Re-take - Useful Information for 2394 :

[amberleaf]

Blast from the past :

Also,the IEE’s " Design participants notes " for the 16thEdition BS-7671: confirms that if an RCD is selected to provide indirectprotection, it is not necessary to undertake the disconnection calculations required for Overcurrent devicesbecause the RCD will always trip within 0.2 seconds

( An RCD will trip in 0.04s , under Earth-fault-conditions ) compared to 0.2 seconds

17[SUP]th[/SUP]Edition : Chapter 41 Directcontact now refers to basicprotection and indirect contact is called fault protection

 

[amberleaf]

Re-cap :

( RCD operation for Non-time-delayed ) BS-EN-61008-1 . BS-EN-61009-1 … (Part-1 ) :icon_bs:

Table 41.1. gives the maximum-disconnection-timesfor final circuit(s) Not exceeding 32A , of varying nominal-voltages forming part of an ,installation being ?? TN- or TT- system ( Earthing )

P/57 . 411.4.9. States :
That where an RCD is used to meet therequirements of 411.3.2.2. To providethe required disconnection time , the maximum values ofearth-fault-loop-impedance in Table – 41.5 may be applied

The maximum permissible earth-fault-loop-impedance ( Zs ) to ensure ( RCD operation for Non-time-delayed ) ◄ RCDs protectingfinal-circuit(s) Notexceeding 32A are given in Table 41-5 .

Disconnection times required by Table41.1. ( Whether ) Protective-device(s) Fuses , Circuit-breakers , RCDs / RCBOs

2392-10 : in your Understanding .
There is NO requirement toconfirm that the required disconnection time can be ( Achieved ) bytesting the protective-device / (s) .

You are confirming the , Earth-fault-loop-impedance ( of the Protective-circuit ) does not exceed the relevant tabulated maximum earth-fault-loop-impedance , for the Type / Sensitivity of the ( Protective-device)

 

[amberleaf]

Old to New : BS /BS-EN :icon_bs:

Operatingtimes of residual current operated devices (RCDs) to satisfy the relevantrequirements for automatic disconnection of supply given in Chapter 41 of BS-7671:

2008.According to Chapter 41, RCDs may provide faultprotection and /or additional protection.

RCDs to BS 4293: 1983 were first introduced into the Wiring Regulations bythe 15th Edition.
The harmonised standard BS EN 61008-1:1995, which superseded BS 4293: 1983, was introduced by Amendment 1 to the 16thEdition (BS 7671: 1992). The same amendment also introduced socket-outletsincorporating RCDs to BS 7288: 1990, portable RCDs to BS 7071: 1992 and RCDsincorporating overcurrent protection to BS EN-61009-1: 1995 (Regulation412-06-02 referred).
Whenthe 17th Edition (BS 7671: 2008) was published, Only BS EN 61008-1 and BS EN61009-1 were still listed (Regulation 411.4.9 refers).

However,this does not preclude the use of RCDs to BS 4293, BS 7288 and BS 7071, whereappropriate, for fault protection and/or additional protection, provided theymeet the relevant operating time requirements.

 

[amberleaf]

2392-10 : This is just to referyou to some studying .

P/33 .. Residual-current :
Algebraic sum of the currentsin the live-conductors of a circuit at a point in the electrical-installation .

p/34 .. Residual-current-operated-circuit-breaker ( Without ) integral overcurrent-protection ( RCCB )
p/34 .. Residual-current-operated-circuit-breaker ( With ) integral overcurrent-protection ( RCBO)

4 terminals (2 top, 2 bottom)

( RCCB ) RCDnot RCBO ! BS-4293 RCD

Therefore the circuit connectedto it in theory has no Over-load-protection.

 

[amberleaf]

Where an RCDis employed to achieve the disconnection time required by Table 41.1, it isnecessary to satisfy yourselves that the maximum earth-fault-loop-impedance (Zs) Statedfor a , particular sensitivity of RCD inTable 41.5 is not exceeded in the circuit to which they provide-protection .

 

[amberleaf]

Re-cap :

BS-EN-61557-6 , has requirements’ forthe following tests to be ( Appliedto RCDs )

□ Non-tripping ( 50% / 0.5 ) test

□ Tripping ( 100% / 1x ) test. C&Gs ... RCD 100mA tested at 100% . 1x BS-EN-300mS . Scenario TT – system .
▲ ( 100mA ... DoNot Test at 5x times rating ) This is what C&Gs want to hear .

Theregulations apply to the Design, Erection and Verification of any electrical-installation

□ 5 I∆n ( 500% ) test

2392-10 ... These two are the ones you will Use □ / Fast trip

 

[amberleaf]

2392-10 : Locations containing a Bathor Shower

Regulations – 701.411.3.3. P/199 “Additional-protection “

Shall be provided for all ( Low-voltage-circuits of the location ) by the use of one or more having the ,characteristics specified in , Regulation 415.1.1. P/66

Note : also regulation 314.1. (iv) 531.2.4. concerning avoidance of ,unwanted-tripping Etc .

Regulation – 415.1.1. P/66

The use of RCDswith a rated-residual-operating-current ( I∆n ) not exceeding 30mA & an operating time not exceeding 40mS ata residual-current 5x I∆n is recognised in A.C. systems as additional-protection in the eventof failure of the provision for basic-protection and / or the provision for fault-protection or careless by Users .

 

[amberleaf]

2392-10: Domestic – installations

Note : BS-7671: definition of ( Wiring-system )
Does not include lights, but in mostcases the opening made for lighting would be larger and more onerous than openings created for cables.

BS-7671:2004:2008: 2011 : definition of ( Wiring-system ) P/36
An assembly made upof Cables or busbars and parts which secure and, ifnecessary, enclose the cable or busbars .

 

[amberleaf]

2392:10 . Designer(s) Installer(s) , first of all you have to decide what you are trying to Achieve & Why.
The O.S.G. section3 . P/25 Guidance :

The requireddisconnection times for TT – systems can ( except in most exceptional circumstances ) Only be achieved byprotecting every-circuit with an RCD .

Electrode-résistance inTT – system(s) 411.5.3. P/57
The Regulations requirethat the earth-résistance at the electrode ( Ra or Zs ) be as low as practicable . Table – 41.5.

States that: 41.5. specifies a maximum-résistance required for a ( 30mA RCD ) to comply is 1.667Ω *
Note 2 : * The résistanceof the installation earth-electrode should be as low as practicable .

Note 2 : A valueexceeding 200Ω may not be stable .
RCD / 30mA earth-current would trip the device within the required ( 0.2s ) conditions comply with 411.5.3.

Fault disconnectiontimes for, TN – TT – systems
BS-7671:2011: specify the requirements forAutomatic-Disconnection of Supply . byprotective-device(s) circuit-breaker(s)of a fault occurring .

BS-7671:2011: disconnection time ( fault’s Occurring )
BS-7671: have statedthe facts . Type of Earthing-systems ?? You , decidewhat you are trying to Achieve & Why.

P/53 , Regulation 41.1. “ Stipulates “ Maximum-disconnection-times

Typeof Earthing-systems
Circuits rated , 32A or less , TN – installation(s) must disconnect within ( 0.4s ) 400mS
Circuits rated , over 32A , TN – installation(s) must disconnect within ( 5s )
Circuits rated , 32A or less , TT – installation(s) must disconnect within ( 0.2s ) 200mS
Circuits rated , over 32A , TT – installation(s) must disconnect within ( 1.0s )

2392-10 : Where does BS-7671:2011: “ Start “
Metal-clad or Plastic all insulated consumer-unit ? What makes thedifference in the eyes of BS-7671:2011 & O.S.G.
Re-cap : 2392-10 : P/29 / O.S.G. The Enclosures of RCDs
Or consumer-units incorporating RCDs in TT – installation(s) should have an ( All-insulated or Class-11 construction oradditional-precautions )
Out of curiosity, Whydoes an RCD allow for a ( Zs of 1667Ω ) P/57 / Table 41.5.

[ I = V/R , R = V/R , 50V maximum-touch-voltage ] / 0.03 ( 30mA ) = 1667Ω :
50V ÷ 30mA = 1.666666667Ω [ round – up to 1667Ω ]
[ 30mA ÷ 1000 = 0.03A]

O.S.G. P/23, ( Protection)
Firstly : Type of protective-devices
The consumer-unit ( or distribution-board ) contains devices for the ( Protection) of distribution-circuits & final-circuits against .
• Overload .
• Short-circuit .
• Earth-fault .

2392-10 : Circuit-breaker & RCBOs don’t stop at , BS-EN.

Stillout there . ( Overload-protection ) BS-3871, O.S.G. P/23
Appx 3 , 533.1. Overload-protection will be provided by the ( Use) of any of the following devices .
Fuses to BS-88-2 , BS-88-3 , BS-88-6 , BS-1361 & BS-3036 .
Under the 16[SUP]th[/SUP] Edition they where called this , Miniature – circuit - breakers to BS-3871-1 types ( 1 , 2 , & 3 )
Circuit-breaker(s) to BS-EN-60898 types , B , C , & D .
Residual-current-circuit-breaker(s) ( With ) integral-overcurrent-protection ,RCBOs, to BS-EN-61009-1

 

[amberleaf]

Any & Allsuch liability is disclaimed .

GN-3: All parties must rely upon their ownskill & judgement when making use of them . ( Use as a guide / Guidance Only )
O.S.G.: All parties must rely upon their own skill & judgement when making use ofthem . ( Use as a guide / Guidance Only)

P/25 Competent-person:
A person who possessessufficient technical-knowledge, relevant practical skills & experience forthe nature of the electrical-work undertaken & is able at all times toprevent danger & , where appropriate, injury to him / herself & others .

BS-7671:2011: All parties must rely upon their own skill & judgement whenmaking use of them .

2392-10 & any Electrician takes responsibilityfor there OwnAction . ( in Our case here Moral-responsibility )

 

[amberleaf]

Operation of the Test-button . The Why’s

Tripping of the RCD in response to operation of the ( Test-button ) does NOTverify that the RCD will provide protection “ Additional-protection “

“ Verification “ 2392-10

P/36 , All measures by means of which compliance of the electrical installation withthe relevant requirements of BS-7671:are checked :
Inspection .
Testing . Verification of the ability ofthe RCD , to provide-protection can only be ( Assured ) by Testing :icon_bs:
Certification.

 

[amberleaf]

RCDs - Testing can be done from any point of the circuit ( e.g. socket-outlet ) or at the outgoing-terminals of the RCD itself.
Prospective-fault-current. 2392-10 .
612.11. ... ( PFC ) is a generic term .

Either :
( PSCC )prospective-short-circuit-current .
( PEFC ) prospective-earth-fault-current.

 

[amberleaf]

Some facts 2392-10 . RCD - Tests: :svengo:

Where RCDs ( form ) part of the installation,
Whether , they are for Fault-protection of Additional-protection or both ,

The requirements’ of Regulation(s) 612.8.1. & 612.10.respectively that such devices must be Tested .

This test is in ( Addition ) to the test carried out bythe use of the manual-test-button incorporatedwithin the RCD .

 

[amberleaf]

( half-cycles 0°& 180° ) ◄ 2392-10. 2394 . relying on the Megger on Auto . Your marks are costing you money. Yeah Pass or Fail .

GN-3 . P/58 . Operation & functional-testing of RCDs :rant:

The operating times of RCDs are required to be ( Tested) in the following circumstances

612.8.1. ► where they are relied on for disconnection for compliancewith Chapter - 41
612.10. ► where they are installed as additional-protection asspecified in Chapter - 41

Where RCDs areinstalled with circuit-breakers and the circuit has the characteristics to satisfy Chapter – 41without the RCD, then testing of the RCD is not essential unless it is specified for , Additional-protection .

C&Gs . 2392-10 & 2394 . on Exams .

Operation of RCD
411.4.5. ◄◄◄
for each of the ( Tests ) readings should be taken on ( Both positive & negative half-cycles ) and the longer operating-time recorded . ( mS) ( half-cycles 0°& 180° ) ◄

Do we have anEarth ??
► Prior to these RCDs - tests it is essential ,for ( Safety-reasons ) thatthe earth-loop-impedance is tested tocheck the requirement’s have been met.

2392-10 / 2394 . You are :
Verifying protection by automatic supply disconnection

GN-3. P/59 Additional-protection 415.1.
Where an RCD with arated-residual-operating-current, I∆n not exceeding 30mA is used to provide Additional-protection inthe event of failure of basic-protectionand / or the provision forfault-protection or carelessness byusers, the operating time of the device must not exceed 40mS when subjected toa test-current of ( 5x I∆n ) the maximumtest time should not exceed 40mS , Etc

415.1.
612.10. Additional-protection
The verification goesthe effectiveness of the measures applied for Additional-protection is fulfilled by ( Visual-inspection )&( Test )
Where RCDs are requiredfor additional-protection,

The effectiveness ofautomatic-disconnection of supply by RCDs shall be verified usingsuitable-test-equipment , according to BS-EN-61557-6 , see Regulation – 612.1.to confirm that the relevant requirements in Chapter 41 are met .

In the eyesof BS-7671:2008/2011:
612.9. Before ( Circuit-loop-impedance ) Earth-fault-loop-impedance .
612.10. After .

Anearth-loop-impedance-test will measure the resistance offered to the flow ofcurrent in the path that a fault current would take from line to protectiveearth. This resistance must be sufficiently low to allow enough current to flowpast to trip the circuit protective device in place, a Circuitbreaker or something else.

Inspection &Testing .
As GN-3 reminds us . The inspector to be fully-versed in the ( Capabilities& Limitations ) of instruments &be aware when a test is likely to createa dangerous-situation . Regulation -610.1. Your testing , not lead to persons or damage to property orequipment during Inspection & Testing .

Even when the circuitbeing tested is ( Faulty )

632.4. Defects or omissions revealed during , inspection & testing of the installationwork covered by the certificate shall be made good before the Certificate isissued .

 

[amberleaf]

Check list : Fused-connection-units .
Re-cap . that require Visual-inspection . prior to carryingout Testing . :icon_bs:

Suitably-fused , whereappropriate . 433.1.1. 434.2.