcinogenic symptoms.
d) mild aching.
28- Heath & Safety Executive inspectors are primarily concerned with ?
a) skills levels within the workforce.
b) workplace safety standards and practices.
c) companies health and safety policies.
d) accidents of all types.
29 – The reactance created by a 4.5 µF capacitor in a circuit connected to a 50Hz supply is ? a) 708 Ω. b) 1.08 kΩ. c) 0.0014 Ω. d) 14 kΩ.

1) A - P = √3VL x IL cosθ . 2) C - slip .
3) C - raise the alarm, call for help or get someone to go for help . 4) B - gate . 5) A - break all phases .
6) A - allow current to flow in one direction only . 7) A - Z = √ [R2 + (XL - XC)2] .
8) B - movement of a conductor within a magnetic field . 9) B - connected in parallel with the armature .
10) A - 0.055 Ω . 11) - 109.9 Ω .. 12) D - current carrying capacity of the cable .
13) C - slip rings and brushes . 14) D - 12.37 Ω . 15) A - 750 rpm . 16) A - 0.6V .
17) A - the supply voltage to be developed across the 18) C - P = l²R .
19) B - an accumulation of rubbish . 20) B - electronic components .
21) A - thermal and magnetic . 22) D - should be accompanied . 23) B - kVA .
24) D - rotating magnetic fields . 25) D - 20% . 26) C - high fault currents and short term overloads .
27) C - carcinogenic symptoms . 28) B - workplace safety standards and practices . 29) A - 708 Ω .
2330 level 3 unit 1 , 301 paper 3 ( Q/A s )

 

[brucelee]

This is Something I knocked Up

Instruments and Testing
Installation Testing

REMEMBER
Visual inspection must precede all testing
→→ Remember →→→ Dead testing precedes

LIVE Testing :

Dead Testing
Isolate before carrying out dead tests ( A Must ) ←←←
* Approved voltage indicator to GS-38
* Maximum of 4mm on exposed prods
* Preferably not more than 2mm
* Fused leads
* Finger guards


Continuity Testing ( Low-Resistance ohmmeter ) ps. You may be asked this on P.Testing )
Battery operated instrument Low voltage d.c.
200mA / 4 – 24V ( 612.2.1 )
Verifying Continuity ( Method 1 ) Caution Supply must be isolated :
( Temporary Link / Instrument Measures ( R1 + R2 )
Along with verification of the cpc, state the Two other tests which are automatically undertaken when carrying out this test
( The value of (R1 + R2) ↔ ( Polarity ) -&-s
***** { Unacceptable practice of connecting c.p.c. to outgoing side of fuse or circuit breaker } *****
Why is it unacceptable ? :-
Unacceptable practiceof connecting c.p.c. tooutgoing fuse orcircuit breaker way

Verifying ContinuityMethod 2
Caution Supply must be isolated :
( Meter Lead on MET ↔ Meter Lead on Pendent or at the Switch )

State Two disadvantages of using Method 2, as compared to Method 1

Use of long wander leadValue of ( R2 ) only obtained
* What consideration should be given to the long wander lead ?
* Its Résistance must be measured anddeducted from the measured value of ( R2 )

Continuity of bondingconductors

Why is it necessary to remove one endof a bonding conductor when verifyingits continuity ?

To avoid the possibility of parallelearth paths ) ←←←←← -&-s
( Break in c.p.c.Parallel path )

Continuity of ferrous enclosures
* visual inspection
* low resistance ohmmeter

Insulation Testing
Instrument must be capable of producing a short-circuit current of 1mA
( you are looking for ! -&-s No Breakdown of the Conductor Insulation )

Caution Supply must be isolated :

Prior to insulation resistance testing :- close main switch if testing from tails
fuses in circuit breakers closed
local switches closed/operate two-way
switches during test
neon's/capacitors disconnected
remove voltage sensitive equipment

Insulation resistance testing between live conductors ( Live & Neutral ) ↔ Neutral is a Live Conductor ←←←← -&-s
Insulation resistance testing between live conductors and earth ( 2 – Leads , one on Earth / one on Brown/Blue Together )

BS 7671 Table 61 - Page 158

State the test voltage and minimum value of insulation permitted for the following circuits :-
* 230V domestic lighting circuit ? 500V – ≥ 1.0MΩ
* 3 phase, 400V motor circuit ? 500V - ≥ 1.0MΩ
* 12V SELV circuit ? 250V ≥ 0.5MΩ
* 750V discharge lighting circuit ? ≥ 1000V - 1.0MΩ
* 50V FELV circuit ? 250V ≥ 0.5MΩ

Live Testing :
Measurement of external impedance ( Ze )
* Main switch open
* Earthing conductordisconnected
* impedance tester ( .35Ω ) ↔ This is Mock Reading

WHY MUST the supply be isolatedbefore disconnecting the earthing conductor ?
Because if you don’t you could possibly kill somebody. If there is a defect with the insulation, and line touches exposed metalwork, the whole of the installation earthing could become live

*** State THREE other instances whereearth-fault loop impedance testing wouldbe required.
* At the furthest point in every final circuit
* At every distribution board
* At every socket outlet

What precautions should be observedwhen undertaking impedance tests withina circuit ?
( Ensure that persons or livestock are not in contact with exposed metalwork )

Measurement of prospective earth fault current
* Prospective faultcurrent tester
* Bonding conductorsconnected

Measurement of prospective short circuit fault current
* Prospective fault current tester

Why is it necessary to verify the valueof prospective fault current at the originof an electrical installation ?
To ensure the rated breaking capacity of the main switch and overcurrent devicesare capable of breaking the prospective fault current level

* State the effect on insulation resistance of an installation if :-

a. additional circuits are added
b. circuits were disconnected/removed
c. the length of a 6A lighting circuit was extended

a. insulation resistance decreases
b. insulation resistance increases
c. insulation resistance decreases

* State FOUR external influences that you would need to consider during the inspection process :-
• corrosion (corrosive atmospheres)
• mechanical damage
• vandalism
• extremes of temperature
• ingress of moisture or water
• extremes of temperature
• explosive atmospheres

cheers mate for always taking time to post all this info i have read a lot of your posts and found them extremely helpful
I am doing the 2391 course at college for 8 week evenings and i am half way through exam is june 3rd. I have been revising everyday for last 16 week as at the minute i am not working as i am a full time carer for the misses at minute
I am doing all this studying to hopefully pass first time so if you have any more info and advice for 2391 i would be grateful is the any chance you could tell me best way to explain test procedures if asked in exam any help cheers

 

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Non-statutory Requirements
Within BS 7671:2008, the following are of particular relevance in terms of safe isolation:

Regulation 132.15.1
contains the following fundamental principle:

Effective means, suitably placed for ready operation, shall be provided so that all voltage may be cut off from every installation, from every part thereof and from all equipment, as may be necessary to prevent or remove danger.

Regulation group 537.2
contains the requirements relating to isolation

Regulation group 537.3
contains the requirements for switching off for mechanical maintenance.

Table 53.2 summarises the suitability of particular protective, isolation and switching devices to be used as an isolator, an emergency switch, or a functional switch

Basic Safe isolation procedure :-
The following steps are the minimum that would be expected in terms of confirming safe isolation of a circuit or item of equipment.

Locate / positively identify correct isolation point or device

Check condition of voltage indicating device

Confirm that voltage indication device is functioning correctly

Switch off installation / circuit to be isolated

Verify with voltage indicating device that no voltage is present

Re-confirm that voltage indicating device functions correctly on known supply / proving unit

Lock-off or otherwise secure device used to isolate installation / circuit

Post warning notice(s)

( Any current will travel along the path to earth offering the least resistance. )

Electrical test equipment for use by electricians (GS 38) HSE

Statutory Requirements
requirement concerning work The most important statutory requirement concerning work carried out on or near electrical installations is the Electricity at Work Regulations (EWR) 1989. Those regulations within EWR of particular relevance to safe isolation are numbers 12 (Means for cutting off the supply and for isolation) and supply and for isolation) and equipment made dead). Regulation 12 (1) (b) states that where necessary to prevent danger, suitable
means shall be available for the isolation of any electrical equipment, where isolation means the disconnection and separation of the electrical equipment from every source in such a way that the disconnection and separation is secure

 

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Fitting Downlights :-

Once you have decided that you wish to install Downlighters in your room it is important for you to decide several things :- 1. How many Downlights do I want ? Or need ? 2. Should the Downlights be 12V or 230V ? 3. Do the Downlights need to be Fire rated ?
4. Can the existing lighting circuit support the extra light fittings ?

Should the Downlights be 12v or 230v?
Low voltage (LV or 12v) downlights are wired to a transformer, which is then wired to the mains supply. Although the transformer wastes approximately 10% of the power through stepping down the voltage to 12v this is more than compensated by the improved performance of low voltage downlights.
Due to a thicker filament, the halogen 12v bulbs (size MR16) are more efficient than the halogen 230v (size GU10) equivalent. The thicker filament also means that the bulbs are more robust.
Another advantage of 12v is that low voltage bulbs use halogen gas, which provides a much whiter and brighter light with higher clarity than the more traditional mains voltage incandescent bulbs.

Mains voltage downlights are wired directly to the mains without the need for a transformer.
The mains voltage (230v) downlights are generally cheaper, and can be simpler to install, as there is no need to install a transformer.

Ceilings provide an important barrier that helps to prevent the spread of fire and noise between the floors of a building. Installing recessed downlights punctures this barrier and can reduce the effectiveness of this safety barrier.

Can the existing lighting circuit support the extra light fittings? Lighting circuits are usually on 6 amp circuit breakers .To calculate how many Amps are loaded onto the lighting circuit a simple calculation is made. 230 volts, now assume that each light on the circuit is 100 watts, and you have got 12 lights on the circuit.

The calculation would be: So taking the above information the calculation would be: ( 1200 watts ÷ 230 volts = 5.22 amps )
So now we can see that the above described lighting circuit is using 5.22 amps meaning that the circuit breaker of 6 amps is not being overloaded.

Now to confuse things a little but very helpful on lighting circuits when you are wishing to add more lights. On lighting circuits once you have worked out the amps you can now apply a thing called Diversity, which for lighting circuits is 66% of the total load. So to work out this calculation we can do the following sum: ( 5.22amps ÷ 100 x 66 = 3.45 amps )
​

So now we can see that we are able to add more lights to the circuit now that diversity has been applied to it.

Remember to carry out your calculations before you start any work!

 

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2330 Level 2 Unit 4 / Updated to BS7671:2008 ( some old notes )

SINGLE PHASE:- Brown – Live Blue – Neutral Green/Yellow – Earth (protective conductor)


OLD COLOURS WERE:- Red – live Black - neutral


THREE-PHASE:-

Brown – Line one

Black – Line two

Grey – Line three

Blue – Neutral

Green/yellow – Earth (protective conductor) OLD COLOURS WERE:- Red – phase one

Yellow – phase two

Blue – phase three

Single and 3-phase supplies :

Star Point , L1 230V N , L2 400V L3 :


* Single phase supplies (230v AC 50Hz) are used for DOMESTIC PREMISES and ‘standard’ circuits within Industrial and Commercial premises (sockets, lights etc).


* 230v AC is acquired from ANY ONE phase and Neutral connection of a 3-phase supply.


* The supply transformer in a residential street is a 3-phase DELTA/STAR arrangement – supplying EACH house with a LIVE and NEUTRAL connection. ( Line )


Each house is supplied with a different phase (brown, black, grey, brown, black, grey, brown etc) and the SAME neutral.

3-phase supplies :


* 3-phase supplies are used for Commercial and Industrial installations.

* Because these premises have lots of electrical equipment – it can be more efficiently supplied when balanced across 3 ‘mains’ supplies rather than just one.

* 400v is acquired between ANY TWO phases (lives).

* Larger electrical equipment requires less current when supplied at 400v 3-phase AC – which is acquires using ALL THREE phases ( and sometimes the Neutral as well ).
* Switchgear and Cable designs are available for both single and 3- phase systems.

Lighting control :

* Lighting circuits can utilise different switch configurations and 2 and 3-core cable (+ cpc) – depending on the type of circuit required;

* One-way control

* Two-way control

* Intermediate two way control

Lighting – one way control :

Example : a light in a bathroom ,
- A ‘live’ feed cable supplies a single-pole switch .

- A ‘switched live’ conductor (blue with a brown marker) connects to the lamp .

- Neutral always connects directly to the lamp in lighting circuits.

- A cpc (circuit protective conductor – earth) connects the main earth at the supply to EACH accessory point in the circuit.

 

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Lighting – two way control :

* Example: upstairs/downstairs control of a landing light.

- A 3-core cable connects two, 2-way switches together .

- A two core cable connects the supply to the lamp.

- A cpc is connected to each accessory in the circuit.

- This circuit allows ANY one of the switches to turn the lamp on or off, from any position.

Power circuits :

* Available as RADIAL or RING circuit configuration.

* Radial is the simplest; sockets installed one after the other.

* Ring is more complicated; circuit is installed as a ring so TWO cables supply EACH socket.

Radial and Ring socket circuits :

* Use BS1363 ‘standard’ 13A socket outlets – single gang, twin-gang or ‘multiple-gang’.

* Either can have the following installed onto them – but regulations WILL apply!;

* Fused spurs

* Non-fused spurs

* Permanently connected equipment

A1 ring circuit :-

- Maximum 32A rating for circuit.

* Installed using 2 x 2.5mm² cables in a ring.

* Maximum 100m² floor area for EACH ring circuit.

* Unlimited number of sockets allowed on each circuit.

* ONLY a single non-fused spur is allowed – per number of sockets on the ring. Must be same size cable.

* Unlimited number of sockets allowed on a ‘fused spur’ (minimum 1.5mm² cable size).

* Radial circuits MUST NOT be ‘interconnected’ in a ring so as to form a ‘ring within a ring’

A2 Radial circuit :-

* Maximum 32A rating for circuit when wired in 4mm² cable.

* Maximum 75m² floor area for EACH A2 circuit.

* Unlimited number of sockets allowed on each circuit.

* ONLY a single non-fused spur is allowed – per number of sockets on the radial circuit.

* Unlimited number of sockets allowed on a ‘fused spur’

A3 Radial circuit :-

* Maximum 20A rating for circuit when wired in 2.5mm² cable.

* Maximum 50m² floor area for EACH A3 circuit.

* Unlimited number of sockets allowed on each circuit.

* ONLY a single non-fused spur is allowed – per number of sockets on the radial circuit (same size cable)

* Unlimited number of sockets allowed on a ‘fused spur’ (minimum 1.5mm² cable)

Permanently connected equipment :-

* Should have ‘local’ protection close to the equipment (maximum 13A fuse or 16A mcb) – see chapter 46 in BS7671:2008

* A switch connection unit can do this

* Items include certain types of heater, items of equipment that are not generally moved around (freezer or washing machine etc).


Q) Voltage drop can be evaluated by using Which one of the following Test Values ?
A) VD. Final Circuit Earth Fault Loop Impedance ( Zs )

Regs .p/361 : Zs ( m ) ≤ 0.8 x Uo / Ia , ( 230 ÷ 24A = 9.58 ( Ze – 0.8 x Zs – 9.58 = 7.66 )

( am trying to get my head around this Windows Vista Ultimate . my comp has a mind of it own )

 

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Special Installations : 2330 Level 2 Unit 4
Contents - Special Installations ,

* Caravan and Caravan Site Installations ,
* Temporary Installations ( Construction Sites )
* Rooms that contain a Bath or Shower ,

Regulation Requirements for Caravans :-
1) Caravan and Caravan Site MUST comply with Electrical Wiring Regulations in the same way that Buildings must – if they are to Utilize a Mains” Electric Supply
2) Section 721 of BS-7671:2008 details Requirements ,
3) “ Hook up “ cable must be NO longer than 25Metres ( +/ - 2m ) Regs p/213 : ► 721.55.2.6 / ( ii )
( Regs p/192 Note : Typical Requirements for Cord Extension Sets !!!! ) worth a Look , Note : Table 51 , Identification of Conductors’ . p/92
4) Electrical Wiring or Accessories MUST NOT be Installed in any Fuel Storage : Compartment(s) in a Caravan or Motorhome UNLESS
Regulation ( 721.528.3.5. ) is Adhered to :

* Section 721 of BS-7671:2008 details Requirements for Caravans ( Including Motorhome – Known as Motor- Caravan ) and Caravan Park Installations .
* Fuel Storage Compartment refers to Gas Cylinder Storage Compartments , ► Risk of Explosion and Fire may Result ,
* A “ Hook up “ cable is the Power Lead that connects the Caravan to the “ Provided “ power “ Hook Up “ point at the Caravan Park ,

Specific Regulations :-
BS-EN 60309-2 Plug and Socket ,
►( Remember to wire Up : ►Female ◄ / to the Supply First !!!!! ( Male , ◄ Connected to the Load Side ) Female ↔ Male / Unique Keyway ‼‼‼
708.530.3 / Caravan/Pitch – Electrical Supply ! “ Blue Flex Cable “ 20 m from ?

* Because caravans are used intermittently, recommended inspection and test intervals should be between 1 and 3 years (max) – see Fig 721 in BS7671:2008

* Extra-low voltage circuits (i.e.12v DC) MUST NOT come into contact with ‘mains’ voltage circuits in caravans and motorhomes – regulation 721.528.3.5

* Because caravans flex when being towed, wiring must be installed with either flexible or stranded conductors (minimum 1.5 mm/sq). regulation 721.524.1

* Conductors must be supported at least every 25cm within a caravan or motorhome/*. regulation 721.522.8.1.3

* Any metalwork within the caravan or motorhome, including the chassis must be bonded. regulation 721.411.3.2.1


Caravan Site Power Supplies :-
* Caravans must be supplied via a ‘Blue’ 16A BS4343 socket outlet adjacent to caravan pitch.

* Sockets are to be protected by an RCD

* RCD rating is 30mA . ◄

* Each socket outlet must be BSEN60309-2 (minimum IP44)

* No caravan should be more than 27 metres from a socket outlet (maximum).

* Connecting cable should be 2.5mm/sq minimum OR comply with table 721. ► p/213 Min/ CSA ????


Caravan Site Power Supplies :-
* Notices regarding the voltage supply and maximum loading MUST be displayed at the supply source.

* A caravan MUST be supplied with a mains disconnector as detailed by regulations 721.537.2.1.1

* A notice MUST also be displayed stating ‘how to connect and disconnect the supply safely’ – for the benefit of holidaymakers.

* Buried supply cables (SWA type) to power outlet points on a caravan site MUST be run outside the pitch area and buried to a depth so they are unlikely to be damaged by awning pegs.

 

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FibreOptics Systems – Precautions :-

* Light source is usually via LASER – so beware of damage to eyes (special glasses).

* Do NOT bend fibreOptic cable ‘too sharply’ – this will affect its ability to transmit light effectively.

* Beware of breaking a fibreOptic cable – sharp shards may cut you!.

* Well installed fibreOptic systems can transmit light for many kilometres with virtually NO LOSS in signal strength.

( Transmitted Light / 99.99% Output ) 100km

Other Data Cable System – Cat 5 /

* CAT 5 is a ‘standard’ data cable systems found in many IT applications (home pc networks, office IT networks).

* Special tools are required for BOTH FibreOptic and CAT 5 cable systems.

Summary :
* Section 543.7 of BS7671:2008 regulations detail ‘leakage circuit recommendations’ for circuits with high protective conductor currents.

* IT equipment ‘leaks current to earth – normally.

* IT systems require special precautions (data loss).

* Networks use lasers and fibreoptics – so care and safety is required.


( Remember , CSCS Signs ► Yellow/Black Means ?? ► Hazard or Danger ) Laser Sign !!! )

 

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Uo – voltage to earth for TN systems
Ia - current causing operation of overcurrent device
Zs - impedance measures in ohms at the point in the circuit, which is furthest most the origin of the supply

 

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Q) The Four Most Common Voltages at which Soldering Irons Operate as follows ?
a) 230V AC. For Workshop Use .
b) 110V AC . for Site Work .
c) 50V AC. For Production Work and Motor Vehicle Repair Workshops .
d) 12/24V DC. For Field Tasks ( where there is No Mains Electricity )

 

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Confirmation of the Effectiveness of the Integral Test Facility : -

RCDs have an integral test device to Simulate the passing through the detecting device of a Residual Current . This makes possible Periodic Testing of the Ability of the Residual Current device to Operate . However , it should be remembered that operation of the Integral Test button merely confirms the continuing functioning of the Electrical and Mechanical Components of the RCD . it Does Not Confirm that the Device is capable of operating in Accordance with the Specification of the Relevant product standard or , indeed the Requirements of BS-7671 ,

Test Procedure :- With the Supply to the RCD Switched On and with the RCD in the “ ON : Position the Button marked “ T “ or the RCD is pressed . The RCD should switch off ( 514.12.2 ) recommends’ that the Integral Test Button of an RCD is pressed Quarterly ( Every 3 Months ) ◄ -&-s / 17th Edition

Summary :- RCDs should be Tested at ( 50% , 100% ) and, if ► Providing Additional Protection ◄► 500% of their Residual Operating Current ( I∆n ) in Addition . the integral Test Device should be Operated Quarterly . Where an RCD is Employed to Achieve the Disconnection Time ◄► Required by Table 41.1 ( Regs p/ 46 ) it is Necessary to Confirm that the Maximum Earth Fault Loop Impedances ( Zs ) stated for a Particular Sensitivity of the RCD in Table 41.5 ( Regs p/ 50 ) are Not Exceeded in the Circuit to which they Protection . ( you are Using the Calculations’ of the Touch Current ) “ Circuit Protective Conductor “ Does NOT rise above Earth Potential More Than ( 50V ) ◄ P/50 – R ≤ 50V ÷ 30mA = 1667Ω : ) Zs x Ia ≤ Uo ? ( Zs = Ia ÷ Uo = 32A ÷ 230 = 0.13Ω )

 

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17TH Edition ( 1 )
Test your self

1 . what colour is the 17th edition ?
a. yellow / b. green / c . brown / ► d . red :

2 . after what date in 2008 must you use the 17th edition :-
a. January 31st / ► b . june30th / c . july31st / d . December 31st :

3 . General use sockets-outlets in bathrooms ?
a . are not allowed
b . must be at least 0.6m from the bath
► c . must be at least 3m from bath :
d . must be un-switched

4 . the type of protection against electric shock under fault-free conditions is :-
a . safety / ► b . basic / c . fault / d . indirect :

5 . the type of protection against electric shock under single-fault conditions is :-
a . safety / b . basic / ► c . fault / d . direct / answer :

6 . which of the following is new to the testing sequence ?
a . continuity / ► b . phase sequence / c . functional testing / d . polarity :

7 . all circuits in a bathroom must ?
a. disconnect in 0.4s / ► b . be RCD protected / c . be MCB protected / d . be run as a radial :

8 . an RCD provided for fire protection on a farm must have an In not exceeding ?
a . 30mA / b . 100mA / ► c . 300mA / d . 500mA :

9 . in the 17th which of the following has a new Section in Part 7 ?
a . petrol filling station b . rooms containing a sauna ► c . floor and ceiling heating systems
d . mine or quarry

10 . The maximum recommended voltage drop for a standard domestic lighting circuit is ?
► a . 3% b . 4% c . 5% d . 6% :

11 . water utility supply pipes can be used as earth electrodes ?
► a . under no circumstances .
b . if their CSA is larger than 6mm2 .
c . if they are metallic .
d . if precautions are taken against removal :

12 . a socket-outlet in a domestic lounge should be ?
► a . protected by a 30mA RCD
b . arranged as part of a ring final circuit
c . switched
d . protected by a 32A circuit-breaker

13 . Supplementary bonding in a bathroom ?
a . is always required
b . is never required
► c . may be omitted if certain conditions met
d . must be at least 4mm2

14 . Twin and earth, cables shallow-chased into a wall in a domestic installation should be ?
a . run in the form of a ring
► b . installed in safe zones and protected by a 30mA - RCD
c . installed in safe zones only
d . protected by a 30mA – RCD only

15 . MI cable shallow-chased into a wall in a domestic installation ?
a . should be installed in safe zones and protected by a 30mA – RCD
b . should be installed in safe zones only
c . should be protected by a 30mA –RCD only
► d . can be installed outside safe zones without RCD protection

16 . the maximum permitted Zs values for low voltage circuits are based on nominal voltage of ?
► a . 230%V b . 240V c . 250V d . 400V

17 . PV stands for ?
a . Preferred voltage
► b . Solar photovoltaic
c . Protective voltage
d . Phase voltage

 

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17th final score ( 2 )

10 . answer : A appendix 12 now gives a recommendation of 3% for lighting and 5% for other uses.
The figure in the 16th for all users was 4% for LV installations fed from private
LV supplies the figures are 6% and 8% respectively

11 . answer : A Supply pipes may not be used. Other metallic water supply pipes may be used as long as they are suitable and precautions are taken against removal .

12 . answer : A all socket-outlets for general use must be protected by a 30mA RCD they are two exceptions : ( i ) if the socket-outlet is under the supervision of a skilled or instructed person. However this would not apply to a domestic installation .
( ii ) if a socket-outlet is specifically labelled or identified for connection to a particular item
Of equipment , eg .c a fridge .

13 . answer : C Supplementary bonding may be omitted if all of the following conditions are met :
( i ) Disconnection times of all circuit in the bathroom are satisfactory
( ii ) All final circuits in the bathroom have 30mA RCD protection
( iii ) All extraneous parts are effectively connected to the protective equipotential bonding

14 . answer : B This is as for the 16th , but with the added requirement that 30mA RCD protection is required even where cables are installed in safe zones ..

15 . answer : D
The regulations allow cables in earthed conduit / trunking ,with an earthed metallic covering or
Mechanically protected to prevent penetration by nails , screws, drills etc, to be run outside
Safe zones without RCD protection ( the cables ,trunking and conduit used must meet the appropriate standards listed in the regulations ) . it would not be recognized as good practice to do this with MI and similar cables as they would still be susceptible to penetration ,
Albeit not presenting a shock risk .

16 . answer : A
Now 230V, previously 240V. This means that the maximum permissible Zs values given
In tables 41.2,41.3 and 41.4 are slightly lower than in the 16th .

17 . answer : B
Solar photovoltaic systems and other means of micro-generation are becoming increasingly common . in the 17th there are fifteen new definitions relating to PV systems . Section 712 is new and concentrates on PV supply systems .