***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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“ Certification& Reporting “ resents3:

Listfour characteristics of the Electrical Supply that should be recorded on theDocument - this could come Up on-&-s .

313 – Supplies .

313.1. General The followingcharacteristics of the supply or supplies . from whatever source . & thenormal range of those characteristics where appropriate . shall be determinedby Calculation . Measurement . Enquiry or Inspection .

i) The nominal voltage(s) & its characteristics includingharmonic distortion .
ii) The nature of the current & frequency .
iii) The prospective short-circuit current at the Origin of the installation. ◄
iv) The Earth Fault Loop Impedance of that part of the systemexternal to the installation ( Ze )
v) The suitability for the requirements of the installation .including the Maximum Demand .
vi) The type & rating of the overcurrent protective device(s)acting at the Origin of the installation . ◄

These characteristics shall be ascertained for an External Supply& shall be determined for a private source . These requirements are equallyapplicable to main supplies & to safety services & standby supplies . ◄

NOTE : The above information should be provided by distributors’on request ( see Appendix 2 sec 2 )

Appendix 2 – Informative ) Some things have been Changed . inWording .

Definitions’ - p/39 . ( Ze )
That part of the Earth Fault Loop Impedance which is External tothe Installation ( Ω ) 313.1.

 

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Fundamental requirement to understandthe basic principles . Measured / Calculated results and what affect they haveon a circuit . :rofl:

Conductor Résistance .

Whywe divided the Length ( x . mΩ/m figuresby ( 1000 )

Wedivided the length ( x . mΩ/m figures by ( 1000 ) to obtain a résistance value in Ohms .

O.S.G.– 9A )- milli-ohms per meter values . Weneed to covert them to Ohms for our Calculations’ ( dividing by 1000 does this )

 

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Chapter 61 :

Initial Verification – Inspection 611 & Testing 612

Initial Verification [ Inspection & Testing ] Therefore helpsto ensure that Electrical Installations are Safe before being put into Service.

611 )- Inspection .

611.1. – Inspectionshall precede Testing & shall normally edone with that part of the installation under Inspection disconnected from theSupply . ◄◄

 

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Therequirements of BS-7671:

BS-7671requires that every installation shall be Inspected& Tested to verify that the Regulation(s) havebeen met before [ Being put into Service ]

On completion of an installation or an addition or alteration toan installation . appropriate Inspection & Testing shall be carried out toverify so far as is reasonably practicable that the requirements of thisstandard have been Met .

133.2.1. Voltage :
Electrical equipment shall be suitable with respect to the maximumsteady-state voltage ( r/ms value for a.c. ) likely to be applied . as well as overvoltage’slikely to occur .

Note : for certain equipment . it may also be necessary to takeaccount of the lowest voltage likely to occur .

610.1. Every installation shall . during erection & oncompletion before being put into service . be inspected 7 tested to verify . sofar as is reasonably practicable . that the requirements of the regulation(s)have been Met .

Precautions’ shall be taken to avoid danger to persons &livestock . & to avoid damage to property & installed equipment . duringInspection & Testing .

612 )- Testing . InitialVerification .
612.1. General .
The tests of regulation 612.2. to 13 . Where relevant . shall becarried out the results compared with relevant criteria .

The Test of Regulation(s) 612.2.1. to 612.6. where relevant shall be carried out in thatorder before the installation is Energised .

If any Test indicate a failure to comply . That Test & any precedingTest . the results of which may have been influenced by the fault indicated .shall be repeated after the fault has been rectified

Three Important Tests .

612.2. – Continuity of Conductors .
612.2.1. - Continuity of Protective Conductors including main& supplementary equipotential bonding .

A continuity test shall bemade . it is recommended that the test be carried out with a supply having a (No-load ) voltage between 4V & 24V .ETC.

612.2.2. Continuity of the Ring Final Circuit Conductors .

Your Earthing is your First Line of Defence . ◄◄ :19:

 

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( T ) 134.2. InitialVerification . -&-s :19:

134.2.1. During erection& on completion of an installation or an addition or alteration to aninstallation .
& before it is put into service . appropriate inspection &Testing shall be carried out bycompetent persons to verify that the requirements of this Standard have be Met.

 

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612.13.1.

The Effectiveness of RCDs test facility will be Verified .

 

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Exclusions from Scope . 702.11.

Except for Areas designed especially for Swimming Pools . The requirementsof Section 702 . Do Not Apply to .

Natural waters . Lakes or Coastal Beaches .

 

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(T) 711.6. Inspection& Testing .

All TemporaryElectrical Installation(s) ofExhibitions .
Shows& Stands are required to be Inspection& Tested in line with Chapter 61 after EACHASSEMBLY on SITE.

First Amendedment . No change . 711.6.

 

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What is the Maximum value of Insulation résistanceof a 230V lighting circuit .

( 1MΩ ) - 612.3.2. – Table 61. 500V / d.c. . -&-s . 2392-10 :19:

612.3.2.
The insulation résistance measured with the test voltage(s) indicatedin Table 61 . shall be conceded satisfactory if the main switchboard and eachdistribution circuit tested separately . with all its final circuit(s)connected but with current-using equipment disconnected . has an insulation résistancenot less than appropriate value given in Table 61.

Note 2 . Insulation résistance values are usually much higher thanthose of Table 61.


Whichof the following is Verified by the Polarity Test . -&-s . 2392-10

A) That there is a separation of live partsfrom other circuit(s) & from earth .
B) The Phase sequence of multi-phasecircuits is maintained throughout the installation .
C) Every fuse &single-pole control & protective device is connected to the line conductoronly . 612.6. & 612.1. :19:
D) All assemblies are properly mounted .adjusted . & installed correctly as required by the reverent regulation(s) .

 

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Which IET Guidance Note . describes methods of Testing ElectricalInstallation(s) ◄► -&-s

IET Guidance Note 1
IET Guidance Note 2
IET Guidance Note 3 ◄◄ :19:
IET Guidance Note 4

 

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Taken for old Notes .

Calculationwhen the protective device is an RCD orRCBO . :rofl:

ResidualCurrent Devices ( RCDs )

Wherethe installation is part of a TN-system . the basic requirement is given in Regulation 411.4.5. i.e..

Zs x Ia ≤ Uo volts.

Foran RCD ( Ia ) is the rated residual operatingcurrent providing disconnection in the required time .

ForTT systems the additional requirement that ( Ra x I∆n ≤ 50V )is given in regulation 411.5.3. In this requirement ( Ra ) is the sum of the earth electrode résistanceof the protective conductor connecting it to the Exposed Conductive Parts .

Inthe above expression . of course . ( I∆n ) is in amperes . limitingconsideration to residual current circuit breakers ( RCBOs ) to BS-EN 61008 . the values of ( Zs ) & ( I∆n ) encountered in practice are such that there is no difficulty in meeting therequirement given above .

Theearth fault current is limited by the value of ( Zs ) & will be of the same order as occurs when fault protection . is provided byOvercurrent protective devices . It should be checked that the RCD complieswith Regulation 531.2.8. which requiresthat it is capable of withstanding without damage the Thermal & Mechanical Stresses caused by the earth faultcurrent .

Ifan ( RCCB ) to BS-EN 61008 does notincorporate an intentional time delay it is required by the British Standard tooperate within ( 0.04 sec ) at aresidual current of ( 5 I∆n A ) &the designer merely has to check that the circuit is Thermally protected forthat time .

531.2.8.

Wherean RCD is used for fault protection with . but separately from . an Overcurrentprotective device . it shall be verified that the residual current operateddevice is capable of withstanding . without damage . the Thermal &Mechanical Stresses to which it is likely to be subjected in the case of afault occurring on the load side of the point at which it is installed .

 

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BS-7671:2008. does not Demand that diversity be taken into account but . for the economicdesign of an installation . diversity cannot be ignored .
Thediversity factors used must be optimistic . an adequate margin of safety mustalways be allowed .

Asindicated in Regulation 433.1. whichgives the general requirement concerning Overload protection .
Circuitsshall be so designed that small Overloads of long duration are unlikely toOccur .

 

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Inspection: 2392-10

Carryout the Initial Verification ( Inspection . Testing & Certification ) of aninstallation to BS-7671:2008

As -&-s rightly asks the Q/As . State the Human Senses that may need to be employed the Initial Verification of an Installation .

Definitions p/29 – Inspection : Examination of an Electrical Installationusing all the Senses as Appropriate . BS-7671:2008 . Amendment No 1 :2011

2392-10. Fundamental Initial Verification of ElectricalInstallation(s) - Three areas to this Unit . :19:
Preparationfor Initial Inspection & Testing .

Inspection.
Testing.

 

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General Requirement : :19:

Regulation 6101. ( p/156) - ( p/189)

Every installation shall . during erection and/or on completion beforebeing put into service be Inspected & Tested to verify . so far asreasonably practicable . that the requirements of the Regulation have been Met.

As an Inspector 2391-10 :2392-10 : )- The reason(s) for an Inspection & Test of an ElectricalInstallation is to verify that the installation complies with the Regulationswith regards to its ( Design & Construction )

Asan Inspector )- Carrying out the Inspection to for fill these requirements the Regulations . Call forthe following information to be “ MADE AVAILABLE “

Results of the assessment of General characteristics required bySection(s) ( 311. 312 . & 313 . )

Youare looking at .

313.1. General The followingcharacteristics of the supply or supplies . from whatever source . & thenormal range of those characteristics where appropriate . shall be determinedby Calculation . Measurement . Enquiry or Inspection .

i) The nominal voltage(s) & its characteristics includingharmonic distortion . ◄
ii) The nature of the current & frequency . ◄
iii) The prospective short-circuit current at the Origin of theinstallation . ◄
iv) The Earth Fault Loop Impedance of that part of the systemexternal to the installation ( Ze ) ◄
v) The suitability for the requirements of the installation .including the Maximum Demand . ◄
vi) The type & rating of the overcurrent protective device(s)acting at the Origin of the installation . ◄

These characteristics shall be ascertained for an External Supply& shall be determined for a private source . These requirements are equallyapplicable to main supplies & to safety services & standby supplies . ◄

Regulations call for the informationto be made available . ( 514.9. )
( Provide all the necessaryinformation as to circuit type . number of points & their positions . cablesizes . protective device types & their ratings . )

InitialInspection :
611.1. ( p/156 ) – ( p/189 )

Inspectionshall precede testing & shall normally be done with that part of the ( Installation Disconnected from the Supply ) ◄◄◄◄◄◄

Just a Reminder !

Regulation(s) states134.1.1. ( p/19 ) – ( p/21 )
Good workmanship by a Competent Person or Persons under theirsupervision & proper materials shall be used . in the erection of the electricalinstallation . Electrical equipment shall be installed in accordance with theinstructions provided by the ( MANUFACTURES of the EQUIPMENT )

Regulation 612.2. ( p/159 ) – ( p/191 )
Calls for the inspector to confirm that equipment has been selectedin accordance with Section 511 . of theWiring Regulations . & the equipments compliance with the relevant Britishor Equivalent Standard .

 

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2392-10:

Of what use to us is the Measuring of Earth Fault Loop or ( Zs ) of the circuit .

Ifwe know the value of it we can use “ Ohm(s) Law “ to calculate the Fault Current that will flow. ( if a FaultOccurs )

Formulawe can apply is ( Voltage = Current ) Résistance .

Wecan see that Fault Current & EarthFault Loop Impedance are directly linked . The lower the Earth Fault Loop theHigher the Fault Current & Vice Versa .
Therefore - The lower the Earth Fault Loop / The Higherthe Fault Current . The quicker the Protective Device will operate to cut theCurrent .

Ifwe limit the Maximum Value of the Earth Fault Loop we can be confident that theFault Current will be of a Higher Magnitude to operate the protective device .
Regulation– 411.3.2. :- Automatic Disconnection inCase of a Fault .