Re-take - Useful Information for 2394 :

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Some of the Basic’s .we take for Granted . So what’s my point here . !!!!!! :banghead:

When asked to explainhow a ( PFC -test ) result may be used to determine if a circuit--breaker was suitable
Wrong .)- many candidates incorrectly referredto disconnection times of 0.4s or 5s.

Many descriptions did not make it clear thatthe circuit breaker's maximum breaking capacity must be at least equal to the ( PFC – test-result )

Prospectiveshort circuit current ... ( PSCC ) :30:

Is the highest electric-current which can existin a particular electrical system under short-circuit-conditions . It isdetermined by the voltage & impedanceof the supply-system.
When designing an electrical installation circuit-breakers must bechosen so that they can safely break the current of a short circuit .

Isolation: Circuit-breakers conforming toBS-EN-60898 are suitable for Isolation .
16[SUP]th[/SUP]Edition , Miniature-circuit-breakers (MCBs ) manufactured to earlier-standards ( such as BS-3871 ) are unlikely to besuitable .

Note :There is no ( Type A instantaneous-tripping-characteristic ) to avoid confusion with the ( A abbreviation for amperes )
Overcurrent-protective-device ( OCPD )

Rated-short-circuit-capacity ( Icn) of the circuit-breaker .

GN-3. P/56 .
Thedifference between the two-short-circuit-ratings described is the condition ofthe ( Circuit-breaker ) after manufactures-testing .
Two-short-circuit-capacity-ratingsare ( Defined ) in BS-EN-60898 & BS-EN-61009-1

( Icn ) of the circuit-breaker .
( Icn ) The rated-short-circuit-capacity, ( marked on the device ) The ( Icn) → [ 6000 ] & for the majority of applications the ( PFCurrent ) atthe terminals of the circuit-breaker shouldnot exceed value

( Icn ) The service-short-circuit-capacity
( Icn ) is the maximum-fault-current the device caninterrupt safely , although it may no longer be usable .

Note: GN-3 . P/56 . FOR-DOMSTIC-INSTALLATIONS . 2392 / 2394 .
The ( PFCurrent ) isunlikely to exceed ( 6kA ) up to which-value ( Icn) willequal ( Ics)

RCD's work by means of the , current balance principle
RCDs :- Residual - dual / Line & Neutral-conductor(s) Two in Balance

Operation of RCD

411.4.5. ◄◄◄ ( Very-important RCDs ) Question why do we loss-points in Exams.
for each of the ( Tests ) readingsshould be taken on ( Both positive & negative half-cycles ) and the longer operating-time recorded . ( mS) ( half-cycles 0° & 180° ) ◄

 

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Understand the requirementsfor completing the safe isolation of electrical circuits and installations
Assessmentcriteria . 2392-10 2394 .

1.1 state the requirements of the Electricity atWork Regulations for the safe inspection of electrical systems and equipment
1.2 specify the appropriate procedurefor completing safe isolation
1.3 state the reasons for carrying outsafe isolation
1.4 state the implications of carryingout safe isolation
1.5 state the implications of notcarrying out safe isolation
1.6 identify the Health and Safetyrequirements which apply when inspecting, testing and commissioning electricalinstallations and circuits

Safe-Isolation , of ( LV ) installations
HSE . point out thatthere is no excuse for not being able to safely isolate an installation, circuitor item of equipment.
Statutory requirements
The most importantstatutory requirement concerning work carried out on or near electricalinstallations is the Electricity at WorkRegulations (EWR) 1989.

Those :
Regulationswithin EWR of particular relevance to ( safe-isolation )

Numbers- 12 . ( Means for cutting off the supply and forisolation )
Numbers- 13 . ( Precautions for work on equipment made dead ).

Regulation - 12 (1) (b) States thatwhere necessary to prevent danger, suitable means shall be available for theisolation of any electrical equipment, where isolation means the disconnectionand separation of the electrical-equipmentfrom every-source in such a way thatthe ( disconnection & separationis secure ) (Para (2) refers).
TheMemorandum of Guidance on the Electricity at Work Regulations 1989 (HS(R) 25)published by the Health and Safety Executive advises with reference toRegulation12 (1) (b) above that isolation is the process of ensuring that thesupply to all or a particular part of an installation remains switched off andthat inadvertent reconnection is prevented.

Theissue of preventing inadvertent reconnection is covered in Regulation 13 (of EWR1989) which requires EWR 1989) which requires that :

“ Adequate precautions shall be taken toprevent electrical equipment , which has been made dead in order to preventdanger while work is being carried out on or near that equipment, from becomingelectrically charged during that work if danger may thereby arise ”.

Thecoverage of Regulation-13 in HS(R) 25highlights the need to lock off any switching device being used to provide isolation,or where isolation has been achieved by a fuse, by their removal and retention ina safe place during the isolation period.

Non-statutoryRequirements
WithinBS-7671:2008, the following are of particular relevance in terms of safe isolation:

Regulation- 132.15.1 contains the following fundamental principle:

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

Regulationgroup - 537.2 contains the requirementsrelating to isolation
Regulationgroup - 537.3 contains the requirements for switching off for mechanical maintenance

Table53.2 summarises the suitability of particular protective, isolation and switchingdevices to be used as an isolator, an emergency-switch, or a functional switch

adoption of incorrect isolationprocedures ‘ in the field ’ still appears to be far too frequent. Clearly, the commonlyoccurring practices of simply switching circuit-breakers off, and placing insulationtape over them, ( Yes , I have seenthis 2013 ) when a circuit needs to be isolated,or merely removing a fuse and leaving it on top of the distribution board arenot acceptable and do not give compliance with Regulation – 13 as stated

Isolation
Circuit-breaker - BS-EN-60898 , Yes , Yes, Yes
Circuit-breaker - BS-EN-60947-2 , Yes(1) , Yes , Yes
Circuit-breaker - BS-EN-61009-1 Yes , Yes , Yes

2392-10, startas you mean to go ON . Cover you’re A*se at all times . :13:

Fused connection unit isolated by means of a small-padlock, I use MK , for this reason . Isolation .
Before you say , remove the fuse . ?? Can It be replaced . Yeah . small-padlock, I use MK , for this reason . Isolation .

 

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Electricalinstallation work-trainees and apprentices that have attended college for appropriateinitial training should have been taught how to carry out safe-isolation, includingsecuring the device in the “ OFF ” position.

Basic , Safe isolation procedure . Taken fromExtracts .

Thefollowing steps are the minimum that would be expected in terms of confirmingsafe isolation of a circuit or item of equipment.

• Locate / positively identify correctisolation point or device
• Check condition of voltage indicatingdevice
• Confirm that voltage indication device is functioningcorrectly
• Switch off installation / circuit to be isolated
• Verify with voltage indicating device thatno voltage is present
• Re-confirm that voltage indicating devicefunctions correctly on known supply / provingunit
• Lock-off or otherwise secure device usedto isolate installation / circuit

• Post warning notice(s)

Anywarning notice posted should convey in simple terms that the installation,circuit or item of equipment has been deliberately disconnected from thesupply. It should inform the reader that care must be taken to ensure thesafety of persons who are reliant upon the continued effectiveness of the isolationand should state that the installation, circuit or equipment should not be shouldnot be reenergised until it has been confirmed that it is safe to do so

 

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P/39 . GN-3 . Extracts . ( IR ) Insulation-résistance 612.3.

( IR ) testing is a fundamental-test forInspector(s)
612.3. BS-7671: requires that ( IR ) is measured between , all of thelive-conductor(s) & between thelive-conductor(s) & the protective-conductor with theprotective-conductor-connected to the earthing-arrangement .

This key-change to the procedure was introduced inthe , 17[SUP]th[/SUP] Edition in 2008 . & is an important-change topractice for many-Installer’s &Inspector(s) ... ( Taking-cables) example .

Previously it wasacceptable to test a cable , between the various-cores , & test to earth ( Often the armouring or sheath of the cable )

Sometimes these-cableswere terminated without ( Further-testing )

P/39 . GN-3 , States that :- Thisis not acceptable now & it is essential to ( TEST ) to the armouring with it connected
( with a fly-lead if necessary ) refer to . Fig , 2.4c – P/42

It is a good-idea totest all cables including those tested-during the , construction-stage usingthis method .

Exams Wording. Yeah . P/39 . 2394 . by the Book :yes:
( IR ) Qs , The purpose of the insulation-résistance-test, is to verify that the insulation of conductor(s) provided adequate-insulation , is not damaged & that live-conductor(s) or protective-conductor(s) , are not shorted-out .

 

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Has the Regulation(s)came a long-way. ( Blast from the Past )
P/3 . Sixteen – Edtion 1991 ◄ . Object & Effects
120-01-01 . The Regulationsare designed to ( Protect )
i) Persons.
ii) Property.
iii) Livestock in locations specifically for them ,
against hazards arisingfrom an electrcal-installation used with reasonable-care having regard to thepurpose for which the installation is intended .

the requirementsrelated to protection against :

iv) electric-shock .
v) fire .
vi) burns,
vii) injury from mechanical-movment ofelectrically-actuated-equipment , in so far as such injury is intended to beprevented by electrcal-emergency-switching or by electcal-switching for mechanical-maintenanceof non-electrcal-parts of such-equipment .

The Regulations are intended to be ( Cited in their-entirety if referred to in any contract) They are not intended to take theplace of a detailed-specification or to( Instruct-untraned-persons or to provide for every-circumstance) Installation(s) of a difficult or special-character will require the
( Advice of a Suitably-Qualified-Electrical-Engineer)

2011: P/16. Object & Effects

120.1. This Standard-contains the rules for the ,design & erection of electrical-installation(s) so asto provide for safety & proper-functioning for theintended-use .

 

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What has changedover the Years ? 1991 / 2011. :30:
Sixteen –Edition 1991 ◄
Initial-Verification Chapter- 71.
711-01-01 : Every installation shall , during-erection& / or on completion before beingput into service be inspected & tested to verify , so far isreasonably-practicable , that the requirements of the regulations have been met.
The method of test shall be such that no-dangerto , persons , livestock or property or damage to equipment can-occur even if the circuit-tested , is defective .

17[SUP]th[/SUP] Edition . 2011: Initial-Verification Chapter– 61 .
610.1 : Everyinstallation shall , during-erection & / or on completion before being put into service beinspected & tested to verify , so far is reasonably-practicable , that therequirements of the regulations have been met .
Precautions shall be taken to avoid-danger to persons & livestock , & to avid damageto property & installed-equipment , during-inspection & testing .

 

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What has changedover the Years ? 1991 / 2011. 2013 . :30:

Testing: 713-01-01. The tests of Regulation(s) , 713-02 to 713-09 where relevant shall be carried out in thatsequence .

In the event of any-test indicating-failure to comply ,that test & those-preceding , the results of which may have been influencedby the fault-indicated , shall be repeated after the fault has been rectified .


612.1. Testing . The tests of Regulations , 612.2 to 13 , where relevant , shall becarried out & the results compared with relevant criteria .

If any test indicates a failure to comply , thattest & any preceding-test , the results of which may have been influencedby the fault-indicated , shall be repeated after the fault has been rectified

 

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Whatare the appropriate testing criteria for a time-delayed RCD when connected intoa TT system, where the installation was designed prior to the introductionof the , 17th - Edition ?

It would be necessary to verify that the RCDoperates within the criteria stated in the relevant product standard ( BS-EN-61008-1) and reproduced in Table 3A of Appendix 3 - that is between 130mS and 500mS.

 

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( IR ) You can compare for your Self. ( The Question is , Has BS-7671:2011improved in Any-Way )

Extracts : Sixteenth-edition– 1991 . 21 , years on . !! ( IR )

713-04-01 . Insulation-résistance . between live-conductor(s) shall be measured , before the installationis connected to the supply .

713-04-02 : Particular-attention shall be giving to the ( presence ofelectronic-devices connected in the installation )
Where necessary , such devices shall be isolated sothat they are not damaged by the test-voltage & thereafter tested in accordance with , Regulation - 713-04-06.

713-04-03 : The insulation-résistance shall also be measured between each-live-conductor& earth , the PEN-conductor in TN-C - systems being considered as part of the earth . Where appropriate-during this measurement , Line & Neutral-conductor(s) may be connected together .

713-04-04 : The ( IR ) measured with the ( d.c.test-voltages indicated in Table –71A ) 2011:Table -61.

713-04-06: Where-equipment ,such as electronic-devices , is disconnected for the tests prescribed inRegulation – 713-04-01 . to 05 , & the equipment has ,exposed-conductive-parts required by the Regulations to be connected to ( Protective-conductor(s)the insulation-résistance between the ,exposed-conductive-parts & all live-parts of the disconnected-equipmentshall be measured-separately & stillcomply with the requirements of the appropriate-British-Standards for the equipment . if there is no appropriate, British-Standards the insulation-résistance shall be not less than

Change when the , 17th came in (reg 612.3.1) - the words " connected to the earthing arrangement " were inserted. :30:

( IR ) 612.3.1. The insulation-résistance shall be measured between ( Live-conductor(s) & betweenLive-conductor(s) & the :
( Protective-conductor) connected to theearthing-arrangement .

( Protective-conductor)

Including:
Earthing-Conductor(s)
Circuit-Protective-Conductor(s)
Main-Protective &Supplementary-Bonding-Conductors

Thedifference between , Earthing and Bonding.
P/27 . Earthingis defined in BS7671 as: “ Connection ofthe exposed-conductive-parts of an installation to the main earthingterminal of an installation ”.

P/27 . Equipotential-bonding is defined as: “ Electricalconnection maintaining various exposed-conductive-parts andextraneous-conductive-parts at substantially the same-potential ”.

Both ofthese functions are carried out using protective conductors (as defined in the BS-7671:2011: Regulations)
Protectiveconductors for , Earthing are known as , Circuit Protective Conductors (CPCs)
Protective-conductors for Bonding are known as Bonding Conductorsand may be either Main Protective or Supplementary.

p/23 . BondingConductor , A protective-conductor providing equipotential-bonding .

Used as a ( Protective-conductor ) 543.2.2. ... 2392-10: in your case .

i) . A single-core-cable
ii) A conductor in a cable

 

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Testing: Note: P/56

Note : BS-7671: States . by name , Circuit-loop-impedance ( Zs ) 16[SUP]th[/SUP] / 2008 : 2011: :icon_bs:

The, Circuit-loop-impedance ( Zs ) should not exceed the value given in the tables when the conductors areworking at their normal-operating-temperature, The ( Zs ) if the conductors are at a different-temperature when tested , the reading should be adjusted-accordingly

 

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Do they have to be a Reason . ??

RCBOs: Functional-earths must be identifiedby a different-colour to that of protective-earths.( Identification )

Functional-earths must therefore be identified by a different colour to that ofprotective-earths and Table - 51 in BS-7671requires that functional earths be identified by the colour ( Cream)

P/279 . BSI .
The colour ( Cream ) for functionalearths is also required by BS-6701:2010 ( Telecommunications-equipment and telecommunications-cabling. Specification for installation, operation & maintenance )

P/28 . Functional-earths
A functional-earth is providedsolely to enable , Electrical-equipment to operate-correctly

 

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2392/10. BS-7671: has always stated the facts. :icon_bs:

1991: Relationships ofcurrent-carrying-capacity to othercircuit-parameters
Inall circumstances ( Iz ) must be not less than ( Ib ) & ( In ) also must be not less than ( Ib )

2008:2011: P/307 . Relationships of current-carrying-capacity to other circuit-parameters
Inall circumstances ( Iz ) must be not less than ( Ib ) & ( In ) also must be not less than ( Ib )

The rated-current or current-setting of the protective-device( In ) must not be less than the design-current( Ib ) of the circuit, and the rated current or current-setting of the rated-currentor current-setting of the protective-device ( In ) must not exceed the lowest of thecurrent-carrying-capacities ( Iz ) ofany of the conductors of the circuit .

 

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Taking from , Extracts . ( Example- Only ) 2392-10 .

A circuit-supplying a shower with a loading of , 6 kW would have a design-current ( Ib ) given by :

(Ib ) = 6 x 100W / 230V = 26A

The nominal-current-rating in amps, ( In ) of the protective-device ( fuse orcircuit-breaker ) for a circuit isselected so that ( In ) isgreater than or equal to the design-current, ( Ib ) of the circuit.

( In ≥ Ib ) , 6 kW shower ( In ) must be ≥ 26A

Select, 32A circuit-breaker , that is (In = 32A )

Acable must now be selected so that its rating, ( Iz ) in the particular-installation-conditionsexceeds the design current of the load, ( Ib )

Iz ≥ Ib ) , 6 kW shower-load , ( Ib = 26 , so (Iz ) ≥ 26A

Where , Overload-protectionof the cable is to be provided, as is usual, the cable is also selected so thatits rating in its installed-conditions ( Iz ) exceeds the current-rating of the circuit-protective-device.

Iz ≥ In )

6kW shower-circuit with Overload-protection, ( Iz ≥ 32 ) It maybe argued that no overload need be provided for a shower as the load is fixed.

Therefore- ( Iz ≥ In ≥ Ib )

6kW shower with Overload-protection,this relationship will be satisfied if :

(Ib = 26A , In = 32A, & the circuit-conductors are sized such that ( Iz ≥ 32A ) To calculate the tabulated cable-ratings,It, the following formula ( from Appendix - 4 of BS-7671)

( Iz = It Ca Cg Ci Cc )

Overload-protection is provided in practicallyall circuit-designs in order to protect the cable should the load be increased,

by adding further lights to a lighting-circuitor changing a shower for one of ahigher-rating without proper checks being made. However, for a fixed load e.g.a shower-circuit, this is not an actual requirement of BS-7671.

Note that the term , Overcurrent includes both-Overload-current & Fault-current.

Whereprotection is being provided against overload, protection will also be providedagainst fault currents, however, the reverse is not true Knowing ( Iz ) it isnecessary to select a tabulated cable rating such that , ( It ≥ Iz --- Ca Cg Ci Cc )

Checkyour , relevant-symbols used in the , Regulations . P/307 . symbols’ used in the Regulation(s) , P.39

 

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( Ib = 6 x 1000W / 230V . = 26A )

 

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Part - 6 of BS-7671:2008:2011: Inspection & Testing

The purpose of , Initial-verification is toconfirm :- by means of Inspection and testing , ( Visual :30: & Testing ) :icon_bs:

Has the , Verification-process been carried out Correctly

Demonstrates that ( Persons ) who carry out Inspection andTesting must be , Competent to do so .