Re-take - Useful Information for 2394 :

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Definitions of the terms:

( CNE ) Combined neutral & earth
( DNO ) Distribution network operator
( Earth ) Capital ‘ E ’ to imply the general mass of Earth, i.e. true Earth, e.g. the ground that you walk on
( earth ) Lower-case ‘ e ’ to imply the earth of the electrical installation
( PEN ) conductor , A conductor combining the functions of both protective-conductor & neutral-conductor

 

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Short-circuit
A short-circuit is a connection between line & neutral, or between line & earth

Line & Neutral . live-conductor(s)
Circuit-protective-conductor , under earth-fault-conditions .

P/34 . Short-circuit-current
An overcurrent resulting from a fault of negligible impedance between ( Live conductors ) having a difference in potential under normal operating conditions .

 

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Four concepts

Provision of : Isolation . 537.2 . P/150
• Purpose : " Electrically skilled persons "
To enable electrical work to be carried out on .. ( Isolated circuit with safety )

Provision of : Switching OFF for mechanical maintenance . 537.3. P/151
• Purpose : " Non-electrically skilled persons "
To enable non-electrical work to be carried out on switched circuit with safety

refer : Table 53.4. P/149
Switching off for mechanical maintenance .
A Shower or Cooker switch may perform the function of switching off for mechanical maintenance .

Provision of : Emergency switching . 537.4 . P/152
• Purpose : " Anyone "
To cut off rapidly electrical energy to remove any unexpected hazard

Provision of : Functional switching . 537.5 ( BS-7671: Control ) P/153
• Purpose : Installation user
To enable proper functioning and control of current - using equipment

a switch in a socket-outlet
a switch in a lighting switch / pull-cord
a contactor switching the supply
push buttons
a thermostat
a pressure switch

The requirements for functional switching are contained in Section 537.5. & also referred to in Section 612.13. for functional testing in BS-7671:2011

Functional switching is defend in part 2 , Definitions of BS-7671: P/28
An operation intended to switch " on or off " or vary the supply of electrical energy to all or part of an installation for normal operating purposes

Functional switching is for " Normal operating purposes " & that it can be either one of two-functions .
• Switching on or off
• Varying the supply of electrical energy

Functional switching can be either Manually operated or Automatic operated Regulation 537.5.2.2.

Regulation 537.5.1.1. requires that a functional switching device be provided for each part of a circuit which may require to be controlled of other parts of the installation .

2392 / 2394 .
Functional switches do not have control all the ( Live-conductors of a circuit ) they can be single-pole-devices , such ( light switches ) Regulation 537.5.1.2. Neutral-conductors are not permitted to be switched independently of their associated line conductors .

Functional switches do have to be " appropriate " & a single device is allowed to control two or more items of equipment intended to operate simultaneously , Regulation 537.5.1.3.

Regulation 537.1.3. which requires that functional switches be " Appropriate "
functional switching devices , the operation , location & type of must be suitable for the most onerous duty they are intended to perform Regulation 537.5.2.1.

 

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Inspection & Testing

Functional switching is included among the items requiring Inspection in BS-7671:
The Schedule of inspections lists " Selection of appropriate Functional switching devices .

Functional switching is also included among the examples of items requiring inspection for an ( EICR ) The presence & condition of appropriate devices in accordance with Regulation 537.5.1.1. must be verified , Correct operation of the functional devices as required by Regulation 537.1.3. & 537.5.2.2. must also be confirmed

the ( EICR ) Inspection Schedule for domestic & similar premises , require a functional check of the manual operation of main switches ( item 4.8 ) further checks would be required on larger installations where the sample checklist in Appendix 6 of BS-7671: list Functional Switching as part of the Inspections .

BS-7671:2011: P/400 ( item 4.8 ) Condition Report Inspection Schedule for Domestic & Similar Premises with up to 100A Supply
Manual operation of circuit-breakers & RCDs to prove disconnection . 612.13.2.

Inspection & Testing of functional switching devices is not specifically included on the ( MEIWC ) Although , the Notes require " Appropriate Inspection & Testing " should always be carried out

Functional testing :
the requirement for functional testing in Regulation 612.13.1. & 612.13.2. include functional switching.
Functional testing includes ensuring that installed electrical equipment is working .

 

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P/193 . Protection by Automatic Disconnection of the supply ( Reg. 612.8 )

Where RCDs are applied also for protection against fire, the verification of the conditions for protection by automatic disconnection of the supply may be considered as satisfying the relevant requirements of Chapter 42.

612.8.1 General

a) TN system


Compliance with Regulation 411.4. shall be verified by :

1) Measurement of the earth fault loop impedance (see Regulation 612.9)
2) Verification of the characteristics and/or the effectiveness of the associated protective device. This verification shall be made:

- For overcurrent protective devices, by visual inspection (i.e. short-time or instantaneous tripping setting for circuit breakers, current rating and type for fuses)

- For RCDs, by visual inspection and test.
The effectiveness of automatic disconnection of supply 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.

The disconnection times required by Chapter 41 shall be verified.

Compliance with Regulation 411.5. shall be verified by :

b) TT system

1) Measurement of the resistance of the earth electrode for exposed-conductive-parts of the installation (see Regulation 612.7)
2) Verification of the characteristics and/or the effectiveness of the associated protective device. This verification shall be made:

- For overcurrent protective devices, by visual inspection (i.e. short-time or instantaneous tripping setting for circuit breakers, current rating and type for fuses)

- For RCDs, by visual inspection and test.
The effectiveness of automatic disconnection of supply 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.

The disconnection times required by Chapter 41 shall be verified.

P/193/194 . Regulation 612.8.1. & 612.10.
Residual current device , Test instrument(s)
require the use of an RCD test instrument to BS-EN-61557-6 .. (Part 6 ) to test the operation RCDs used for fault-protection & additional-protection respectively .

in Exams : 2394. this will get into Exams . ▼
GN-3 , P/58 411.4.5.
operation of residual current devices
for each of the tests , readings should be taken on both positive & negative half-cycles and the longer operating time recorded . 0º / 180º degrees

GN-3 2008 : 612.8.1. In order to test the effectiveness of residual current devices after installation , a series of tests may be applied to check that they are within specification and operative satisfactorily . This test sequence will be in addition to proving that the test button is operational .

GN-3 2008 : Facts : The effectiveness of the test button should be checked after the test sequence .
GN-3 2011: The RCD test button will only operate the RCD if it is energized

for each of the tests , reading should be taken on both positive & negative half-cycles & the longer operating time recorded .

GN-3 2011: P/58 . 2.7.18
Operating times of RCDs are required to be tested in the following circumstances :
612.8.1. Where they are relied on for disconnection for compliance with Chapter 41 .
612.10. Where they are installed as additional protection as specified in Chapter 41 .

Where RCDs are installed with circuit-breakers & the circuit has the characteristics to satisfy Chapter 41 without the RCD , then testing of the RCD is not essential unless it is specified for additional protection .

for each of the tests , reading should be taken on both positive & negative half-cycles & the longer operating time recorded .

 

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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 .

 

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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 .

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...