Re-take - Useful Information for 2394 :

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2392-10 .

The most important, & overlooked, aspect of safety in electrical-testing is that of a , skill of theoperator-undertaking the testing .

Residual-current-device ,test-instrument

Regulation(s) 612.8.1. & 612.10 require the use of an RCD-test-instrument toBS-EN-61557-6 , to test the operation RCDs used for fault-protection &additional-protection . respectively .

Sources of information

Initial-verification isintended to confirm that the installation complies with the designer’srequirements and has been constructed, inspected and tested in accordance with BS-7671. In your case here. 2392-10. Installer / Designer .

Functional 612.13. : & 612.13.1. 612.13.2.

Activities to becarried out: Etc.

All RCDs to be checked both by , Testinstrument and by Test button
All Manually-operated-circuit-breakers tobe operated to verify they open and close correctly.

Operation of circuit-breakers . ( Don’t overlookCircuit-breaker(s) because of RCDs / RCBOs )

All circuit-breakersshould be inspected for visible signs of damage or damage caused by Overheating.
Each circuit-breaker should be manually operated to ensure that the device opens and closescorrectly

 

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IET-Guidance-Note 3 . 2.1 p/15 . 2392-10 / 2394 .
Chapter -2 “ Pupose of Initial-verification ”
610.1. Initial-verification is carried out on a , New-installation before it is put into service .

2.7. P/31 . Initial-testing .
The test-methodsdescribed in this section are recommended to be used for verification. In this respect , GuidanceNote-3 is cited in Regulatrion 612.1
This does not rule out the use of othertest-methods provided they give valid-results .

610. Testing
610.1. General:
The tests Regulations 612.2. to 13 , where relevant, shall becarried out & the results compared with relevant-criteria .

2.7.1. Test-results.
The test-results must berecorded on the Schedule(s) of Test-results & compared with relevant-criteria.
2.7.4. P/32 The sequence of tests
Initial-testsshould be carried-out in the following , sequence where relevant &practical: Regulation 612.1.

( Wording ) Reg.P/33 . Reporting : Communicating the results of , Periodic-inspection & testing of an electrical-installation tothe person-ordering the work .

Verification : All measures by means of which compliance ofthe electrical-installation with the relevant-requirements of BS-7671:are checked ,
Comprising :

Inspection . “ Visual “
Testing .
Certification .

 

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Which one of thefollowing best describes the operation of a RCD ?

□ Magnetic
□ Thermal
□ Current balance
□ hydraulic

 

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Replacing a consumer-unit in an ( Existing-installation) is an , Addition or Alteration to thatinstallation .
The work must therefore be , Designed ,Erected & Verified , in accordance with the requirements of thecurrent-edition of BS-7671: &must not impair the safety of the , existing-installation
Regulation(s) 110.1.2. ( vi ) 610.4. refer .
P/14 . 110.1.2. additions & alterations to installations& also parts of the , existing-installation affected by an addition &alteration

Initial-Verification .

P/189 . 610.4.
For an addition &alteration to an ( Existing-installation) it shall be verified that the additionor alteration complies with the ,Regulation(s) & does not impair the safety of the ( Existing-installation)

610.5. The verification shall be made bya , Competent-person .
610.6. On completion of the verification, according to , Regulation(s) 610.1 to 5 , a Certificate shall be prepared .
P/36 . Verification .
All measures by means of which compliance of theelectrical-installation , with the relevant requirements of BS-7671: are ( Checked ) comprising inspection , testing , & certification .

Re-cap : P/190 .612.1 General .
The tests of Regulation(s) 612.2. to 6 , whererelevant , shall be carried out in that ( Order ) before the installation is energized .

 

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Guidance Note-3 , is concerned principally with Inspection and Testing
" IET Wiring Regulations( BS-7671:2011: ) 17th Edition ".

Coverage

Initial-verification
Periodic-inspection
Test-instruments.

GN-3 : Which enlarges upon and amplifies the particularrequirements of a part of the 17th Edition Wiring Regulations BS-7671:2011:
Each of these guides GN-3. is extensively cross-referenced to the Regulations

 

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Main-earthing-terminal(MET)

The function of the MET is to , provide a reference point for the installation. :icon_bs:
It consistsof a terminalor bar provided for the connection of protective conductor(s), including main-protective-bonding-conductor(s),& conductors for functional-earthing.

Although the MET is connected to Earth it is seldomat , Zero potential because of the potential-difference caused byleakage and other currents flowing to Earth.

 

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Re-cap : System(s)

TN-S system (Figure 3.8 - 2011)
In a TN-S the Neutraland Protective conductors should be kept separate throughout the system and thesource is solidly earthed.

Commentary on :

A TN-S system has a particulardisadvantage that in the event that the protective conductor becomes opencircuit, there is no indication that a fault has occurred and installations canunknowingly be left without an earth. In the event of an earth fault all of theexposed-conductive-parts within a consumer installation may be raised to ahazardous potential. Earth fault protection devices will not operate as therewill be no flow of current to earth.

TN-Csystem
Ina TN-C system (Figure 2.2 - 2008) the neutraland protective functions should be combined in a single conductor (PEN)throughout the entire system. Multiple connections to earth are recommendedalong the PEN conductor and the source is solidly earthed.

Commentary on :
The need for multiple earth connections is becauseif the neutral becomes open-circuit for any reason, theexposed-conductive-parts will rise to line to earth voltage in the case ofsingle-phase connections and a value up to line to earth voltage in the case ofthree-phase connections, depending on the degree to which the load isunbalanced.

TN-C-Ssystem
Ina TN-C-S system, (Figure 3.9 - 2011) theneutral and protective functions should be combined in a single conductor (PEN)from the source (solidly earthed) up tothe consumers intake. Multiple connections to earth are recommended along thePEN conductor. Within the consumer’s installation the neutral and protectiveconductors should be kept separate.

Commentary on :

The TN-C-S system is also known as a “ protective multiple earthed ” (PME) system.The PEN conductor, which is referred to as a combined neutral and earth (CNE)conductor, is earthed at the source and extremities of the distribution mainsand points in-between; hence the reference to multiple earthing. Multipleearthing of the CNE conductor ensures that if the conductor becomesopen-circuit for any reason, exposed-conductive-parts remain connected toearth; under such conditions the supply voltage between the installation lineand neutral conductors is substantially reduced and consumers will experienceunacceptable voltage variations.

TTinstallation
ATT system (Figure 3.10 - 2011) has a solidly earthed source; theexposed-conductive-parts of the consumer’s installation are earthed through aninstallation earth electrode which is electrically independent of the sourceearth.

Commentary on :
In the TT system the earth fault loop impedance isgenerally high as the fault path includes the earth electrode resistance of thesupply and the earth electrode resistance of the consumer’s installation.

IT System
AnIT system (Figure 2.6 - 2008) has the sourceeither connected to earth through an earthing impedance or is isolated(Insulated) from the earth. All of the exposed-conductive parts of aninstallation are connected to an earth electrode in a similar manner to a TTarrangement.

Commentary on :

Generally an IT system would be chosen in locationssuch as medical centres and mines where the supply has to be maintained even inthe event of a fault, and where the connection with earth is difficult (forexample a mobile generator).

 

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RCBOs. RCD / MCB . Exams . Wording . Yeah

Meansfor removing the supply to the protected circuit ( a circuit breaker element ) when the residual currentexceeds the rated residual operating current of the device.

 

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RCCB differs from an RCBO in that the RCBO will additionallyrespond to overcurrent conditions whereas the RCCB will not respond tosuch conditions.

p/34. RCBO . with integral-overcurrent-protection
p/34. RCCB . without integral-overcurrent-protection

RCD's work by means of the , current balance principle
Thatis, the algebraic sum of all the electric currents meeting at any point in acircuit must be zero,otherwise the circuit will be broken.
AnRCD's circuit is broken when the residual current is between 50% & 100% ofthe rated tripping current, as required by the relevant British Standards.

Principle of Operation
Inan electrical installation, current will flow from the supply to a load andback to the supply. The load can be connected between Line and Neutral on asingle phase installation.

Underperfect conditions, the magnitude of the current flowing to the load will equalthe magnitude of the current returning from the load back to the supply. Anydifference in the current flowing to the load and returning from the load isknown as a residual-current. Under earth fault conditions, a current will flowto earth, giving rise to a residual-operating-current.

Definition P/34.
Residual-operating-current, Residual-current whichcauses the RCD to operate under specified-condition(s)

 

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Electrical contractor has an obligation to ensure that the workhe undertakes to the existing-circuits and the alterations and additions complies with the IET Wiring Regulations. 2011:

P/390 . EIC , should identify the electrical-workthat was carried as “ New “

An Addition or anAlteration , The term New is appropriatewhere the , whole-installation had been installed
The term : “ Addition “ isrelevant if an existing-installation has been modified by the Addition of oneor more new-circuits .
The term : “ Alteration “ is appropriate to where one or moreexiting-circuits have been modified or extended , or items such asconsumer-units

MEIWC , Limited-application

Current-ratings ofconductors, Extracts .

“ if the wires become perceptibly warmed by the ordinary current, it isa proof that they are too small for the work that they have to do and that theyought to be replaced with wires of a larger size ”

Conductors shouldbe sufficient in size for the work which they are called upon to do.

 

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Re-cap : 2392-10 / 2394 .
Additions & Alterations :icon_bs:
No addition or alteration, temporary orpermanent, shall be made to an existing installation, unless it has beenascertained that the rating and the condition of any existing equipment,including that of the distributor, will be adequate for the altered circumstances.Furthermore, the earthing and bonding arrangements, if necessary for theprotective measure applied for the safety of the addition or alteration, shallbe adequate. 132.16 p20
During erection and oncompletion of an installation or an addition or alteration to an installation,and before it is put into service, appropriate inspection and testing shall becarried out by competent persons to verify that the requirements of theStandard have been met.
Appropriate certificationshall be issued in accordance with Sections 631 and 632. 134.2.1 p22
Upon completion of the verification of anew installation or changes to an existing installation, an ElectricalInstallation Certificate based on the model given in Appendix 6, shall beprovided. Such documentation shall include details of the extent of theinstallation covered by the Certificate, together with a record of theinspection, the results of testing and a recommendation for the interval untilthe first periodic inspection. 631.1 p195
The requirements of Sections 631 and 632for the issue of an Electrical Installation Certificate or a Minor ElectricalInstallation Works Certificate shall apply to all the work of the additions oralterations. 633.1 p196
The contractor or other personresponsible for the new work, or a person authorized to act on their behalf,shall record on the Electrical Installation Certificate or the Minor ElectricalInstallation Works Certificate, any defects found, so far as is reasonablypracticable, in the existing installation. 633.2 p196

 

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Re-cap : 2392-10 / 2394 .
Additions & Alterations

No addition or alteration, temporary orpermanent, shall be made to an existing installation, unless it has beenascertained that the rating and the condition of any existing equipment,including that of the distributor, will be adequate for the altered circumstances.Furthermore, the earthing and bonding arrangements, if necessary for theprotective measure applied for the safety of the addition or alteration, shallbe adequate. 132.16 p20

During erection and oncompletion of an installation or an addition or alteration to an installation,and before it is put into service, appropriate inspection and testing shall becarried out by competent persons to verify that the requirements of theStandard have been met.
Appropriate certificationshall be issued in accordance with Sections 631 and 632. 134.2.1 p22

Upon completion of the verification of anew installation or changes to an existing installation, an ElectricalInstallation Certificate based on the model given in Appendix 6, shall beprovided. Such documentation shall include details of the extent of theinstallation covered by the Certificate, together with a record of theinspection, the results of testing and a recommendation for the interval untilthe first periodic inspection. 631.1 p195

The requirements of Sections 631 and 632for the issue of an Electrical Installation Certificate or a Minor ElectricalInstallation Works Certificate shall apply to all the work of the additions oralterations. 633.1 p196

The contractor or other personresponsible for the new work, or a person authorized to act on their behalf,shall record on the Electrical Installation Certificate or the Minor ElectricalInstallation Works Certificate, any defects found, so far as is reasonablypracticable, in the existing installation. 633.2 p196

 

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If an installation in theUnited Kingdom does not comply with Chapter 13 ( Fundamental Principles p16 ) of BS-7671 the electricity-supplier does not have to provide a supply to theproperty. p293

 

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Additional- Precautions , Extracts HSE. :svengo:

New installations

Newinstallations can be a particular hazard as some of the circuits or equipmentmay require to be modified after the installation has been energised. It istherefore important ( that every protective device is correctly identified) at each distribution board before anyenergising takes place, and safe isolation procedures, such as locking-offcircuit breakers, are adopted, particularly where a number of electricians areworking on the same installation.

Neutral conductors

Care should be taken when working on neutral conductors ofcircuits. The practice of ‘ borrowing ’ neutrals, i.e. making use of the neutral of one circuit for use onanother circuit, is notpermitted by BS-7671. This dangerous practice, however, isnot uncommon. Lighting and control circuits are the most common examples wherethis practice is found. In these circumstances the neutral conductor can becomelive when the conductor is disconnected, if a load is connected to thatcircuit.

It is also difficult to identify specific neutral conductors in ‘bunches ’ of single core cables, e.g. where enclosed in trunking or conduit,and care should be taken when severing such cables that the correct conductorhas been identified.

• If doubt exists, liveworking measures, such as the use of eye protection, electricians insulatinggloves, insulated tools etc, should be employed until the circuit has beenproved dead.

2392-10. can you get ‘ borrowing’ neutral(s) in domestic-premises. Yeah , take noting for granted .

ProvingDead Isolated Equipment or Circuits

Followingisolation of equipment or circuits and before starting work it should be provedthat the parts to be worked on and those nearby, are dead. It should never be assumed that equipment is deadbecause a particular isolation device has been placed in the off position.

The practice of placing PVC – insulating-tape over a circuit breakerto prevent inadvertent switch-on is not asafe means of isolation.

Just back from a school Devonshire , 5 circuit-breakers had insulation-tape over a circuit breaker . askedwhat , was that all about . no idea was the reply , old coloured-insulation-tape . 2013 .

2392-10 - Consumer-unit(s), TN-S , TT , Do we have the choice , Double-pole-isolation . at main-intake (DP mains isolator switch 100A )
Or single-pole isolation . MCBs , line-conductor only . Etc Locking-OFF

 

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Protective-conductor(s) .& Main-protective-bonding-conductor

2392-10 , 2394: Question , Do you or don’t you disconnect the (Protective-equipotential-bonding-conductor(s))from the MET . ??

Initial-verification .New-Installation . VERIFICATION & TESTING OF AN ELECTRICAL INSTALLATION
Existing-installation . Periodic-Inspection &Testing

Question , dependent upon whether the installationis already-connected tothe Supply .

Initial-verification . New-Installation , it is permissible to disconnect the , protective& equipotential-bonding-conductor(s) from the MET . to carry out Testing .

Installation is an Existing-installation, ( Periodic ) protective & equipotential-bonding-conductor(s)must not be disconnected .

Existing-installation : Periodic-inspection-testing... Continuity of Protective-conductors & Equipotential-bonding-conductor(s)Initial-testing can be carried out safety on an , “ Existing-installation” if it is isolated fromthe Supply .

Existing installation , does not impair the safety of that installation . Etc