Re-take - Useful Information for 2394 :

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Pleaseread - carefully .

Earth-fault-loop-impedance:
Theearth-fault-loop-impedance ( Zs ) at any point in a circuit . is made up of theearth-fault-loop-impedance ( Ze ) of that part of the system external to the installation plus the sum of the impedances . in the Line and protective-conductors in the installation ( Z[SUP]1[/SUP] & Z[SUP]2[/SUP] )

Note : that for circuits rated at . Less than 100A and operating at the supply-frequency not exceeding 50Hz . it is generally considered acceptable to ignore . Inductive-reactance & to replace ( Z[SUP]1[/SUP] & Z[SUP]2[/SUP] ) by ( R[SUP]1[/SUP] & R[SUP]2[/SUP] ) the résistances of the . Line and protective-conductors .

Zs = Ze + ( R[SUP]1[/SUP] & R[SUP]2[/SUP] )

 

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Basic: 2394 :

Protective-equipotential-bonding- ( Bonding for short ) is sometimes confused with .Earthing . even resulting occasionally in the use of the meaninglessterm - “ Earth-Bonding “

Bonding“ is quite distinct form . Earthing in its. Purpose . its general-arrangement . & inmany of the requirements of BS-7671: - That it has to Satisfy .

Thepurpose of ( Earthing ) whereused for the . protective-purposes . within aninstallation . ( is to limit the Duration of the voltages ) :icon_bs:

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

 

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Distribution-Network-Operator - ( D.N.O. ) :banghead:

2394. What we should NOT - DO .

(i). Responsibility for Earthing :

Where it is necessary for an installation to be . Earthed to meet the requirements for safety . it is the consumer’s -responsibility to ensure the installation is correctly-earthed . This is because . in order to receive a supply . the consumer is required to have an installation that . meets the safety-requirements of regulations . 26(1) & 26(2) of the . Electricity Safety. Quality & Continuity Regulations . 2002 - ( ESQCR )

Thesafety-requirements of . Regulation 26(1) & 26(2) are that the consumer’s installation is so constructed . installed . protected & used or arranged for use so as to prevent . so far is reasonably-practicable . danger or interference with the . D.N.O. or withsupplies to others . a consumer’s -installation that complies with . BS-7671 : is deemed to meet these requirements .

2394: this is the bit you are interested in .
Inpractice the . electrical-contractor . on behalf of the Consumer . should ensure that the installation iscorrectly-earthed . before issuing an .( EIC ) Electrical-Installation-Certificate. or where applicable . a Domestic-Electrical-Installation-Certificate. ( DEIC )

(ii). New-supply-connections - distributors. Obligation to provide an . Earthing-terminal .

D.N.O.- An electricity-distributor is obliged to provide anearthing-terminal for the consumer’s use. in the case of anew-supply-connection at ( LV) Low-voltage . except where this is inappropriate for . safety-reasons . - Regulation - 24(4) of the ( ESQCR refer ) a . distributor is NOT obliged to provide an .earthing-terminal in the case of an . existing-supply-connection . but may bewilling to do so.

Wherean . earthing-terminal is provided by the electricity-distributor . the distributor is responsible for ensuring that the terminal & its . Earthing-connection . tothe D.N.O. are installed & . so far as . reasonably-practicable . maintained so as to prevent danger . &are suitable for the purpose -Regulation - 24(1) of the ( ESQCR )

Nevertheless:- the Installer . or Contractor . on behalf of the consumer . must-ensure that theearthing-terminal is suitable for the requirements . of the installation concerned . & that it is properly-connected to . the Main-earthing-terminal - ( MET ) of the installation .

(iii). Basic-design .
Itis important to establish at an early-stage of the design . either of a New-installation . or an . Alteration or Addition to an Existing-installation . whetheran earthing-terminal for the consumer’suse . is already-available at the ( Service-position ) wherethere is ( NO) such terminal . it should be ascertained whether the distributor is prepared to make one-available .

2394: Do We Need a “ Reason “

Theeffectiveness of any existing-earthing-terminal . & its connections to the D.N.O. should be established . this should be done both by ( Inspection & by Measurement ) of the .External-earth-fault-loop-impedance - ( Ze )

2394: That’s why you get this on Exams . “ Recognition “

Forall installations . the Type of Earthing-systems . needs to be established . & the appropriate-arrangementsmade for connecting the ( MET ) main-earthing-terminal . of that installation with-Earth .

TN-C-S. system whereprotective-multiple-earthing - ( PME ) is provided . means have to be provided for the ( MET ) to be connected by the . D.N.O. to the Neutral of the source of energy . Regulation - 542.1.3. - Installation-earthing-arrangements .

( Whereno earthing-terminal is available at theservice-position ) the D.N.O. is NOT prepared to make-one-available . theinstallation will need to beconnected with Earth . by its own-electrically-independent-earth-electrode . Regulation - 542.1.2.3. in such . circumstances the requirements applicable to a TT- system have to be MET.

The “ Metal-work “ of a “ Gas. Water or other service-pipe must NOT be USED ) inany circumstances . be used as an .Earth-electrode for safety-purposes. this does not-preclude the bonding of such . metalwork whererequired by . Section - 411 . Regulation- 542.2.6. refers

(iv). Cable “ Sheath “ earthing . the contractor should NOT make the connection to the ( Metallic-sheath or Armour )

Where “ Cable-sheath “ earthing is provided ( TN-S system ) the earthing-connection to the distributors-metallic-cable-sheath or armour is made by the . distributor generally-prior to the electricity-metering-equipment beinginstalled . however . there areoccasions when such an earthing-connection has not been made & no earthing-terminal is available .

D.N.O.- Under-No-Circumstances . should the electrical-installation-contractor-clamp. sweat or in any other-way connect the consumer’s Earthing-conductor the distributor’s metal-cable-sheath or armour . the cable is the D.N.O. - property & the contractor is Not Authorized to Interfere with it .

Any-attempt by the contractor to make a ( Connection )to the metallic-cable-sheath or armour could result in an .Internal-fault . between the conductors. of the cable or between the metallic-sheath or armour . & one or more conductors . such-faults can lead to . injuries due to the . explosive-effects of arcing-current & / or by any associated fire or flames .

 

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Facts: BS-951 Earth-clamp . What to look out for .

Firstly: 27/9/12 . N***** - Inspector .because it is an Exiting-installation . he used an .Domestic-electrical-installation-condition-report .

Typeof Earthing-systems . My system is an . TN-S .

D.N.O. - Under-No-Circumstances . should the electrical-installation-contractor ( clamp ) .sweat or in any other-way connect the consumer’s Earthing-conductor the distributor’s metal-cable-sheath or armour . the cable is the D.N.O. - property & the contractor is Not Authorized to Interfere with it .

Someperson has done this . put on a BS-951 . Earth-clamp . the Inspector took a reading . ( Very-Low Ω ) he could move it by using two-finger . :icon13:

Inspector has putthis on . the Certificate . for the Attention of the “ Client “ . So its in Writing .

Metallic-cable-sheath or armour could result in an .Internal-fault . between the conductors .

 

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Electricity is Invisible . this initself makes it dangerous .

Stability of Résistance .

Clause 18.2.4.3. - of BS-7430 :1998 . States .

That an . Earth-electrode-résistance . which is in the excess of ( 100Ω ) may beunstable . although this statement is made in the contents ofan . Earth-electrode used for eathing a Generator. it is equally true for ( say ) the Earth-electrode of aninstallation forming part of a TT- system . However - Note-2 of Table 41.5 in BS-7671:2011: requires the résistance of the . Earth-electrode to be as . Low as practicable . & a value 200Ω . may not be stable .

The Use ofAdditional-Earth-Electrode(s)

Where the résistance of a single-electrode . is Unacceptably-high . a number of such electrodes’ may be connected in ( Parallel ) Clause- 10.2. of BS-7430 :1998 . States . that where a number of ( Vertical-rod or pipes-earth-electrode(s) are so connected . the combined résistance is then practically-proportional to the reciprocal of
thenumber-employed . provided thateach is situated outside the résistance-area . of any other . the same clause-states that . inpractice . it is often assumed that such-rods or pipes are outside of each-others-résistance-area . if the mutual-separation-distance is not ( Less than the driven depth ) the cause also mentions that little is to be gained by a separation beyond twice the driven-depth .


Useful-Junk: 2394: you will not get this on Exams .

Determining. Touch-Voltage - (Ze x Rated . mA / IΔn / RCD )

TT-system - Ze /200Ω < Main-RCD is rated ( 100mA )

200Ω x 100mA ÷ 1000 = 20V ……. ( 100mA x 20Ω ÷ 1000 = 2V /Touch-voltage .

 

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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.

 

[amberleaf]

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 . ??

 

[amberleaf]

Trying this out . changed mysettings to .” Times Roman “ font

Calculate the speed at which a four-pole synchronous motor will run from a50Hz supply

f = n x p .
∴ 50 = n x 2 ( 4 poles gives 2 -pairs )
∴ n = 50 / 2 .
= 25 revs .

 

[amberleaf]

Q) 2394 : The Regulations are designed to protect ( Who & what ) : Persons .Property . Livestock .

BS-7671: Wiring Regulations 2008:2011: ( 17[SUP]th[/SUP]Edition ) is the British standard for electrical installation in the United Kingdom. it is a non-statutory document . the purpose of the wiring regulations is toprotect - persons . property and livestock . from harm which could arise from theuse or presence of electricity .

Regulations are designed to protect . “ Property “ RCDs provide someprotection against electrical fires .

 

[amberleaf]

BS-3871 replaced by BS-EN-60898 . there still out there .for years to come .
Miniature circuit breaker(s) BS-3871-1 .cant stress this enough ( part - 1 ) M1 to M9 . that’s what Inspectionis all about .

“ Room for improvement “ ( is the protective device BS-3871 . BS-EN-60898 )
Can we alter it from an Circuit breaker to an RCBO ? one option .

There is no requirement to change the consumer unit if you are installing anew final circuit . various requirements to provide mechanical protection . orRCD protection to the installed wiring & socket outlets . 411.3.3 .522.6.101 . 522.6.102 .

2394 : keep in mind : BS-7671:2008:2011 . does notdefine a kitchen as a special location .

( BR ) covering Approved Documents P . kitchen(s)
Is defined in the Building Regulations as a “ room or part of a room whichcontains a sink & food preparation facilities “

There can be some misunderstanding of correct terminology . Earthingconductor . upgraded to 16.00mm[SUP]2[/SUP] . ◄ This is the importantone .
Main protective bonding conductor 10.00mm[SUP]2[/SUP] .

Pont to note : Isolation & Switching .??
BS-EN-60898 . circuit breaker . Yes
( Genetic - RCD ) BS-EN-61009-1 .RCBO . Yes
BS-3871 replaced . This is the one you have to be awareof . can we use this to isolate .


2394: take it in the contents that its meant .
A Street is short . A Road is long . what you put In you willget Out . Studying .

 

[amberleaf]

2394: What’s in a Book .
O.S.G. Simplifies

GN-3 . tells us where . The Tables in this appendix are as Appendix 2 ofthe O.S.G. .
The Tables provide ( Maximum ) permissiblemeasured earth fault loop impedance ( Zs ) 612.9 . “ Circuit-loop-impedance “

For compliance with BS-7671 where conventional final circuits are used .the values are those that must not be exceeded in the tests described at a testambient temperature of ( 10°C to 20°C ) 411.4.6. 411.4.7. 411.4.8. 543.1.3.

( Protective device(s) “ Genetic “ Fuse . Circuit breaker .
411.4.6. Where a fuse is used . Etc . ( ► 0.4s ) watch the wording )
411.4.7. Where a circuit breaker is used . ( re-minder the values specified in Table 41.3 for thetypes & ratings of overcurrent devices listed may be used instead of calculation )
411.4.8. where a fuse is used for a distribution circuit or final circuit .Etc . ( ► 5s ) watch the wording)
543.1.3. C.S.A. where calculated shall be not less than the valuedetermined by the . Etc

Regulations
Tables 54.2. p.161 . where the assumedinitial temperature is ( 30°C ) ◄

O.S.G. P.184 . Note 1 . see Table 54.3 ofBS-7671: which applies where the protective conductor is not incorporated or bunchedwith cables . or for bare protective conductors in contact with cables covering. ( 70°C ) ◄

O.S.G. P.184 . Note 2 .see Table 54.3 ofBS-7671: which applies where the protective conductor is a core in a cable oris bunched with cables

 

[amberleaf]

Taken form old note . & tweaked . Leaning curve .

Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

Zs - Circuit-loop-impedance .

Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )
Zs ) circuit-loop-impedance

The resistance of these conductors can be obtained from .
O.S.G. - Table 11 .
GN-3 p107 tells us . Maximum permissiblemeasured earth fault loop impedance .

Shower circuit . 30m in length is wired in . 6.0mm[SUP]2[/SUP] / 2.5mm[SUP]2[/SUP] cable.
BS-1361 . BS-88-3 32A fuse . Ze is given as (0.15Ω )

Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] )

6.0mm[SUP]2[/SUP] = 3.08 mΩ/m . 2.5mm[SUP]2[/SUP] = 7.41 mΩ/m .
Note : 6.0mm[SUP]2[/SUP] /2.5mm[SUP]2[/SUP] =10.49Ω . O.S.G. table - 11 ( 20°C )

Ze ) - 0.15Ω . length = 30m . multiplying factor 1.2

Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) x lengthx multiplier ---- 1000 .

Zs ) = 0.15 + ( 10.49 x 30 x 1.2 ) --- 1000 . = 0.15 + 0.38 = 0.53Ω

 

[amberleaf]

(AMD ) - the Assumed MaximumDemand can be still greater than the supply fuse . you will find that thesupply fuse has been in place for manyyears . & never been a problem . because of diversity .

Mostoff the time . 2394 : We are using. consumer-units with split-loads .

 

[amberleaf]

What is the requirements of Part - P . from Extracts .

2005 it is a legal requirement for all work of fixed electricalinstallations in dwellings and associated buildings to comply with relevantstandards .
The relevant UKstandard is BS-7671: Requirements for electrical installation . the IET wiringregulations - 17[SUP]th[/SUP] Edition .
As . BS-7671:2008:2011: covers requirements for . design . installation .inspection . testing . Verification . Certification .

re-minder 2394:

Notifiable work includes new installation(s) house re-wires . and theinstallation of a new circuit(s)
Notifiable work also includes addition(s) toexisting circuits in kitchens . bathrooms .outdoors and in other special locations .

Non - notifiable :
- Replacing accessories such as socket-outlets . cooker - switch andceiling rose(s)
- Replacing the cable for a single circuit only . where damaged . by fire .rodent or impact .

impact
on condition that the replacement cable has the same current carryingcapacity . follows the same route and does not serve more that one sub -circuit through a consumer unit .

- re - fixing or replacing the enclosures of existing installationcomponents :- if the circuit(s) protective measures are unaffected by increasedthermal insulation .
- installing or upgrading main or supplementary equipotential bonding :- suchwork shall comply with other applicable legislation . such as the Gas Safety - installationand use Regulations .

- Work that is not in a kitchen or special location and does not involve aspecial installation and consists of .
• Adding lighting point - light fittings &switches to an existing circuit(s)
• Adding socket-outlet and fused spurs to an exitingring or radial circuit(s)
Only : if the existing circuit protective device is suitable and provideprotection for the modified circuit . and other relevant safety provisions aresatisfactory .

BS-7671:2008:2011:recommend that the voltage drop in a circuit should not exceed a certainpercentage of the volte at the Origin of a circuit .

Percentage is 3% for lighting .
Percentage is 5% for power . powercircuit 5 x 230V ÷ 100 = 11.5V

Uo / 230V single - phase supply the voltage drop on a lighting circuitshould not exceed ( 3% of 230V ) 3 x 230V ÷ 100 = 6.9V

This will creep into the Exams .

 

[amberleaf]

Useful Junk . taken from Extracts .

Main protective bonding for boilers .
There is No Requirement with BS-7671: to provide supplementary protectivebonding to the pipework connected to domestic boilers . however there is a requirementto provide main protective bonding to central heating systems . although nospecific detail is provided where the bonding conductor should be connected . youwill be advised this could be connected at the flow or return pipes of the boiler.

However in a domestic central heating installation it may be that centralheating pipework is not considered as an ( Extraneous conductive part ) andmain protective bonding would then not be required . the decision ultimatelylies with the installation designer to determine what is not an ( Extraneousconductive part )

 

[amberleaf]

Useful-Junk

“ De-NeutralisingBlack “ Blast from the Past

Underthe new indemnification colours for fixed-wiring introduced by Amendment - 2 . to BS-7671: Black is now used to indentify a ( Phase-conductor . Not a Neutral ofcourse ) . all single-phase applications. it would be preferable to use cables .marked for such use . that is with brown . blue . green-and-yellow . cores

Breaking the Black /Neutral association .

Wherethree-core cables marked in the . New three-phase colours used . for single-phase applications . it isproposed that . as a convention . the Black-core is ( Usedfor the Protective-conductor ) the Brown for the .phase-conductor . andthe ( Gray for the Neutral ) This convention is intended to break . theassociation between Black andNeutral . it mean that the ( Black-corewould normally be overmarked . Green-and-yellow . and the ( Gray-core overmarked Blue or ( N ) the Brown-core would not need additional-marking .

 

[amberleaf]

Useful-Junk

“ De-NeutralisingBlack “

Where SWA - cables with Brown. Black and Gary -cores . are used for Street-lighting applications . the ( Black-core ) being used as a circuit-protective-conductor in parallel with the .Armouring to minimise circuit-lengths .

Fire-alarm system’s

Applying the same convention to a ( Flat-three-core ) fire-alarm - interlink cable . the Gray would be overmarked as the ( Neutral) and the Black - interlink overmarked Brown .

3- core & Earth .
Brown- Phase-conductor .
Black- . overmarked brown .
Gray- Neutral . overmarked blue .
Earth is Earth .

 

[amberleaf]

Approved Document P . 2005 - Extracts .

There are Two : simply - stated . Legal-requirements .

the first isthat .
“Reasonable provision shall be made in the design . installation . inspection and testing of electrical -installation in order to protect persons from fire or injury .

The second requirement is that .
“ Sufficient-information shall be provided so that persons wishing to operate .maintain or alter an electrical-installation . cando so with reasonable-safety .

My- Limitations . on the application of the requirements .
Yes : p.16 / 2008.
Therequirements of this . Part apply only to electrical-installations . that areintended to . operate at . Low or Extra-low voltage .

Installation(s) in Dwellings . To operate at . Low or Extra-low-voltage . The Extra-low-voltage band was included to cover such things as . Extra-low-voltage downlights . cause of a number of house - fires .

 

[amberleaf]

Medical-Grounds . Equipment . ESC .

I have posted this for a reason. ( SPDs ) which can be used in Domestic - installations.

Q) . Is it necessary to install . Surge-protective-devices . indomestic and similar premises .

Generally No .

However . where a risk-assessment is carried out and this indicates that unacceptable-consequences-exit . such as to human-life . ( as a result of damage to essential-medical-equipment ) Example .

( SPDs ) must be installed . in addition . where the consequences of equipment-failure due to an . Overvoltage are deemed to be unacceptable after discussion with the customer . ( SPDs ) protection should be provided .

 

[amberleaf]

GN-3 - p70 . Periodic-Inspection . (Take nothing for Granted )

2394 : With any . New-Installation . re-wire . it does not mean that the . DNO - Electrical-intake-equipment. is New . ( Visual - inspection )
GN-3 . and Regulations . reminds us .

Example . checklistof items that require - inspection .
The following is acopy of the checklist in . Appendix - 6 . BS-7671:2008:2011: which lists items at various-locations within an installation that may requireinspection .

Electrical-intake-equipment. GN-3

Service-cable .
Service-cut-out /fuse .
Meter-tails -Distributor .
Meter-tails -Consumer .
Metering-equipment .
Isolator .

Distributor’s / Supply-intake-equipment .

BS-7671:2008:2011: P.400 . Condition-Report-Inspection-Schedule .

Service-cable . -condition .
Condition of - service-head.
Condition of - tails- Distributor .
Condition of - tails- Consumer .
metering-equipment .
Condition of isolator - where-present .

 

[amberleaf]

Youwill use BS-7671:2011: as the documentagainst which a professional judgement needs to be made . along with theRegulations .

The Regulations Must - State the Facts .

MultipleChoice Questions from all Sections . 2394 : those will come in Handy . 2008:2011:

Contactof persons or livestockwith exposed-conductive-parts which have become live-under-fault-conditions .is referred to as .
• Basic-protection .
• Fault-protection .
• Electric-shock .
• Earthing .

▲ Regulation - p.28 . ( By definition )
Fault-protection: Protection against electric-shock under single-fault-conditions .

▲ Note : for low voltage installations . systems aequipment . 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 becomelive under fault-conditions )

The disconnection of the nearest “ appropriate “ protection-device is called : ( All in the Wording . Yeah )
• Discrimination.
• Diversity .
• BS-EN-60898 .
• 30mA RCD .

▲ Regulation - p.26 .
Abilityof a protective-device to operate in preference to another protective device inSeries .

Ring-final-circuit. NOT exceeding 32A must disconnect within :
• 5 seconds .
• 300mS .
• 40mS .
• 0.4 seconds .

▲ Regulation - p.53 . 411.3.2.2.
Themaximum disconnection-time stated in Table - 41.1. . shall be applied tofinal-circuits Not exceeding 32A . ( 0.4s tells us it’s a TN - system )

Whichof the following devices would be suitable for protecting a . 9.5kW shower:
• BS-88-2 .
• BS-88-3 .
• 30mA RCD.
• 100mA RCD .

▲ Manufactureinstructions - New shower fitted andthe ( Manual )says an RCD must be fitted . it is a requirement of BS-7671:2011: that all equipment is installed in accordance with the . manufacturer’s instructions and documentation.
▲ BS-7671: requires circuitsof locations containing baths or showerto have RCD - protection .
▲ Regulation - 701.411.3.3. requires that all circuits within this location shall be provided with additional-protectionby a . residual-current-device ( RCD ) not exceeding . 30mA with an opening-time . not exceeding . 40mS .at a residual-current . of 5 x IΔn . thiswould effectively be . 150mA . the RCD -requirement will include . ( LV) low-voltage . lighting-circuit(s) . shower-circuit(s) . electric-towel-rails .

 

[amberleaf]

MultipleChoice Questions from all Sections . 2394 : those will come in Handy . 2008:2011:

Whichof the following would be the appropriate protection-device for a Large-motor :
• BS-EN-60898 - Type D .
• BS-EN-61009-1 .
• BS-EN-60898 - Type B .
• BS-1362 .

Usingtables within BS-7671:2011: if the supply cables coming into a domesticproperty is 25mm[SUP]2 [/SUP] . what size should the Earthing-conductor be .
• 16mm[SUP]2[/SUP].
• 25mm[SUP]2[/SUP] .
• 10mm[SUP]2[/SUP] .
• 50mm[SUP]2 [/SUP] .

Usingtables within BS-7671: 2011 . what size earthing-conductor should be used whenbonding to the main incoming gas and water pipes when the incoming supply is (25mm[SUP]2 [/SUP]) .
• 16mm[SUP]2 [/SUP].
• 10mm[SUP]2 [/SUP].
• 4mm[SUP]2 [/SUP].[SUP][/SUP]
• Any of the above .

Whenperforming an insulation-résistance test on an SELV system . what should the test-voltage be :
• 50V .
• 24V .
• 500V .
• 250V .

Table- 61 . p.191 .
Whatis the . Minimum-insulation-résistance (MΩ ) for an SELV system :
• 0.5 MΩ .
• 0.2 MΩ .
• 1.0 MΩ .
• 0.4 MΩ .

2394: The Regulations Must - State the Facts .

Appendix - 6 . ( Informative ) p.389
Model-forms . Certification and Reporting .

iv) Competent-persons will . as appropriateto there function under . (i) (ii) & (iii) have a sound knowledge and experience relevant . to the nature of the work . undertaken and tothe technical-standards set down inthese Regulations . be fully versed in the . Inspection and Testing procedures contained in the . Regulations and employ . adequate testing equipment .

Periodicinspection and testing must beundertaking by : (iii)
• Special Company .
• Competent Person.
• Apprentice .
• Electrician .

▲ All installations must be . Inspected and Tested- periodically to ensure that they are safe for . continued-use .

Pointto note : 621.3 . Precautions shall betaken to ensure that the . periodic-inspection & testing shall not cause danger to ( Persons or Livestock ) and shall not cause ( Damage to Property ) and equipment even if the circuit isdefective .

(i)(ii) & (iii) ( EIC ) - ( MWC ) - ( EICR ) Authenticated - by a Competent Person .

 

[amberleaf]

2394: The Regulations Must - State the Facts .

Willcome in on both angles . Q / As .

Themaximum allowed voltage-drop on a lighting circuit is :
Themaximum voltage drop allowed for a lighting circuit in a consumers lighting .supplied by a public ( LV) system is :

• 11.5% .
• 10% .
• 0.75 .
• 3% .

2394:-Re-cap . Table - 4Ab - Voltage-drop - ( Vd ) . p.314 .
i). ( LV ) Low-voltage installation supplied directly from a public low voltagedistribution system . Lighting - 3%. ( 3 x 230V ÷ 100 = 6.9V )
ii). ( LV ) Low-voltage installation supplied directly from a public low voltagedistribution system . Lighting - 5%. ( 5 x 230V ÷ 100 = 11.5V )

 

[amberleaf]

Cable- surrounded by Thermal - Insulation .

2394: Coming in on both . angles Q / As

A ( de-rating-factor ) . of 0.88 is applied to cables travelling throughthermal insulation . how thick is this thermal insulation :
• 200mm .
• 100mm .
• 500mm .
• 50mm .

Cablesurrounded by thermal insulation for 400mmor more has a ( de-rating-factor ) of :
• 0.63 .
• 0.51 . Table - 52.2. p.129
• 0.55 .
• 0.5 .

 

[amberleaf]

Whenautomatic disconnection of supply is used as a measure of protection .additional protection by RCD shall be provided for :
• Mobile equipment having a rating of greaterthan 32A .
• Socket-outlets in commercial and industriallocations .
• Only for sockets rated at 32A or less whereit is reasonable to expect they may be used to supply equipment for the useoutdoors .
• Socket-outlets rated at 20A or less in a domesticinstallation . 411.3.3.

i). Socket-outlets with a rated-current not exceeding - 20A that are forthe use by . Ordinary-persons. and are intended for general-use .

The maximum-measured-value for aBS-EN-60898 - 20A Type-B . circuit-breaker . is ( in orcase only ) Table . 41.3
• 2.30Ω . -Table . 41.3. & Appendix - 14 . p.424 .
• 2.87Ω.
• 1.44Ω.
• 2.27Ω.

 

[amberleaf]

2394: Exams.

Q). The load-current in any part of aRing-final-circuit . should be unlikely exceed for long periods the current-carrying-capacity of the cable . this can be achieved by .

Regulations must state the facts . Appendix - 15 - ( Informative ) p.425

The load-current in any part of a Ring-final-circuit . shouldbe unlikely exceed for long periods the current-carrying-capacity of thecable . Regulation - 433.1.103 .
This can be achieved by .

i) . Locating socket-outlets to provide reasonable sharing of the load around the ring . Appendix - 15

 

[amberleaf]

Somefacts : 16[SUP]th[/SUP]Edition . End - OFF .

regulations containing a bath or shower . a requirement to provide allcircuits installed in the location with additional-protection .30mA RCD . is now- included .
this effectively . ends the old-argument . whetheror not to provide RCD - protection for anElectric-shower . not previously a requirement of . BS-7671: provided the circuit-overcurrent-protection . operated automatically within the required-disconnection-time. time under earth-fault-condition . but was commonly recommended in . manufactures-installations for equipment and often left the designer of the installation with the dilemma of whether or not to provide the RCD .

Regulations- 701.411.3.3. RCDs . Additional-protection by RCD. Containing a bath or shower