***Useful Information For The Working Sparky***

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Split load board with RCBOs on critical circuits : ● ( PCA ) Partially Compliant Assembly : ←

By reviewing the wiring scheme employed with the split load assembly proposed the cost of the finished assembly can be reduced, and partial compliance with the regulations achieved. The split load board laid out here will meet the17th Edition requirements for the following:
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA.:
However, depending on the installation design, it is unlikely to satisfy the regulations on:
* To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD.
* Separate circuits shall not be affected by the failure of other circuits. :
there is still the risk of one circuit failure impacting on another (regulation 314.2); however the level of inconvenience could be considered to be acceptable (only the sockets and showers are affected ), and no hazard or safety issues are inherent. Again, the installer will need to consider the amount of leakage in the installation, due to electronic devices in the house, and it may be a consideration to split the power sockets and have one of them on an RCBO.
The end result is that no base consumer unit exists that complies with the 17th Edition. The choice of
consumer unit and the configuration of devices within it can only be made after the wiring scheme has been finalised. :

Key extracts from 17th Edition of the IEE Wiring Regulations BS 7671 : 2008

314 Division of Installation
314.1 Every installation shall be divided into circuits, as necessary, to (i) avoid hazards and minimize inconvenience in the event of a fault(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.
411.3.3 Additional protection
In a.c. systems, additional protection by means of an RCD in accordance with Regulation 415.1 shall be provided fori) socket-outlets with a rated current not exceeding 20A that are for use by ordinary persons and are intended for general use.
531.2.4 An RCD shall be so selected and the electrical circuits so sub divided that any protective conductor current which may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.
Section 701 Locations containing a bath or shower
701.411.3.3 Additional protection by RCDs
Additional protection shall be provided for all circuits of the location, by the use of one or more RCDs having the characteristics specified in Regulation 415.1.1 (30mA RCD)
( Note: see regulations 314.1 and 531.2.4. )

Note: There are exceptions when the socket outlets are used by skilled or instructed persons, but not relevant in residential property. For example 411.3.3 relates to socket outlets located anywhere in a home, including the socket in the cooker outlet. However RCD protection for the cooker outlet is required if any of the cables are buried in the wall and not deeper than 50mm, as indicated in 522.6

Fire Alarms :

The entire system should be tested to ensure that it operates satisfactorily and that, in particular,
automatic fire detectors and any manual call points function correctly when tested. Smoke detectors should
be smoke tested with a simulated smoke aerosol that will not damage the detector. Heat detectors should be
tested by means of a suitable heat source unless detector damage would otherwise result. The heat
source should not have the ability to cause a fire. A live flame should not be used.
It should be established that any interlinking works and that sounders operate correctly.
Manufacturer’s tests should be carried out.

Certification :
A certificate should have been issued to the user and this should be available for inspection. For Grade F
systems a certificate should be issued if installed by a professional installer.

User instructions :
The supplier of the fire alarm system should provide the user with operating instructions, which should be
sufficient to enable a lay person to understand, operate and maintain the system. Silencing and disablement facilities should be explained but it should be stressed that system readiness must not be compromised. Recommended action in the event of a
fire must stress the importance of all occupants leaving the building as quickly as possible and that
the fire service is summoned immediately regardless

Routine testing and maintenance :
instructions to users must stress the importance of routine testing. The system should be tested weekly by
pushing the test button. If the dwelling has been unoccupied for a period during which the supply (yes)
could have failed, the occupier should check that the system has not suffered total power failure and is still operable.

Maintenance :
Smoke alarms in Grade D, E and F systems should be cleaned periodically in accordance with the
manufacturer’s instructions. Where experience shows that undue deposits of dust and dirt are likely to
accumulate, so affecting the performance of the system before detectors are cleaned or changed, more frequent
cleaning or changing should be carried out.

Commissioning :

The system should be inspected. Electrical tests made to the mains supply circuit
should include earth continuity, polarity, and earth fault loop impedance. Insulation tests should be made
of all installed cables as required by BS 7671. Electronic equipment should be disconnected to avoid damage.

Supply to a Grade E system where the installation forms part of a TT system.
The 100 mA time-delayed RCD provides protection for the fire alarm system ( and other circuits )
and operates independently of the RCD protection for the socket-outlets


main switch
( 100 mA time delayed RCD )
S-type, double pole to BS EN 61008 :

interconnected by wiring should be connected on a single final circuit. Note that certain alarms are radio linked and such alarms
need not be on the same final circuit ,
Wiring systems :
All cables should be selected and installed in accordance with the requirements of BS 7671 and the recommendations of BS 5839-6.

“ RCCB “

Residual Current Circuit Breaker (RCCB). This is a term that does not appear in the current wiring regs, and does not have a consistent definition or usage. Some manufacturers use it to differentiate RCDs without overcurrent protection from those with it ( i.e. RCBOs ).
Nuisance trips :
A Nuisance trip is an unexpected operation of a RCD that does not appear to be related to an immediately obvious fault. There can be many reasons that these trips occur, some indicate that there is a latent problem with the electrical installation, some may indicate the presence of a serious but as yet unobserved fault, and others may be the result of a minor fault that in itself poses little or no risk ,
Tracing the cause of nuisance tripping can prove to be very difficult and time consuming.

What causes nuisance trips :
Using the wrong busbar
If you have a new circuit that trips the moment you attempt to draw power from it, the most likely cause is common wiring mistake in the CU. Split load CUs will have two or more sections, with a dedicated neutral bus bar for each. If you connect the live of a circuit to a MCB on a section of the CU protected by an RCD, but return the neutral to a bus bar not associated with that RCD, you will get an immediate trip sine the RCD can only "see" one half of the current flow. The same logic applies if using a RCBO, then the neutral for the circuit must be returned to the neutral connection on the RCBO ( and the RCBO's flying neutral wire in turn connected to the appropriate neutral bus bar in the CU).
Excess earth leakage
The RCDs operating principle is to measure the current imbalance between that flowing into and out of a circuit down live and neutral wires. In an ideal world the current difference would be zero, however in the real world there are a various different types of equipment that will legitimately have a small amount of leakage to earth, even operating normally. If the RCD is protecting too many such devices then it is possible that the cumulative result of all these small leakages will be enough to either
● trip the RCD
● or by passing most of the RCD's trip threshold current, make the RCD excessively sensitive to any additional leakage currents

 

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“ Domestic RCD “
This is a deprecated way of installing an RCD such that a single low trip threshold device ( typically 30mA ) protects all the circuits in a property. While counter to the advice given in the present wiring regulations. installations of this type are still commonly found. Whole house RCDs are very vulnerable to nuisance trips, and any such trips remove all power to the property
Wiring faults :
Fault : Neutral to Earth shorts ,
Mechanism :
A particularly problematic fault is a short between neutral and earth on a circuit. Since Neutral and earth are nominally going to be at a similar potential (especially in buildings with TN-C-S / PME . earthing
You can arrive at a situation where the current flow between neutral and earth is lower than the trip threshold of the RCD some of the time, however once the neutral current reaches a high enough level, its potential will be "pulled" away from that of the earth, and you get increased leakage current flow which may cause a trip. Needless to say this threshold will often be reached during transient current peaks caused by equipment being switched on or off.

Insulation breakdown or damage :
As cables and wires age, their Insulation can become less effective .

Faulty RCD :
One obvious possibility (and often overlooked) is that the RCD itself is actually faulty and not tripping at the correct current. A RCD that refuses to reset even when all output connections are removed is an obvious candidate for landfill. Swapping the device with a known good one, or using a RCD test facility , are other ways of finding faulty RCDs. Many RCDs include a "test" button that verifies the unit functions. This simulates a imbalance current internally, which causes the device to operate. Note however that because the test current may be several times the trip threshold, it does not test if the trip threshold has drifted too low or the mechanism has become slow - only that the trip detection and basic mechanics still work.
How to locate the cause of nuisance trips :
There are a number of empirical tests or experiments that you can try to narrow down the source of the problem. We cover some here. The first job is to identify which circuits the RCD is protecting. There is no need to concentrate efforts on examining circuits that are not connected and hence can not be affecting the outcome!
“ Techniques to try “
Do what : Turn off circuits in turn ,
Why : You may be able to identify which circuit is causing the problem by isolating circuits in turn, and seeing which prevents the trip from reoccurring ,

“ Remove appliances from suspect circuits “

Disconnecting appliances from suspect circuits can let you identify if the fault is in an appliance (the most common situation) or the circuits fixed wiring. If you still get trips with everything disconnected then you may have a wiring fault.
If it looks like appliances are to blame, you can apply the "binary chop" principle to narrow down the field quickly - i.e. unplug half of them and see what happens. If it still trips you know in which half the dodgy appliance probably is. The carry on in the same way - halving the list of remaining suspects, until you get close to the answer. (This method isn't bulletproof with RCDs.)
“ Check the likely culprits “
Identifying which appliances you have from the "high risk" categories listed above can help to take you to the cause of the trouble faster :

“ Check the likely culprits “
Identifying which appliances you have from the "high risk" categories listed above can help to take you to the cause of the trouble faster :

“ Identify coincidental factors “
Check for any patterns and relationships between trips and other events. Do they occur only in Damp
weather, or only at certain times of day, or only when the Freezer switches on, or the Central Heating
Pay particular attention to automated systems ( timers, thermostats etc ) that can be controlling significant bits of electrical equipment in your home without your manual intervention .

Notes on Schedule of Test Results ( 2392-10 ) Nice Wording for 2391 ←←

* (1) Type of Supply : is Ascertained from the Distributor or by Inspection ,
* (2) (Ze) at Origin : when the Maximum Value Declared by the Distributor is Used , the Effectiveness of the Earth must be Confirmed by Test , if Measured the Main Bonding will need to be Disconnected for the Duration of the Test ,

* (3) Prospective Fault Current ( PFC ) the Value Recorded is the Greater of Either the Short-Circuit Current or the Earth Fault Current
Preferably Determined by Enquiry of the Distributor ,

* (4) Short-Circuit Capacity : of the Device is Noted , see table 7.2 - OSG – table 2.4 – GN3
The Following Tests , where Relevant , shall be Carried Out in the following Sequence :
Continuity of Protective Conductors , including Main & Supplementary Bonding .
Every Protective Conductor , including Main & Supplementary Bonding Conductors , should be Tested to Verify that it is Continuous and Correctly Connected
* (6) Continuity :
Where Test Method (1) is Used , Enter the Measured Résistance of the Line Conductor Plus the Circuit Protective Conductor ( R1 + R2 )
See 10.3.1 – OSG – 2.7.5. – GN3 : During the Continuity Testing ( Test Method 1 ) the following Checks are to be Carried Out :
(a) Every Fuse and Single-Pole Control and Protective Device is Connected in the Line Conductor Only
(b) Centre- Contact Bayonet & Edison Screw Lampholders have Outer Contact Connected to Neutral Conductor
(c) Wiring is Correctly Connected to Socket-Outlet & Similar Accessories , Compliance is to be Indicated by a Tick in Polarity Colum ( 11 ) ,
( R1 + R2 ) need Not be Recorded if ( R2 ) in Column ( 7 )
* (7) Where Test Method (2) is Used , the Maximum Value of ( R2 ) is Recorded in Column ( 7)
See 10.3.1 – OSG – 2.7.5 – GN3
* (8) Continuity of the Ring-Final Circuit Conductors
A Test shall be Made to Verify the Continuity of Each Conductor Including the Protective Conductor of Every Ring-Final Circuit
See 10.3.2 – OSG – 2.7.6.- GN3
* (9) * (10) Insulation Résistance :
All Voltage Sensitive Devices to be Disconnected or Test Between Live Conductors’ ( Line & Neutral ) Connected together & Earth , The Insulation Résistance between Live Conductors’ is to be Inserted in Column ( 9)
The Minimum Insulation Résistance Values are Given tables : 10.1 – OSG – 2.2 – GN3 :
( All the Preceding Tests should be Carried Out before the Installation is Energised )
* (11) Polarity :
A Satisfactory Polarity Test may be Indicated by a Tick in Column ( 11 )
Only in a Schedule of Test Results Associated with a Periodic Inspection Report is it Acceptable to Record Incorrect Polarity ,
* (12) Earth Fault Loop Impedance ( Zs )
This may be Determined Either by direct Measurement at the Further Point of a Live Circuit or by Adding ( R1 + R2 ) of Column
6 to ( Ze . Zs ) is Determined by Measurement at the Origin of the Installation or Preferably the Value Declared by the Supply Company Used , ( Zs = Ze + ( R1 + R2 ) – Zs should be Less than the Values given in Appendix 2 – OSG or Appx 2 – GN3
* (13) Functional Testing :
The Operation of RCDs ( including RCBOs ) shall be Tested by Simulating a Fault Condition , Independent of any Test Facility in the Device . Record Operating time Column (13) Effectiveness of the Test button must be Confirmed ,
See : Section (11) – OSG or 2.7.15 / 2.7.18 – GN3 ,
* (14) All Switchgear & Controlgear Assemblies , Drivers , Control & Interlocks, etc must be Operated to ensure that they are Properly Mounted , Adjusted , and Installed : Satisfactory Operation is Indicated by a tick in Column (14) ,
( Earth Electrode Resistance )
The Earth Electrode Resistance of ( TT ) Installations must be Measured , and Normally an RCD is Required ,
For Reliability in Service the Resistance of any Earth Electrode should be below ( 200Ω ) Record the Value on form 1- 2 - 6 ,
As Appropriate , see 10.3.5 – OSG or 2.7.12 – GN3

 

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“ Isolation of individual circuits”

Where it is not practical to isolate a distribution board, individual circuits supplied from it can be isolated
by one of the methods described below, depending on the type of protective device used. However, bear
in mind the overriding advice to avoid energising any outgoing electrical distribution services, preferably
until the distribution switchgear and all connected circuits are complete and have been inspected and the
relevant tests carried out.
If any items required to carry out the procedures recommended below are not manufactured for the DB in
question or cannot be obtained through retail/trade outlets, it is acceptable to disconnect the circuit from
the DB as long as the disconnected tails are made safe by being coiled or insulated. Suitable labelling of the
disconnected conductors is important to prevent the supply being re-instated, particularly if other
electricians are present.
It should be remembered that work carried out inside a live DB is regarded as live working when there is
access to exposed live conductors. In this case the appropriate precautions should be taken as described in
HSG85 with respect to Regulation 14 of the Electricity at Work Regulations.
i. Isolation of individual circuits protected by circuit breakers
Where circuit breakers are used the relevant device should be locked-off using an appropriate locking-off
clip with a padlock which can only be opened by a unique key or combination. The key or combination
should be retained by the person carrying out the work.
Note
Some DBs are manufactured with ‘Slider Switches’ to disconnect the circuit from the live side of the circuit
breaker. These devices should not be relied upon as the only means of isolation for circuits as the wrong
switch could easily be operated on completion of the work.
ii. Isolation of individual circuits protected by fuses
Where fuses are used, the simple removal of the fuse is an acceptable means of disconnection. Where
removal of the fuse exposes live terminals that can be touched, the incoming supply to the fuse will need to
be isolated. To prevent the fuse being replaced by others, the fuse should be retained by the person carrying
out the work, and a lockable fuse insert with a padlock should be fitted as above. A caution notice should
also be used to deter inadvertent replacement of a spare fuse. In addition, it is recommended that the
enclosure is locked to prevent access as stated above under ‘Isolation using a main switch or distribution
board (DB) switch-disconnector’.
Note
In TT systems, the incoming neutral conductor cannot reliably be regarded as being at earth potential.
This means that for TT supplies, a multi-pole switching device which disconnects the phase and neutral
conductors must be used as the means of isolation. For similar reasons, in IT systems all poles of the
supply must be disconnected. Single pole isolation in these circumstances is not acceptable.

“ Electrical Permits-to-Work “
An electrical permit-to-work must be used for work on HV systems that have been made dead, and can
be useful in certain situations for LV work. These permits are primarily a statement that a circuit or item
of equipment is isolated and safe to work on. They must not be used for live working as this can cause confusion..

“ Caution Notices “
In all instances where there is a foreseeable risk that the supply could be reinstated as above, an
appropriate “caution” notice should be placed at the point of isolation. For DBs with ‘multiple
isolations’ a single suitably worded notice on each DB, such as the example shown below, would suffice:

* CAUTION: THIS DISTRIBUTION BOARD HAS A NUMBER OF CIRCUITS THAT ARE
SEPARATELY ISOLATED. CARE SHOULD BE TAKEN WHEN REINSTATING THE
SUPPLY TO AN INDIVIDUAL CIRCUIT THAT IT HAS BEEN CORRECTLY IDENTIFIED.

Question 1 :
State the necessary action that should be taken by an inspector on discovering a damaged socket outlet with exposed live parts during a periodic inspection and test :
GN-3 ( Required Competence )
Make an immediate recommendation to the client to isolate the defective part :
Question 2 :
State the documentation that should accompany an Installation Certificate or Periodic Inspection Report :
GN-3 ( Certificates & Reports )
1. Schedule of items inspected :
2. Schedule of test results :
Question 3 :
Why is it necessary to undertake an initial verification ?
GN-3 ( Initial Verification ) G
1. Confirm that installation complies with designers intentions :
2. Constructed, inspected and tested to BS- 7671:2008 :
Question 4 :
State the requirements of Part 6 of BS- 7671 with regard to initial verification :
GN-3 ( Initial Verification )
1. All equipment and material complies with applicable British Standards or acceptable equivalents :
2. All parts of the installation are correctly selected and erected :
3. Not visibly damaged or defective :
Question 5 :
Identify FIVE non-statutory documents that a person undertaking an inspection and test need to refer to
General Knowledge
1. BS -7671:2008 :
2. IEE On-Site Guide :
3. GS 38 :
4. Guidance Note 3 :
5. Memorandum of Guidance to The Electricity at Work Regulations :
Question 6 :
Which non-statutory document recommends records of all maintenance including test results be kept throughout the life of an installation ?
GN-3 ( Initial Verification )
Memorandum of Guidance to The Electricity at Work Regulations (Regulation 4(2) :
Question 7 :
Appendix 6 of BS 7671 allows the use of three forms for the initial certification of a new installation or for an alteration or an addition to an existing installation. State the title given each of these certificates :
GN-3 ( Initial Verification )
1. Multiple signature Electrical Installation Cert :
2. Single signature Electrical Installation Cert :
3. Minor Electrical Installation Works Certificate :
Question 8 :
Under what circumstances would it be appropriate to issue a single signature Electrical Installation Certificate ?
GN-3 ( Certificates )
Where design, construction inspection and testing is the responsibility of one person :
Question 9 :
State the information that should be made available to the inspector:
GN-3 ( Required Information )
1. Maximum demand :
2. Number and type of live conductors at the origin :
3. Type of earthing arrangements :
4. Nominal voltage and supply frequency :
5. Prospective fault current ( PFC ) :
6. External Impedance Ze :
7. Type and rating of overcurrent device at the origin :
Question 9 ( cont,d ) :
The following information should also be made available :
GN-3 ( Required Information )
1 Type and composition of circuits, including points of utilisation, number and size of conductors and type of cable :
2. Methods of compliance for indirect shock protection :
3. Identification and location of devices used for protection, isolation and switching :
4. Circuits or equipment vulnerable to testing :
Question 10 :
Where should the proposed interval between periodic inspections should be noted :
GN-3 ( Frequency )
1. On the Electrical Installation Certificate :
2. On a notice fixed in a prominent position at or near the origin of an installation :
Question 11 :
State in the Correct Sequence the first FIVE tests that would need to be undertaken on an A1 ring circuit during an initial verification :
1. Continuity of protective conductors :
2. Continuity of ring final circuit conductors :
3. Insulation resistance :
4. Polarity :
5. Impedance Zs :
Question 12 :
State TWO disadvantages of using Method 2 in order to verify the continuity of c.p.c.’s :
GN-3 ( Test Method 2 )
1. Long wander lead :
2. Gives R :
does not provide R :

 

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Question 14 :
State the British Standard number for a transformer used to provide electrical separation :+
GN-3 ( Electrical Separation )
Transformer complies with BS 3535 , Note: Transformer double-wound type :
Question 15 :
List FOUR types of external influence that affect the safety/operation of an electrical installation :
GN-3 ( Electrical Separation )
1. Ambient temperature :
2. Heat :
3. Water :
4. Corrosion :
Question 16 :
Identify the TWO procedures required when verifying the continuity of a ferrous enclosure used as a c.p.c. for a circuit
GN-3 ( Test Method 2 )
1. Inspect the enclosure throughout its length :
2. Carry out low resistance ohmmeter test :
Question 17 :
State in the Correct Sequence the Test required to verify the continuity of a ring final circuit :
GN-3 ( Continuity of Ring Circuit )
1. Identify and measure the resistance of each ring (end to end) r
1 / r :
2 / rn :
2. Apply figure of 8 (cross connection) between phase and neutral conductors at distribution board and then measure resistance between phase/neutral at each socket outlet :
Question 17 : ( con,d )
GN-3 ( Continuity of Ring Circuit )
3. Apply figure of 8 (cross connection) between phase and cpc at origin and measure resistance between phase and cpc at each socket outlet :
Note: where dead Tests are made the supply must be isolated before any work commences:
Question 18 :
The following measurements were taken at the origin of an A :
1 ring circuit. r 1 = 0.4Ω :
2 = 0.67Ω R n = 0.4Ω :
Determine the measured value of resistance at each socket outlet when the ends of the circuit are cross-connected to form a figure 8 :
GN-3 ( Continuity of Ring Circuit )
1. r , 1 + R n = 0.4 + 0.4 = 0.8/4 = 0.2Ω ;
2. r , 1 + r 2 = 0.4 + 0.67 = 1.07/4 = 0.267Ω :
Question 19 :
Identify ONE other test that is automatically performed when undertaking a ring final circuit test :
GN-3 ( Continuity of Ring Final Circuit )
Polarity :
Question 20 :
State FOUR items of equipment/components that may need to be removed prior to carrying out a test for insulation resistance on a circuit :
GN-3 ( Insulation Résistance )
1. Pilot or indicator lamps :
2. Dimmer switches :
3. Touch switches :
4. Electronic r.c.d.’s etc :
Question 21 :
State the test voltage and minimum acceptable value of insulation resistance for the following circuits :
1. 400V 3 phase motor
2. 760V discharge lighting circuit
3. 45V FELV circuit
GN-3 ( table – 61 )
1. 500V d.c. 0.1 MΩ
2. 1000V d.c. 1.0 M
3. 500V d.c. 0.5 M
Question 22 :
State the Correct Sequence for undertaking an insulation resistance test on a filament lamp circuit containing two-way switching :
GN-3 ( Insulation Résistance Testing )
1. Supply must be isolated : ← ← ←
2. All lamps removed :
3. Insulation test between live conductor :
4. Insulation resistance test between live conductors and earth :
5. Two-way switches operated during test
Question 23 :
State the type of test that should be applied where protection against direct contact is by site-applied insulation :
GN-3 ( Site applied Insulation )
1. Test at 3750V a.c :.
2. Apply test voltage for 60 seconds during which time insulation failure or flashover should not occur :
3. Instrument used: Site applied insulation3. Instrument used: Site applied insulation :
Question 24 :
State the THREE specific requirements for verification of polarity with regard to accessories : 612.6 ,
1. All single-pole devices are connected in the phase conductor
2. The centre contact of Edison screw lamps are connected in the phase conductor
3. All socket outlets : wiring has been correctly connected to socket-outlets and similar accessories :
Question 25 :
Identify the test that should be applied to verify polarity after the supply is energised :
GN-3 ( Polarity )
Test to verify correct polarity of the incoming live supply (PES ). Test made at the origin using approved voltage indicator :

Question 26 :
Identify the THREE electrodes used when used with a proprietary earth resistance tester:
GN-3 ( Earth electrode resistance )
1. Main electrode :
2. Potential electrode ( auxiliary electrode ) :
3. Current electrode ( auxiliary electrode ) :
Note: This method can be use for electrodes used for transformers, lightning protection systems etc.:
Question 27 :
State the action to be taken regarding the earthing conductor before measuring the resistance of an earth electrode
GN-3 ( Earth electrode for RCD’s )
Normal 100Ω ← ← ←
Special locations 50Ω
By calculation 50V ÷ 0.5A = 100Ω
Dry 25V ÷ 0.5A = 50Ω
Special Loc,
Question 27 :
State the action to be taken regarding the earthing conductor before measuring the resistance of an earth electrode :
GN-3 ( Earth electrode resistance )
1. Disconnect earthing conductor at MET to avoid parallel earth paths :
2. Do NOT disconnect any protective conductors before isolating the supply :
Question 28 :
State the maximum recommended value of resistance for an earth electrode :
GN-3 ( Earth electrode for RCD’s )
Electrodes having resistances in excess of 200Ω :
will require further investigation.
Note: Electrode resistances obtained in excess of 200Ω :
may indicate unstable soil conditions :
Question 29 :
State the formula used to calculate Impedance
Zs, at the furthest point within a circuit
Zs = Ze + ( R1+R2 ) Where Ze is by measurement or enquiry
and ( R1+R2) by measurement
State the formula used to calculate Impedance Zs, at the furthest point within a circuit :
GN-3 ( Earth Fault Loop )
( Zs = Ze + ( R1+R2 )
Where Ze is by measurement or enquiry and ( R2 ) by measurement :
Question 30 :
State TWO reasons why it is necessary to measure external earth fault loop impedance at the origin of an installation :
GN-3 ( Determining Ze )
1. To verify an earth connection :
2. The value is equal to or less than the value determined by the designer :
Question 31 :
State TWO methods by which the impedance of a circuit may be obtained without operating any r.c.d.’s protecting the circuit :
GN-3 ( Residual current devices )
1. Soft test ( 15mA )
2. By calculation Zs = Ze + ( R1 + R2 )
Question 32 :
Determine the prospective fault current given following information ( Three phase supply 1. Impedance between P and N = 0.25Ω :
2. Impedance between P and E = 0.5Ω :
( General knowledge )
1. 230V ( Uo ) ÷ 0.25 = 920A = 0.92kA
2. 230V ÷ 0.5 = 460A = 0.46kA
3. For three phase multiply P to N value by 2 ( 0.92 x 2 = 1.84kA )
Question 33 :
State the reason for undertaking a prospective fault current measurement at the distribution board at the origin of the installation :
( Prospective fault current )
1. To ensure the adequate breaking capacity of the overcurrent devices :
2. To ensure the adequate breaking capacity of the main switch :
Question 34 :
State the three required electrical Tests required to be undertaken on a 30mA r.c.d. complying with BS 4293
( Functional testing ) Old BS- Only – 200mS
1. 1/2 test - 15mA for 2 seconds - device does not trip ;
2. 1 x test - device tested at full rated current trips within 200mS ( 0.2 seconds ) :
3. 5 x test when tested at 150mS device operates within 40mS :
Question 35 :
State FIVE items of electrical equipment that would require functional testing
( Functional checks )
1. R.c.d.’s :
2. Circuit breakers :
3. Isolators :
4. Interlocks :
5. Switches :

 

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Basic applications MCBs : Apprentice ,
The essential distinction between Type B, C or D devices is based on their ability to handle surge currents without tripping. These are, typically, inrush currents associated with fluorescent and other forms of discharge lighting, induction motors, battery charging equipment etc. BS 7671 specifically refers to Types B and C, and the choice will normally be between these two types :
• Type B devices are generally suitable for domestic applications. They may also be used in light commercial applications where switching surges are low or non-existent.
• Type C devices are the normal choice for commercial and industrial applications where fluorescent lighting, motors etc. are in use.
• Type D devices have more limited applications, normally in industrial use where high inrush currents may be expected. Examples include large battery charging systems, winding motors, transformers, X-ray machines and some types of discharge lighting :
The classification of Types B, C or D is based on the fault current rating at which magnetic operation occurs to provide short time protection ( typically less than 100ms ) against short-circuits. It is important that equipment having high inrush currents should not cause the circuit-breaker to trip unnecessarily, and yet the device should trip in the event of a short-circuit current that could damage the circuit cables :
The tripping characteristics
• Type B devices are designed to trip at fault currents of 3-5 times rated current (In). For example a 10A device will trip at 30-50A.
• Type C devices are designed to trip at 5-10 times In (50-100A for a 10A device ).
• Type D devices are designed to trip at 10-20 times In (100-200A for a 10A device ).
Normal cable ratings relate to continuous service under specified installation conditions. Cables will, of course, carry higher currents for a short time without suffering permanent damage. Type B and C circuit breakers can generally be selected to achieve tripping times that will protect the circuit conductors against normal surge currents in accordance with BS 7671. This is more difficult to achieve with Type D devices, which may require a lower earth loop impedance (Zs) to achieve the operating times required by Regulation 411.4.7 / 411.3.2.3 -
Overcoming unwanted tripping:
Sometimes failure of tungsten filament lamps can trip Type B circuit-breakers in domestic and retail environments. This is caused by high arcing currents occurring at the time of failure and is generally associated with inferior quality lamps. If possible the user should be encouraged to use better quality lamps. If the problem persists then one of the measures listed below should be considered :
A Type C device may be substituted for a Type B device where unwanted tripping persists, especially in commercial applications. Alternatively it may be possible to use a higher rated Type B MCB, say 10A rather than 6A. Whichever solution is adopted, the installation must be in accordance with BS 7671 :
A change from Type C to Type D devices should only be taken after careful consideration of the installation conditions, in particular the operating times required by Regulation 411.4.5 :
Other considerations:
Combined overcurrent and residual current circuit breakers (RCBOs) are available as integrated units or, in one case, as a modular device with a field-fittable clip-on RCD 'pod'. It should be borne in mind that if an RCBO trips it is not always clear whether tripping has been caused by an overcurrent or a residual current. Type B devices should only be used in domestic situations where high inrush currents are unlikely and Type C devices should be used in all other situations.

Short Circuit Capacity: Basic Calculations and Transformer Sizing : ( kVA ) ,

Short circuit capacity calculation is used for many applications: sizing of transformers, selecting the interrupting capacity ratings of circuit breakers and fuses, determining if a line reactor is required for use with a variable frequency drive, etc.
The purpose of the presentation is to gain a basic understanding of short circuit capacity. The application example utilizes transformer sizing for motor loads ,
Conductor impedances and their associated voltage drop are ignored not only to present a simplified illustration, but also to provide a method of approximation by which a plant engineer, electrician or production manager will be able to either evaluate a new application
or review an existing application problem and resolve the matter quickly ,

The following calculations will determine the extra kVA capacity required for a three phase transformer that is used to feed a single three phase motor that is started with full voltage applied to its terminals, or, "across-the-line."

Two transformers will be discussed, the first having an unlimited short circuit kVA capacity available at its primary terminals, and the second having a much lower input short circuit capacity available ,

kVA of a single phase transformer = V x A
kVA of a three phase transformer = V x A x 1.732, where 1.732 = the square root of 3.
The square root of 3 is introduced for the reason that, in a three phase system,
the phases are 120 degrees apart and, therefore, can not be added arithmetically They will add algebraically,

Transformer Connected To Utility Power Line ,

The first transformer is rated 1000 kVA, 480 secondary volts, 5.75% impedance. Rated full load amp output of the transformer is ,

1000 kVA / (480 x 1.732) = 1203 amps :

The 5.75% impedance rating indicates that 1203 amps will flow in the secondary if the secondary is short circuited line to line and the primary voltage is raised from zero volts to a point at which 5.75% of 480 volts, or, 27.6 volts, appears at the secondary terminals. Therefore, the impedance (Z) of the transformer secondary may now be calculated ,

Z = V / I = 27.6 volts / 1203 amps = .02294 ohms :

The transformer is connected directly to the utility power lines which we will assume are capable of supplying the transformer with an unlimited short circuit kVA capacity. The utility company will always determine and advise of the short

With unlimited short circuit kVA available from the utility, the short circuit amperage capacity which the transformer can deliver from its secondary is

480 volts / .02294 = 20,924 amps :

An alternative method of calculating short circuit capacity for the above transformer is:

1203 amps x 100 / 5.75% = 1203 / .0575 = 20,922 amps :

transformer and the value of the short circuit capacity The short circuit capacity is given as 20,900 amps.

Now we are ready to apply a motor to the terminals of the transformer secondary. We must determine the voltage drop which will be
We must determine the voltage drop which will be caused by the motor inrush on start. If the voltage remains within the rated voltage of the motor, then no oversizing ,

of the transformer is required. Motors rated for 460 volts are for use with distribution systems that are rated at
480 volts. The rating system allows a twenty volt drop in the distribution system which may occur along the feeder cables which connect the power transformer to the load.
The NEMA specification for a standard motor is that it requires the motor to be capable of operating at plus or minus 10% of nameplate voltage. Therefore, the voltage drop on inrush should not be allowed to drop below 460 volts less 10%, or, 414 volts ,

The transformer will be asked to supply power to a motor which has a full load amp rating of 1203 amps, which will fully load the transformer. Therefore, we will rate the motor at 460 V x 1203 A x 1.732, or, 958.5 kVA. We will assume that our motor will have an inrush of 600% of its full load rating which will cause an inrush of The transformer will be asked to supply power to a motor which has a full load amp
rating of 1203 amps, which will fully load the transformer. Therefore, we will rate the motor at 460 V x 1203 A x 1.732, or, 958.5 kVA. We will assume that our motor will have an inrush of 600% of its full load rating which will cause an inrush of ,

460 V x 1203 A x 600% x 1.732 = 5751 kVA :

The voltage drop at the transformer terminals will be proportional to the motor load. The voltage drop will be expressed as a percentage of the inrush motor load compared to the maximum capability of the transformer. [2] The transformer has a maximum kVA capacity at its short circuit capability, which is ,

480 V x 20,924 A x 1.732 = 17,395 kVA The voltage drop on motor inrush will be
5751 kVA / 17,395 kVA = .331, or, 33.1% :

The transformer output voltage will drop to 480 x .669, or, 321 volts. Thus, we can see that the transformer is much too small to use a motor that has a full load rating equal to the full load capacity of the transformer

The transformer must be sized so that its short circuit capabilty is equal to or greater than 5751 kVA times 10, or, 57,510 kVA in order to have a voltage drop of 10% or less. Therefore, the short circuit amperage capacity of the transformer to be used must be a minimum of ,



The transformer must be sized so that its short circuit capabilty is equal to or greater than 5751 kVA times 10, or, 57,510 kVA in order to have a voltage drop of 10% or less. Therefore, the short circuit amperage capacity of the transformer to be used must be a minimum of ,

57,510 kVA / (480 V x 1.732) = 69176 amps

 

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A typical 2500 kVA, 5.75% impedance transformer will have a short circuit capacity of 52,300 amps. The next highest standard size transformer at 3750 kVA will have a 6.5% impedance and would have a short circuit output capability of 69,395 amps which will be sufficient. ,


In the particular application discussed, the ratio of the selected standard size transformer kVA to motor kVA is 3750 kVA / 958.5 kVA = 3.91. Thus the transformer rating is 391% larger, or, nearly four times, the rating of the motor. Note the non-linear effect of the impedance rating of the transformers on their short circuit capacities ,

Transformer Connected To An Upstream Transformer ,

The second transformer we will examine will have a finite short circuit capacity available at its primary rather than an unlimited capacity. We will assume that a facility derives its power from the same 1000 kVA transformer mentioned above and that the
second transformer is connected directly to the terminals of the 1000 kVA transformer.
Thus, feeder cables between the two transformers are eliminated and the impedance of cables are not taken into account. However, the smaller the motor leads, the less will be both the short circuit capacity and the voltage delivered to the motor terminals ,

The second transformer, which will have a 480 volt primary and a 480 volt secondary, will be used to power a 20 HP, 3 phase, 460 volt motor which will be started at full voltage. The motor will be the only load on the transformer. The minimum transformer kVA ratings are for use with multiple motors on a single transformer. The 21.6 kVA is calculated as follows:

480 volts x 26 nominal amps x 1.732 = 21.6 kVA

The transformer manufacturers will give a 20 HP motor a nominal full load amp rating of 27 amps, thus allowing no extra capacity:
460 volts x 27 nominal amps x 1.732 = 21.5 kVA ,
One motor manufacturer has rated a 20 HP motor at 26 Full Load Amps, 460 VAC, 205 Locked Rotor Amps, 81% Power Factor. The motor will present a load of , 460 volts x 26 amps x 1.732 = 20.7 kVA ,
The starting motor kVA load with inrush current will be : 460 V x 205 A x 1.732 = 163.3 kVA ,

We will consider using a 30 kVA general purpose transformer to supply the 20 HP motor. The transformer will have a nominal impedance of 2.7% and an ouptut of 36.1 amps at 480 volts. The short circuit current capacity that can be delivered to the 21.6 kVA
transformer by the upstream 1000 kVA transformer is 20,924 amps, or, 17,395 kVA.
The short circuit amperage capacity of a transformer with a limited system short circuit capacity available at its primary is :

transformer full load amps / (transformer impedance + upstream system impedance as seen by the transformer)
Where : upstream system impedance as seen by the transformer = transformer kVA / available primary short circuit capacity kVA
Therefore, ( 36.1 amps / [2.7% + (30 kVA / 17,395 kVA ) = 36.1 / (2.7% + .0017%) = 36.1 / .0287 = 1258 short circuit amps )
The transformer output voltage drop upon motor inrush will be :
motor inrush kVA / short circuit kVA =163.3 kVA / (480 V x 1258 A x 1.732 ) = 163.3 kVA / 1046 kVA =156 = 15.6 % )
A 30 kVA transformer rating is too small as the motor voltage drop will exceed 10% ,

A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush would be 9.66% ,

For a single motor and transformer combination, one transformer manufacturer recommends that the motor full load running current not exceed 65% of the transformer full load amp rating. [3] Thus, for our 26 amp motor the transformer rating should be a minimum of 40 amps, or, 33.3 kVA.

The transformer output voltage drop upon motor inrush will be : motor inrush kVA / short circuit kVA =
163.3 kVA / (480 V x 1258 A x 1.732) = 163.3 kVA / 1046 kVA = 156 = 15.6 %
A 30 kVA transformer rating is too small as the motor voltage drop will exceed 10% ,
A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush ,
A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush would be 9.66%. , A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts
would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush
would be 9.66% ,
For a single motor and transformer combination, one transformer manufacturer recommends that the motor full load running current not exceed 65% of the transformer full load amp rating. [3] Thus, for our 26 amp motor the transformer rating should be a minimum of 40 amps, or, 33.3 kVA. ,
Multiple Motors On A Single Transformer ,
The minimum transformer kVA is given by transformer manufacturers so that a transformer may be sized properly for multiple motors. If there are five motors on one transformer, add the minimum kVA ratings and then add transformer capacity as necessary to accommodate the inrush current of the largest motor , The transformer thusly selected will be capable of running and starting all five motors provided that only one motor is started at any one time. Additional capacity will be required for motors starting simultaneously , Also, if any motor is started more than once per hour, add 20% to that motor's minimum kVA rating to compensate for heat losses within the transformer.
Motor Contribution to Short Circuit Capacity ,
When a fault condition occurs, power system voltage will drop dramatically. All motors that are running at that time will not be able to sustain their running speed. As those motors slow in speed, the stored energy within their fields will be discharged into the power line. The nominal discharge of a motor will contribute to the fault a current equal to up to four times its full load current.
With our 1000 kVA, 1203 amp transformer example given above, we will assume that all
1203 amps of load are from motors. The actual short circuit current will equal 20,924 amps
plus 400% of 1203 amps for a total of 25,736 short circuit amps.

When sizing the transformer for motor loads, the fault current contribution from the motors will not be a consideration for sizing. However, the motor contribution must motors will not be a consideration for sizing. However, the motor contribution must be
considered when sizing all branch circuit fuses and circuit breakers. The interrupting capacity ratings of those devices must equal or exceed the total short circuit capacity ratings of those devices must equal or exceed the total short circuit capacity available at the point of application..

Motor contribution to short circuit capacity must be included when adding a variable frequency drive to the system ,

Do you know what an impedance test is ? Max Earth fault loop impedance is ( Zs=Ze+R1+R2 )
You are testing your ( R1 + R2 ) if there is no continuity of your CPC you will have an open circuit.


Easily check your Earth Loop Impedance compliance!
: Cable size and capacity
: Voltage drop in volt and percent
: Maximum length of run
: Fuse or Circuit Breaker size
: Working Temperature
: Fault level
: Minimum trip current needed to comply with Earth loop Impedance test
: Actual let through current
: Maximum impedance values (Ze) and the actual impedance values (in ohms)
: Total impedance values(Zs) for the complete installation (in ohms)

“ Inspection & Testing before into Service “ 2392-10 Electrical Installations should be Inspected and Tested as Necessary and Appropriate During and the End of Installation , Before they are taken into Service , to Verify that they are Safe to Use ,Maintain and Alter and Comply with Part P of the
Building Regulations and with any Other Relevant Parts of the Building Regulations

 

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Machinery and equipment must be maintained in efficient working order, so it is in good repair and kept safe -
This is required by Regulation 5, of the Provision and Use of Work Equipment Regulations 1998.

What is Three Phase Power ?

Three phase power is a method of electric power transmission using three wires.
Three phase power systems may have a neutral wire that allows the system to use a higher voltage while still allowing lower voltage single phase appliances. In high voltage distributions, it is not common to have a neutral wire, as the loads can simply be connected between phases :
Three phase power is a very efficient form of electrical power distribution. All three wires carry the same current and have a constantly balanced power load. Three phase power does not generally power domestic houses, and when it does, a main distribution board splits the load. Most domestic loads use single phase power.
Conductors used in the three phase power system are colour-coded. Most countries have their own colour codes. The colour codes of the wires vary greatly. There may be a standard for each installation, or there may be no standard at all :
Three phase power flow begins in a power station. An electrical power generator converts mechanical power into alternating electric currents. After numerous conversions in the distribution and transmission network, the power is transformed into the standard mains voltage. At this point, the power may have already been split into single phases or into three phases. With three phase power, the output of the transformer is usually star connected with the mains voltage, 230 volts in Europe and 120 volts in North America :
Electric motors are the most common use for three phase power. A three phase induction motor combines high efficiency, a simple design and a high starting torque. Three phase electric motors are commonly used in industry for fans, blowers, pumps, compressors and many other kinds of motor driven equipment. A three phase power motor is less costly than a single phase motor of the same voltage and rating :
Other systems that use three phase power include air conditioning equipment, electric boilers and large rectifier systems. The main reasons for using the three phase power system are efficiency and economy. While most three phase motors are quite big, there are examples of very small motors, such as computer fans. An inverter circuit inside the fan converts DC to a three phase AC current. This serves to decrease noise, as the torque from a three phase motor is very smooth, and it also increases reliability :

What are Electrical Transformers ?
The name itself offers a simple definition. Electrical transformers are used to transform electrical energy. How electrical transformers do so is by altering voltage, generally from high to low. Voltage is simply the measurement of electrons, how many or how strong, in the flow. Electricity can then be transported more easily and efficiently over long distances :
While power line electrical transformers are commonly recognized, there are other various types and sizes as well. They range from huge, multi-ton units like those at power plants, to intermediate, such as the type used on electric poles, and others can be quite small. Those used in equipment or appliances in your home or place of businesses are smaller electrical transformers and there are also tiny ones used in items like microphones and other electronics :
Probably the most common and perhaps the most necessary use of various electrical transformers is the transportation of electricity from power plants to homes and businesses. Because power often has to travel long distances, it is transformed first into a more manageable state. It is then transformed again and again, or “stepped down,” repeatedly as it gets closer to its destination :
When the power leaves the plant, it is usually of high voltage. When it reaches the substation the voltage is lowered. When it reaches a smaller transformer, the type found on top of electric poles, it is stepped down again. It is a continuous process, which repeats until the power is at a usable level :
You have likely seen the type of electrical transformers that sit on top of electric poles. These, like most electrical transformers, contain coils or “windings” that are wrapped around a core. The power travels through the coils. The more coils, the higher the voltage. On the other hand, fewer coils mean lower voltage :
Electrical transformers have changed industry. Electric power distribution is now more efficient than ever. Transformers have made it possible to transfer power near and far, in a timely, efficient, and more economical manner. Since many people do not wish to live in close proximity to a power plant, there is the added benefit of making it possible for homes and businesses that are quite a distance from power plants to obtain dependable, affordable electricity. Much of the electricity used today will have passed through many electrical transformers before it reaches users. Power distribution :

What are AC Motors ?
There are many different types and sizes of electric motors. Electric motors can be divided into two types: Alternating Current (AC) motors and Direct Current (DC) motors. An AC electric motor requires an alternating current, while a DC motor requires direct current.
AC motors are further subdivided into single phase and three phase motors. Single phase AC electrical supply is what is typically supplied in a home. Three phase electrical power is commonly only available in a factory setting. The most common single phase AC motor is known as a universal motor. This is because this motor can also run with DC current.
This type of motor is very inefficient but can be very inexpensively made. It is also used almost exclusively for small factional horse power AC motors. The other advantage this AC motor has is that the rotational speed of the motor can be easy changed. This type of AC motor is commonly found in mixers, hand drills, and any other application requiring variable speed and low cost and small size.
For larger single phase AC motors, a electrical component known as a capacitor is used to create a second phase from the single phase AC current. This type of AC motor is known as an induction motor and there are two basic types; a capacitor start motor and a capacitor run motor. The capacitor is used to create a second phase from the single phase power source and it is the interaction between these two phases that causes the motor to turn.
This introduction of a second phase eliminates the need for the brushes used in a universal AC motor. This greatly increases the both the efficiency of the AC motor and increases the life expectancy of the AC motor as brushes are a
major source of wear and failure. This type of motor is a fixed speed motor. It is commonly used as the drive for refrigerator compressors, shop air-compressors, and as a general utility type AC motor.
AC motors are usually sized in horsepower. The most common sizes are what are called fractional horsepower motors, i.e. ½ horse power or ¼ horsepower. Larger motors are typically only found in factories, where they can range in size to thousands of horsepower.
AC motors also come with various speed ratings. Speed is usually specified as rotations per minute (RPM) at no load condition. As the motor is loaded down, the speed will slow down. When the AC motor is running at its rated power draw, the speed of the shaft measured in RPM is the full load speed. If the electric motor is loaded too heavily, the motor shaft will stop. This is known as the stall speed and should be avoided. All of these speeds are typically listed on the specification sheet for an AC motor.
Finally, before you order an AC motor, you should determine the mounting type you require, the start up torque, the type of enclosure required, and the type of shaft output required :

 

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What is the Difference between a Generator and Inverter ?
The difference between an generator and an inverter may at first seem simple. However, as more research is done, the issue can quickly become confusing, especially to those who are not technically inclined and familiar with types of electricity. For example, while the definitions of an inverter and generator are clearly distinct, there are such things as inverter generators. However, though the terms may seem contradictory, they can be explained fairly easily.
Before discussing the difference between an inverter and generator, it is first necessary to understand a little about electrical currents. Electricity is divided into two types of currents, alternating current (AC) and direct current (DC). AC, a more common current for home use, works by allowing electrons to flow in two different directions. In DC currents, electrons flow only one way.
An inverter takes existing power that comes in the form of DC current and converts it to AC current. This is a popular option for those wanting to run home electronics in automobiles. Such cars often produce on DC current, which is not compatible with most electronics meant to run off standard outlets. Therefore, an inverter becomes necessary.
A generator, on the other hand, is a machine that converts mechanical energy into energy in an electrical form. In most cases, electric generators are responsible for the energy a home receives. Large-scale electrical generators may be powered by coal, natural gas or nuclear energy. A portable generator commonly uses gasoline, which is burned to create electrical energy. Generators usually produce AC electricity.
Simply stated, the difference between the two is that an inverter is only effective if there is already a source of electrical energy. It cannot generate its own. It can simply convert electrical energy that is already there. On the other hand, a traditional generator cannot make AC current into DC current.
On the other hand, there are things known as inverter generators. These are like traditional generators in that they convert some other form of energy into electrical energy. However, they produce AC power, which is then converted to DC power before being converted back to AC. The reason for this conversion is that the power gained during the process. It allows the generator to be more fuel efficient, as well as operate more quietly than standard generators.
Some people also confuse an inverter with a power converter, even using the terms interchangeably. However, a converter is used to change voltage from one level to another. For example, in Europe, a converter may be used to convert the voltage from 220 to 120, for electrical components meant to run on a lower voltage,

What is IPS ?
IPS, or integrated power systems, is simply a method of ensuring that the power supply needed to keep a place of business functional in the event of a problem with the primary source of energy. With so many of our home and work environments dependent on a steady supply of power, it is no wonder that the concept of IPS has gone from being a good idea to an essential. Here is some background on the concept of IPS and how many companies choose to implement their backup power supply procedures these days :
IPS plans and procedures are nothing new. As far back as the 1940’s, manufacturing facilities relied on backup power stations that could be run with gas generators in the event of a massive power failure. Hospitals also have operated with a full-fledged disaster recovery program that would ensure power to all vital functions, such as oxygen for the patients and enough power to keep operating rooms going in a crisis :
What is different today is that IPS strategies have become more sophisticated as technology has improved and demand for more reliable IPS options has become necessary. Where once a gas generator would be needed to power a small power station, many organizations can now relay on compact battery backups as part of the IPS escalation procedures :
In telephone, everything from switch stations to bridging centres will utilize state of the art battery backup that can last for in excess of twelve hours before losing power. Many IPS plans will still incorporate generator backup as well, usually as a third alternative if it appears that battery backup is about to fail. More frequently, businesses are beginning to incorporate solar panels and battery storage as part of the overall IPS directives for the organization :
The loss of valuable data as a result of a complete shutdown in the face of a power outage could be devastating to any business. Preparing a workable IPS plan, including an escalation procedure for implementing the backup power sources, ensures that even in the face of a short-term problem with a node on the national power grid, life will go on as usual :

What is a DC Motor ?
A direct current (DC) motor is a fairly simple electric motor that uses electricity and a magnetic field to produce torque, which turns the motor. At its most simple, a DC motor requires two magnets of opposite polarity and an electric coil, which acts as an Electromagnets. The repellent and attractive electromagnetic forces of the magnets provide the torque that causes the DC motor to turn.
If you've ever played with magnets, you know that they are polarized, with a positive and a negative side. The attraction between opposite poles and the repulsion of similar poles can easily be felt, even with relatively weak magnets. A DC motor uses these properties to convert electricity into motion. As the magnets within the DC motor attract and repel one another, the motor turns.
A DC motor requires at least one electromagnet. This electromagnet switches the current flow as the motor turns, changing its polarity to keep the motor running. The other magnet or magnets can either be permanent magnets or other Electromagnets. Often, the electromagnet is located in the centre of the motor and turns within the permanent magnets, but this arrangement is not necessary.
To imagine a simple DC motor, think of a wheel divided into two halves between two magnets. The wheel of the DC motor in this example is the electromagnet. The two outer magnets are permanent, one positive and one negative. For this example, let us assume that the left magnet is negatively charged and the right magnet is positively charged.
Electrical current is supplied to the coils of wire on the wheel within the DC motor. This electrical current causes a magnetic force. To make the DC motor turn, the wheel must have be negatively charged on the side with the negative permanent magnet and positively charged on the side with the permanent positive magnet. Because like charges repel and opposite charges attract, the wheel will turn so that its negative side rolls around to the right, where the positive permanent magnet is, and the wheel's positive side will roll to the left, where the negative permanent magnet is. The magnetic force causes the wheel to turn, and this motion can be used to do work.
When the sides of the wheel reach the place of strongest attraction, the electric current is switched, making the wheel change polarity. The side that was positive becomes negative, and the side that was negative becomes positive. The magnetic forces are out of alignment again, and the wheel keeps rotating. As the DC motor spins, it continually changes the flow of electricity to the inner wheel, so the magnetic forces continue to cause the wheel to rotate.
DC motors are used for a variety of purposes, including electric razors, electric car windows, and remote control cars. The simple design and reliability of a DC motor makes it a good choice for many different uses, as well as a fascinating way to study the effects of magnetic fields. Electromagnets

 

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What is MIG Welding ? you’ll see a lot in you careers !! tripping ,
MIG (Metal Inert Gas) welding, also sometimes called GMAW (gas metal arc welding), is a welding process that was originally developed back in the 1940's for welding aluminium and other non-ferrous metals. MIG welding is an automatic or semi automatic process in which a wire connected to a source of direct current acts as an electrodes joins two pieces of metal, as it is continuously passed through a welding gun. A flow of an inert gas (originally Argon ) is also passed through the welding gun at the same time as the wire electrode. This inert gas acts as a shield, keeping air borne contaminants away from the weld zone.
The primary advantage of MIG welding is that it allows metal to be welded much quicker than traditional welding "stick welding" techniques. This makes it ideal for welding softer metals such as aluminum. When MIG welding was first developed, the cost of the inert gas (i.e., argon) made the process too expensive for welding steel. However, over the years, the MIG welding process has evolved and semi inert gases such as carbon dioxide can now be used to provide the shielding function which makes MIG welding cost effective for welding steel.
Besides providing the capability to weld non-ferrous metals, MIG welding has other advantages:
• It produces long continuous welds much faster than tradition welding methods.
• Since the shielding gas protects the welding arc, MIG welding produces a clean weld with very little splatter.
• The versatility of MIG welding means it can be used with a wide variety of metals and alloys
The primary disadvantages of MIG welding are:
• The welding equipment is quite complex (MIG welding requires a source of direct current, a constant source and flow of gas as well as the continuously moving wire electrode). Plus, electrodes are available in a wide range of sizes and made from a number of metal types to match the welding application.
• The actual welding technique used for MIG welding is different from traditional welding practices, so there is learning curve associated with MIG welding even for experienced welders. For example, MIG welders need to push the welding puddle away from them and along the seam.
• The necessity for the inert gas shield means that MIG welding cannot be used in an open area where the wind would blow away the gas shield.
Since it's development in the middle of last century, MIG welding has become commonplace in many manufacturing operations. For example MIG welding is commonly used in the automobile industry because of its ability to produce clean welds, and the fact that it welds metals quickly.

ELECTRICAL INSTALLATION CERTIFICATES NOTES FOR FORMS 1 AND 2 : 17th Edition ,

1. The Electrical Installation Certificate is to be used only for the initial certification of a new installation or for an addition or alteration to an existing installation where new circuits have been introduced.
It is not to be used for a Periodic Inspection, for which a Periodic Inspection Report form should be used. For an addition or alteration which does not extend to the introduction of new circuits, a Minor Electrical Installation Works Certificate may be used.
The "original" Certificate is to be given to the person ordering the work (Regulation 632.1). A duplicate should be retained by the contractor.
(2) This Certificate is only valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test Results.
(3) The signatures appended are those of the persons authorized by the companies executing the work of design, construction, inspection and testing respectively. A signatory authorized to certify more than one category of work should sign in each of the appropriate places.
(4) The time interval recommended before the first periodic inspection must be inserted (see IEE Guidance Note 3 for guidance).
(5) The page numbers for each of the Schedules of Test Results should be indicated, together with the total number of sheets involved.
(6) The maximum prospective fault current recorded should be the greater of either the short-circuit current or the earth fault current.
(7) The proposed date for the next inspection should take into consideration the frequency and quality of maintenance that the installation can reasonably be expected to receive during its intended life, and the period should be agreed between the designer, installer and other relevant parties :

TESTING :
NOTES ON SCHEDULE OF TEST RESULTS

*1 Type of supply is ascertained from the distributor or by inspection.
*2 Ze at origin. When the maximum value declared by the distributor is used, the effectiveness of the earth must be confirmed by a test. If measured the main bonding will need to be disconnected for the duration of the test.
*3 Prospective fault current (PFC). The value recorded is the greater of either the short-circuit current or the earth fault current. Preferably determined by enquiry of the distributor.
*4 Short-circuit capacity of the device is noted, see Table 7.2A of the On-Site Guide or Table 2.4 of GN3
The following tests, where relevant, shall be carried out in the following sequence:
Continuity of protective conductors, including main and supplementary bonding Every protective conductor, including main and supplementary bonding conductors, should be tested to verify that it is continuous and correctly connected.
*6 Continuity Where Test Method 1 is used, enter the measured resistance of the line conductor plus the circuit protective conductor (R1+ R2). See 10.3.1 of the On-Site Guide or 2.7.5 of GN3. During the continuity testing (Test Method 1) the following polarity checks are to be carried out: (a) every fuse and single-pole control and protective device is connected in the line conductor only (b) centre-contact bayonet and Edison screw lampholders have outer contact connected to the neutral conductor (c) wiring is correctly connected to socket-outlets and similar accessories. Compliance is to be indicated by a tick in polarity column 11.
(R1 + R2) need not be recorded if R2 is recorded in column 7.
*7 Where Test Method 2 is used, the maximum value of R2 is recorded in column 7. See 10.3.1 of the On-Site Guide or 2.7.5 of GN3.
*8 Continuity of ring final circuit conductors A test shall be made to verify the continuity of each conductor including the protective conductor of every ring final circuit. See 10.3.2 of the On-Site Guide or 2.7.6 of GN3.
*9, *10 Insulation Resistance All voltage sensitive devices to be disconnected or test between live conductors (line and neutral) connected together and earth. The insulation resistance between live conductors is to be inserted in column 9. The minimum insulation resistance values are given in Table 10.1 of the On-Site Guide or Table 2.2 of GN3. See 10.3.3(iv) of the On-Site Guide or 2.7.7 of GN3.
All the preceding tests should be carried out before the installation is energised.
*11 Polarity A satisfactory polarity test may be indicated by a tick in column 11. Only in a Schedule of Test Results associated with a Periodic Inspection Report is it acceptable to record incorrect polarity.
*12 Earth fault loop impedance Zs This may be determined either by direct measurement at the furthest point of a live circuit or by adding (R1 + R2) of column 6 to Ze. Ze is determined by measurement at the origin of the installation or preferably the value declared by the supply company used. Zs = Ze + (R1 + R2). Zs should be less than the values given in Appendix 2 of the On-Site Guide or Appx 2 of GN3.
*13 Functional testing The operation of RCDs (including RCBOs) shall be tested by simulating a fault condition, independent of any test facility in the device. Record operating time in column 13. Effectiveness of the test button must be confirmed. See Section 11 of the On-Site Guide or 2.7.15 and 2.7.18 of GN3.
*14 All switchgear and controlgear assemblies, drives, control and interlocks, etc must be operated to ensure that they are properly mounted, adjusted, and installed. Satisfactory operation is indicated by a tick in column 14.
Earth electrode resistance The earth electrode resistance of TT installations must be measured, and normally an RCD is required. For reliability in service the resistance of any earth electrode should be below 200 Ω. Record the value on Form 1, 2 or 6, as appropriate. See 10.3.5 of the On-Site Guide or 2.7.12 of GN3.

 

[amberleaf]

GUIDANCE FOR RECIPIENTS
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration or to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such an inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended : Page 2 of (note 5) ,

ELECTRICAL INSTALLATION CERTIFICATE GUIDANCE FOR RECIPIENTS (to be appended to the Certificate)
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such a periodic inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended :

ELECTRICAL INSTALLATION CERTIFICATE GUIDANCE FOR RECIPIENTS (to be appended to the Certificate)
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such a periodic inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended :

NOTES ON COMPLETION OF MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE
Scope
The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not extend to the provision of a new circuit. Examples include the addition of socket-outlets or lighting points to an existing circuit, the relocation of a light switch etc. This Certificate may also be used for the replacement of equipment such as accessories or luminaires, but not for the replacement of distribution boards or similar items. Appropriate inspection and testing, however, should always be carried out irrespective of the extent of the work undertaken.
Part 1 Description of minor works
1,2 The minor works must be so described that the work that is the subject of the certification can be readily identified.
4 See Regulations 120.3 and 120.4. No departures are to be expected except in most unusual circumstances. See also Regulation 633.1.
Part 2 Installation details
2 The method of fault protection must be clearly identified e.g. earthed equipotential bonding and automatic disconnection of supply using fuse/circuit-breaker/RCD.
4 If the existing installation lacks either an effective means of earthing or adequate main equipotential bonding conductors, this must be clearly stated. See Regulation 633.2.
Recorded departures from BS 7671 may constitute non-compliance with the Electricity Safety, quality and continuity Regulations 2002 (as amended) or the Electricity at Work Regulations 1989. It is important that the client is advised immediately in writing.
Part 3 Essential Tests
The relevant provisions of Part 6 (Inspection and Testing) of BS 7671 must be applied in full to all minor works. For example, where a socket-outlet is added to an existing circuit it is necessary to:
1 establish that the earthing contact of the socket-outlet is connected to the main earthing terminal
2 measure the insulation resistance of the circuit that has been added to, and establish that it complies with Table 61 of BS 7671
3 measure the earth fault loop impedance to establish that the maximum permitted disconnection time is not exceeded
4 check that the polarity of the socket-outlet is correct
5 (if the work is protected by an RCD) verify the effectiveness of the RCD.
Part 4 Declaration
1,3 The Certificate shall be made out and signed by a competent person in respect of the design, construction, inspection and testing of the work.
1,3 The competent person will have a sound knowledge and experience relevant to the nature of the work undertaken and to the technical standards set down in BS 7671, be fully versed in the inspection and testing procedures contained in the Regulations and employ adequate testing equipment.
2 When making out and signing a form on behalf of a company or other business entity, individuals shall state for whom they are acting.