***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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Definitions– Part 2 . BS-7671:2008 :17:

Bonding Conductor . p/20 .
Aprotective conductor providing equipotentialbonding .

Class1 Equipment . p/21 .
Whereprotection against electric sock does not rely solely on basic insulation alone. Exposed – conductive parts being connected to a protective conductor whiththe fixed wiring of the installation . (See BS-EN 61140 )

Class11 Equipment . p/21 .
Whereprotection against electric shock relies on the application of additional orsupplementary insulation .

Thereis no provision for the connection of a protective conductorto exposed metalwork .

DoubleInsulation . p/23 .
DoubleInsulation ( Class 11 ) Insulation comprising both basic Insulation &supplementary insulation .

Earth. p/23
Theconductive mass of Earth . whose electricpotential at any point is conventionally taken as Zero. ◄◄

EarthElectrode . p/23
Conductivepart . which may be embedded in the soil or in a specific conductive medium .e.g. concrete or coke . in electrical contact with the Earth .

Aconductor or group of conductors in intimate contact with . & providing anelectrical connection to Earth .

EarthElectrode Résistance . p/23 .
Therésistance of an Earth electrode to Earth .

EarthFault Current .
Anovercurrent resulting from a Fault of negligible impedance between a Lineconductor & an Exposed – conductive – part or a protective conductor .

AFault current which flows to Earth .

EarthFault Loop Impedance . p/23
The impedance of the EarthFault current loop starting & ending at the point of Earth Fault . This impedance isdenoted by the symbol ( Zs )
Symbol( Z ) - Unit ( Ω )

TheEarth Fault Loop .

The impedance of the EarthFault current loop starting & ending at the point of Earth Fault . Consists of :-
• The circuit protective conductor ( C.P.C. )
• Consumers Earthing terminal & Earthingconductor
• for TN – Systems . Themetallic return path .
• for TT – Systems & IT Systems Earth return path .
• The path through the Earthed neutral point ofthe Transformer .
• The Transformer winding & phase conductor to point of Fault .

 

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543-Protective Conductors .

543– provides information on the Selection of “ BOTH “ type & Cross – sectional Area of Protective Conductors .
Protective Conductors . areconductors provided for the purposes of Safety . protectionagainst Electric Shock .

GenericTerm “ ProtectiveConductors “ :thinking2:

 

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2392-10. as designer(s) . Am making you Aware of the Facts .

Cross-sectional Areas of Protective Conductors .

Thereare two Methods that may be Employed when choosing a Protective Conductor asrequired by Regulation 543.1.1.

TheCross- sectional Areas ( C.S.A. ) of every ProtectiveConductor . other than Protective BondingConductors .

MustBe :-

► Selected . in accordance with Regulation 543.1.4. - :icon4:

Or

► Calculated . in accordance with Regulation 543.1.3. - :icon4:

 

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2392-10: Yes we still use it in Industry :icon4:

543.2.7. Earthing Tail Requirement .

WhereMetallic Conduit . Trunking . etc is used for a ProtectiveConductor . The Earthing Terminal ofeach Accessory is required to be connected by a Separate Protective Conductor to the Earthing Terminal incorporated in theassociated box ( Back – Boxes) or other Enclosure .

 

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Fault Protection . “ Simply “

Automatic Disconnection Supply . :icon4:

 

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Applicationsof Earthing : :vanish:

All Metallicenclosures & Extraneous conduciveparts . are at Equipotential .

Functionsof Earthing :

EquipmentEarth : Path for Fault Current . lowertouch voltage . protection against Electric Shock .
LightingEarth : Low résistance path to diversethe current . Under lighting attack .
TelecommEarth : Signal Earth . reduce noise & interference . stabilize D.C. supply voltage & prevent ElectricShock .
ComputersEarth : Reduce interference . maintain supply voltages .

 

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Typeof Earthing :- :vanish:

SupplySystem – Neutral / Earth .
SystemEarth
ElectricalSafety Earth .
LightingEarth .
GeneratorEarth .
ProtectiveEarth . - Surge arrestor .
Telecom/ Computer Earth .
ShieldingEarth .
IntegratedEarthing System -
ElectrostaticEarth – Clean / room – Hospital .

 

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Factors affect to the EarthImpedance . TT Systems

Soil.
Weather.
Electrodetype .
Electrodesize .
Near by Utilities .
Electrode in Parallel . -&-s
Distance between Electrode .

 

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:thinking2:TT Systems

EarthRésistance of an Electrode

Soil Exhibits a resistance to the flow an Electrical Current .
Not an “ Ideal “ conductor
Résistance – can never be Zero . betweenthe Earth Electrode & “ True Earth “
The résistance between the Earth Electrode & “ True Earth “

SoilResistivity in ( Ωm )
Buriedlength of the Electrode in ( m )
Diameter of the Electrode in ( m )

 

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Fault :icon4:

A circuitcondition in which current flows through an abnormal or unintended path .

Thismay result from an Insulation failure or a bridging of Insulation .

Conventionallythe Impedance between Live conductors or between Live conductors & Exposed or Extraneous conductiveparts at the Fault position isconsidered Negligible.

 

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Regulation. Appendix 4 – ( 4D1A ) p/274 :17:

Caremust be taken tie sure that any Conductors’ which is operating above ( 70°C) is terminated into Equipment that canwithstand the higher temperature .
TheBritish Standard only requires that our Equipment is suitable for ( 70°C)

Ambient Temperature mustalways be taken into account .

TheCurrent Carrying Capacities given in the Tables in appendix 4 Calculated for a Cable operating in an Ambient Temperature of ( 30°C ) .

( 4D1A ) for4.0mm[SUP]2[/SUP] – Copper Conductor clipped direct can carry a currentof ( 37A ) at ( 30°C ) Pass a current of ( 37A ) through the conductor it would rise to ( 70°C )

Ambient Temperature were to increase to . ( 40°C ) then theTemperature of the conductor when we passed ( 37A ) through it would rise to ( 80°C )

Side– Effect . of this would be an Increase in Voltage Drop .

• The Maximumpermissible operating temperature of Cables are dependent mainly on the Type ofInsulation Material used in the Cable Construction

( 4D1A )
Ambient Temperature ( 30°C ) ◄◄
ConductorOperating Temperature ( 70°C )

Temperature is the Factor which dictates the size of theConductor in relation to the Number of Circuits Installed.

Thermoplastic : ( 70°C ) :44:

 

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Measurement of ExternalEarth Fault Loop Impedance ( Ze ) iscarried out between the Incoming Line & Protective Earth . :19:
Earthing Conductor Detachedfrom the ( MET ) & test probe clipped toit .

Measurementof the External Earth Fault Loop Impedance ( Ze ) at the Origin of theInstallation for compliance with regulation 612.9

EarthFault Loop Impedance :

Live Tests & great careshould be taken when carrying them out .

Thereare Two Measurements for Earth Loop Impedance .

i) One is for External Loop Impedance ( Ze )
ii) Other is for the Circuit Loop Impedance ( Zs )

Bothof these tests are carried out Using an Earth Fault Loop Impedance TestInstrument with Leads & Probes compliant to ( GS-38 )

(Ze ) Earth Fault Loop Impedance :

TheInstallation must be ( Isolated ) – “ Live Test “ ◄◄ -&-s & the Earthing conductor disconnected .
Connectone Lead to the disconnected Earthing conductor& then insert a Probe into the Terminal ofthe Incoming Line .

TheMeasured Value will be ( Ze )

I use the Megger 1552 : Two Leads .
►► Instrument has ThreeLeads then the Third Lead must be connected to the Incoming Neutral ofthe Supply .

Thisis what -&-s want to Hear . ▼

TheEarthing Conductor must be Reconnected beforere-energising the Supply to the Installation .

 

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(Zs ) Circuit Earth Fault Loop Impedance : :19:

Thisis a Live Test . ◄◄ for-&-s 2392-10 - ( At Socket Outlets)

“ Simple“ What is required . The Instrument is plugged into the Socketusing the Lead supplied & the resultRecorded .

TheHow’s & Why’s ??

Wherethe Circuit has NO socket outlets the instrumenthas to be ( Connected ) to the Exposed Terminalsof the Accessories on the Circuit being Tested .

ALL – POINTS must be tested & the Highest testresult Recorded as ( Zs ) for the Circuit

“ Certification& Reporting “
Onyour Test result sheet & add the Measured ( Ze ) to the Recorded ( R1 + R2 ) value . Then compare the totalvalue with the Measured ( Zs ) if it is Equal toor Lower then all is Fine .

Ifit is Higher then it may be that there is a Loose Connection & further Investigation is required .

Froma Testers point of View (- The Measured value will often be Less than theCalculated value due to the Presence of Parallel Path.

Measured( Zs ) must be compared to the Maximum value of ( Zs )

From-&-s point of View (- Ensurethat it complies with the Requirements for the circuit disconnection time .

 

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O.S.G.p/13 .
BasicInformation Required . 313.1. Beforestarting Work on an Installation . Etc

ForExisting Installations Electricians’ should Satisfy themselves as to the Suitability ofthe Supply including the Earthing Arrangement. :speechless:

 

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Regulations: Table 41.3 - Maximum Earth Fault LoopImpedance ( Zs )

Table 41.3 -For Circuit Breakers with ( Uo ) of 230V . ForInstantaneous operating giving Compliance with the ( 0.4s )disconnection time of Regulation 411.3.2.2.
BS-EN 60898 . / BS-EN 61009-1
MaximumMeasured Earth Fault Loop Impedance ( Ωs ) Overcurrent Protective Device is a Circuit Breaker .

Table 41.1.
MaximumDisconnection Times ( 0.4s ) - 411.3.2.2.
TheMaximum Disconnection Time stated in Table 41.1. shall be applied to FinalCircuit NOT Exceeding ( 32A ) - The regulations are using the Words . Final Circuit(s)

Apprentices. if we look at Table 41.1. - Maximum Disconnection Time stated in Table 41.1.is for a ( TN- system ) A.C. ≈ ( 0.4s )

MaximumEarth Fault Loop Impedance .
TheMaximum Earth Fault Loop Impedance is used to Calculate the available EarthFault Current within an Installation connected at ( Low – Voltage – below 1000V) :17: