***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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(3 )

For. BS-3871 )- Types 1 , 2 , 3 , & 4 ,

Themaximum value of . Earth Fault LoopImpedance ( May be Calculated ) &using the Manufactures Tripping Characteristic .

formula.O.S.G. p/72 . Table 7.2.7. (ii) - ( b ) . Now withdrawn )

Thesetypes of circuit breakers are identified by the use of numbers . 16[SUP]th[/SUP] Edition . still in Use .

BS-3871 - formula. To be Used :

1 . 2.7 / 4 – ( In ) …. BS-3871
2 . 4 / 7 – ( In ) ….
3 . 7 / 10 – ( In ) ….
4 . 10 / 50 – ( In ) ….

TypeB )- 3 to 5 ( In ) …. BS-EN-60898 .
TypeC )- 5 to 10 – ( In ) ….
TypeD )- 10 to 20 – ( In ) ….

Circuitbreakers . …. BS-3871

Type( 1 ) … Multiplier ( 4 ) .. In
Type( 2 ) … Multiplier ( 7 ) .. In
Type( 3 ) … Multiplier ( 10 ) .. In
Type( 4 ) … Multiplier ( 50 ) .. In

Zs) value for a 20A type ( 1 ) – BS-3871. ( 4 x20 = 80 ) ( 230÷ 80 = 2.87Ω )

 

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Short Circuit Capacity according to BS- 3871 )- now obsolete .
Was( Expressed as an ( M ) value .

M 1– 1000A
M –1.5 . 1500A
M 3– 3000A .
M 4.5– 4500A .
M6 – 6000A .
M9 – 9000A

 

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-&-s. Any circuit or equipment vulnerable to a particular test should beindentified by . ?
p/117- 514.9.1. The provision of a Legible diagram . chart ortable prior to testing .
2392-10: The purpose of the Inspection conducted prior to Testing an installation isto verify that . ?
p/189- 611.2. (iii) “ equipment ” is not damaged or defective so as to impairsafety .
2392-10: No alteration shall be made to an existing installation unless the ?
p/20- 132.16 . it is established that the alteration will notimpair the safety of the existing installation .

2392-10: The Inspecting & Testing required duringa Periodic Inspection should be recorded on a Electrical Installation Condition Report . & be carried out by .
p/195- 621.5. Competent Person .

2391-10: Q) prior to an Inspection in accordance with BS-7671:2011 , The competentperson carrying out the work shall normally . ?
p/189- 611.1.
A) Inspection shall ( Precede Testing ) & shall normally bedone with that part of the installation under Inspection disconnected from thesupply .

2391-10: Q) Installations should be arranged so as to avoid hazards in the event ofa fault . & to facilitate safe operation inspection . testing & maintenance . .? Onemethod of complying with this is to .
p/46- 314.1.
A) divide the installation into circuits .

 

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Reasons) ( IR ) Testing . 2392-10 .

InsulationRésistance . Details of such equipmentshould be recorded on the Schedule of Test Results . “ Inspector “ TestResults . so that the Inspector carrying out ( Routine ) Periodic Testing in thefuture is aware of the presence of such equipment .

□ “ Generic Scheduleof Test Results . “ p/402 . Apprentices .

Aswith the 17[SUP]th[/SUP] Edition 2008 - “ Schedule of TestResults . “ ( Test Results – ► Functional Testing ) RCD time 13 / Other 14 .

Withthe 2011 : the Wording has gone . ( RCD ) – ( mS ) 1 x / 5x / Testbutton operation . ( Same thing -Functional Testing )

Apprentices.
612.13. – p/194 .

The Effectiveness of ANY Test Facility

 

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2392-10: for -&-s . they will work into 2011 .

Keychange is to the “ Schedule of Inspections “ That is to be used when carrying out a ( PeriodicInspection )

“ Now “ a Condition Report. will need to have a “ Schedule of Inspections “ relevant to thePeriodic Inspection . workcarried Out .

BS-7671:2008

Previously . Schedule of Inspections was ► ( Generic ) ◄ & used for both the (Periodic Inspection Report ) & ( Electrical Installation Certificate )

Thisis were -&-s will trip you Up .2392-10 ▲

134.2.2. : The designer of the Installation shall make arecommendation for the interval to the ( First ) Periodic Inspection & Test. as detailed in Part 6 . 2011

 

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Understanding of the Underpinning Knowledge . BS-7671:2011 .

Selection& Sizing of C.P.C.& Earthing Conductors .

C.P.C.& Earthing conductors are selected in accordance with Section – 543 .
543.1. deals with Sizing : 543.2. with types & 543.3. with preservation of Continuity .

A ProtectiveConductor may be common to more than OneCircuit . Regulation – 543.1.2. p/160 .

Thefollowing can be used as a Protective Conductor . Regulation – 543.2.1. . p/ 163 .

i)Single core cable .
ii) Conductor in a cable .
iii)Insulated or bare conductor in a “ Common Enclosure with Insulated live conductors .
iv) Fixed bare or Insulated conductor .
v) Metal covering . Sheath screen or armouringof a cable .
vi)Metal conduit . Metal cable management . or other Enclosures or Electricallycontinuous support system for conductors .

vii) Extraneous –conductive – part complying withRegulation . 543.2.6. p/163.

 

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Whensizing the C.P.C. & Earthing conductor the following must be conceded .

i)Earth Fault Loop Impedance requirements : Section - 411
ii) Thermal Constraints – conductor does notoverheat during Fault Conditions . Regulations – 543.1.3. & 543.1.4. p/160 / p/162 .
iii) Additional requirements for ( PME ) supplies . Regulation – 544.1.1.
iv) Additional requirements for Protective conductors where in the ground .Regulations – 542.3.1. & 543.1.1. p/159 . p/160

EarthFault Loop Impedance : P/39 . Zs = Ze + R[SUP]1[/SUP] + R[SUP]2[/SUP] . -&-s . where to find it .

 

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Understanding of the underpinning knowledge .

Earthing& Bonding . Requirement for SpecialInstallations or Locations .

Section701 . Location Containing a Bathor Shower .
SupplementaryBonding – is not required in NEW installation as an RCD is always required for bothDomestic & Commercial Installations .

(Additional Protection : Supplementary Equipotential bonding )

Section702 . Swimming Pools & Fountains
Regulation. 702.415.2. p/205 . require local Supplementary bonding betweenall Extraneous – conductive –parts . in Zone 0. 1. & 2. the CPCs of allExposed – conductive-parts in these Zones . ( See – Regulation – 415.2. )

(Additional Protection : Supplementary Equipotential bonding )

Section705 . Agricultural & Horticultural Premises .
For( These premises ) where ( Livestock ) iskept . the requirements . 705.415.2.1. – p/216. should be Noted .
Supplementarybonding shall . connect together all Exposed-conductive-parts . & Extraneous-conductive-partswhich can be touched by ( Livestock ) ifthere is a Metallic Grid laid in the floor it should be Supplementary bonded .

( Protection against Electric Shock ) )

Section706 . Conducting Locations with Restricted Movement .
Whereautomatic disconnection is used for protection against Electric Shock .Regulation . 706.410.3.5.- ( iii ) requires SupplementaryEquipotential Bonding

Section711 . Exhibitions’ . Shows & Stands. p/239
Structuralmetallic parts . which are ( Accessible ) fromwithin the Unit . shall be connected to the Main Earth Terminal “ Within “ theUnit .

( Earthing arrangements & ProtectiveConductors )
Section– 712 . Solar Photovoltaic ( PV ) power Supply Systems .
Whereprotective bonding conductors are installed . These shall be run parallel &in close contact with the . D.C. & A.C. cables . Regulation – 712.54 . p/243

(Protective Equipotential Bonding )
Section717 . Mobile ofTransportable Units .
717.411.3.1.3. p/247 . requires Main Protective Bonding to the ( Accessible ) conductive partssuch as the Chassis .

( Protective Earthing & ProtectiveEquipotential Bonding )
Section 721 . 721.411.3.1.p/254. calls for ( Additional ) bonding of . Extraneous – conductive– parts within the Caravan & MotorCaravan .

(Additional Protection : Supplementary Equipotential bonding )

Section740 . Temporary Electrical Installation for Structures . Amusement Device &Booths at Fairgrounds . Amusement Parks & Circuses .
Locationsintended for ( Livestock) require Supplementary Bonding - Regulation . 740.415.2.1. p/ 269 – see 705

 

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(IR ) .
Whymay a ( largeinstallation ) give a pessimistically low overall Insulation Résistancevalue . Because there are a large numberof circuits all in parallel . 2391-10

Why. do capacitors . Neon’s . need to be disconnected . To avoid misleadingtest results .
Handle “ Capacitors “ with care . They could be fully charged.

What. Test voltage & minimum value of Insulation Résistance are appropriate forcircuits ( Incorporating ) Surge Protective Devices . ( 250V d.c.– 1MΩ ) 2011 .

Thefrequency in Hertz ( Hz ) is . Cyclesper second - of the Electrical Source .

 

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MedicalLocations .

Forthe sake of -&-s . 2011 .

Typesof System Earthing . 710.312.2. p/230 .

PEN) conductors shall not be used in ( Medical Locations & Medical Buildings ) downstreamof the main distribution board .

Note : in Great Britain , Regulation 8(4) ofthe Electricity Safety . Quality & Continuity Regulations 2002 prohibitsthe use of ( PEN ) conductors in Consumer’sInstallation .
□ Plain English . “ Typesof System Earthing “
The ( TN-C . System ) is not allowed inMedical Locations & Medical Buildings downstream of the main distributionboard .

Example(- Load & Earth Fault Currents ) associatedwith TN-C systems . can circulate through the casing of a ( Class 1 ) equipment thus causing Electromagnetic Interference with SensitiveElectronic Medical Equipment .

 

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MedicalLocations .

Forthe sake of -&-s . 2011 .

710.531.2. RCDs .

710.531.2.2. Socket-outletsprotected by RCDs

For each circuit protected by an RCD having the characteristicsspecified in Regulation 415.1.1. consideration shall be given to reduce thepossibility of ( Unwanted Tripping ) of the RCD due to excessive protectiveconductor currents produced by equipment in normal operation .

Regulation 415.1.1. Additional protection : Residual Current Devices ( RCDs )
The use of RCDs with a rated residual operating current ( IΔn ) not exceeding 30mA & an operating time notexceeding 40mS at a residual current of ( 5 x IΔn ) is recognized in A.C. systems as additionalprotection in the event of failure of the provision for basic protection &/ or the provision for Fault protection or carelessness by ( User )

InMedical Locations of Group ( 1 ) & Group ( 2 ) ◄►-&-s . 2011 . Medical Locations isin the Regulations . Q/As

710.411.4.– TN- system. -&-s .
InFinal circuits of ( Group 1 ) rated up to ( 63A) . RCD having the characteristics specified in Regulation . 415.1.1. shall be Used.

 

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MedicalLocations .

Forthe sake of -&-s . 2011 .

710.411.3.2. Automatic disconnection in Case of aFault .

710.411.3.2.1. (-&-s ) in Medical Locations of ( Group 1) & ( Group 2 ) WhereRCDs are required . ONLY type ( A ) or Type ( B ) shall be selected . depending on the possibleFault Current arising .

NOTE : Type ( AC ) RCDs SHALL NOT be USED . this is what -&-s are looking . Q/As .2011 .

 

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MedicalLocations .

710.559 . Luminaries’ &Lighting Installations .

InMedical Locations of ( Group 1 ) & (Group 2 ) at least two different sources of supply shall be provided . One ofthe sources shall be connected to the electrical supply system for SafetyServices .

Note : Safety Services are synonymouswith ( Emergency Services ) Refer to “ SafetyLighting “ for the recommended percentage of Luminaries suppliedfrom Safety Source .

710.560.9.1. Safety Lighting .
Note : The Luminaires ofthe Escape Routes shall be arranged on Alternate Circuits .

 

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Main EarthingTerminal .

Circuit protective conductors.
Protective bonding conductors.
FunctionalEarthing conductors – if required .
Lightingprotection system bonding conductor . if any – Regulation 411.3.1.2.

542.4.1. - Main Earthing Terminal must be easilyaccessed . This is primary to allow disconnection of any of the aboveconductors as required when Testing the Installation .

• MinorElectrical Installation Works Certificate does NOTrequire a record OF . p/393

i) System Earthingarrangements . P
ii) Departures fromBS-7671:2008. P
iii) Method of faultprotection . P
iv) Prospective fault current .

InitialVerification .

632.1Following the Initial Verification required by chapter 61 .
an Electrical Installation Certificate. ( EIC ) together with ( Schedules ofInspection ) & ( Schedules of Test Results ) shall be givento the person ordering the work

632.4.Defects or Omissions revealed during inspection £ testing of the installationwork covered by the Certificate shall be made good before the Certificate isissued .

• Any itemthat does NOT need Inspection during “ Initial Verification“ should be Marled . ( Schedule of Inspections ) p/395

i) P
ii) N/A .

2011 - p/395 . Bottom . N/A – toindicate an Inspection is NOT applicable to aparticular item
2011 - p/395 . Bottom . P – to indicate an Inspection has been carried OUT & the result is satisfactory .

► donot get mixed up with , OLD 17[SUP]th[/SUP] Edition ( Schedule of Inspections ) 2008 . “ of the Internet “

P . to indicate an Inspectionhas been carried out & the result is satisfactory .
N/A . to indicate an Inspection has been carried out& the result is NOT satisfactory ( applicable for a periodic inspectionOnly )
X . to indicate the inspection is notapplicable to a particular item .
LIM . to indicate that . exceptionally . alimitation agreed with the person ordering the work prevented the inspectionbeing carried out ( applicable for a periodic inspection only )

 

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The( P ) shouldhave been a Tick Sign . did not get throw .sorry

 

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• NewInstallation is protected against fault by ( ADS )When Inspecting this method of protection . Which of the following is NOT a essential check .

i) Earthing conductor . P
ii) Circuit protective conductors . P
iii) Main protective bonding conductors . P
iv) Fire barriers .

Hint : 531.2.5.- The use of an RCD associated with a circuit normally ( Expected )to have a ProtectiveConductor . ←

GN-3 –p/22 . 441 . AutomaticDisconnection of Supply– ( ADS )
Thepresence . correct sizing . connectionof the appropriate protective conductors . MUST be CONFIRMED as FOLLOWS.

542.3. – Earthing conductors. P
543 – Circuit protectiveconductors . P
544 – Protective bondingconductors . P
544.1. – Mainbonding conductors . P

• this Non-statutory document that is applicable to theconstruction & use of ( Test Equipment ) IS .

i) HSE . Guidance Note-38 .
ii) IET . Guidance Notes 3 .
iii) IET . O.S.G. BS-7671:2008 ( 2011 )
iv) BS-7671:2008. No 1 :2011 .

• Test Method 1 (- as well as checking theContinuity of the protective conductor . also measures ( R[SUP]1[/SUP] + R[SUP]2[/SUP]) which when added to the External Impedance ( Ze ) enables the Earth FaultLoop Impedance ( Zs ) to be checked .

 

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Megger1552

BondedMetalwork Testing [ HI ]

Testleads set . Option . 1 or 2 .

i) Connect the ( GreenLead ) to the Bonded Metalwork .
ii) Connect the ( RedLead ) to Line .
iii) Supply voltage is displayed .
iv) The test will “ Bleep “ & automaticallystart when voltage is detected .
v) Measured résistance value is displayed .

Thisis how . -&-s like to hear about GN-38 – Leads . !!!! 2391-10 . -&-s Exams :banghead:

• MFT . 1552 : ( Ze ) Testing .

Supplyis turned OFF. 100A - Disconnector is Isolated from Supply . ◄ ( MainIncomer )

Disconnectthe Main incoming Earth Conductor from the ( MET )

Then. Connect your ( Black ) GS-38. Lead fullyinsulated leads onto the Earth Conductor . making sure you get a good connection ) ► Wording . GN-38 – Leads :banghead:

Turnon Megger to the setting of ( Hi –Loop)

Thentake your ( Red ) GS-38. Lead fully insulated lead / with “ TIP “ placethis onto the Main incoming left hand terminal ( Main - Line Conductor )

Fewseconds the . Megger 1552 – will Automatically Read - ( .28Ω ) - Ohms’

Recordthis onto your . ( Certificate ) Thenconnect Earth Conductor. back UP . to the ( MET )

MFT . 1552 – 3 . : if circuitsare RCD protected then you’ll need to use “ Three-wires “ onthe ( No– Trip Setting ) for Zs .
( Ze ) & ( PFC ) is generally carried out at the ( Intake )where ( No RCD ) protection exists so that willbe ( Two-Leads ) ON the ( Hi ) currentsettings .

( Ze & Zs ) aremeasured in ( Ohms ) & (PFC ) ismeasured in ( kA)

• Non-trip – 3 – Leads for RCD side . ←

• Hi ) setting& 2 – Leadsfor Non-RCD ←

 

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EarthFault Loop Impedance . D/B –1 : D/B – 2 : there areTwo distribution board on site ,

Ata distribution board ( D/B-2 ) . This measurementis called ( Ze ) is only really correct when its measured at the ( First Distribution Board )of the Installation . for the External Impedance of the Installation .

Whenconnected & button pressed it fires a current of up to ( 25A ) or so through the loop. it depends on theImpedance of the circuit . the time ofthe pulse is limited to ( 40mS ) Two cycles on a 50Hz supply . this is for . Safety Reasons.

DirectMeasurement ( Ze ) . The reason that (Ze ) is required to be Measured are Twofold .

i) Verify that there is an Earth Connection .
ii) Verify that the ( Ze ) value is equal to orless than the value determined by the designer & used in the DesignCalculations .

 

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Faultfinding when RCCB Trips . ( blast from the past )

Switch OFF all the ( Switches / MCB ) connectedin the circuit downstream the . RCCB . Switch ON . RCCB & switch ON the switches . Oneby One . You will find that during switching ON of a particular Appliance / Switch . RCCB trip again & again

Whichshows that is the Faulty ( Circuit / Appliance ) .Isolate the Faulty Circuit . as you know. ( Rectify the Fault & Switch ON the RCCB )

 

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➥ .MCBs . are designed for One Faultlevel irrespective of SIZE.

 

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Wording: 2391-10 : -&-s Exams .

Earth Fault Loop Impedance .

-&-s) Test that has to be carried on anEnergized Installation . ( Safety Precautions must be Taken )

➥ Purpose of thetest is to ensure that . in the event of a ( Line – to – Earth Fault ) enough current will flow around the ( Earth Fault LoopImpedance )
Tooperate the protection within a specified time . Example )- Ring Final Circuit – 411.3.2.2.– p/53 . The maximum disconnection timestated in ( 41.1.) shall be applied to Final Circuits NOT exceeding 32A . (Time – 0.4s )

Themeasured value of Loop Impedance is then compared with that given in )- ( 41.1. )

Wording : -&-s Exams . Earth Fault LoopPath .

TheEarth Fault Current Loop ( Line – to – Earth Loop ) comprises the followingparts .
( Starting ) at the point of Fault . → the circuit protective conductor . → the consumer’s earthing terminal &earthing conductor : For .

TN- systems the (Metallic return path ) Or .
TT– systems the earth return path – the path through the earthed neutral point ofthe transformer & the windings . & the Line conductor from thetransformer to the point of Fault . Theearth fault loop impedance ( Zs ) at apoint distant from the origin of the installation is measured with the ( Main protective bonding conductor )conductors in place .

 

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ElectricalSeparation : 612.4.3.p/192.

Test. is usually an Inspection to ensure that certain circuit(s) are separatedfrom one another .

612.4.3. : The separation of the Live parts from those ofother circuit(s) & from earth .

 

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● Thisis – Only the Basics .

-&-s. Q/As . BS-7671:2011. make NOmistake . -&-s will get them IN somewhere .

BS-7671:2011. IS an OPEN BOOK . to -&-s . Yeah . Q/As

Choosethe correct type of Þ ( SPD ) for the Installation& Site in the correct location .

Regulation 534.1 : For the protection of ( A.C. ) power circuits . ( SPDs ) are allocated a Type Number .

Regulation 534.2 : Type ( 1 ) SPDs . are “ ONLY “ usedwhere there is a risk of direct lighting current . ↯↯ ( Origin of theInstallation ) -&-s
( Equipotential bonding . Or . Lighting protection / current . SPD) ▲▲
(Overvoltage ) - Type ( 2 ) SPDs .are “ USED “ at distribution boards. ( Distribution board / Consumer unit ) -&-s . 2392-10 . - ( CU) ⇇

(Overvoltage ) - Type (3 ) SPDs . are “ USED “ nearTerminal equipment . ( Terminal equipment ) -&-s

534.2.1. : Use of ( SPD )
Whererequired by Section 443 . or Otherwise specified . ( SPDs shall be Installed )

i) Near the Origin of an Installation . OR
ii) in the Main distribution assemblynearest the Origin of an Installation .

➥ if we look at . Regulation – 534.1. Scope & Object . Concept describes the Installation of . Type 1 : Type 2: Type 3:

 

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EAWR– 1989 . Regulation ( 5 )
Strength& Capability of electrical equipment which “ States “ NO electrical equipmentshall be put into USE where its strength &capability may be exceeded in such a WAY as may give rise to danger .

CircuitArrangements .

Therequirements of Regulations . 521.8.1. &521.8.2. “ Reference “ Designer & Electricians’ installers ofElectrical Installations .

521.8.1. p/122
Eachpart of a circuit shall be arranged such that the conductor(s) are notdistributed over different muiticore cables . conduit . ducting systems .Trunking systems . or Tray or ladder systems .

521.8.1.
Theconductor(s) of a circuit must NOT be distributed over different multicorecables . Conduits . Ducting . Trunking or Ladder systems . “ However “
Where multicore cables arerun in Parallel . forming ONE circuit this requirement need NOT be met . if multicore cables are installed in Parallel. then each cable must contain ONE conductor of each Line .

521.8.2. The Line & Neutral conductors of each final circuit.

Thisrequirement need NOT be met where a number ofmulticore cables forming ONE circuit areinstalled in Parallel .

 

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Class11 . Lights - NoEarth Required . Double Insulated .
Class11 . lights which can be used where the Earth is missing .

( Lighting can onlyreally be corrected by a re-wire )

Westill have houses without an Earth tothe Lights . 2392-10 . you will find this during Inspections .

Regulations. As far as getting an Earth from somewhere else it ( States ) :Earth Wire must run along the same route as the Live supply & it will to beat least 4mm sq if not part of the cable .

542.1.8.– 543.1.1. – 521.8.

542.1.8. p/158 .
Wherea number of installations have separate Earthing arrangements . any protectiveconductors common to any of these installations shall either be capable ofcarrying the maximum fault current likely to flow through them or ( be Earthed) within one installation only & insulated from the Earthing s
Arrangementsof any other installation . in the latter circumstances , if the protective conductor forms part of a cable. the protective conductor shall be Earthed only in the installation containingthe associated protective device .

521.8. p/122 .
521.8. 1. Each part of a circuit shall be arranged such that theconductors are not distributed over different multicore cables .conduits . ducting systems . trunking systems . or tray or ladder systems . Etc.

 

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Condition Report Inspection Schedule for Domestic & Similar Premises with up to100A Supply . -&-s

● Nice one Bruce . Good Call . :yes:

 

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2392-10 : -&-s : What isthe status of an Electrician who will be carrying an Inspection of anInstallation
Competent Person . 621.5. Testing & Inspection shouldonly be carried by a competent person .

 

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710.411.3.2.1. (-&-s ) in MedicalLocations of ( Group 1) & ( Group 2 ) Where RCDs are required . ONLY type ( A ) or Type ( B ) shall beselected . depending on the possible Fault Current arising .

NOTE : Type ( AC ) RCDs SHALLNOT be USED . this iswhat -&-s are looking . Q/As .2011 .

Note – Type ( A ) RCDS . tripping is ensured for residual ( sinusoidal ) alternating current & for ( pulsatingdirect currents ) D.C.
Note – Type ( AC )RCDS . tripping is ensured for residual ( sinusoidal alternating current ) . A.C.

 

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Justa Reminder .

O.S.G. – p182 . Table 11 .
( 10mm[SUP]2 [/SUP][SUP] [/SUP]- Copper / 1.83 )

Continuityof Protective Conductors .

“ Main Protective Bonding Conductor . “
Asthe résistance of copper conductor is known . is continuous throughout itslength .
10m– length . of 10mm[SUP]2 [/SUP] MainProtective Bonding Conductor . Reading ( should givea reading of approximately . 10 x 1.83 ÷ 1000 = 0.0183Ω )

Résistanceof copper conductors in milliohms per metre ( mΩ/m ) at 20°C . ◄

 

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LightingCircuit(s) . Lampholders in damp situation(s) oraccessible to persons in contact with Earthed Metalor within ( 2.5mm of a Bath or Shower ) should be fitted with “ Home Office Skirts “

TheName has NOT died out Yet . ( H/O – Specifications – Straight ◄ )

BattenLampholder(s) : Straight BattenLampholder . C/W Home Office Skirt . Long Skirt . Conformsto BS-EN-61184 .

Useful Junk .

Inthe . 30”s & 40”s . The factoriesAct was also known as the Home Office . ( H.O. ) Regulations& parts of this are still referred to in ( H.S.E. ) publications .

Appendix3 – of the Memorandum of Guidance on the . Electricity at Work Regulations .1989 .

( H.O. ) Shroud – or Skirt . achieved compliance withthese regulations .. because it prevented the metal cap of the lamp beingtouched in damp situations .

Blastfrom the past . ? IET .

Years ago (in the30's/40's) the Factories Act was also known as the Home Office (H.O.)Regulations and parts of this are still referred to in HSE publications (seeAppendix 3 of the Memorandum of guidance on the Electricity at Work Regulations1989). I was told that the H.O. shroud (or skirt) achieved compliance withthese regulations because it prevented the metal cap of the lamp being touchedin damp situations. There were various other standards around in those daysincluding Ministry of Works and Parker Morris requirements ? when I was anapprentice maintaining old domestic properties, I was told this required one lightingpoint and one socket outlet in each room. That was in the days when the bedroom lightingpoint was not positioned in the centre of the ceiling but offset towards thewindow because this wouldprevent the shadow of anyone undressing in the room being seen on the curtainsoutside! ?apparently, the H.O. shroud has even outlived this requirement.

 

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UsefulJunk

CircuitBreaker . BS-3871 . 10A - Replaced ◄◄ BS-EN

Thisvalue of current can be carried indefinitely by the device . & is known asits nominal setting ( In )
Thevalue of the current which will cause operation of the device ( I[SUP]2[/SUP] ) will be larger than ( In ) & will be dependenton the device’s “ fusing factor “ . this is a figure which . when multipliedby the nominal setting ( In ) willindicate the value of operating current ( I[SUP]2[/SUP])

Thisfusing factor is approximately ( 1.45 ) our 10A devicewould not operate until the currentreached ( 1.45 ) x 10A = 14.5A . the Regulationsrequire co-ordination between conductors & protection when an Overloadoccurs .

( 1.45 ) x 10A =14.5A …… 10A– Lowest =14.5A

 

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Takenform my old Notes . blast from the past .

Ratingof fluorescent circuits . “ Banks of Fluorescent tubes “

Fluorescenttubes are rated in Watts .
Forany reason .we are not working to ( Watts ) plant is not rated in ( Watts ) now inVolt amps . ??? ( VA ) it is recommended that . if NO other information is Available . The lamp wattage may be multiplied by ( 1.8 ) in order to determine the ( VA ) rating .

VA) rating of a Fluorescent Unit with an 80W tubeis ( 1.8 x 80 = 144VA )

Whensupplied at 230V the current taken would be : I = VA / A : = 144 ÷ 230V = 0.6A .

● Stroboscopic Effect. the Reason(s) ????

forthe sake of Apprentices .

whilea Fluorescent lampis in operation the light may flicker .

undersome circumstances this may make it appear that ( Rotating Machinery ) has ( Slowed down or Even Stopped ) this is calledthe “ Stroboscopic Effect “

One of the following methods .

Balancingthe Lighting Load – Three – phase .

Ifa large lighting load is installed in a Three – phase . Installation where there is some rotatingMachinery . the “ Stroboscopic Effect “ effect may be overcome by connecting alternategroups of lamps to a different “ Phase “

Advantage of balancing the lighting load . Brown – Neutral - 6 / lights . : Black –Neutral - 6 / lights . : Gray – Neutral - 6 / lights . :

 

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Note :

Some of these questions arenow out of date but some are still usable .

State – 3 circumstances thatwould result in an ( Increase inconductor résistance )

Increase in conductortemperature due to Overload .
Increase in conductortemperature due to Fault Current .
Increase in conductortemperature due to increase in Ambient temperature .
Reduction of C.S.A.
Increase in conductor length.

A Single phase ( TN-C-S )installation has a measured value of external loop impedance of ( 0.015W )
Show bycalculations the expected value of Prospective FaultCurrent . at the Origin .

Ipfc = Uo / Ze . Thus a Prospective Fault Current of circa ( 16kA) can be expected at this Point . ( 2011 – Ipf )

The Continuity of a lightingcircuit protective conductor is to be tested . if the test method uses atemporary link between Line & Earth in the Distributionboard – Consumer Unit . State .

At which points in thecircuit the test should be conducted .
The conductors between whichthe tests should be made .
The significance of the testreading at the end of the circuit .

i) at each point .
ii) Line & CPC .
iii) ( R1 + R2 ) for the circuit .

 

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2392-10 .

the Assessment is in twoparts .
i) Practical assessment . ( On the Boards Testing )
ii) Multi – choice examination .

612.5 – theVerification shall be made by a (Competent Person )
610.6. – On completionof the Verification , according to regulations . 610.1. to 610.5. a certificate or Certificates . shallbe prepared .

· Assessing the Risk. 2392-10 :

Hazard – means anythingwhich can cause harm .
Risk – is the change .great or small . that someone will actually be harmed by the hazard .

 

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2391-10 : the problem is being able to transfer theknowledge from your head onto paper .
never assume that the examiner will know what I mean as you will only gain marksif you can clearly ( Demonstrate ) by your answers . that you are Competent inthe Theory of the 2391:10
Question may contain words such as (State . List . Explain with the Aid of a Diagram . Explainbriefly . Show All Calculations )
Explain Briefly ) would require a brief explanation . usually no more than one ortwo sentences .
State ) maybe a short statement & may even be only a few words or Less .
Show All Calculations ) are self explanatory . buta Correct Answer without showing the calculations would only gain a smallpercentage of the actual marks .available for that question .

 

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Testing Insulation Résistance ( Insulation Résistance value with circuit(s) tested in Parallel )

the more résistance there are in parallel . thelower the overall resistance .& in consequence . the longer a cable thelower the insulation résistance . add to the fact that almost all installation circuits are also wired inparallel .

test on large installationsmay give . if measured as a whole . pessimistically low values . even if thereare no faults .

from a Inspector point of View ( floor by floor . periodic testing . tominimize disruption )

 

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(1 ) . 2011

AlternatingCurrent Motors . ( A.C. )

Thereare many different types of . A.C. motor operating from either Three-phase or Single-phase . A.C. supplies .

TheThree-phase motor depends on the rotation of a ( Magnetic field) for it’s movement .

Coilsor Poles are ( Arranged 120° apart ) &connected as to an Alternating ( Three-phase supply ) Each pole willbecome fully energized at a different time in relation to the Others .

TheIron core of eachcoil becomes ( Magnetized ) as the coil is energized . the arrangement gives the effect of a ( Magnetic field ) rotating around the coils .

-&-s : Thespeed of rotation of the ( Magnetic field) is called the ( Synchronous Speed ) & is dependent on the ( frequency ) ofthe supply & the number of ( Pairs of Poles ) . Hence .

ƒ = N[SUP] S [/SUP] . P

ƒ ) is the supply frequency in Hertz . ( Hz )
N[SUP] S [/SUP] ) is the Synchronous Speed in ( revs / second .
P ) is the number of ( Pairs of Poles )

Calculatethe : ( SynchronousSpeed ) of a ( Four – pole machine ) if the supply ( frequency ) is ( 50Hz )

ƒ = N[SUP] S [/SUP] . P

Therefore: N[SUP] S [/SUP] = ƒ / p . = 50 ÷ 2 = 25 . revs / second – Or 1500 revs / min .

p ) 4 .poles are 2 .

 

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(2 ) Eight – pole Induction Motor . 2011 .

Eight– pole Induction Motor runs at ( 12 revs/second ) &is supplied from a ( 50Hz ) supply . ◄► Calculate the ( Percentage Slip ) – ( % )

ƒ = N[SUP] S [/SUP] . P

50 ÷ 4 = 12.5 revs/second )

S( % ) = ( N[SUP] S [/SUP]- N[SUP] [/SUP][SUP]r [/SUP][SUP] [/SUP]) / N[SUP] S [/SUP]x 100

=( 12.5 [SUP] [/SUP]- 12 ) / 12.5 x 100 .

= 0.5 x 100 / 12.5 [SUP] . [/SUP]= ( 4% )

 

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FunctionalTests .

Circuitbreakers .
Youshould operate the manual mechanism of each circuit breaker to make sure thedevice opens & closes as it should do .

Recordin your Report any of the following items found while Testing or Inspecting .circuit breakers .

i) Doubts about the reliability or effectivenessof the device .
ii) Damage .
iii) Parts that have worn away unexpectedly .
iv)Evidence that a device has failed to operate as it should .

 

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(3 )

“ Three-phase . four – wire system “ !!

Three– phase Circuits .

Three– phase supply comprises ( Three – Wave forms ) each separated by ( 120° ) &the resultant waveform is ( ZERO )

Two main ways ofconnecting Three – phase equipment. ( Star ) & ( Delta )

( Star ) → . Star or Neutral point .
( Delta ) → .Usually - Motor Windings .

( Star Connected Load ) → . Natural Conductor )- “ Generator → Load . “
Fedfrom a Star connected supply . The addition of the conductor between the ( Star points ) converts the system into what is Known as a “ Three-phase . four – wire system “

Currentssupplied by “ Generator “ flow along the Lines . thought the Load .& return via the ( Neutral Conductor)

Currentsin a ( Balanced Three– phase supplyadd up to ZERO ) Therefore - IB = IBLK + IG = In = 0 . thecurrent flowing in the Neutral is ZERO .

Since NO currentflows between the Star points . they MUST both be atthe same (Potential ) which is also ZERO . the Star point of a Transformer is ( Earthed ) is alsoat ( ZERO VOLTS )

i) - One reason for the connection of the ( Neutral Conductor) is to provide a path for currents if the system became ( Unbalanced )
ii) – Another is that it enables ( Single-phase Loads )to be connected to a ( Three – phase supply )

the ( Windings )of most ( Three – phase Motors )are connected in ( Delta ) as the ( Line – Windings ) areperfectly ( Balanced &No Neutral is Needed )