Re-take - Useful Information for 2394 :

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Q/As 2394

A 100mA BS-EN-61008 RCD is installed in a TT installation to provide fault-protection .
Which of the following identifies the maximum test current to be applied and the maximum disconnection time at test current when testing the RCD

100mA & 200mS
100mA & 300mS *** :icon_bs:
500mA & 200mS
500mA & 300mS

The RCD is provided for fault-protection and not additional protection and the ( 1 x IΔn ) is the maximum test current that needs to be applied

As this is a BS-EN-61008 device the maximum disconnection time is ( 300mS )

Re-cap NOTE : ... ((( BS- )))
A maximum disconnection time of ( 200mS ) applies to some older RCDs manufactured to a ((( British Standard ))) but not to BS-EN-61008 devices

 

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Revision : 2394:

List the Instruments used for : :yes:
a) Continuity of circuit-protective-conductor(s)
b) Continuity of ring-final-circuit(s)
c) Insulation résistance ( IR )

List the Units used to measure with the following instrument

a) Low résistance ohmmeter
Instruments to - GN-3 P/82 ... BS-EN-61557-4 ( part 4 )

b) Insulation résistance tester’s
Instruments conforming to - GN-3 P/83 ... BS-EN-61557-2 ( part 2 )

Earth fault loop impedance tester’s
Instruments conforming to - GN-3 P/83 ... BS-EN-61557-3 ( part 3 )

Earth electrode résistance tester’s
► GN-3 - 2008 P/84 .
The instrument potential and current spikes are within the operating limits of the instrument .. it may be helpful to note that instruments complying with BS-EN-61557-5 ( part 5 ) incorporate this facility . Care should be exercised to ensure that temporary spikes are positioned with reasonable accuracy .

c) RCD tester’s
Instruments conforming to - GN-3 P/84 ... BS-EN-61557-6 ( part 6 )

Phase rotation instruments
BS-EN-61557-7 ( part 7 )

 

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Ask the Question , What can Guidance Note 3 do for YOU. :svengo: It’s a must in any Exams’

a) List two methods utilised for Basic protection ... usually provided by insulation and / or enclosures

► GN-3 - 2008: Basic protection 416
Insulation of live parts
Although protection by insulation is the usual method , there are other basic protection methods . 416.1.

Barriers or enclosures
Where live parts are protected by barriers or enclosures , these should be checked for adequacy and security . 416.2.

► GN-3 - 2011: P/19 . Basic protection 416
Basic protection is most usually provided by insulation and / or enclosures . The inspection of this measure is to check that insulation has not been damaged during installation and that enclosures have been selected for at least IPXXB or IP2X and , for top surfaces , at least IPXXD or IP4X , and are not damaged . ( Insulation résistance is of course a fundamental test to be carried out )

b) List one method utilised for Fault protection
► GN-3 - 2011: P/19 . Fault protection Sec 411 ( 1 )
Fault protection
The various methods of fault protection are classified in a number of subsections in BS-7671: and are :
( 1 ) Automatic disconnection of supply .

P/20 . Method 1 .
Automatic disconnection of supply ( ADS )
For each circuit , automatic disconnection is required and , although the main part of verification is measurement of earth fault loop impedance in order to confirm disconnection times , there are inspection aspects to consider for verifying ADS as follows :

Presence of appropriate protective conductor(s)
Earthing-conductor
Circuit-protective-conductors
Protective bonding conductors
- Main bonding conductors
- Supplementary bonding conductors ( where required )

312.2. The earthing system must be determined e.g.
TN-C-S ( Protective multiple earthing ( PME ))
TN-S system
TT system ( earth electrode(s))

411.4.5. The earth fault loop impedance must be appropriate for the protective device , i.e. RCD or Overcurrent device .

BS-7671:2011: P/23 :icon_bs:
Basic protection .
Protection against electric shock under fault-free conditions .

Note : For low voltage installations , systems and equipment, basic protection generally corresponds to protection against direct contact , that is “ contact of person or livestock with live parts “

BS-7671:2011: P/28 :icon_bs:
Fault protection .
Protection against electric shock under single fault conditions .

Note : For low voltage installations , systems and equipment , fault protection generally corresponds to protection against indirect contact , mainly with regards to failure of basic insulation .

Indirect contact is “ contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions “

411 Protective Measure : Automatic Disconnection of Supply .
(ii) fault protection is provided by protective earthing , protective equipotential bonding and automatic disconnection in case of a fault . refer

410.3.3. The following protective measures generally are permitted :
(i) Automatic disconnection of supply - section 411.1.

P/51 Note : In electrical installations the most commonly used protective measure is automatic disconnection of supply .

 

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R/P29 . Inspection ; Examination of an electrical installation using all the senses as appropriate .
R/P36 . 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 .

R/P 22 . 135 Periodic inspection and testing
135.1. It is recommended that every electrical installation is subjected to periodic inspection and testing , in accordance with Chapter 62 .

135 Periodic inspection and testing
Installations must be inspected and tested periodically to ensure that they are safe for continued use .

Chapter 13 will ensure that all of these principles have been addressed and that the best possible protection is in place .

Chapter 13 : Fundamental principles
135 Periodic inspection and testing .

R/P 36 . Verification . :icon_bs:
All measures by means of which compliance of the electrical installation with the relevant requirements of BS-7671: are checked , comprising inspection , testing and certification .

Chapter 13 : Fundamental principles
134 : Erection and initial verification of electrical installations
134.1. Erection
134.2. Initial verification

 

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Requirements of BS-7671: :icon_bs:

Replacing a consumer unit in an existing installation is an addition or alteration to that installation. The work must therefore be designed, erected and verified in accordance with the requirements of the current edition of BS-7671: and must not impair the safety of the existing installation. ( Regulations 110.1 (vi) & 610.4 .

610.4 .. Verification
For an addition or alteration to an existing installation
it shall be verified that the addition or alteration complies with the Regulations and does not impair the safety of the existing installation

P/390 re-cap : EIC - Safety certificate
Addition to an existing installation
Alteration to an existing installation

 

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State three non-statutory documents which the inspector may need to refer to relating specifically to inspection and testing
BS-7671:
On Site Guide
Guidance Note 3 :35:

Inspection and testing of Electrical Installations

The British Standard for electrical installations is BS-7671:208:2011: The requirement for Electrical installations Within this standard , Regulation 610.1

Requires that (( every installation )) shall be inspected and tested to verify , so far as is reasonably practicable, that the Regulations have been met before being put into service. The requirements are stated in the following Regulations:

Regulation 134 .. Initial verification
134.2.1. During erection and on completion of an installation or an addition or alteration to an installation and before it is put into service , appropriate inspection and testing shall be carried out by competent persons to verify that the requirements of this Standard have be met .

Regulation 621.1. States that :
Where required periodic inspection and testing of (( every installation )) shall be carried out in accordance with regulations 621.2 to 621.5 in order to determine as far as is reasonably practicable, whether the installation is in a satisfactory condition for continued service .

17[SUP]th[/SUP] Edition requirements for testing RCDs
Requirements in terms of verification of installed RCDs :

612.8.1. requires the effectiveness of automatic disconnection of supply by RCD to be verified using test equipment meeting the requirements of BS-EN-61557-6 ( Electrical safety in low voltage distribution system up to 1000V a.c. & 1500V d.c. – Equipment for testing , measuring or monitoring of protective measures . Residual current devices ( RCD ) in TT , TN systems )

This is to confirm that the relevant requirements of chapter 41 ( Protection against electric shock ) are met .

BS-EN-61557-6 has requirements for the following tests to be applied to RCDs :

Non-tripping ( 50% or ½ ) test .. RCD should not trip .
The purpose of this test is to confirm that the RCD of any type or trip is not overly sensitive and is a measure intended to enable unsuitable RCDs to be indentified and removed from service .

Tripping current test :
The purpose of this test is to confirm that the residual operating current of the (( protective-device )) is less than or equal to the rated residual operating current . This is a measure of the continued effectiveness of the device to work as required by BS-7671: and in accordance with its product specification when installed for the purpose of providing automatic disconnection in the event of a fault . it does not demonstrate its suitability in terms of providing additional protection .

Note : GN-3 tell us – The test should be performed in both the positive & negative half-cycles . ( 0° & 180° )

Tripping ( 100% / 1 x ) test
5 x IΔn ( 500% ) fast trip

RCDs ( G ) should be tested at ( 50% , 100% , 500% ) 5 x if providing additional protection
Q ) 30mA BS-EN-61009-1 is installed on a socket-outlet circuit to provide (( additional protection )) Which of the following identifies the maximum test current too be applied and the maximum disconnection time that test current .

A ) 150mA and 40mS .. 5 x 30mA = 150
The RCBO is provided for (( additional protection and the 5 x IΔn is the maximum fault current that needs to be applied .
As this device is providing additional protection , the maximum disconnection time is 40mS , as required by BS-7671: Regulation 414.1.1.

612.13.1. requires :
Where fault protection and / or additional protection is to be provided by an RCD , the (( effectiveness )) of any test facility incorporated in the device shall be (( verified ))

415.1.1. States :
That where an RCD having an IΔn of 30mA is installed to provide additional protection . it’s operating time should not exceed 40mS at a residual current of 5 IΔn .

Q - Explain why the sequence of testing for ((( Periodic ))) inspection may be different to ((( That ))) given in BS-7671: for initial verification
You’re Q . (( The installation has been inspected and tested and placed in service )) Periodic inspection verifies the current condition or the safety of the installation and not the confirmation of the safety of the installation before placing in service .

 

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Sect 514 . Presence of danger notices and other warning notices

GN-3 P/25 . refer to . :aureola:

Extracts .
514.10. Voltage :
► Where a nminal voltage exceeding 230V to earth exists within an iten of equipment or enclosure and where the presence of such a voltage would not normally be expected .

The wording of this regulation was revised for Amendment No 1 to BS-7671:2008: and is carified that only “ unsual “ system voltage exceeding 230V to earth require waring labels .

Anexample would be the use of a 690V three-phase a.c. power tranformer used on an American air base located in the UK .

 

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GN-3 . P/32
612.2.1. Continuity of protective-conductor(s) Etc main & supplementary bonding

Regulation 411.3.1.1. ((( requires ))) that installations which provide protection against electric shock using automatic disconnection of supply ( ADS ) must have a ((( circuit-protective-conductor ))) run to and terminated at each point in the wiring and at each accessory .

Regulation 612.2.1. (((requires ))) that a continuity check be carried out on all circuits including ring-circuits

There are two widely used ((test methods)) that have evolved for checking conductor continuity. “ Test method 1 “ uses the circuit cable shorted out.

“ Test method 2 “ uses a supplementary length of test cable (this method being popularly known as the “ wandering lead “ method.

Test method 1 . as well as checking the continuity of the protective-conductor . also measures ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) which , when added to the external impedance ( Ze ) enables the earth-fault-loop-impedance ( Zs ) to be checked against the design . ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) is the sum of the résistance of the line conductor ( R[SUP]1[/SUP] ) and the circuit-protective-conductor ( R[SUP]2[/SUP] )

 

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Periodic inspection of electrical installations ( -&-s ) :30:

Candidates should be aware that generally the installations being inspected and tested (( are energised ))
-&-s . unless they are given information to the contrary. ◄◄◄ Exams :13:

Don’t fall on our Laurels
To be so satisfied with your own achievements that you make no effort to improve

 

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Facts : -&-s

The three-step test is not needed for radial circuits. Therefore the time needed to comply with BS-7671 testing requirements is greatly reduced.

Ring-final-circuit
GN-3 reminds us .

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

1 ) Step .
2) Step .
3) Step .

Correct wiring of every ring-final-circuit
The test results show if the ring has been interconnected to create an apparently continuous ring-circuit which is in fact broken or connected as a (( figure of eight )) configuration

I have a funny side as well . Amberleaf . :smilewinkgrin:

When mosses find the 10 commandment a Conner broken off. The IET got their little hands on it . split it into the BS-7671:2008:2011: & GN-3 making Outstanding information . Guidance Notes , BS-7671:2008:2011: has Stated the facts British Standards ... Facts

 

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demonstrate that candidates are not aware of the ((( periodic inspection process ))) That minimal dismantling should be involved and the extent and limitations section of the standard form in BS-7671 & GN3

 

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Q) What is the equation used to determine Earth fault Loop Impedance ( i.e.: Zs = ? ) Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

Q) List three-items of information relating to the incoming supply that should be listed on the ((( Generic Schedule of test results )))
Page 391 .. Nature of Supply Parameters ( EIC )

U/Uo ( [SUP]1 [/SUP]) single-phase 230V
Nominal frequency ( ƒ ) ( [SUP]1 [/SUP]) 50Hz
Prospective fault current ( Ipƒ ) ( [SUP]2 [/SUP]) .. kA
External loop impedance ( Ze ) ( [SUP]2 [/SUP]) .. 0.18Ω

Why is it necessary to ((( Verify ))) the continuity of circuit-protective-conductor(s) prior to undertaken any further testing
How important is circuit-protective-conductor(s) CPCs

• Insulation résistance checks ( IR ) .. No circuit-protective-conductor , incomplete
• RCD tests .. relies on circuit-protective-conductor for ( ADS )
• Loop impedance tests ( Zs loop ) circuit-protective-conductor(s) & ( Ze loop ) you must confirm you have an Earthing-conductor or other means earth electrodes

State the danger that may arise if earth fault loop impedance tests are undertaken prior to verifying the Continuity of the circuit-protective-conductor :icon_bs:

Method 1 method :- relies on verifying continuity when undertaken tests . circuit-protective-conductor(s)

R/P196 . Initial verification
Defects or omissions revealed during inspection and testing of the installation work covered by the Certificate shall be made good before the Certificate is issued .

R/P190 . If any test indicates a failure to comply , that test and any preceding test , the results of which may have been influenced by the fault indicated , shall be repeated after the fault has been rectified .

 

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R/P 46 . 314 Division of installation

i) In the event of a Fault
By dividing the installation into circuits
Separate circuits also provide you with a means of ((( Isolation ))) for a section of an installation . :icon_bs:

 

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2011: 131.2. Protection against electric shock :icon_bs:

“ Protection against direct contact “ 131.2.1. - Basic protection
“ Protection against indirect contact “ 131.2.2. - Fault protection

131.2.1. Basic protection ( protection against direct contact )
Note : for low voltage installations , systems and equipment , “ Basic protection “ generally corresponds to protection against “ direct contact “

Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation

This protection can be achieved by one of the following methods :

i) Preventing a current from passing through the body of any person or any livestock
ii) Limiting the current which can pass through a body to a non-hazardous value

131.2.2. Fault protection ( protection against indirect contact )
Note: for low voltage installations , systems and equipment , “ fault protection “ generally corresponds to protection against “ indirect contact “ mainly with regards to failure of basic insulation

Persons and livestock shall be protected against dangers that may arise from contact with exposed-conductive-parts during fault

This protection can be achieved by one of the following methods :

i) Preventing a current resulting from a fault from passing through the body of any person or any livestock
ii) Limiting the magnitude of a current resulting from a fault , which can pass through a body , to a non-hazardous value
iii) Limiting the duration of a current resulting from a fault , which can pass through a body , to a non-hazardous time period

In connection with fault protection , the application of the method of protective equipotential bonding is one of the important principles for safety

 

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Q) Which measurement would you use when recording the continuity of the ring final conductors . ( mΩ , mS , Ω , MΩ ) -&-s

Q) Whilst conducting a circuit-protective-conductor continuity test , GN-3 recommends a temporary link to be made ?
A) Between Line and CPC in the consumer unit

Continuity of ring-final-circuit conductor(s) (( :leaving: THREE-STEPS TEST )) -&-s .. to verify the continuity :13:

As GN-3 reminds us ; Initial check for continuity
2.7.6. A three-step test is required to verify the continuity of the Line , Neutral , Protective-conductors . etc

Step 1 . Connections for testing , initial check for continuity at ends of ring
The line , neutral and protective-conductors are visually identified at the distribution board or consumer unit and the (( end-to-end résistance )) of each is measured separately. ................ making me / Step 1

Check between each end in turn (( L / L , N / N & Cpc / Circuit-protective-conductor ))
Testing results - Little r[SUP]S[/SUP] ( r[SUP]1[/SUP] , r[SUP] N[/SUP] , r[SUP]2[/SUP] ) r[SUP]1 [/SUP]Line , r[SUP] N[/SUP] Neutral , r[SUP]2[/SUP] Circuit-protective-conductor .

R/P 402 . Generic Schedule of Test Results . (( Am using the wording - Generic Schedule etc ) -&-s GN-3 & BS-7671: States this
Ring final circuit continuity ( Ω ) 10 , 11 , 12 .

As GN-3 reminds us ; Step 1 .
A finite reading confirms that there is No open-circuit on the ring conductors under test .

Q) A continuity test is conducted on a ring final circuit , 6 sockets give a ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) reading of 0.41Ω but one socket gives a reading of 0.69Ω .
What could this indicate ? “ Houston you have a problem “ remember that you .Pass or Fail . -&-s

Trapped circuit-protective-conductor in the back of a box
Spur on the circuit
High résistance fault
Short circuit ... 0.00 ... As your Résistance approaches Zero, your current approaches Infinity.

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

 

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My main point is to make you aware of the (( :skep: THREE-STEPS TEST )) -&-s .. to verify the continuity , (( Ring-final-circuits ))

Step 2 . ((Cross connect )) Line and Neutral

GN-3 reminds us : The open ends of the Line & Neutral conductor(s) are then connected together so that the outgoing Line-conductor is connected to the returning Neutral-conductor and vice versa (( refer to Figure 2.2b )) P/37 connecting for testing Step 2 .

• Measure between Line-conductor and Neutral-conductor at each socket-outlet .
Values should be the same at each socket-outlet .. should be ( r[SUP]1[/SUP] + r[SUP] N[/SUP] ) / 4

Step 3 . ((Cross connect )) Line and Circuit-protective-conductors
• Measure between Line-conductor and Circuit-protective-conductors at each socket-outlet .
Values should be the same at each socket-outlet .. should be ( r[SUP]1[/SUP] + r[SUP] 2[/SUP] ) / 4
(( refer to Figure 2.2c )) P/37 connecting for testing Step 3 .

Value is recorded as ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) on the . (( Am using the wording - Generic Schedule of Test Results ) -&-s GN-3 & BS-7671: States this
R/P402 . Continuity ( Ω ) ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) 13 .

You have proven continuity long before now . Step 1 : Little r[SUP]S[/SUP] ( r[SUP]1[/SUP] , r[SUP] N[/SUP] , r[SUP]2[/SUP] )

This is still a Dead test :- Why is it ( r[SUP]1[/SUP] + r[SUP] 2[/SUP] ) / 4
By Cross connecting the opposing Lines and circuit-protective-conductors creates a perfect resistive circle
( By Cross connecting the ) Lines and circuit-protective-conductors , resistances are in parallel

As GN-3 reminds us .
A higher résistance value will be recorded at any Socket-outlet wired as Spurs . (( watch this in Exams Q/As ))

Schedule of Test Results :leaving:
The value can be used to determine the earth-fault-loop-impedance ( Zs system ) of the circuit to verify compliance with the loop impedance requirements of the Regulations

 

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Testing 2012
Questions related to testing appeared to create difficulty for candidates :rant:

The question relating to the testing of ring final circuit conductors was generally poorly answered with marks lost due to incomplete procedures, incorrect terminology when referring to conductors, incorrect instrument names, failure to state the need to test at each socket and failure to state the conductors between which the tests are carried out. ((( Step 1 , Step 2 , Step 3 )))

 

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Definitions

R/P 28 . Final circuit .
A circuit connected directly to current-using equipment , or to a socket-outlets or socket-outlets or other outlet points for the connection of such equipment .

A radial final circuit is not defined in Part 2 of BS-7671: but is generally considered to be a final-circuit connected to the supply at one end only

R/P 28 . Ring final circuit .
A circuit connected directly to current-using equipment , or to a socket-outlet or socket-outllets, or other outlet points for the connection of such equipment .

P/34 ( Spur ) A branch from a ring or radial-final-circuit .

O.S.G. p/68 . 7.2.2. Socket-outlet circuit .
As a rule of thumb for rings , unfused spur lengths should not exceed 1/8 the cable length from the spur to the furthest point of the ring .

 

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O.S.G. P/129 . Table D1 Spacings of supports for cables in accessible positions

Cable overall diameter (d) mm

Non-armoured cable thermosetting or thermoplastic ( PVC ) Sheathed cables ( † )

Up to d ≤ 9 .. Horizontal 2 . 250 , Vertical 3 . 400
Exceeding 9 but not exceeding 15 .. 9 < d ≤ 15 .. Horizontal 300 , Vertical 400
Exceeding 15 but not exceeding 20 .. 15 < d ≤ 20 .. Horizontal 350 , Vertical 450
Exceeding 20 but not exceeding 40 .. 20 < d ≤ 40 .. Horizontal 400 , Vertical 550

Cable overall diameter (d) mm

Armoured cable maximum support spacing ( † )

Up to d ≤ 9 .. Horizontal 6 . 250 , Vertical 7 . 400
Exceeding 9 but not exceeding 15 .. 9 < d ≤ 15 .. Horizontal 350 , Vertical 450
Exceeding 15 but not exceeding 20 .. 15 < d ≤ 20 .. Horizontal 400 , Vertical 550
Exceeding 20 but not exceeding 40 .. 20 < d ≤ 40 .. Horizontal 450 , Vertical 600

Note : Wiring used in the electrical installation of a caravan must be of a type listed in Regulation 721.521.2.

721.521.2. Types of wiring system

The wiring systems shall be installed using one or more of the following :
i) Insulated single-core cables , with flexible class 5 conductors , in non-metallic conduit
ii) Insulated single-core cables , with stranded class 2 condutors ( mininum of 7 strands ) in non-metallic conduit
iii) Sheathed flexible cables .

All cables shall , as a minimum , meet the requirements of BS-EN-60332-1-2.
Non-metallic conduits shall comply with BS-EN-61386-21.
Cable management systems shall comply with BS-EN-61386.

In Caravans maximum support spacing ( † )

Up to d ≤ 9 .. Horizontal 4 . 250 for all sizes , Vertical 5 . 400 for all sizes
Exceeding 9 but not exceeding 15 ..
Exceeding 15 but not exceeding 20 ..
Exceeding 20 but not exceeding 40 ..

* For flat cables taken as the dimension of the major axis .
† ) The spacings stated for horizontal runs may be applied also to runs at an angle of more than 30° from the vertical . for runs at an angle of 30° or less from the vertical , the vertical spacings are applicable .

- Spacings smaller than given in the O.S.G. will often be necessary for good workmanship / visual appearance .
- Horizontal spacings include for runs at an Angle of more than 30° from the vertical
- Vertical spacings include for runs at an Angle of 30° or less from the vertical

Cross-section through a flat-type cable indicating the major axis .. ¦ ← Major axis → ¦

 

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Initial Verification , Order of tests

Order of tests for the initial verification of an installation as required by Regulation 612.1. of BS-7671:
Which also requires that :

Testing

i) The test results are compared with the relevant criteria .. (( where required ))
ii) Any test that indicates a failure to comply with the criteria is repeated after the fault is rectified , Together with any preceding test influenced by the fault .

Test must not be carried out until inspection has been completed , as required by Regulation 611.1.

610.1.
Precautions shall be taken to avoid danger to (( persons )) and livestock , and to avoid damage to (( property )) and installed equipment during testing

BS-7671:2008:2011: 612.2. to 612.6.
Lists the order of tests (( where relevant )) to be carried out before the supply is connected or with the supply disconnected as appropriate .

612.7.
Where the earthing system incorporates an earth-electrode as part of the installation , the earth-résistance to Earth shall be measured .