Re-take - Useful Information for 2394 :

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Recap .

Following testing for effectiveness by instrument , RCDs are required to be operated by their integral test facility to verify functionality (Regulation 612.13.1 refers).

612.13.1 Functional testing . " Push the Button "
Where fault-protection & / or additional protection is to be provided by an RCD , the effectiveness of any test facility incorporated in the device shall be verified .

 

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Recap .

Regulations RCBO . P/57
in the case the maximum-earth-fault-loop-impedance ( Zs ) is determined according to the residual current characteristic , given in BS-7671: clause 411.4.9. & table 41.5.

Non-delayed RCDs to BS-EN-61008-1 & BS-EN-61009-1 , for a nominal voltage Uo of 230V ,
In such cases , an overcurrent protective device shall provide protection against overload-current & fault-current .

The characteristic of the circuit-breaker ( B,C,D ) according to the application .. Overload , Short-circuit

O.S.G. p/23 . Overload-protection : circuit-breakers to BS-EN60898 types ( B,C,D ) &
Residual current circuit-breakers with integral overcurrent protection ( RCBOs ) to BS-EN-61009-1 .. RCD side / Earth-fault

Types of RCD

Residual current operated switching device NOT designed to perform the functions of Protection against ( Overload & or Short-circuit )
BS-EN-61008-1 RCCB : we need , Overload-protection : circuit-breakers to BS-EN60898

RCBO , being a unit with a combined circuit-breaker & RCD , will carry out functions , ( 3/1 ) Overload . Short-circuit , Earth-fault .

Circuit-breakers Note : There is no Type (A) instantaneous tripping characteristic to avoid confusion with the ( A abbreviation for amperes

Circuit-breakers ( Fig 3A4 ) Type B circuit-breakers to BS-EN-60898-1 & RCBO to BS-EN-61009-1

P/55 . The values specified in Table 41.3. for the Types & ratings of overcurrent-devices listed may be used instead of calculation .

by calculation ( B ) : 3 x 6A = 18A .. 5 x 6A = 30A
by calculation ( C ) : 5 x 6A = 30A .. 10 x 6A = 60A
by calculation ( D ) : 10 x 6A = 60A .. 20 x 6A = 120A

 

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Recap .

RCDs are used to provide protection against the specific dangers that may arise in electrical installations, including:

Fault protection :
Additional protection;
Protection against Fire

An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors.
In the case of a single-phase-circuit, the device monitors the difference in currents between the line & neutral-conductors.

Note that the term ‘ live ’ conductor includes both the line & neutral-conductors .. residual current .. dual current Line & Neutral

Under-Fault-free-conditions .
In a healthy circuit, where there is no fault current flowing to earth or protective conductor current, the sum of the currents in the line & neutral conductors is ( zero )

Under-fault-conditions
If a line-to-earth fault develops a portion of the line conductor current will, therefore, not return through the neutral conductor

The device monitors this difference, operates and disconnects the circuit when the residual current reaches a preset limit, the residual operating current

An RCD does not provide protection against overcurrent
Overcurrent protection is provided by a fuse or a circuit-breaker.
Combined RCD & circuit-breakers are available and are designated RCBOs.

O.S.G. p/23 3.1 Protection
Types of protective device RCBO
RCBO , being a unit with a combined circuit-breaker & RCD , will carry out functions , ( 3/1 ) Overload . Short-circuit , Earth-fault .

434 : P/83 Protection against Fault-current
This section only considers the case of a fault between conductor(s) belonging to the same circuit .

Types of RCD
RCCB :
Residual current operated circuit-breaker without integral overcurrent protection .. P/34
A residual current operated switching device NOT designed to perform the functions of Protection against ( Overload & or Short-circuit )

RCBO :
Residual current operated circuit-breaker with integral overcurrent protection .. P/34
A residual current operated switching device designed to perform the functions of Protection against ( Overload & or Short-circuit )

P/25 Circuit-breakers :
A device capable of making , carrying & breaking normal load current , Etc refer .
Appendix 1 , P/285 , BS-EN-60898:1991
Specification for circuit-breakers for overcurrent protection for household & similar installations

• BS-EN-60898 was further developed into parts 1 & 2 . BS-EN-60898-1 was first published in the UK in 2003 for A,C circuit-breakers

BS-EN-60898 specifically deals with circuit breakers intended for use by uninstructed or untrained people
Table 53.4. p/149 . further point is that BS-EN-60898-1 breakers are always suitable for isolation .

► Miniature circuit breakers conforming to ( MCBs ) manufactured to earlier standards ( such as BS-3871 ) are unlikely to be suitable for Isolation

P/24 Circuit :
A assembly of electrical equipment supplied from the same origin & protected against overcurrent by the same protective-device .

Overcurrent protective device ( OCPD )

 

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Recap : Need a Sanity check !!
I always , check my Polarity on the supply side before throwing the main-switch .

GN-3 P/75 . Table 3.4 Testing to be carried out where practicable on Existing installations .
Under the heading of ( Polarity ) At the following positions ( Origin of the installation ) Etc .

Recap :
GN-3 P/47 2.7.12 Polarity testing
( Visual inspection )
Alternatively , Polarity can be verified by visually checking core colours at the terminations , thus verifying the installer's connections

Regulation P/31 . Origin of the installation
The position at which electrical energy is delivered to an electrical installation .

 

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Inspection checklist :
O.S.G. P/85 .
611.3. The inspection must include at least the checking of relevant items from the following checklist :
526 ( vi ) correct connection of accessories & equipment ( including polarity )

Regulations P/189 611.3. ( vi ) Correct connection of accessories & equipment .

Regulations P/23 . Accessory :
A device , other than current-using equipment , associated with such equipment or with the wiring of an installation .

SWA . Mechanical protection .. protection against physical damage .

 

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612.10. Additional protection .. Breaking in down .
the verification of the effectiveness of the measures applied by additional protection is fulfilled by visual inspection & test

Where RCDs are required for additional protection , the effectiveness of ( ADS ) by RCDs shall be verified using suitable test equipment according to BS-EN-61557-6 see Regulation 612.1. to confirm that the relevant requirements in Chapter 41 are met .

Plain English , 612.13.1. The effectiveness of RCD test facility will be verified . Etc

 

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( Extracts )
Some light headed reading .

Past to Present . Has it gone pear shape .

Part P , comes into Force . 2005 : ◄
Many electrical faults are not caused by bad workmanship, so why bother with Part P ?

In the Regulatory Impact Assessment, the Government estimated that around ► 30% of electrical accidents could be prevented through regulation, and that this would justify bringing electrical work in dwellings under Building Regulations control.

Design , Installation , Inspection & Testing .

third party certification
1.28 . Unregistered installers should not themselves arrange for a third party to carry out final Inspection & Testing , The third party - not having supervised the work from the outset - would not be in a position to verify that the Installation work complied fully with BS-7671:2001 requirements , An Electrical Installation Certificate can be issued only by the installer ( responsible for the installation work )

1.29 . A third party could only sign a BS-7671:2001 . Periodic Inspection Report , or similar , The Report would indicate that electrical safety tests had been carried out on the installation which met BS-7671:2001 criteria fully with BS-7671:2001: but it could not verify that the installation complied fully with BS-7671:2001: requirements - for example with regards to routing of hidden cable .

 

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Useful Junk .

Testing Continuity of ring-final-circuit conductors
Two main reasons for conducting this test :

To ensure that the ring circuit conductors are continuous , & indicate the value of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) for the " Ring " .
To establish that interconnections in the ring-final-circuit do not exit .

Exams , by calculation .
Earth electrode / Three lead . (3)
Earth electrode résistance testing , readings obtained from an earth electrode résistance . 181Ω + 185Ω + 179Ω = 545 ÷ (3) = 181.67Ω

E1 : Three - or Four terminal type
Caution : if this is the only earth-electrode this may leave the installation unprotected against earth-faults & complete isolation of the installation must be made .

One other test not included in Part 6 of the IET Regulations but which nevertheless has to be carried out is external earth-fault-loop-impedance ( Ze )

Obtaining ( Ze ) This entails isolating the installation
By measurement : Undertaken in order to prove an earth connection
By Enquiry .. Must test to ensure Earth is present .

Exams , 2394 Wording .
External Loop Impedance ( Ze )
The value of ( Ze ) is measured at the origin of the installation on the supply side with the ( Means ) of earthing disconnected
Exams , Do Not conduct this test if the installation cannot be Isolated . " make a statement "

Testing for ( Ze , Zdb & Zs ) loop impedance .

Direct measurement of ( Zs ) can only be made on a live installation. No earthing-conductors are disconnected for the purposes of the test
( Zs ) due to the parallel earth paths present within the installation

GN-3 P/53 ( Zdb )
For larger installations with consumer units or distribution boards not at the origin , there can arise confusion over the term ( external earth loop impedance (Ze ) & some prefer to write or note the earth fault loop impedance at the distribution board as ( Zdb ) as strictly speaking , this value is not external to the installation . Thus , the formula is denoted .

 

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You're reason , ( Ze ) confirms the presence of an earth connection . in a court of Law .

for our younger members

GN-3 P/52 Measurement of total earth fault loop impedance ( Zs ) using an instrument .
Measurement of ( Zs) is made on a live installation & for ( safety & practical reasons ) neither the connection with earth nor bonding-conductors are disconnected .

 

[GLENNSPARK]

You're reason , ( Ze ) confirms the presence of an earth connection . in a court of Law .

for our younger members

GN-3 P/52 Measurement of total earth fault loop impedance ( Zs ) using an instrument .
Measurement of ( Zs) is made on a live installation & for ( safety & practical reasons ) neither the connection with earth nor bonding-conductors are disconnected .

well...you want the parallel paths on Zs as its system loop.

this is the normal operating scenareo of the system..that is with earthing, bonding and any other parallel paths connected...

will also affect the PFC....which is why prospective fault current is measured with all parallel paths connected...

 

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Certification :

( EICR ) Prospective fault-current ( Ipƒ ) [SUP]2 [/SUP]
( EICR ) External loop-impedance ( Ze ) [SUP]2 [/SUP]

( EIC ) Prospective fault-current ( Ipƒ ) [SUP]2 [/SUP]
( EIC ) External loop-impedance ( Ze ) [SUP]2 [/SUP]

( Note : (2) by enquiry or by measurement

By Enquiry .. Must test to ensure Earth is present .
By measurement : Undertaken in order to prove an earth connection

( Generic Schedule of Test Results ) P/402 .. Correct supply polarity confirmed □

 

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Extracts .
p/400 , Domestic & Similar Installations Condition Report Inspection Schedule

Acceptable condition (✓)
Description : The condition of the particular item inspected has been classed as acceptable

Not Verified (N/V)
Description : A particular item on the schedule is relevant to the installation but has not been verified as to its condition

Limitation (LIM)
Description : A particular item on the schedule is relevant to the installation but there were certain limitations in being able to check the condition

Not Applicable (N/A)
Description : The particular item on the inspection schedule is not relevant to the installation being inspected

Unacceptable condition (C1)
Description : The condition of the particular item inspected has been classed as unacceptable. Immediate danger is present and the safety to those using the installation is at risk (e.g. a live part is directly accessible)

Unacceptable condition (C2)
Description : The condition of the particular item inspected has been classed as unacceptable. There is potential danger and the safety to those using the installation may be at risk (e.g. absence of main protective bonding)

Improvement recommended (C3)
Description : The installation is not dangerous for continued use but the inspector recommends that an improvement could be made in relation to the item inspected (e.g. no RCDs for additional protection are installed)

For the inspector included in Appendix 6 should have a statement highlighting that any older installations designed prior to BS-7671:2008 may not have been provided with RCDs for additional protection. If this is the case then the inspector should record a ( C3 ) classification code as a minimum in relation to item 5.12 of the schedule. This is to highlight that the installation could be improved in this respect.

 

[GLENNSPARK]

Certification :

( EICR ) Prospective fault-current ( Ipƒ ) [SUP]2 [/SUP]
( EICR ) External loop-impedance ( Ze ) [SUP]2 [/SUP]

( EIC ) Prospective fault-current ( Ipƒ ) [SUP]2 [/SUP]
( EIC ) External loop-impedance ( Ze ) [SUP]2 [/SUP]

( Note : (2) by enquiry or by measurement

By Enquiry .. Must test to ensure Earth is present .
By measurement : Undertaken in order to prove an earth connection

( Generic Schedule of Test Results ) P/402 .. Correct supply polarity confirmed □

except this dont...does it...

 

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The measurement of ( Ze requires disconnection of parallel paths )
whilst ( PFC requires parallel paths ) & therefore these tests at the origin of the supply should be carried out separately.

Where ( Protective measures are used ) that require knowledge of the earth-fault-loop-impedance, as is the case where ( ADS ) is used , Regulation 612.9. requires the relevant impedances , to be measured or determined by an ( Alternative method ) by implication , this makes a demand for testing , Line / Earth-fault-loop-impedance . Etc .

612.9. Earth fault loop impedance ( Zs )
&
612.11. Prospective fault current . ( pƒc )

Prospective fault current ( PFC )

Like many of the modern multifunction testers on the market today, the Megger series displays the ( PFC ) at the same time as the loop test results - in the upper display.

it is important to understand that the measurement of ( PFC ) should not be recorded unless the particular requirements for the test are taken into account - in other words, the measurement of ( Ze ) requires disconnection of parallel paths )) whilst ( PFC requires parallel-paths ) therefore these tests at the origin of the supply should be carried out separately.

The value of earth-fault-loop-impedance may be determined by :

Direct-measurement of ( Zs )
Direct-measurement of ( Ze ) at the origin of the circuit & adding to this the value of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) measurement during continuity tests :
Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

( Ze ) in order to eliminate any parallel earth return paths . The Earthing-conductor are disconnected for the duration of the test .
Will ensure that the reading is not distorted by the presence of , Gas & Water-service-pipes acting as part of the earth-return-path .

 

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Do we learn by our mistakes !!! Purpose of Initial Verification

Chief Examiners’ report , 2011 . Blast form the past .

GN-3 , 2011: P/15. refer

The lack of knowledge of the requirements of Guidance Note 3 continues to be apparent in answers given by candidates.

Few candidates were able to correctly identify the purpose on an Initial Verification process as identified in GN-3.

► Purpose of Initial Verification
Initial Verification is carried out on a new installation ( before ) it is put into service .

► The purpose of initial verification is to confirm by way of ( Inspection & Testing ) during construction & on completion , that the installation complies with the design & construction aspects of BS-7671: in so far is reasonably practicable .
610.1 , 611.2. , 612.1.

 

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BS-7671: P/36 ( Verification )
All measures by ( means ) of which compliance of the electrical installation with the relevant requirements of BS-7671: are checked , comprising Inspection , Testing , & Certification .

P/29 , Inspection
Examination of an electrical installation using all the senses as appropriate .

P/36 , Testing
Implementation of measures to assess an electrical installation by ( means ) of which its effectiveness is proved .
This includes ascertaining values by ( means ) of appropriate measuring instruments , where measured values are not detectable by ( Inspection )

 

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The Inspection & Testing of new work is known as initial verification . As the Regulation suggests .

BS-7671:2011: Regulation 621.1. States that " Where required " , periodic inspection & testing of every installation shall be carried out in accordance with Regulation 621.2. to 621.5. in order to determine , so far as is reasonably practicable , whether the installation is in a satisfactory condition for continued service .

 

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Useful Junk .

Determination of 3 - phase fault current .

Highest single phase value measured = 2.28kA
( 2.25kA , 2.28kA , 2.25kA )

By calculation : 2.28 x √3 = 3.95kA
An approximation can be done as ( 2 x ) the reading .. 2 x 2.28 = 4.5kA

 

[SirKit Breaker]

Useful Junk .

Determination of 3 - phase fault current .

Highest single phase value measured = 2.28kA
( 2.25kA , 2.28kA , 2.25kA )

By calculation : 2.28 x √3 = 3.95kA
An approximation can be done as ( 2 x ) the reading .. 2 x 2.28 = 4.5kA

True enough, but for the exam keep it simple and double the highest single phase reading as it errs on the side of caution.

Cheers...........Howard

 

[Knobhead]

This really should be back as a sticky.