Re-take - Useful Information for 2394 :

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P/391 . Description and Extent of Installation ... ( EIC )
Describe the extent and limitation of the certificated work. Tick as appropriate, the box for either

New installation
Addition to an existing installation
Alteration to an existing installation

Signatories to the ( EIC ) Electrical Installation Certificate . ( 3 or 1 person ) Signatories
Designer .
Constructor .
Inspector .

 

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Periodic Inspection .. ( EICR )
for an Electrical Installation (BS 7671: 2011)
A report on the condition of an Existing electrical installation. " details of the Visual inspection "

Electrical Installation Certificate (BS 7671: 2011)
For initial verification of New electrical installations, including alterations and additions to existing installations, where the contractor has carried out the design, construction and inspection & testing. .. Domestic installation , Single Signatory

in Exams' : Stay focus

► Existing electrical installation .. ( EICR ) Report
► New electrical installations .. ( EIC )

 

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On rant mode .

Earth fault loop impedance .
Determination of external (at the origin)

Methods of determining ( Ze ) " The pit falls "

Calculation ... calculation does not verify that the intended means of earthing is in fact present
Therefore, where ( Ze ) is determined by calculation, measurement of ( Ze ) is still required before the installation is put into service .

Enquiry
Regulation 28 of the Electricity Safety, Quality and Continuity Regulations 2002 (ESQCR) requires a distributor providing a low voltage supply to an installation to declare information, including the following, concerning that supply, on request:

- the maximum value of ( Ze )
- the maximum value of prospective short-circuit current (Isc) at the origin .. Regulations P/38 . ( Isc - short-circuit-current )

The designer of the installation must obtain the above information by direct enquiry ... ( DNO - Distribution Network Operator )

Typical maximum values of ( Ze ) & (Isc) declared by ( DNO ) for 230V single-phase and 230/400 V three-phase supplies are shown in the following table:

Characteristic : External earth-fault-loop-impedance ( Ze )
O.S.G. P/11. Type of system :- TN-S .. Maximum value 0.80Ω
O.S.G. P/11. Type of system :- TN-C-S ( Protective Multiple Earthing ) Maximum value 0.35Ω

Type of system :- TT- .. Important . The résistance of the installation earth-electrode & earthing conductor must be ( Added ) to this value which is for the source earth-electrode only .

recap . O.S.G. P/11. TT - arrangement ( 21Ω ) is the usual stated ( Maximum résistance ) of the ( DNO ) earth-electrode at the supply transformer .
The résistance of the consumer's installation earth-electrode should be as low as practicable & a value exceeding ( 200Ω ) may not be stable .

Measurement .
The measurement will verify that a means of earthing is present and also confirm that ( Ze ) is within the expected range.

 

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it is the Basic's that let you down .

Read GN-3 . Everything you need for the exams can be found in it.

You will need to know GN-3 inside out
You will also need to know the Regulations inside out

2394 : Introduction

Earth fault loop impedance ( Zs ) is a characteristic vital to the protective measure Automatic Disconnection of Supply (ADS), which is used for fault protection in most electrical installations.

Each circuit is required not to exceed the limiting (or maximum) value permitted by BS-7671:2011:

The meaning of earth fault loop impedance ?

( known as the earth-fault-loop ) .. comprises

GN-3 . P/52 . &

R/P26 .. refer
Earth fault loop impedance ( Zs ) is the impedance of the intended path of an earth fault current starting and ending at the point of the fault to earth.

This impedance is denoted by the symbol ( Zs )

 

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Note : Earth fault loop impedance .

Consumer unit at the Origin . Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

Larger installations with consumer units , or distribution boards not at the Origin . Zs = Zdb + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) in Exams , indicate Sub mains somewhere

GN-3 . P/53 . ( Zdb ) as , strictly speaking , this value is not external to the installation . Thus , the formula is denoted .

 

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What is insulation résistance ??

GN-3 . /39
The purpose of the insulation résistance test is to verify that the insulation of conductors' provides adequate insulation , is not damaged and that live conductor's or protective conductor's are not short-circuited .

 

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2395-302 Chief Examiners Report . ◄ refer to .

learn by mistakes .

When asked why the earthing conductor must be connected to the installation earthing system during a prospective fault current test, common answers given by candidates included that it would be dangerous if it wasn't connected and you would not be able to carry out the test if it wasn't connected.

Few candidates appreciated that the earthing conductor would be connected when a fault occurred and the parallel paths would increase the level of fault current that would flow, and it is this maximum value that must be determined during the test.

Chief Examiners' 2394 . (13)

Testing

When asked to explain why an earth fault loop impedance test needed to be carried out on existing circuits after a board change,
many candidates failed to state that the protective devices for these circuits would have changed

Few answers identified the need to confirm that the maximum earth fault loop impedance values was not exceeded in order to ensure the appropriate disconnection times would be met in the event of an earth fault.

Some candidates had difficulty explaining why the earthing conductor must be disconnected from the installation earthing arrangements during a measurement of external earth fault loop impedance. Most answers included comments relating to the removal of parallel paths, but

answers indicated the need to confirm the intended external path was effective. from the installation earthing arrangements during a measurement of external earth fault loop impedance. Most answers included comments relating to the removal of parallel paths, but

► few answers indicated the need to confirm the intended external path was effective. ◄◄◄

 

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C&Gs have asked this question many times .. & will not stop asking

Question on earth electrode testing . ( One method ) not typing out two pages . sorry

GN-3 2008: ◄► P/46
Earth electrode résistance . example .

Measurement by standard method
When measuring earth-electrode-résistances to earth where low values are required as in the earthing of the neutral point of a transformer or generator , test method 1 below may be used

Instrument used as earth electrode résistance tester for this test .

Test method 1
before this test is undertaken , the earthing conductor to the earth-electrode must be disconnected either at the electrode or at the main earthing terminal to ensure that all the test current passes through the earth-electrode alone

Note : This will leave the installation unprotected against earth-faults . ◄◄ safety

Note : After completion of the Testing ensure that the Earthing-conductor is Reconnected. ◄◄ safety

GN-3 2011: ◄
Earth electrode résistance testing .
Three methods' of measuring the résistance of an earth-electrode. refer . Test method E1 , Test method E2 , Test method E3 . ▼

GN-3 2008: Earth electrode for RCDs .
if the electrode under test is being used in conjunction with a residual current device the following method of test may be applied as an alternative to the earth electrode résistance test . where the electrical résistance to earth are relatively high& precision is not required , an earth fault loop impedance tester may be used .

TT- systems always get heads turning in Exams .

with TT - systems C&Gs are looking for safety at all times .

 

[Richard Burns]

Chief Examiners' 2394 . (12)
The final question on the paper required the candidate to describe an (earth fault loop path) for the system given in the scenario.
Many diagrams were incomplete.
Candidates failed to identify the component parts of the earth fault loop path and so lost considerable marks. A large number of marks are allocated to the labelling, or identifying in a written description, the component parts of the earth fault loop path as indicated in GN 3.

GN3 states the following elements of the earth fault current loop path:
The circuit protective conductor
The main earthing terminal and earthing conductor
For TN systems the metallic return path or for IT or TT systems the earth return path
The path through the earthed neutral point of the transformer
The source line winding
The line conductor from the source to the point of the fault

These are example diagrams with the parts of the EFLI identified as well, for understanding (Zs, Ze, R1, R2, R1+R2)

 

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Thank you . You.r a Star Richard . Outstanding . my friend .
This is what it is all about . A better understanding . 100%

 

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Useful Junk .

Residual current devices ( RCDs ) in TN systems

For a circuit using an RCD for fault protection, Regulation 411.4.5 requires that the product of the earth fault loop impedance (Zs) and the rated residual operating current ( I∆n ) of the RCD does not exceed Uo volts (V)
therefore follows that the maximum permitted value of (Zs) is given by equation : ( Zs = Uo / I∆n ) Ω

Where: ( I∆n ) is the rated residual operiting current of the RCD in amperes .

For a circuit of nominal voltage Uo 230 V supplied through an RCD having a rated residual operating current ( I∆n ) of 100mA (0.1 A), the maximum permitted value of (Zs) produced by equation : is 2300 ( 230 V 0.1 A ) = 2300Ω

100mA ÷ 1000 = 0.1A

10mA ÷ 1000 = 0.01A
30mA ÷ 1000 = 0.03A
300mA .
500mA . Etc

 

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" Continuity " Small rant .

(i) O.S.G. P/90 / 91 . 10.3.1.
(ii) GN-3 . 2.7.6. Continuity of ring final circuit-Conductor(s)
612.2.2. A three-step test is required to verify the ( Continuity ) of the , Line , Neutral , & Protective-conductors .

Step 1 . is end-to-end ( Ω ) measure the résistance of each Ring / Loop .. Identify
( Certification ) R/P.402 .. Schedule of test results . Ring final circuit continuity ( Ω ) 10 , 11 , 12 . Little ( r [SUP] 1 N 2[/SUP] )

Measurements taken at the Origin of an ( A1 ring circuit 100m[SUP]2[/SUP] ) O.S.G. table H2.1.
( r[SUP]1 [/SUP] = 0.4Ω ) .. T&E
( r[SUP]N [/SUP] = 0.4Ω ) ..
( r[SUP]2[/SUP] = 0.67Ω ) ..

Determine the measured value of résistance ( at each socket-outlet ) ends of the circuit are cross connected to form a ( Figure of 8 )

( Figure of 8 ) Step 2 . Connections for testing , Line & Neutral .
( Figure of 8 ) Step 3 . Connections for testing , Line & Circuit-protective-conductor . CPC

cross connection between Line & Neutral at origin ... measure résistance between Line & Neutral at each socket
cross connection between Line & CPC at origin ... measure résistance between Line & Circuit-protective-conductor at each socket

recap . GN-3 . tells us .

Line & Neural is measured at each socket-outlet , The ( Readings ) obtained at each of the sockets wired into the ring will be substantially the same & the value will be approximately one-quarter of the résistance of the line plus , CPC loop résistance . ( r[SUP]1 [/SUP]+ r[SUP]2[/SUP] ) / 4 .

Line & Earth is measured at each socket-outlet , The ( Readings ) obtained at each of the sockets wired into the ring will be substantially the same & the value will be approximately one-quarter of the résistance of the line plus , CPC loop résistance . ( r[SUP]1 [/SUP]+ r[SUP]2[/SUP] ) / 4 .

( r[SUP]1 [/SUP]+ r[SUP]N [/SUP]= 0.4 + 0.4 = 0.8 ÷ 4 = 0.2Ω ) line & neutral
( r[SUP]1 [/SUP]+ r[SUP]2 [/SUP]= 0.4 + 0.67 = 1.07 ÷ 4 = 0.267Ω ) line & circuit-protective-conductor .

The highest value recorded represents the maximum ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) of the circuit & is recorded on the Schedule of test results .

Note : A higher résistance value will be recorded at any ( socket-outlets wired as Spurs )

Note : R/P.402 . Where there are no spurs connected to the ring-final-circuit this value is also the ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) of the circuit .

The other test confirmed is : Polarity by Continuity method .

Three specific requirements for ( Verification ) of polarity with the regard to ( Accessories )
612.6. Polarity
(i) All single-pole devices are connected in the line conductor only .
(ii) The centre contact of Edison screw lamps . refer . ( LED lights are taken centre stage now ) 2 Dee ,
(iii) Wiring has been correctly connected to socket-outlets & similar accessories

( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) am single narrowed out ( R[SUP]2[/SUP] ) what has you achieved , you have verified , by test that must be carried out to confirm that your circuit-protective-conductors are continuous throughout you loop . .. under earth-fault-conditions your RCD will take it out

( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) am single narrowed out ( R[SUP]1[/SUP] ) what has you achieved , you have verified , by test you carried out to confirm that your line-conductors are continuous throughout your loop . *

612.6. Polarity
(i) All single-pole devices are connected in the line-conductor only * Circuit-breaker or RCBO . etc

GN-3 & BS-7671: have their merits of each test . nock on affect .

 

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State the action to be taken regarding the Earthing-conductor before measuring the résistance of an earth-electrode .
( Earth electrode testing ) ... Do not disconnect any protective-conductors before ( Isolating the supply )

Disconnect earthing conductor at ( MET ) to avoid parallel earth paths .

GN-3 : 2.7.12. Q/As

recap . Test method 1 .
before test is undertaken , the earthing-conductor to the earth-electrode must be disconnected either at the electrode or the ( MET ) to ensure that all the test current passes through the earth electrode alone .

This will leave the installation unprotected against earth faults .

 

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Useful Junk

Any surface potential ( V )

The potential ( V ) arising on an installation earth-electrode under earth fault conditions will have a value relative to the nominal voltage to Earth of the supply ( Uo ) as follows:

V = Uo x R[SUP]A[/SUP] / Zs (V )

Where :
( Uo ) is the normal voltage of the supply
( R[SUP]A [/SUP]) is the sum of the resistances of the earth electrode and the protective conductor connecting it to the exposed-conductive-parts
( Zs ) is the earth fault loop impedance of the faulty circuit

For example , suppose an earth fault of negligible impedance has occurred in a circuit of an installation in a TT system and suppose the nominal voltage of the supply ( Uo ) is 230V, the earth fault loop impedance ( Zs ) is 100Ω and the earth electrode resistance is 80Ω.

By substituting these values into equation : V = 230V x 80Ω ÷ 100Ω = 184V

it is found that the potential ( V ) appearing at the earth electrode is 184 V.

the duration over which the potential exists must be considered, account being taken of the fact that persons or livestock will generally be in contact with the general mass of Earth .

 

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Changes to existing electrical installations, such as additions or alterations

Regulation . 132.16 . What are they asking us for . Simple . Assessment of an Existing Installation

‘ No addition or alteration, temporary or permanent, shall be made to an existing installation, unless it has been ascertained 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 the protective measure applied for the safety of the addition or alteration, shall be adequate ’.