***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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EarthFault Loop Path .

Thisis an extremely important concept which is often a requirements of anyexamination . EarthingSystem . may be broken down into ( 2 ) areas .

i) External to the installation ( Ze )
ii) Internal to the installation ( R[SUP]1 [/SUP] + R[SUP]2 [/SUP] ) [SUP] [/SUP]
[SUP] [/SUP]
[SUP] [/SUP]Although ( Ze ) for each of the systems can be Measured. DNO . may also be consulted for values. O.S.G. p/11 . generallyquote the figures .

TN-S. 0.8Ω
TN-C-S. 0.35Ω
TT. 21Ω [SUP][/SUP]

 

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Circuitdiagram of the Earth Fault Loop Impedance path . ETC .

Diagrams “ look up in the regulations . 44 / 45

Ina TN-S system the protective earth connection back to the supply transformer isprovided by the ( metallic covering of the cable supplying theinstallation(s) or a separate conductor )

Ina TN-C--S system the protective earth connection back to the supply transformeris provided by the ( PEN . conductor is earthed at two or more points & an earth electrodemay be necessary at or near a consumer installation )

2392-10. Useful Junk .
p/164. 543.4. Combined Protective & Neutral ( PEN ) conductors .

► No 1 -2011 . the ( PEN system is deleted ) Fig 2.2.

Under . 543.4.1.
Note - in Great Britain .Regulation 8(4) of the Electricity Safety . Quality & Continuityregulations 2002 prohibits the use of ( PEN) conductors in ( Consumer’s Installation )

p/32– 2008 . . Regulation 8(4) of the Electricity Safety .Quality & Continuity regulations 2002 states that a Consumer shall NOTcombine the Neutral & Protective functions in a single conductor in his (Consumer Installation )

2391-10. is an extension of the . BS-7671:2011 . IET WiringRegulations . -&-s . recommends that you are broadly familiar withthe use of test instruments & appropriate test(s) . ……….. GN-3

SupportiveTexts .

BS-7671:2008 . No 1 : 2011
GN-3– Essential .
O.S.G.. Desirable .
Others. Helpful .

□ In the event ofa Fault the Earthing system shall provide a ( Low ImpedancePath ) to the source of supply .
□ Such a path must provide ( High Fault Currents ) & disconnection times inline with the requirements of BS-7671:N01 . 2011

□ Identify four Earthing Conductor(s) p/37

CPC.
MainEquipotential Bonding Conductor .
EarthingConductor .
SupplementaryProtective Bonding Conductor . where required .

 

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FaultCurrent Occurs :

Theimpedance of the fault current path . ( Fault Loop Impedance Path ) must be low enough to allow sufficientcurrent to flow to ensure the protective device will operate ( within ) the specified time .

Conductors. ( PEN ) Protective EarthedNeutral .
CPC. Circuit ProtectiveConductor .
S)- Cross-sectional area of liveconductor . p/39 . S )- Size ( nominalcross-sectional area ( mm[SUP]2[/SUP] ) of theconductor
p/39. tp )- maximum permitted normal operating conductor temperature( °C )

Current)- p/38 .
Ia) Currentcausing automatic operation of protective device . within the time stated.
Ib) Designcurrent of circuit . ( or Loadcurrent )
In) Ratedcurrent or current setting of protective device . ( A )
Iz) current-carryingcapacity of a ( Cable ) for continuous service under the particular installationconditions concerned . ( A )

I[SUP]2[/SUP] ) Current causingeffective operation of the overload protective device . ( A )
Currentcausing the effective operation of an overload device ( with overload current )

If) Faultcurrent . ( A ) Earth fault current . = Uoc + Zs . ( Uoc . Open – circuit voltage ) p/39
Ipf) Prospectivefault current . ( A )

It) Tabulatedcurrent-carrying capacity of a ( Cable ) ( A )
Thetabulated current-carrying capacity required for a ( Conductor )

IΔn) Rated residual operating current of the protectivedevice in amperes . ( RCD )
mA) Milliamp – ( 0.001A )

 

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Impedance& Résistance . ( You will see this a lot through drawing )

□ R[SUP]1[/SUP] ( Z[SUP]1[/SUP] ) Résistance ( Impedance ) of Line conductor from the origin to the end of thecircuit .
□ R[SUP]2[/SUP] ( Z[SUP]2[/SUP]) Résistance ( Impedance ) of the Protectiveconductor from the origin to the end of the circuit .

p/39. R[SUP]1 [/SUP])[SUP][/SUP] Résistance of the line conductor of adistribution or final circuit . ( Ω )
R[SUP]2 .[/SUP]) Résistance of circuit protective conductor ( CPC ) of a distribution or final circuit . ( Ω )

R[SUP]E .[/SUP]) Résistance of the earthing arrangements of the transformersubstation . ( Ω )
R[SUP]A .[/SUP]) The sum of the resistances of the earth electrode & theprotective conductor connecting it to the exposed – conductive – parts . (Ω ) p/39 .

Z [SUP]E .[/SUP]) That part of the earth fault loop impedance which is external to theinstallation . ( Ω ) p/39 .
Z [SUP]E .[/SUP]) Impedance of the Line / Earth loopexternal to the installation . ( Ω )

Z [SUP]s .[/SUP]) Earth fault loop impedance . ( Ω )
Z [SUP]s .[/SUP]) Line / Earth loop impedance from the source of energy tothe end of a final circuit .

Mathematical .

< ) Lessthan .
≤ ) Lessthan or equal to .
> ) Morethan .
≥ ) Morethan or equal to .
► ∞ ) Infinity. ( Testing )

 

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Current – Carrying – Capacity .
Themaximum current which equipment or cable can carry under specified conditions withoutexceeding the designed operating temperature of the equipment or cable . witha ( givenambient temperature )

Disconnector- another name for an Isolator .

EnergyLet Through . ( I[SUP]2[/SUP]t )
energy let – through value of device . ( A[SUP]2[/SUP]s )
Thetotal energy let – through experienced by a protective device before theprotective device finally interrupts the fault current flowing into the circuitconcerned .

► EquipotentialBonding . p/27 . ( 17[SUP]th[/SUP] Edition / No1 . . MainProtective Bonding Conductor ) p/37 – ( 2 = )
Electrical connection maintaining various exposed-conductive-parts& extraneous- conductive-parts at substantially the ( same potential ) .
AnElectrical connection between exposed-conductive-parts & extraneous-conductive-parts ( Which puts them at approximately the same potential )

p/32. Protective MultipleEarthing ( PME )
anearthing arrangement . found in ( TN-C-S ) Systems .in which the supply ( Neutral Conductor ) is used to connect the earthingconductor of an installation with ( Earth ) in accordance with the Electricity Safety .Quality & Continuity Regulations 2002 .

UsefulJunk . ( Thismay come up on 17[SUP]th[/SUP] Edition / No 1– 2011 ) ◄
Reduced Low Voltage System .p/61 . Table 41.6.
Anelectrical supply in which the voltage between . Phases is 110 voltage . &the Line to Earthdoes NOT exceed ( 63.5. ) voltage for Three-phase . or ( 55 voltage for single– phase supplies .

TheHumble MCB. ( Made way for the RCD )
ProtectiveDevice .
Itis a device installed in a circuit to protect the circuit by disconnecting thesupply to it if there is an ( Overload )( Short – circuit ) or ( Fault to Earth )

 

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TransformerSource of Electrical Energy . P/44 / 45.

TN-S. – Separate Neutral & Protective conductorsystem . ( L1 – L2 – L3 – N . CPC. )
TN-C . – Combined Neutral & Protective conductor system. ( L1 – L2 – L3 – N & CPC = PEN )

TN-C-S. – Neutral & Protective conductor (Combined ) from the source to the origin of theinstallation . ( & then separated within the installation ) ◄◄◄ ( L1 – L2 –L3 – N & CPC = PEN ) …………. Do Notmix this up with a normal ( PEN )

UsefulJunk . Residual Current Device(s) – RCD.
Wherean RCD is used for Additional Protection . only theLine & Neutral conductors are topass through the magnetic circuit . The Protective Conductorbeing Outside that Circuit .

Maximum Demand & Diversity . p/41 .
311.1. - Maximum Demand . The maximum demand of the installationhas to be calculated in ampere’s .
311.1. - Diversity . Whencalculating the maximum demand current for an installation or circuit .diversity may be taken into account .

 

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The first letter indicates the Utilisation category . Table 41.2. p/55
g) indicatesfull range breaking capacity .

the second letter indicates the Utilisation category .
G) denotesgeneral application including the protection of Motor Circuits .
M) indicates protection of Motor Circuits or circuitswith an inrush current .

P/37 – No 1 -2011 .
ProtectiveConductors . Earthing & Equipotential Bonding .
Fig 2.1.
ProtectiveConductors – General .
Itis important to recognise that the “Term “ Protective Conductor is generic& embraces the following particular ( Protective Conductors )

□ Circuit protective conductor . ( 1 )
□ Main protective bonding conductor ( 2 )
□ Earthing conductor . ( 3 )
□ Supplementary protective bondingconductors ( Where required )

• Main earthing terminal .
• Exposed – conductive – part .
• Extraneous - conductive – part .
• Main metallic water pipe ►► ( Extraneous - conductive – part . )
• Earth electrode ( TT & IT systems )
• Other means of earthing ( TN- systems )

Mainprotective bonding conductor

Theprincipal purpose of providing Main ProtectiveBonding Conductor is to protect against dangers resulting from EarthFaults on the supply so that any Fault voltage on the ( MET ) & all exposed– conductive – parts connected to it are substantially at the samepotential ( Under these conditions ) toExtraneous – conductive – parts . such as water pipes .

 

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OpenCircuit
Acircuit that is not complete or continuous .
OpenCircuit
Acircuit is said to be Open when a break exists in a complete conducting pathway.

Continuity
Thestate of being continuous . or connected together . circuit that is not brokenor does not have an open .

Whatis a Short ?
AShort Circuit may be defined as an undesired very low résistance path in or around a given circuit .
Shortto be a virtually Zero résistance path that disrupts the normal operation ofthe circuit .

MCB– is a device that cuts of power when the current being drawn is to high .Usually as a result of a Short Circuit .remember it has a ( Low Résistance )& so it “ Encourages “ more current to flow .

Short Circuit . When thishappens ( 99.9% )of the time the results will be a spike in Amps . so tripping any circuitprotection MCBs .

ShortCircuit
Alow résistance path . it usually creates high current flow .

Short Circuit - When a cable is cut in a circuit . A gap ismade & the current can no longer circulate . known as ( Open Circuit)

Q) Why do the résistance is Zero in case of Short Circuit .
A) Since the current is maximum in the Short Circuited path . current alwaysprefers easy path to go so whenever the current is maximum obviously therésistance is minimum .

ParallelCircuit : is formed when two or more circuits are connected across the same twopoints .

Thecurrent in a parallel circuit equals the voltage applied across the circuitdivided by the résistance between thetwo points where the voltage is applied

 

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Overload . An overcurrent occurring in a circuit which iselectrically sound . p/32

Short Circuit Current . p/34
An overcurrent resulting from a fault of negligible impedancebetween live conductors having a difference in potential under normal operatingconditions .

Protectionagainst Overload Current .
Forthe protection against Overload Current . protective devices must be providedin the circuit to break any Overload Current following in the circuitconductors before it can cause a temperature rise which would be detrimental toinsulation .

433.1.1. p/81
Inorder to achieve this protection the nominal current of the protectivedevice ( I[SUP] [/SUP]n ) should be NOT less than the design current of the circuit ( Ib ) & that( In ) should NOTexceed the current-carrying-capacity of the conductor ( Iz ) & that the current causing effective operation of theprotective device ( I[SUP]2[/SUP] ) does NOT exceed ( 1.45 times ) thecurrent-carrying-capacity of the conductor ( Iz ) expressed as .

Ib≤ In ≤ Iz .
I[SUP]2[/SUP]≤ 1.45 . Iz .

( I[SUP]2[/SUP]) p/38
Current causing effective operation of the Overload ProtectiveDevice .

Ifthe résistance ( R ) remains constant oris very small compared with the current ( I ) as in the case of ( Short Circuit Current ) then energy becomesproportional to ( I[SUP]2[/SUP]t ) which is way the energy let-through of a MCB isexpressed in ( Ampere squired seconds & referred to as ( I[SUP]2[/SUP]t)

European Standard requires the breaker to carry ( 1.13 times ) the rated current without tripping for atleast one hour . & when the test current is increased to ( 1.45 times ) the rated current . it MUST tripwithin one hour . & again from cold if the last current is increased to ( 2.55 times ) the rated current the breaker must tripbetween ( 1 & 120sec ) This inverse time delay characteristic of all MCBs clamming compliancewith EN-60898 must operate within these limits.

433.1. Co-ordination between conductor & Overload ProtectionDevice . p/81 . 2392-10
Every circuit shall be designed so that a small overload of longduration is unlikely to occur .

 

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Guideto the Wiring Regulation .
BS-EN-60898 device thermal characteristics

Current . ( 1.13 – In) … Desired result - Must not tripwithin ( 1h )
Current . ( 1.45 – In ≤ 63A ) … Desired result - Must trip within ( 1h )
Current . ( 1.45 – In ≥ 63A ) … Desired result - Must trip within ( 2h )
Current . ( 2.55 – In ≤ 32A ) … Desired result - Must trip between ( 1 & 60s )
Current . ( 2.55 – In ≥ 32A ) … Desired result - Must trip between ( 1 & 120s )

Formof Residual Current .

Supply . Sinusoidal A.C. - Suddenly applied – Slowly rising .
Supply . Pulsating D.C. - Suddenly applied – Slowly rising .
Supply . Smooth D.C.


Bonded ( As Applied to items of Metal Work )
Connectedtogether electrically . not normally for the purpose of carrying current but soas to ensure a ( Common Potential )

Insulation
Suitablenon-conducting material enclosing . surrounding or supporting a conductor .

 

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-&-s . Q ) The maximum disconnection time for a lighting circuit in acommercial premises protected by a TT system is . A ) 0.2s . table 41.1
Youwill get this on . No 1 2011 .

-&-s . Q ) - A generating set used as an ( Additional Source ) ofsupply in parallel with another source . & is installed on the load side ofall the protective devices for a final circuit . the ( Additional requirement )not applicable . A ) A generating set shall be connected by meansof a plug & socket . 551.7.2.

►► Trip up one . -&-s . A line conductorincludes .
All conductors except neutral, . protective conductors & PENconductor – definitions’ p/29

-&-s . Q ) - The tables listing . Current – Carrying – Capacities . ofvarious cables in Appendix 4 of BS-7671 .. are based on an Ambient Temperatureof ??
A) Wording - ►► 30°C – Appendix 4 . Tables ( 4DIA – 4J4A )

Q) A single-phase circuit using 2.5mm2 single-core pvccables in conduit supplies a design current of 20A. If the cables are 15m longand have a rated voltage drop of 18mV/A/m, the actual voltage drop will be
A ) 5.4V (18mV/A/m x 20A x 15m) ÷ 1000 = 5.4V

Q) . Before issuing an Electrical Installation Certificatefor a new installation, a recommendation must be made with regard to the inspection
A) The design of the electrical installation(134.2.2 or Appendix 6)

Q) . During thetesting Line of an electrical installation which test would be carried outfirst ?
A) Continuity of protective conductors(612.2.1) p/22

Q). Equipment ►►► NOT likely tocause significant harmonics include
A) Under floor heating supplies ( Appendix 11 )

□ Variable speed motor drives .
□ Fluorescence lighting banks .
□ D.C. power supply . ( Remember – anything for D.C. to A.C. harmonics ) change over .
□ Under floor heatingsupplies

 

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Q) . Where can you obtain the voltage drop for a busbarsystem
A) From the manufacturer ( Appendix8 ) p/410 .

□ From the Wholesaler .
□ From the manufacturer
□ From Appendix 4 .
□ O.S.G. part 5 of BS7671 : 2011

Q ) A BS EN 60898 circuit breaker can be used for A ) ( Table53.4 ) p/149


□ Isolation .
□ Emergency switching .
□ Functional switching .
All of the above .

Q) The maximumvoltage drop allowed for a lighting circuit in a consumer’s installation,supplied by a public L.V system is
A ) 3% (App 4 ) 4Ab –p/314

2392-10 . Documentation for every electrical installationshould include that required by regulation (132.13 ) p/20 .


□ 514.9.
□ Part 6 .
□ Part 7 . whereapplicable
All the above

Q ) When consideringif Supplementary Bonding can be omitted from a location containing a bath orshower . the maximum résistance of extraneous conductive parts connected to theMain Earth Terminal is ??
A ) 1667 Ohm’s . ( 415.2.2. )if calculated you get 1667Ω .

p/243 . Q) All junction boxes fitted to solar photovoltaic systems ( P.V. generator and PV array) shall carry a warninglabel indicating
A) Thatparts may still be alive after isolation from PV converter (712.537.2.2.5.1)

p/242 . Q) Which is the preferred method of protection on the dc sideof a photovoltaic power supply ?
A ) Class II or equivalent insulation ( 712.412 )

 

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ClassificationCode outcomes used for the ( Inspection Schedule ) for domestic & similarpremises with up to 100A supply .

Classificationcode outcomes : Acceptablecondition (✓)
Description : Thecondition of the particular item inspected has been classed as acceptable

Classificationcode outcomes : Unacceptable condition (C1)
Description : Thecondition of the particular item inspected has been classed as unacceptable. Immediatedanger is present and the safety to those using the installation is at risk(e.g. a live part is directly accessible)

Classificationcode outcomes : Unacceptablecondition (C2)
Description : The conditionof the particular item inspected has been classed as unacceptable. There ispotential danger and the safety to those using the installation may be at risk(e.g. absence of main protective bonding)

Classificationcode outcomes : Improvementrecommended (C3)
Description : Theinstallation is not dangerous for continued use but the inspector recommendsthat an improvement could be made in relation to the item inspected (e.g. noRCDs for additional protection are installed)

Classificationcode outcomes : NotVerified (N/V)
Description : A particularitem on the schedule is relevant to the installation but has not been verifiedas to its condition

Classificationcode outcomes : Limitation(LIM)
Description : Aparticular item on the schedule is relevant to the installation but there werecertain limitations in being able to check the condition

Classificationcode outcomes : NotApplicable (N/A)
Description : Theparticular item on the inspection schedule is not relevant to the installationbeing inspected

 

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PME . Protective Multiple Earthing .
PVC. Polyvinyl Chloride .
SP. Single-pole .
TP - Triple-pole
4P – Four-pole .

SP&N. Single-pole & Neutral .
TP&N. Triple-pole & Neutral .
XLPE. ( X ) ►Cross-Linked Polyethylene or Ethylenepropylene rubber insulation .
( Vd ) Voltage drop – Vor mV .

CableGrouping Correction Factors .

Ifa number of cables is installed together & each is carrying current . thywill all warm up . Those which are on the outside of the group will be able totransmit heat outwards . but will be restricted in losing heat inwards towardsother warm cables “ buried “ in others near the centre of the group may find itimpossible to shed heat at all . & will rise further in temperature .

i) Widely spaced cablesdissipate heat easily .
ii)Closely packed cable cannot easily dissipate heat &so its temperature rises .

 

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2392-10 / Domestic Level .
Cablesizes & circuit protective devices .

i) Calculate the design load & maximumexpected current of a ( Circuit )
ii) Select cable to suit design current (Installation method effects current carrying capacity of cable ) …… C.C.C.
iii) Select protective device ( MCB ) to suit thecables . … C.C.C.

example. Cooper T&E. using table 4D5. p/340
example. 2.5mm[SUP]2[/SUP] radial circuit – with the cable run down an InsulatedStud Wall with the cable touching the (Inner wall Surface ) ? Plasterboard . has a . … C.C.C. of ( 21A ) so a ( 20A .. MCB or lower couldbe used .

thesame ( Cable ) with the cable run NOTtouching the inner wall { completely surrounded by insulation } has a … C.C.C. of 13.5A & a 10A MCB . would have to be Used .

4.0mm[SUP]2 [/SUP] ( Cable ) would have a … C.C.C. of 27A & 17.5A in the above installationmethod .

Generallya cable’s … C.C.C. needs to be derated by ( 0.50 ) for any run where its surrounded by thermalinsulation for more than ( 500mm ) thisreduces if the length in insulation is less . ( 500 or more – 0.50 ) the 17[SUP]th[/SUP]Edition only goes up to 400mm
-&-s . Cables surrounded by thermal insulation for ? 400mm or more has a derating factor of ?? 0.51 . table 52.2 .

( … C.C.C. … Current – Carrying – Capacity .of the cable )