Re-take - Useful Information for 2394 :

[amberleaf]

Non-Statutory :

Guidance-Notes , are published by the IET are intended to be “ Explanations “ of the requirements of BS-7671:2008:2011:

Guidance-Notes , are for “ Guidance“ Only , theymust not be used independently of BS-7671:2008:2011: for ensuring-compliance .

Guidance-Note - 3 , is based upon the , requirements of Part- 6 in BS-7671:2008:2011:

As part of the competence-requirement , the Inspector must have a sound-working-knowledge of the, test-methods as described in the Guidance-Note .

It provides details of the methods to beused for carrying out the tests as required by BS-7671:2008:2011: for both :

New-installations . ( EIC ) or ( MEIWC )
Existing-installations . ( EICR ) Condition-Report

( EIC , is to be used only for the ,initial-certification of a new-installation . 2392-10 / 2394 :
) for an addition or alteration to an Existing-installation , where new circuits have been introduced .

The “ Verification “ of Electrical-Installations.
All measures by means of which compliance of theelectrical-installation with the relevant-requirements of BS-7671:2008:2011: are confirmed.

A “ Duty ofCare “ responsibility makes the Inspector a “ DutyHolder “ for the duration of the inspection andtesting-process .
The “ Titlein Law “ placedupon the Inspector is that of “ Duty Holder “

Inspector :
BS-7671:2008:2011: requires the inspection andtesting shall be carried out by a competent-person.

Regards to “ Verification “

- Sufficient-technical-knowledge. fully-versed in the inspection andtesting-requirements contained in BS-7671:2008:2011:

Relevant-practical-skills :
- have sufficient-practical-skill to carry out the ,inspection and test-procedures outlinedin Guidance-Note - 3

Experience with regards to the type of electrical-work undertaken : and employ

Appropriate testing-equipment :
Instrument(s) used in the testing-process , where the values are to be recorded in the schedule of test-results , must comply with the appropriate-parts of BS-EN-61557 .

611.1. Precautions for working on equipment made-dead .

Isolation : requires thatinspection shall be carried out beforethe testing-process-commences and shallnormally be done with the part of theinstallation being inspected-isolated from thesupply .

611.1. Installation is securely and securely-isolated prior to this-process being-undertaken

- Indentify the point of Isolation .
- Confirm with the client that it is safe to Isolate .

Regulation - 537.2.2.4.. p.151. requires .
That provision should be made for securing OFF Load-isolating-devices against , inadvertent or unintentional-opening . Etc.

Where Circuit-breakers are to be used as the ( Isolating-device ) then dedicated ( Locking OFF Devices ) with unique keys or combinations should be used . :christmaswreath:

 

[amberleaf]

Instrument Calibration: Calibration is not a warranty or a statement of how-long the instrument will remain-accurate . :gettree:

Instrument(s) regarding the Inspector in BS-7671:2008:2011: isthat you must employ adequate-testing-equipment . !!
Instrument(s) generally be split up into five-separate-categories.

Indicate thepresence of voltage .
Measure - voltage .
Measure - current .
Measure - résistance .
Measure - time .

 

[amberleaf]

Effects of length upon conductor-résistance . Basics . :gettree:

The résistance of a conductor is directly-proportional to its length . short piece of cable - Length - résistance . 5Ω
2 x Length : if length is doubled ( 2 x length ) then the résistance will increase by the same-factor , résistance = 10Ω

Résistance of a 60m length of cable is ( 4Ω) if the length of the cable wasreduced by ( 25% determine the résistance )

New - Length : 75% of 60m = 45m
New - résistance : 4 x new - length / original - length , = 45 / 60 = 3Ω . ( 4 x 45 ÷ 60 = 3Ω )

Cable -Length :

Résistance ofa 50m length of conductor is 0.1Ω . determine the résistance of 200m of the same-conductor ?
New - résistance : 0.1 x 200 / 50 = 0.4Ω

The effects of (C.S.A. ) upon conductor-résistance.
The résistance of a conductor is inversely-proportional to its (C.S.A. ) 25mm[SUP]2[/SUP]

If the cross-sectional-area is , Doubled then the résistance is ( Halved)

50mm[SUP]2[/SUP] Unknown-cable-résistance , = themeasured-résistance , x Original - C.S.A. / New - C.S.A.
Résistance of a length of 4.0mm[SUP]2[/SUP] cable is 0.6Ω , whatwould be the résistance of a 6.0mm[SUP]2[/SUP] cable if the length remained the same ?

New - résistance = 0.6 x original-cable-size / new-cable-size , 0.6 x 4.0mm[SUP]2[/SUP] / 6.0mm[SUP]2[/SUP] = 0.4Ω [ 0.6 x 0.4 ÷ 0.6 = 0.4Ω ]

The résistance of alength of 1.0mm[SUP]2[/SUP] is 0.2Ω. what would be the résistance of a 4.0mm[SUP]2[/SUP] conductor of the same-length ?
2 x original-cable-size / new-cable-size , = 0.2 x 1.0mm[SUP]2[/SUP] - 4.0mm[SUP]2[/SUP] = 0.05Ω [ 0.2 x 0.1 = 0.02 ÷ 0.4 = 0.05Ω ]

 

[amberleaf]

Basics . Some - facts

What does not changewith the increase in , temperature isits Length .

Consider - 1.0mm[SUP]2[/SUP] ( 20°C / 100m )

The résistance /metre , for 1.0mm[SUP]2[/SUP] PVC -insulated-copper-conductors at 20°C . is 18.10 milli-ohms / metre :

O.S.G. Table - 11 . p.182 . 1.0mm[SUP]2[/SUP] - is 18.10 milli-ohms / metre

Therefore : thetotal-résistance of the cable shown , = 100 x 18.1 / 1000 = 1.81Ω

The résistance / metre for 1.0mm[SUP]2[/SUP] PVC -insulated-copper-conductors at 25°C is 18.1 milli-ohms/ metre x 1.02 .

Therefore : thetotal-résistance of the cable at 25°C = 100 x 18.1 x 1.02 / 1000 = 1.846Ω

The table -provided in the O.S.G. gives the résistance / metre for PVC - insulated-copper-conductors, & of ( R[SUP]1[/SUP]+ R[SUP]2[/SUP] ) per / metre at 20°C in milli - ohms / metre . Where ( R[SUP]1[/SUP] ) is the line-conductor , & ( R[SUP]2[/SUP] ) is the circuit-protective-conductor . Etc.

 

[amberleaf]

Basics .

The effects of Temperature , upon conductor-résistance .
Copper : has a positive-temperature-coefficient, the warmer the cable the higher its - résistance . :gettree:

The résistance :tables for conductor-sizes are based upon an ( Ambient temperature ) of ( 20°C ) and the résistance ofcopper-increases by ( 0.004Ω ) per - degree-rise .

If a coil ofcables-temperature-increases by ( 5°C ) the corresponding-increase in résistance will be ( 0.02Ω ) 5 x 0.004 = 0.02

Value of résistance / metre for PVC - insulated-copper-conductors & of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) per/ metre at ( 20°C ) in milli - ohms / metre . O.S.G. - Table - 11 . p.182

Where the résistance of a cable is measured at an ( Ambient temperature ) otherthan of ( 20°C ) and the length is required , a correction/factor must be used .

It must be ensured that when thecircuit-0length . etc needs to beobtained , the values used in the calculations must be at the same-temperature .i.e. either .

Change the values in the résistance table at ( 20°C ) to whatever temperature the résistance-measurement was taken at . O.S.G. table 12 . p.183

GN-3 . P.121 . Table- B2
Expected - ambient-temperature ( °C ) Correction - factor *

5°C - 0.94
10°C - 0.96
15°C - 0.98
20°C - 1.00
25°C - 1.02
30°C - 1.04
35°C - 1.06
40°C - 1.08

Or - change the résistance-measurement , from whatever - temperature it wasmeasured at , to (20°C )

 

[amberleaf]

Basics .

Continuity Measurement :
Calculate ( Assuming the ambient - temperature to be ( 20°C ) the résistanceof the measured - lengths of cable in table- 11 - O.S.G. p.182 .

Scenario : Cable on Coil . !!

1.0mm[SUP]2[/SUP] . Measured-length ( M ) 24 , Cable-résistance mΩ/M - 18.1 , Cable-résistance Ω/M - 0.0181 x 24 , Cable-résistance - Ω 0.434 .
1.5mm[SUP]2[/SUP] . Measured-length ( M ) 36 , Cable-résistance mΩ/M - 12.1 , Cable-résistance Ω/M - 0.0121 x 36 , Cable-résistance- Ω 0.435 .
2.5mm[SUP]2[/SUP] . Measured-length ( M ) 44 , Cable-résistance mΩ/M - 7.41 , Cable-résistance Ω/M - 0.00741 x 44 , Cable-résistance - Ω 0.326 .
4.0mm[SUP]2[/SUP] . Measured-length ( M ) 52 , Cable-résistance mΩ/M - 4.6 , Cable-résistance Ω/M - 0.00461 x 52 , Cable-résistance - Ω 0.239 .

1.0mm[SUP]2[/SUP] . = 18.1 mΩ/M . 0.018 Ω/M

Total - résistance . = 24 x 0.018 = 0.432Ω :carolers:

 

[amberleaf]

Q) from the measurement taken of the 1.5mm[SUP]2[/SUP] / 1.0mm[SUP]2[/SUP] T&E cable .
Determine :

The résistance of the Neutral-conductor .
The résistance of the Circuit-protective-conductor .
The maximum ( R[SUP]1[/SUP]+ R[SUP]2[/SUP] ) value of the circuit .
The Length ofthe cable-connecting theoutlet-point to the consumer-unit .

Megger - 1552 . reading off , Socket-outlet . 1.2Ω / L & N

By - Calculations
1.5mm[SUP]2[/SUP] = 12.1 mΩ/M
1.0mm[SUP]2[/SUP] = 18.1 mΩ/M

Line - loop = 12.1 mΩ/M
Neutral -loop = 12.1 mΩ/M
L + N = 24.2 mΩ/M ,
= 0.024 Ω/M

 

[amberleaf]

Unknown -cable -résistance . = the measured-résistance x original C.S.A. / new C.S.A. .

Solution .

The résistance of the neutral-conductor = 1.2 / 2 = 0.6Ω
The résistance of the circuit=protective-conductor - ( R[SUP]2[/SUP] ) = 0.6 x 1.5 / 1 = 0.9Ω

The maximum ( R[SUP]1[/SUP]+ R[SUP]2[/SUP] ) of thecircuit = 0.6 + 0.9 = 1.5Ω

Cable - length . = measured-résistance of the Line and Neutral - loop / the résistance in Ω/M of the L & N - conductors . = 1.2 / 0.024 = 50M :gettree:

 

[amberleaf]

From old notes , ► 2008 . Useful-junk .

( Line & Neutral - conductor - 1.5mm[SUP]2 [/SUP] / 1.5mm[SUP]2 [/SUP] = 24.20 ) O.S.G. 24.2


Three-phase-board

Determine whether the circuit-complies with thevoltage-drop requirements in Appendix - 12, ► moved Appendix - 4 sec 6.4. 421

Circuit- 4L1 - 6A , lighting-circuit supplyinga large-number of lighting-points is supplied via a , 1.5mm[SUP]2 [/SUP] T&E & CPC .
Line / Neutral , loop=measurement at the ceiling-rose = 0.82Ω

( Ipsc ) on the brown-phase = 1.15kA

Thevoltage-drop on a lighting-circuit = 3% of 230V = 6.9V .
Three-factors need to be taken into account .

i). The mV/A/M of the cable .

i.e.. 29 mV/A/M from tables in Appendix - 4 .
ii). the design-current ( Ib )
can be calculated or . the rating of the protective-device may be used .

regulation- 433.1.1. requires that the rating of the protective-device ( In) p.73 . p.81. must not be less than that of the design-current ( Ib) by substituting ( In) for ( Ib ) in the calculation, the maximum-voltage-drop can be calculated .

if this is in compliance then the actual-voltage-drop must also be in compliance .

iii). the circuit-length ( L )
the prospective-short-circuit-current is given as 1.15kA , ( 1150A )
the résistance of the , L / N loop-external to the installation , = 230V / 1150A = 0.2Ω

therésistance of the , L / N -conductors from the supply to the remote-end of the circuit , = 0.82 sub 0.2 = 0.62Ω

Now from , O.S.G. p.182 - Table - 11 . 24.2 milli-ohms per / metre = 0.024 ohms-per-metre .
Therefore:- Circuit-length = 0.62 / 0.024 = 25.8M

The circuits maximum-voltage = ( mV/A/L) x Ib x L / 1000 , = 29 x 6 x 25.8 / 1000 = 4.49V

Q). does the circuit complies . :christmastree1:

 

[amberleaf]

From my old-notes . ◄◄ Useful-junk . PS its only a leaning-curve . by calculations Only .

Selecting the rated-residual-operating-current of an RCD .

Q). if the measured-earth-loop-impedance on a TT - system was , 150Ω

Determine the maximum-residual-operating-current of the RCD to be installed at thesupply-intake .

Regulation 411.5.3 . Ra x IΔn ≤ 50 : IΔn ≤ 50 /Ra : = 50 ÷ 150 = 0.33A = 330mA .

The RCDs rating must not-exceed 330mA .

Therefore: an RCD with a rated-residual-operating-current of 300mA would be acceptable . ( used only as leaning-curve )

 

[amberleaf]

Inspection : Examination of an electrical-installation using all the senses as appropriate . :icon_bs:
Q/As
Function-testing: Senses Used .
Visual,
Touch,
Hearing.

Q) An RCD is to be used in aninstallation for protection against the risk of fire , State the maximum-rating of the RCD , 300mA .

State : themaximum-disconnection-time of the device.

Within 300mS , if the RCD is to BS-EN-61008-1 or BS-EN-61009-1
Or ,
Within 200mS if the RCD is to BS-4293 .

 

[amberleaf]

415.1.1. - for Additional-protection only . just showing you the regulation number.

Q). State : themaximum-rating of the RCD ,
The maximum-disconnection-time and the applied-test-current as required by Regulation - 415.1.1.

Maximum-rating 30mA .
Maximum-disconnection-time . 40mS
Maximum-test-current up to five-times the maximum-rating .

 

[amberleaf]

Q) Describe how you would carry out aninsulation-resistance-test on a circuit with a Neon-indicator-present . Couldthis come up , Written-exams :gettree:

Limitation : No-insulation-résistance-tests were carried-out between Live-conductors after the point of local-isolation .

Neon-indicator - Switch-closed, Line & circuit-protective-conductor , Neutral & circuit-protective-conductor ,


Neon-indicator - ( Whatnot to do ) Switch-open , Line & circuit-protective-conductor ,

Neon-indicator will adversely affect the result of the test ,

Thepresence of the Neon-indicator can influence the measured-insulation-résistance. typical-résistance of an indicator is approximately 200kΩ or 0.2MΩ


Basic Theory : the effectsof circuit-length on insulation-résistance
The insulation-résistance of a cable ( Decreases ) as its ( Length-increases)

Thelength is doubled the insulation-résistance ( Decreasesby half ) the change in insulation-résistance is inversely-proportional to change in the ( Length)

Basic Theory :
Total-combined-résistance of the circuits within a ? Distribution-board or Consumer-unit ,( Decreases ) asthe total-number of circuits-increases .

The résistance does not increase or decrease-proportionally to the number of circuits . installed-cables are of different-types and differing-cross-sectional-areas .
Circuit-lengths will vary as will the number ofoutlet-point per-circuit . ( All these-factors when combined affect the insulation-résistance )

Basic Theory :
Whetherthe installation is single or three-phase, only Two-insulation-résistance-tests are required
Between Live-conductors . - Neutral is a live-conductor . L / N
Between Live-conductors and Earth. L / N & E .

 

[amberleaf]

Toavoid things going pear-shape .

Insulation-résistance.

Where the circuit-includes electronic-devices such as :
Smoke-detectors . whichcould-damage , Neon-indictors , that could influence thetest-results . Only a measurement between Live-conductors, connected together to Earth needbe made .

Re-cap.

612.3.3.
Where the circuit includes electronic-devices whichare likely to influence the results or be damaged , only a measurement between the , Live-conductors connected together and the earthing-arrangemernt shall be made .

The Regulations have stated the-facts

NOTE : Additional-precautions, such as disconnection , may be necessary to avoid-damage to electronic-devices . :17:

 

[amberleaf]

Old-Notes.

Insulation-résistance :

Main-switch in the On-position and all circuit-breakers - Closed .
Three-phase .

Step- 1 :
Test between L1 and Neutral .
Test between L2 and Neutral .
Test between L3 and Neutral .

Step- 2 :
Now test between
L1 and L3
And then
L2 and L3

Step- 3 :
Finally test between L1 and L2.

Record the Lowest-measured-value .