Re-take - Useful Information for 2394 :

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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 .

 

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Initial Verification ,

Order of tests
Order of tests ( Prior ) To the installation being Energized ( After the completion of Inspection )

• Continuity of protective conductors including , main and supplementary bonding 612.2.1.
• Continuity of ring final circuit conductors 612.2.2.
• Insulation résistance 612.3.
• Protection by SELV , PELV or by electrical separation 612.4.
• Basic protection by a barrier or an enclosure provided during erection 612.4.5.
• Polarity .. for example , at lighting switches . 612.6.

• Where the - earth electrode is part of the installation 612.7. “ Earth electrode to Earth shall be measured “
- Alternatively for a TT system the installation earth electrode résistance may be approximately measured with the incoming supply energized and the main switch OFF , using an earth fault loop impedance test instrument .

Order of tests to be carried out with the supply connected

 

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Order of tests to be carried out with the supply connected

• Earth fault loop impedance 612.9.

• RCDs used for :
i) Where RCDs are applied for protection against fire 612.8.
ii) Fault protection , or 612.8.1. (a) (2) TN- system & (b) (2) TT system .. ( ADS )
iii) Additional protection 612.10.
Prospective fault current 612.11.
( Check ) Phase sequence, maintained for multiphase circuits 612.12.

• Functional testing of RCD ( using test facility in device ) 612.13.1.
Where :
- fault protection ... is to be provided by an RCD .
- additional protection ... is to be provided by an RCD .

• Functional testing of : Equipment . 612.13.2.
- switchgear
- controlgear assemblies
- drivers
- control and interlocks

• Verification of voltage drop 612.14.
Note : Verification of voltage drop is not normally required during initial verification .

 

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Appendix 1 of the HSE Memorandum of guidance on the Electricity at Work Regulations 1989 lists , HSE Guidance Note GS-38 .
Electrical test equipment for use by electricians as a publication being particularly relevant to regulations : are

( 10 - connections )
( 14 - work on or near live conductors )
( 16 - persons to be competent to prevent danger and injury )

 

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The Health and Safety Executive HSR 25

Memorandum of guidance on the Electricity at Work Regulations 1989 is intended to help (( duty holders )) meet the requirements of the regulations

 

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The purpose of providing (( Isolation )) is so that live parts (( normally energised )) can be safely isolated (( separated )) from their source(s) so that work may be carried out on , or near parts without the risk of Electric shock .

it should be noted that isolation is an OFF-load function .

 

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The human body has known limits:
Under normal conditions, voltage limit = 50V

To comply with wiring regulations the earth fault loop impedance in Ohms, multiplied by the rated tripping current of the RCD in amperes must not exceed 50V

For an RCD with a rated tripping current of 30mA, the maximum permissible earth fault loop impedance is calculated as follows: Zs (max) = 50 / In = 50/0.03 = 1666.666667 ( 167Ω )

Table 41.5.
Rated tripping current of the RCD 30mA – Maximum permissible earth fault loop impedance ( Zs / Ω ) 1667Ω (*)
Rated tripping current of the RCD 100mA – Maximum permissible earth fault loop impedance ( Zs / Ω ) 500Ω (*)
Rated tripping current of the RCD 300mA – Maximum permissible earth fault loop impedance ( Zs / Ω ) 167Ω

 

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16[SUP]th[/SUP] Edition : Principal requirements for isolating devices .

537-02-02 . calls for the isolating distance between contacts ( in the absence of international agreement , normally taken to be not less than 3mm in the open position . to be not less than that called for in BS-EN-60947-3 . 17th Edition Table 53.4. Isolating switch . BS-EN-60947-3

 

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Basic’s : The purpose of providing Isolation is to cut Off the supply from the installation , Or part of it (( for safety )) persons carrying out modification or electrical maintenance to affected circuit(s)

513 Accessibility : :icon_bs:
Designer’s selection of types of devices and their positioning in order to expedite ready access for operation , inspection and testing and maintenance of devices . as required by Regulation 513.1.

 

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Whereas Circuit-breaker is an : (( On-Load device ))
Circuit-breaker (( Duties )) Make or Break both normal & abnormal currents .. Manual or Fault-conditions

Circuit-breaker BS-EN-60898-1 (3) Table 53.4. :icon_bs: Guidance on the selection of protective-device’s
(3) - Device is suitable for (( On-load isolation )) i.e. disconnection whilst carrying load-current .

 

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RCD’s work on the principle of a (( load )) being in balance - that is, the current on the Line-conductor is equal to that flowing out of the Neutral-conductor. (( resi / dual-current ))