***Cont../ Useful Information for Electricians & Apprentices***

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O.S.G.. The use of other methods’ of determining Maximum Demand is Not Precludedwhere Specified by the Installation Designer

FirstlyI make no Apologies for the Way am Writing on any Matters . it can be a first day Apprentice or some one Needing aJog of Memory .
Sowe are all in the Same Boat . “ To Learn “

For the Apprentices . The Day we stop learning is the Day we hang Upour Tool-Bag

CookerDesign Current Calculations

Thefirst thing you have to do is get Your Head around the Calculations !!

(From a Design point of View ) 2392-10

DomesticInstallation Oven(s) & Hob(s) are to be Calculated upon their MAXIMUM LOADING
Startwith a simple Calculation ( An Oven has a rating of 2kW ) 2000

(I = P/V ) Formula … I = 2000 ÷ 230V = 8.70A …. Weare Using the Unit Amps


2392-10/ Domestic Installation Oven(s)

Ovenhas 4 Rings ( 2 x 1kW ) & ( 2 x 1.5kW ) & Grill ( 2kW ) & Oven (3kW )

-Controlled via a CookerSwitch with a Socket outlet .

Asa Designer . we’ll have to Apply Diversity ??

Important )- Diversity allowance to be Applied to the FULL LOAD CURRENT for CookingAppliances .

TheO.S.G. is telling us . Purpose of the Final Circuit fed from theConductors )
O.S.G.Table 1B p/97 – column (3) Cooking Appliances → At the Top of the Page Note : Type ofPremises ( 2392-10 → Household Installations ) Domestic Installation(s)

DomesticInstallation(s) Only O.S.G. - 10A + 30% f.l – Full Load ) of connected Cooking Appliances in the Excess of 10A+ 5A if a socket-outlet is incorporated in the Control Unit . ( C.C.U. ) – 45A + 13A Socket Switched with Neon .

Fromyour point of View ( The First 10A ofthe rated current plus 30% of the reminder ( Plus) 5A if the Control Unit incorporates s Socket.

Calculations)- You bank “ Hold OFF“ the first 10 Amps of the Maximum Load Current )
The10A will be used at the End of the Calculations’

-So your Work out the Total Power Rating & then calculate the Full Load Current

Calculations)- Power = ( 2 x 1 ) + ( 2 x 1.5 ) + ( 2+ 3 ) = 10kW

I= 10000 ÷ 230V = 43.48A … round it up to the first four numbers43.47826087 ( 48 ) 43.48A

UsingDiversity allowance stated ↑↑ ( 43.48A sub 10A = 33.48A )

I= 33.48 x 30 ÷ 100 = 10.04A

Youradding the ( 5A ) for Socket outlet . I = 10A + 10.04 + 5A = 25.04A )- Asa Designer this is your Expected Current Demand .

Remember )- Supply Cables Rated to suit DesignCurrent ( Iz )

 

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T&E– cable PVC clipped to a ( Joist )above a ( Plasterboard) ceiling completely surroundedby ( Insulation exceeding 100mm ) … C.C.C. …

1.0mm[SUP]2[/SUP] = 10.5A . - 2415 Watts . ( Calculations’ - 10.5 x 230V = 2415 Watt )
1.5mm[SUP]2 [/SUP] = 13A . ( Calculations’- 13 x 230V = 2990Watt )
2.5mm[SUP]2 [/SUP] = 17A . ( Calculations’ - 17 x 230V = 3910Watt )

Table4D5 . BS-7671:2008 – No 1 2011 . Installation ref . method 101# .

Evenif you take the lower … C.C.C. … of (8A ) for 1.0mm[SUP]2 [/SUP] T&E cablecompletely surround by insulation for over ( 500mm ) its Still gives you up to ( 1840 Watts )

Cable’sshould be routed so as they are NOT covered by or touching insulation wheneverpossible also length of run & potential Volt – dropto be considered . ( Vd )

523.9. p/128 . Cable’s in thermal Insulation . ( Table 52.2. – p/129 )
Quote. Wherenecessary . The nature of the load ( e.g. cyclic ) & diversity shall be takeninto account .

http://www.electrical.------.org/wiring-matters/15/current-ratings.cfm?type=pdf …….. ◄◄ ( Good Reading ) surround by insulation

Just a Reminder . 2392-10 .
6A– MCB . ( 6 x 230 = 1380W … design load max )

Method - C* … clippeddirect
1.0mm[SUP]2[/SUP] = ifjust clippedto a wall . ( Surround by Air) . will take up to ( 16A )
1.5mm[SUP]2[/SUP] = ifjust clippedto a wall . ( Surround by Air) . will take up to ( 20A )
2.5mm[SUP]2[/SUP] = ifjust clippedto a wall . ( Surround by Air) . will take up to ( 27A )

► Zs – ( Max ) ◄◄ Maximum permitted Earth-faultLoop Impedance .
Table. 41.2.
Table. 41.3.
Table. 41.4.
Table. 41.5. – for Non-delayed RCDs .

 

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2392-10.
Thebuilding construction in which an installation is to be carried out MAY affect the Design & Safeoperation of the Installation . Thiseffect is called ???
( An external Influence) App -5

 

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Recall. 2392-10 .

612.8.1. – p/193
Requires the ( Effectiveness of AutomaticDisconnection of the Supply by RCD ) to be ( Verified) using test equipment meeting the requirements of BS-EN-61557-6 .

ElectricalSafety / in Low-voltage distributionsystem(s) up to 1000V a.c. & 1500V d.c.Equipment or Monitoring of ( Protective Measures . Residual Current Devices –RCD . in TT . TN-. & IT.

Reason !! . This is to confirmthat the ( Relevant requirements of Chapter 41 – (Protection against Electric Shock )

BS-EN-61557-6. has requirements for the following ( Tests ) to be Applied to RCDs

□ Non- tripping ( 50%) test - -&-s 2392-10 . All is relevant toyour Exam .
□ Tripping ( 100% ) test . …( 1x ) .. ► Thecommon Q ) -&-s asks you . totest an RCD at ( 1x ) what is the tripping current USED . ( 100% ) … 1x is 100% ◄◄

□ 5 x IΔn – ( 500%) test … ( 5x )
▲▲Test procedure . with aleakage current flowing equivalent to ( 500% )of ( 5 xtimes ) the rated residual operatingcurrent ( IΔn ) of the RCD . operation should OCCUR within ( 40mS )

2392-10 (- Summary . as an Inspector .
RCDsshould be “ Tested“ at
i) - 50%.
ii) - 100% .
iii) - 500% .of their rated residual operating current ( IΔn ) Automatic Disconnection of Supply. ( ADS ) in case of a Fault . ?? ( Additional Protection )

wherean RCD is used . to achieve the disconnection time required by Table 41.1 . itis necessary to confirm that the maximum earth fault loop impedance ( Zs ) stated for a particular sensitivity of theRCD in Table 41.5.. are NOT exceeded in the circuit to which theyprovide protection .

 

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Asan Inspector . 2392-10 .
RCD □ With a leakage current equal to ( 50% ) IΔn . applied ( ShouldNot Operate ) -&-s

612.13.1. requires the ( Effectiveness ) of the ( Integral Test Facility of an RCD ) 2392-10 - As an Inspector. Your job is . Tobe Verified . -&-s

You are checking ?? . it withthe Manufactures Instructions .
A warranty clam WILL NOT be successful if youhave NOT followed the Manufactures Instructions
.
□ Requires Designers / Installers to takeaccount of all relevant BritishStandards & Manufactures’ Instructions .
□ It is a Requirement of BS-7671:2011 . that allElectrical Equipment is installed in accordance with the Manufactures’Instructions . & Documentations .

415.1.1. – States .
Thatwhere an ( RCD having an IΔn of 30mA ) OR LESS . ( is installed to Provide – Additional Protection ) operating time should NOT exceed ( 40mS / Residual current of 5 x IΔn

Reason !! . With theNon-tripping test .
the purpose of this test is to confirm that an ( RCD ) of anytype or trip rating is NOT overly sensitive & is ameasure intended to enable ( Unsuitable RCDsto be indentified & removed for service . this is what -&-s arelooking for .

TestProcedure . “ Wording“ ◄◄ ( BS-EN ) ONLY

►► i) Different RCDs/ General purpose ( RCD to BS-EN -61008 . & RCBO to BS-EN-61009 . ( 100% ) IΔn – operation should OCCUR within( 300mS ) ◄◄◄
►►ii) “ S “ typeRCD . to BS-EN- 61008 . Time Delay . ◄► ( 100% ) IΔn – operationshould OCCUR within ( 130mS ↔ 500mS )

TestProcedure . “ Wording“ ◄◄ ( BS- ) ONLY
►► i) Different RCDs/ General purpose ( RCD to BS-4293 . ◄► ( 100% ) IΔn – operationshould OCCUR within ( 200mS )
►►ii) “ S “ typeRCD . to BS-4293 . Time Delay . ◄► with aleakage currentflowing equivalent to ( 100% ) of the ratedresidual operating current IΔn – of the RCD . operation should OCCUR withina time range from ( 50% ) of the rated timedelay plus ( 200mS ) to ( 100%) of the rated time delay plus ( 200mS )

Appendix 3 – p/295. RCD . Table 3A .Time / current performed criteria for RCDs to . BS-EN-61008-1 &BS-EN-61009-1 … ( BS-EN . ONLY )

 

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Eachcircuit may have MORE than ONE reason for ( Additional Protection by 30mA / RCD)
(Equipment or Socket outlet & Secondly because of a cable installation “Method “ )

Reminder► Additional Protection is provided as ( AdditionalProtection / Only ) it does not Obviate the need for CircuitProtection by ( MCB)

p/54. Regulation :411.3.3. Socket outlets with a ratedcurrent NOT exceeding 20A . that are for general use by ordinary persons (exemption may be permitted )
p/199. Regulation :701.411.3.3. Additional Protection shallbe provided for all circuit of a location by use of one or more 30mA – RCD.
Note(- See / Regulation 314.1 – (iv ) &531.2.4. concerning the avoidance of unwanted tripping .

p/124./p/125 . Regulation : 522.6.101. & 522.6.102. & 522.6.103. cables concealed in a wallor partition at less than 50mm depth & without earthed mechanicalprotection . E.g. Conduit .

p/46. Regulation : 314.1. Every installation shall be divided into circuits as necessary toavoid danger & inconvenience in the event of a fault . take account ofdanger that may arise from the failure of a single circuit such as a lightingcircuit . reduce the possibility of unwanted tripping of RCDs . etc .

p/46. Regulation : 314.2. Separate circuits to beprovided for parts of the installation that need to be separated controlled insuch a way that those circuits are not affected by a failure of other circuits.

Protectionfor Safety . 2392-10 . 131 . to 135 .
The whole reason for BS7671:2011 . being inplace is to provide a Standard which canbe used to ensure the safety of Persons . Property & Livestock .

Erection : 134.1. p/21.
Provided the installation is installed to comply with BS-7671:2011. compliance & all other parts of the regulation(s) will be Achieved .

Initial Verification . 134.2. p/22
On completion of the installation . a final inspection & testis carried out – ” Initial Verification “by Competent Person(s) to ensure that the installation is to the Standardrequired by BS-7671:2011 .

 

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Reminder .

MaximumDemand & Diversity . O.S.G. table A2 . p/111 / 112

( 1 ) . Lighting can be calculated using ( 66% ) of the total demand . two lightingcircuit(s) at 6A = 12A . ( 12 x 66% = 7.92A )
Asthe O.S.G. tells us . p/110 . currentequivalent to the connected load . with a minimum of100W per lamp holder .
Pendent’s. Not less than 100W . ( 0.43A at 230V)

O.S.G. tells us . Table A2.p/111
□Domestic premises – households . including flats . ( 66%) 2392-10
0.9 ) □ Commercial premises – Shops . Offices .Stores & other business premises ( 90%)
□Commercial premises – Guest houses . Small hotels . Boarding houses . ( 75% )

Diversityin an installation can now be applied . 2392-10 .
( 9 ) . Ring final circuits . Diversity is calculatedat ( 100% ) is ►32A .
&( 40% ) for other circuits .

Ringfinal circuit 1 ) 32A .
Ringfinal circuit 2 ) 32A x 40% = 12.8A

Cooker– domestic type . ( 10A plus 30% of remainder of load ) 20kW – ( 86.95A ) cooker on 230V . loading = 10A + ( 0.3 x 86.95 ) = 39A
Cooker – domestic type . with integral socket-outlet oncontrol unit . ( 10A plus 30% of remainder of load plus 5A ) - 24kW ( 104.35A ) cooker on 230V .loading = 10A + ( 0.3 x 104.35 ) + 5A = 46.3A

416.2. Barriers or Enclosures’ . p/67 ( Barrier – Protection fromcontact with Busbar ) Enclosure . “Assessor “
Where barriers or enclosures are used to prevent contact with live parts . 2392-10 . Domestic . Consumer Unit . ( CU )
Top surface . IPXXD . IP4X . 416.2..2. p/67
Sides / front / bottom . IPXXB . IP2X.

 

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It may be Necessary to open an ( Enclosure or Remove a Barrier ) replacement or adjustment of parts . in thiscase precautions must be taken to prevent easy access to Unskilled persons –Regulation . 416.2.4. this can be achieved by providing a ( Door or Barrier ) which can ONLY be opened using ( Key orTool ) . or providingan interlock to ensure that the enclosure cannot be opened until the supply isisolated .

You will be aware that you cannot OPEN the DOOR of an ISOLATORwhen it is switched ON .

Note . p/67 . ThisRegulation does NOT apply to . under 416.2.4.

A ceiling rose complying with BS- 67
A cord operated switch complying with BS-EN-60669-1
A bayonet lamp holder complying with BS-EN-61184
An Edison screw lamp holdercomplying with BS-EN-60238.

TN-C-S. ……. “ C - S “ Neutral conductor & protective conductor. combined in the supply & separated in the installation .
IT . ………… ( I ) All sources live parts insolated from earthor connected by a high impedance to earth .

Table41.1 . p/53 .

50 < Uo ≤ 120V .

TN- a.c. – d.c. ( 0.8a.c. ) ► Note. d.c.– Disconnection is not required for protection against electric shock but maybe required for other reasons . such as protection against thermal effects .

TT- a.c. – d.c. ( 0.3 a.c. ) ► Note . d.c. –Disconnection is not required for protection against electric shock but may berequired for other reasons . such as protection against thermal effects .

 

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PMESupplies .
Rememberthat if you have a ( PME ) supply . thatyour main Earthis the Supply company’s Neutral . there is NO Earth connection brought into the house .
Fineso long as the Supply Neutral remains intact . if the Neutral connection breakers . then youcould be left with NO effective Earth .

Froma Inspectors point of View . A fault inthese conditions could be extremely dangerous .

TheOver-current device which is protecting the ( Cable ) is an MCB
□ Calculate the Nominal Current.
Thenominal current will be rating of the MCB selected to protect the System . mustbe ( Higher ) than the Current required by theAppliance(s) otherwise it will ( Trip ) immediately. we calculate it from the Appliancepower . calculate the current by dividing the power in watts by the supply voltage.
Yourare choosing an MCB whose current rating is a chose as possible above thecalculated figure .

( Cable ) General purpose ( PVC) T&E . with a maximum temperature rating of 70°C degrees celsius

□ Enclosedin a “ Wall “ refers to a ( Cable) that is concealed in plasterwork .
□ Enclosedin “ Conduit “ means fully enclosed that isfastened to the surface . ( Wall or Ceiling )
□ “Clipped “ to a “ surface “ means fastened at intervals to a flatsurface such as brick work or joist’s .
□ “Free “ means completely surrounded by ( Air )

□ “Free “ Also applies to ( Cables ) that are laidon ( Metal Cable Trays ) Industry .

Any( Cable(s) has résistance .
-&-s . When ( Cable ) warmup . it’s résistance will increase . thereby increasing the Voltage drop .
Note (- that it is NOTthe nominal current that we use to work out voltage drop . it is the ( Current ) that we expect to be flowing inNormal Conditions .

 

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Regulation– Table 41.3.

MaximumEarth Loop Résistance . that will allow aprotective device to disconnect in ( 0.4s ) These are the complete loop résistance. including the supply company’s part & full length of cable inside thepremise . the figures are derived by dividing the supply voltage by the currentthat will trip the protective device in ( 0.4s )

 

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Not in the Regulation(s) ◄◄

Overcurrent . “ Plan English “

AnOvercurrent is any ( Increase ) in the ( Current ) in the electrical system . ↔ Above the level for which it is designed.

“ Overload“ “ Plan English“

An Overload occurs when a ( Current) flows that is somewhat to (High ) 50%to 100% to high . for the ( System / Installation ) Overloads don’t immediate cause damage . instead the likehood of damage ( Increases gradually) as the duration of the Overload ( Increases ) ifthe Fault is NOT resolved .

Worst case scenario . Cables will Overheat & Melt . exposingbare conductors’ . The heat generated may be sufficient to cause a fire .

( Cables ) are intendedto become warm in operation . ( Use ) heat is generated whenever a currentflows in anything . & this is perfectly normal .
The level of heat generated by cables is ( Only Safe ) when it is kept within ( Reasonable limits) ► PVC .insulated cables are designed to run at temperatures up to ( 70°C ) beyond this there is a risk of damage .

2392-10 . Overload .
Domestic Insulation . Overloads usually results from using to manyappliances at the same time .

Exposed conductive parts . Cooker Body .
Exposed conductive parts . Metal Socket plates .
Exposed conductive parts . used as circuit protective conductor ( Conduit )

 

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Testing Single Phase Installation .
Test for voltage between the following .
□ Line & Neutral .
□ Line & Earth .
□ Neutral & Earth .

Testing 3-phase four wire system(s)
Test for voltage between the following .

□ L1 & L2 .
□ L1 & L3 .
□ L1 & Neutral.
□ L1 & Earth.
□ L2 & L3 .
□ L2 & Neutral.
□ L2 & Earth.
□ L3 & Neutral.
□ L3 & Earth.
□ Neutral &Earth .

 

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Inspection & Testing .
□ Earth FaultLoop Impedance : The impedance of theearth fault loop ( Line –to-Earth ) starting & ending at the point of earthfault .

In a Domestic Installation ( TN-S or TN-C-S )

Dead Test– “ Safe Isolation is Required “
Such a test ensures conductors are electrically sound& correctly connected .

612.2.1.: Continuity of protective conductors . ( All protective conductors’ . mainprotective & supplementary bonding conductors ) must be tested for ( Continuity using a low-reading ohmmeter) for the sake of -&-s . ←

Important (- what –&-s are looking for !! . ← 2391-10 & 2392-10 .
If the ( Installation ) is in Operation . then neverdisconnect ( Mainprotective bonding conductor(s) unless the supply can be isolated . ) → Safety & Livestock& Person(s) ←

Dead Test– “ Safe Isolation is Required “

612.2.2.: Continuity of “ Ring Final Circuits “ conductors.
They are “ TwoReasons “ . for conducting this test .
ii) To ensure that the circuit conductors are ( Continuous ) & indicate the Value of ( R[SUP]1[/SUP] + R [SUP]2 [/SUP]) ring final circuit . ( “ Continuity “) plus ( Polarity )
“ Radial circuit “ . by linking out at the ( CU ) Line & CPC . you have a complete loop . reading at lastoutlet gives ( R[SUP]1[/SUP]+ R [SUP]2 [/SUP]) value . plus . you have ( “ Continuity “)

□ Socket– outlet circuit(s) in domestic & similar Installation . ( Regulation –411.3.3. – p/54 )

 

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Dead Test– “ Safe Isolation is Required “

612.3.: Insulation résistance . ( IR )
Leakage currents between conductors & betweenconductors & earth . ( it will indicate if any Short Circuit Exist )
Leakage current : p/29 – Electric current in an unwanted conductive part undernormal operating conditions .

Cable Insulation Résistance . ( MΩ ) -&-s . are looking for ?? Q/As
Disconnect all item of equipment . Capacitors : Indicatorlamps 100% : Dimmer switches 100% : Electronic timers : -&-s – Remove all lamps 100% .
( it may beimpracticable to remove lamps . in this case the local switch controlling suchequipment may be left in the OFF position )

612.3. Insulation Résistance .
The Insulation Résistance shall be measured betweenLive conductors & between Live conductors & the protective conductorconnected to the earthing arrangements .
( 2392-10 :Where appropriate during this measurement . Line &Neutral conductors may be connected together ) L/N & E . serprate

p/191 . Note (- Insulation Résistance . values are usuallymuch higher than those of table 61 . (2MΩ ) – GN-3 . -&-s 500V d.c. - 1.0MΩ )

612.6.: Polarity . A test of polarity shall be made & it shall be verified that .
i) 2392-10 . Every fuse & single-polecontrol & protective device isconnected in the ( Line conductor Only ) ←
ii) 2392-10 . Wiring has beencorrectly connected to ( Socket-outlets ) & similar accessories . ←

 

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“ This is a Live Test “ .
612.9.: Earth fault loop impedance ( Z[SUP] s [/SUP]) . The relevant impedance shall be ( Measured ) ◄ 2392-10 . or determined by an alternativemethod
The Regulations chases us to Appendix14 . p/193
i) The Line conductor to Protective conductor loopimpedance of the supply is first measured at the origin of the Installation .
ii) The résistance of the Lineconductor Protective conductorof the final circuit are then measured .
Note : Other methods are NOT precluded .

□ Where the earth fault loop impedance is to high toprovide the required disconnection time . Where the ( DNO ) does not provide anEarth . TT . – Regulation . 411.5. p/57

“ This is a Live Test “ .

612.10.: Additional protection .
As the Regulation tells us .
i) The “ Verification “ ofthe effectiveness of the measures applied for Additional protection is ( fulfilled ) by ( ► VisualInspection & ► Test )
ii) Where ( RCDs ) are required for Additionalprotection . The effectiveness of automatic disconnection of the supply by (RCDs ) shall be verified using suitable test equipment according toBS-EN-61557-6 . ( you what to be lookingup – Regulation 612.1. )

The “ Inspector ◄ -&-s “ . will thoroughlytest the RCD to BS-EN Standard .

2392-10 : The time to operate at the rated current willbe measured ..
This will be carried out with ( Small current tosimulate a Fault ) on both the Negative half cycle . & Positivehalf cycle .
□ The device must operate within ( BS-only 200mS) RCDs designed to BS-4293 & BS-7288 .
□ The device must operate within ( BS-EN only 300mS) RCDs designed to BS-EN-61008 / BS-EN-61009

 

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“ This is a Live Test “ .

612.11.: Prospective fault current ( PFC )
What is the purpose of Measuring Protective Short Circuit Current &Earth Electrode Résistance .
Prospective Fault Current . ( Ipf) The design requirements of Regulation 434.1.
The Prospective Fault Current . shall bedetermined at every relevant point of the installation . This shall be done byCalculation . Measurement or Enquiry. are includedin the testing section in Regulation 612.11.

( PSCC ) Three – leads . Test Instrument . Oneon the Line conductor . & the other Twoon the Neutral &Earth .
As many test Instruments . cannot measure the voltage between ( Phases )Three-phase system . The maximum balanced prospectiveshort circuit current is taken to be ( Twice ) the single – phasevalue .
The Prospective Short Circuit Current willalways be ( Larger ) than the ( Prospective Earth Fault Current ) ◄◄

Measurement of (Prospective EarthFault Current )
( PEFC ) Three – leads. Test Instrument . One on the Line conductor. & One on the Neutral & One on the Earth . ( MET )

“ This is a Live Test “ .

Reason – must ensure Earth ispresent . ◄
Measurement of (External Loop Impedance Ze[SUP] [/SUP]) -&-s . bigtime . ◄◄ 2392-10 ▼▼▼▼ e
“ Remember “ ◄► The main earth is disconnected from MainBonding Conductors & Circuit Protective Conductors for this Test .

“ Remember “ ◄► Main Switch in ( OFFPOSITION ) -&-s . big time . ◄◄ 2392-10