Re-take - Useful Information for 2394 :

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2394:Basics .

BS-7671:2011: States - Three-fundamental-requirements. for fault-protection by ( ADS ) in a TN - system . ( Exams )

- Protective-Earthing. - Regulation - 411.3.1.1.
- Protective-equipotential-bonding - 411.3.1.2.
-Automatic-disconnection in case of afault - Regulation-Group - 411.3.2.

• Protective-Earthing . - ( All Protective-conductor)
Earthing-arrangements consisting of the ( Means ) of earthing . the ( Earthing-conductor ) & the circuit-protective-conductor(s) connecting the . exposed-conductive-parts tothe ( MET ) must be present . adequately-sized & properly-connected such that their contribution to the . Earth-fault-loop-impedance ( Zs ) is sufficiently-low . ( Circuit-loop-impedance)

• Protective-equipotential-bonding
Main-protective-bonding-conductor(s) . complying with Section - 544 . are required to connect all . Extraneous-conductive-parts . to the ( MET )

• Automatic-disconnection .under-earth-fault-condition(s) isrequired . to provide fault-protection .Automatic-disconnection . can be provided by a suitable . Overcurrent-protective-device . under earth-fault-loop-impedance . is sufficiently-low to satisfy the disconnection-time requirements of BS-2011: or alternatively . by a RCD - residual-current-device. provided the appropriate requirements are Met .

Protective-devices. ( Genetic-Name )
For. fault-protection - Regulation - 411.4.4. . requires one or more . of the following types of protective-devices to be used.

• An Overcurrent-protective-device such as a . Fuse or Circuit-breaker .
• An RCD .

The operating-characteristics of overcurrent-protective-devices . complying with the relevant product-standards are given in p.295. Appendix - 3 .


- The purposeof ( Earthing ) where used for the .protective-purposes . within an installation. ( is to limit the Duration of the voltages )

- In ( Contrast ) the purpose of ( Bonding) is to limit the ( Magnitude of the voltages )

 

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Whenan . Earthing-Conductor - isre-moved . What’s in a Regulation . !!!!!

Main-Earthing-Terminal - ( MET ) disconnectionof .

542.4.2. “ let’sget this out the Way “

To facilitate-measurement of the résistance of the . earthing ( Arrangements) means shall be provided in an accessible-position . for disconnecting the earthing-conductor . such means may conveniently be combined with the . ( MET ) or bar . Any joint shall be capable ofdisconnection only be means of a tool .

Regulation- 542.4.2. does not stipulate aparticular-arrangement . for the means of disconnection . ( Any suitable- arrangement may be used which meets all the requirementsstated in the Regulation )

2394:- So what is suitable-arrangements. in which case the ( Earthing-conductor ) iswithdrawn for its ( Terminal ) atthe main-earthing-terminal . by the useof a Tool - Screwdriver . 2394 inorder to facilitate the résistance-measurement . ofmeans of earthing .

Forthe sake of -&-s here . “ Safety “ ( Earthing-conductor ) thenreplaced & re-secured into the terminal after the measurement hasbeen made .

(MET ) incorporating a ( Bolted-link ) which isopened or re-moved by the use of a Toll ( Spanner ) in order to disconnect the ( Earthing-conductor ) & then replaced & re-secured after the résistance-measurement to the means of earthing has been carried-out.

TheRegulation are telling us - whatever ( Arrangement ) is provided as the means fordisconnection . of theEarthing-conductor .

Inaddition to the requirements of Regulation - 542.4.2. Thisrequirements of the . Electricity atWork Regulations & these of Section- 522 - BS-7671:2011: must be Met .

Regulation - 9 . of the Electricityat Work Regulations . requires that .
“ if acircuit-conductor is connected toearth or to any other reference-point . nothing which might reasonably be expected to ( give rise to Danger ) by breaking theelectrical-continuity or introducing . high-impedance shall be placed in that ( Conductor ) unless suitable-precautions are taken toprevent that - “ Danger “

Wherea . joint or bolted-link is provided . it must be arranged to ensurethe ( Integrity ofthe conductor ) theconnection or link . must not be able to be re-moved insuch a way as . would give rise to “ Danger “ ( Ways of achieving this )

□ Disconnection requires a deliberate-act using a Tool .
□ The Joint or Link should be ( Accessible-only ) .when the installation is ( Isolated )
□ The Joint or Link should be ( Accessible ) toSkilled-persons - Only .

Section- 522 . requires that the means fordisconnection must be protected . where necessary against . External-influences.

What- External-influences !! . Vandalism . Unauthorized-interference . Damp . Corrosion . Dust . Vibration or mechanical-impact .

 

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2394: What Implications’ - 132.16. . this one will work its way into Exams .

Additions& Alterations to an installation .

We’llgo by the book . BS-7671:2011:
“ No addition or alteration . temporary or permanent. shall be made to an . existing-installation . unless it has been ascertained that the. rating & the condition of any existing-equipment . including that of the distributor . willbe adequate for the . altered-circumstances . furthermore . the ( Earthing& Bonding-arrangements ) if necessary for the protective-measure applied for the safety of the addition or alteration . shall be adequate .

Adequacy of the Existing-installation . is therefore required to be assessed in three-areas .
- Existing-equipment . including that of the supply . which mayhave to carry - increased-load .
(T) - Earthing and Bonding-arrangements.
- Certain additional-considerations .

(T) - Existing . Earthing and Bonding-arrangements (Assessing the adequacy & suitability of the existing-earthing& bonding-arrangements ) Upgrading .10.0mm[SUP]2 [/SUP]

-Establishing the suitability of the meansof earthing in respect of its type - such as a PME-earthing-terminal or anEarth-rod . & condition .
asan Inspector your looking for . Corroded . damaged . inaccessible .

2394{- most-important-Test . “ Verification “ of the means of earthing by . determination of theexternal-earth-fault-loop-impedance - (Ze ) Regulation - 313.1.

If - ( Ze ) is determined by . ( theRegulations remind us - “ Methods of determining ( Ze ) at least one of the Three-methods ) must be used to determine ( Ze ) .
i). Enquiry .
ii). Calculation .
Itis necessary also to obtain a measured-value to “ Verify “ that the intended-means of earthing is both present andof the expected-value . ( by - measurement Ω )

2394{- in our case here . Only “ (iii) . Measurement “

Determination of external-earth-fault-loop-impedance -at the Origin of the installation . The importance of determining the normal-range of - ( Ze )
Theeffectiveness of the measures of ( Fault-protection ) against thermal-effects & protection against . earth-fault-current in each-circuit of an installation depends on the value of ( Ze ) this is because ( Ze ) contributes to the . total-earth-fault-loop-impedance - ( Zs ) of each-circuit . it is therefore essential that in the design of an installation . account is taken of anychanges that can reasonably be expectedto occur in the value of ( Ze during the life of the installation )

- With the possible ( Exception ) ofa supply from a privately-owned-generator.
Itmust generally be presumed that whateverthe source of supply to an installation . ( changes may occur in the value of Ze atsome time during the life of theinstallation )

- Ascertainingthat the ( Earth-conductor ) isof adequate . cross-sectional-area . mm[SUP]2[/SUP]
The ( Earthing-conductor ) ofan electrical-installation is the . ( Protective-conductor-connecting ) the Main-earthing-terminal - (MET )

(T) - . 2394 {- Means for disconnecting the -Earthing-conductor .
542.4.2. requires means for disconnecting of the . earthing-conductor. to be provided at or near the ( MET )of an installation to facilitate ( Measurement of the résistance ) of the earthing-arrangements.

 

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Additional- Considerations . ◄ ( Wording )

Additional- considerations relating to the . ( Existing-installation ) or any effects that the ( Addition or Alteration ) may have upon it .

Point to Note : not specifically mentioned in Regulation - 131.16. are covered by . other - requirements of BS-7671:2011: making them . applicable .

Grouping-effects.

Rating of all cables . in the wiring-system ( both Existing & the Proposed-additional-cables ) must beassessed to take account of any .additional heat generated by the larger-grouping . & be de-rated as necessary . if theexisting-cables would not be adequate when de-rated . then one option would be to install the .new-cables separately from theexisting-group .

Isolation & Switching .
New-circuit(s) may place - additional-load . on theexisting-isolation &switching-devices . which have to be “ Verified “ as being adequate for the increased-load . New-equipment may have particular-requirements for isolation & switching that must be Met .

- if a . new-circuit is the supply a .discharge-lamp-operating at thevoltage exceeding ( LV) low-voltage . a fire-fighter’s switch would be required Regulation - 537.6.1.

 

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Upgrading of an - Existing-installation . Where-necessary .

Whenan ( Existing-installation ) is not adequate to support aproposed-addition or alteration safely the work . must NOT - proceed.

- The ( Client ) must be . advised - Immediately . & preferably in writing .
- The necessary-upgrading-work . should be recommended to the . ( Client )
- When the . ( Client - consent ) has been given . the upgrading-work should be completed ( Before ) the additionor alteration is put into ( Service )

 

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Upgrading - Work . necessary toenable an installation to . safety accommodate the . Addition or Alteration .

- replacementof any equipment or cabling having-defects . Omissions . Damage or minor-deterioration .
- replacement or upgrading of existing-equipment in theinstallation where its rating is notadequate .
- addition to . or upgrading of ( Main-protective-bonding-conductor ) inan installation relying on the ( Protective-measures - ADS ) for protectionagainst electric-shock . if the ( C.S.A. ) of the exciting bonding-conductor(s) is found to be less than that required - BS-7671: the installer . of the addition oralteration will need to make . a Judgement as to the suitability of those conductor(s) & whether the . new-work mayproceed .

If Exceptionally ) it isdecided that it is safe to proceed . with the new-work without upgrading the ( Equipotential-bonding )the client should be advised that the . ( Bonding ) should be upgraded to the current -standard at the earliest-opportunity .

- replacementof any . voltage-operated-earth-leakage-circuit-breakers . with residual-current-devices- RCDs . if fault-protection relies upon the successful operation of thecircuit-breaker(s) . this would be necessary to ensure compliance with theapplicable Regulations’ in BS-7671: that requires an RCD to be provided .

Whereprotection against electric-shock isprovided by ( ADS ) Regulation -411.3.3. Additional-protection .
411.4. - TN-system . 411.5. TT- systems . require an RCD to be used under . certain-conditions .

A voltage-operated-earth-leakage-circuit-breaker would not be considered to provide adequate protection in such conditions - it does not comply with the requirements of BS-7671:2011:

 

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Chapter- 61 contains the requirements for . Initial-Verification . Inspection & testing must be performed to confirm the adequacy & suitability .

- The relevant-parts of the existing-installation . tosupport the changed-requirement .
- The upgrading of the existing-installation . necessary to support the addition or alteration .
-The addition or alteration itself .

Certification:

Regulation- 610.4 . requires that compliance with . BS-7671:2011: is Verified for every ( Addition or Alteration ) Chapter - 63 contains requirements for . Certification & Reporting . in respectof electrical-installation(s)

631.1. & 631.3. which requires an . ( EIC) or ( MEIWC ) given details of the extent of the . installation covered by the certificate . together with a ( Record ) -Schedule of the Inspection & the ( Results ) - Schedule of testing . be issued the . “ Verification“ of the installation . New or Changes to an existing-installation - required by Chapter - 61 . The ( DEIC ) may be used . under appropriate-conditions . as an alternative to the ( EIC )

Where minor-electrical-installation-work .does not include the provision of a new-circuit . Only for the purposes of BS-7671: a minor-electrical-installation-works-certificate may be issued for ( Each-circuit ) towhich an . alteration is made . insteadof an ( EIC ) of ( DEIC ) - 631.3

 

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Facts. 2394: Itcannot be predicted - where in the range a . Circuit-breaker will Trip . Not -RCBOs

 

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Fault-current:

Prospective.

Themeaning of “ everyrelevant point “ Regulation - 434.1.
Whatis meant by the word . “ Every relevant point “ in - 434.1. that is the regulation requiresthe ( PFC ) at every-relevant-point of the installation - to be determined

Quite-simply “ Everyrelevant point “ means
Every-point where . for reasons of confirming-compliancewith . One or More of the requirements of . BS-7671:2011: it is necessary to determine the ( PFC )

434.1. Determination of ( PFC )
The prospective-fault-current . shall bedetermined at every-relevant-point of the installation . this shall be done by .Calculation . Measurement . or Enquiry .

Forthe installation . suppose it is being checked whether the .rated-short-circuit-breaking-capacity of each . fault-current-protective-device . is at least-equal to the . prospective-short-circuit . or prospective-earth-fault-current at the point where the device is installed . Regulation - 434.5.1. requires each-device to have sucha breaking-capacity . except where appropriate back-up-protection is provided by another device or devices . on the supply-side .

 

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Typesof fault-condition .

Thereare . two-basic types offault-conditions .

A- Short-circuit . this is any fault between live-conductors . that is Three-line . Line-to-Line. Line-to-neutral .
An- Earth-fault . this is a fault between a Line-conductor & an . exposed-conductive-part or the protective-conductor of the circuit .


Resistance & Inductive reactance-values for cable(s) ….. ( r ) & ( x )

Live-conductor(s)

Exceptfor fault-loop . where the impedance is manly due to largesingle-core-cables in flat-formation .values of résistance & inductive reactance for live conductors of most types of cables in common use can be obtained from voltage-drop-tables . in appendix 4 . Values of inductive reactance can also be calculated where . necessary.

Thevalues of ( r ) & ( x ) in tables in appendix - 4. correspond to résistance & inductive reactance . respectively in units of ( mV/A/m ) the equivalent of . milliohms-per-metre . for conductorssizes of up to 16mm[SUP]2[/SUP]. separate-values of ( r) & ( x ) are not given in the tables . because the . inductive-reactancefor such sizes of conductor is negligible compared with the . résistance & may beignored . the single-value of ( mV/A/m ) for conductor-size of up to 16mm[SUP]2 [/SUP] should be taken as the value of ( r )

Inorder to be used in . calculations of .prospective-fault-current . the tabulated-values of ( r) & ( x ) have to be divided by ( 2 ) inthe case of . two-core-cables . &for two-single-core-cables . used for single-phase . & by ( √3 ) in the case three-core . & four-core-cables . & for three or four-single-core-cables . usedfor three-phase .

Togive values of résistance & inductive reactance for a conductor . of a given-length the . ( r ) & ( x ) values - duly-divided by ( 2) or ( √3 ) as applicable . are divided by . 1000 . so as to give the .answer in Ohms rather than . milliohms .& multiplied by the conductor-length in metres .

Consider. a single-phase . circuit consisting of a . 30metre-run of two - 50mm[SUP]2[/SUP]. thermoplastic - ( PVC ) insulated-copper-cables . installed in trunking - reference - method . B

The- tabulated-value of ( r ) & ( x ) given in column . 3 of table -4D1B . appendix - 4
( r) = 0.95 . mV/A/m .
(x ) = 0.30. mV/A/m .

The value of résistance ( r ) foreither the line-conductor . orneutral-conductor is therefore given .by ( R = 0.95 x 30 ------- 2 x 1000 = 0.0143Ω )

Similarly. the value of . inductive reactance ( x ) foreither the . line-conductor . or neutral-conductor is given by . ( X = 0.3 x 30 ------ 2 x 1000 = 0.0045Ω )

I stop there .

 

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2394:This is Only a Learning-curve . taken form - Old / Note . 16[SUP]th[/SUP] Edition / tweaked to 17[SUP]th[/SUP] Edition . [ Getting my way around - O.S.G. ] :svengo:

• Two- 25mm[SUP]2[/SUP] single-core ( PVC ) insulated-cables - copper-conductor(s) are drawninto . ( PVC - conduit ) along with a 10mm[SUP]2 [/SUP]protective-conductor to feed a 230V - industrial - heater .

Thefollowing details are RELEVANT .
Protective-device:- protection atthe Origin by - 80A BS-88 fuses .
Thetested-value of ( Ze ) at the cables-Origin is - 0.35Ω .
Thelength of cables-run is 55m .

(a) Establish the :
i) . value of . ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) of the cables .
ii). prospective-earth-fault-loop-impedance ( Ief )
iii). the disconnection-time of the fuse .

(b). does the clearance-time comply with - BS-7671:

(a) - (i) Using the - O.S.G.
FromTable - 11 . ( R[SUP]1[/SUP] + R[SUP]2[/SUP]) for 25mm[SUP]2[/SUP] / 10mm[SUP]2 [/SUP]cables ( Colum -8 ) = 2.557 .
FromTable - 13 . apply the factor . 1.20. 70°C

Thus- ( R[SUP]1[/SUP] + R[SUP]2[/SUP]) = 55m x 2.557 x 1.20 ÷ 1000 = 1.68762 . rounded up to = 0.169Ω .

So- ( Zs ) at distribution-board = 0.35Ω + 0.169Ω = 0.519Ω .

ii). Prospective-earth-fault-current - ( Ief ) = 230 ÷ 0.519Ω = 443A .

iii). & (b) amleaving out .


O.S.G.- Table - 11 / 12 / 13 .
Multipliersto be applied to Table 11 . to calculate conductors-résistance at maximum-operating-temperature ( note - 3 ) for standard-devices ( note - 4 )
Table- 12 . Ambient-temperature .multiplier to Table - 11 .

O.S.G.- simplifies . “ Genetic “ Protective-devices . Fuses . Circuit-breaker - BS-EN-60898 . BS-3871-1 . part/ 1 ◄ . Wording

► Point to Note : Incorporated in acable or bunched - note - 2 . ( Cf 1.20 ) see Table - 54.3 . BS-7671:2011: which applies where the .protective-conductor is a . core in a cable or is bunched with cables .

(note - 3 ) The multipliers given in Table - 13 . for bothcopper & aluminium-conductors arebased on a [ simplification of the formula given in . BS-EN-60228 . namely that the . résistance- temperature - coefficient is . 0.004per °C at 20°C ]

(note - 4 ) Standard-devices are these described in appendix - 3 . of BS-7671:2011:

 

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2394:simplified : O.S.G. - Table - A2

A2- from the O.S.G. to apply-diversity-factors . we can find the . Assumed-current.
“ Shower “ No-diversity .row - (5) 10.000 : 10000 ÷ 230V = 43.47A . rounded up to . 45A -circuit-breaker .

Because it does not say “ Shower “ people do get confused .
Settingthe record / Straight . A2 / (5) Water-heater. ( Instantaneous - type . “ Shower “ ) power-circuit .

 

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Cooker- (3) of table .
12.000 - 12000W ÷ 230V = 52A. ( fL ) full-load . you are going to applying diversity

First 10A off . 52A is 42A

Table- A2 . Colum - (3) Cooking-appliances .

O.S.G.simplifies . Individual-household-installation .

First - 10A & 30% of remainder . [ 42 x 30% = 12.6A ] for your calculator . 42 x 0.3 = 12.6A.

First - 10A
30% ofremainder = 12.6A .

Total of : 10A + 12.6 = 22.6A .

10A + 30% ( fl ) full-load . ofconnected-cooking-appliances inexcess of . 10A + ( 5A ) ◄► if a socket-outlet is incorporated in the control-unit .

Total of : 10A + 12 = 22A . 22A + 5A = 27A.

 

[rugbyspark]

2394:simplified : O.S.G. - Table - A2

A2- from the O.S.G. to apply-diversity-factors . we can find the . Assumed-current.
“ Shower “ No-diversity .row - (5) 10.000 : 10000 ÷ 230V = 43.47A . rounded up to . 45A -circuit-breaker .

Because it does not say “ Shower “ people do get confused .
Settingthe record / Straight . A2 / (5) Water-heater. ( Instantaneous - type . “ Shower “ ) power-circuit .

Hi there Amberleaf,
Your posts are very helpful and good reminders, thanks.
I imagine you must be a lecturer yourself.

BUT, please use a spell checker and for clarity I would recommend "Times Roman" font.
Also when using words have a space between them, spell checker will show them up.
ie, such as above (Settingthe).
Then, as I have seen earlier an opportunity to download your complete synopsis would be gratefully received, no doubt by all your readers.
Thanks once again.

 

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Table- A2 . Lighting : row (1) Individual-household .

2000W ÷ 230V = 8.69 x 66% = 5.73A . [ for your calculator 8.69 x 0.66 = 5.73A ]

66% oftotal-current-demand .

Rugbyspark . Thank you .

When I send anything down into the forum . its normal from my computer . sorry about theclosing up of words . its sincethe forum changed over . ??