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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 ) 
VoltageRating :
:17:
TheVoltage rating of the Overcurrent Protective Devicemust be at least Equal to or Greater than the circuit Voltage .
Voltagerating of an Overcurrent Protective Device is afunction of its capability to open a circuit under an Overcurrent condition .
Thevoltage rating determines the Ability of the OvercurrentProtective Device to “ Suppress “ & “ Extinguish “ the internal arcing that occurs during the openingof an Overcurrent condition .
Ifan Overcurrent ProtectiveDevice is used with a voltage rating lower than the circuit voltage . arcsuppression & the ability to Extinguish the arc will be Impaired & .under some Overcurrent conditions . The OvercurrentProtective Device may NOT clear the OvercurrentSafely .
Thevoltage rating is required to be marked on all OvercurrentProtective Device .
RCBO is RCD+ MCB - ( RCBOs combines the functions of an MCB &RCD in One Unit )
RCD do Nothave Overload Protection . it needs a separate MCB t o backupprotect it . So an RCBO is formed :17:
Residual Current Breaker with Overload Protection
ExposedConductive Parts : :juggle2:
Thesesare Metallic Parts of an Electrical System .which can be touched & which are not normally Live .
Thesecan become Live under Fault Conditions .
Metalcasings of “ Appliances“ ( Kettles . Ovens . )
Wiringcontainment systems such as Metal Conduit . Cable Tray & Trunking .
ExtraneousConductive Parts : :juggle2:
Theseare Metallic Parts within a Building . which do not frompart of the Electrical System . but canalso become Live under Fault Conditions .
Water & Gas Pipes .
AirConditioning .
Boilers .
AirDucting System .
StructuralSteel Work of the Building .
Purposeof Earthing .
Byconnecting to Earth all Metalwork not intended to carry current . a path is provided for leakage currentwhich can be detected & interrupted by RCDs . MCBs
CleanEarth return path from the Consumers Earth to the Supply Earth .
TheEarth Fault Loop.
Theconnection at the consumers Earth can be by means of either an Earth Electrodeat the building were the Earth isrequired or may be in the form of acable which runs back to the Generatoror Transformer & is then connected to an EarthPoint .
Generatoror Transformer at the point of supply always has an Earthpoint . a circuit is formed when Earth – Fault currents are flowing .
Ifthese Fault Currents are large enough they will operate the protective device . thereby isolating the circuit .
The “ Star point“ of the secondary winding in a Three phase - Four – wire distribution transformer is connectedto the Earth to maintain the ( Neutral at Earth Potential )
OverloadCurrent :
Occursin a circuit which is Electrical Sound . p/27 -
FaultCurrent :
Isthe level of current flowing at a level up to & including the ( Prospective Short Circuit Current ) being the Maximum Current that the SupplyTransformer is capable of delivering .
Prospective Short Circuit Current ) must also be taken into account whenselecting the Type of Overcurrent Deviceto be installed .
FaultOccurs at the point between Line Conductors of negligible Impedance or betweena Live Conductor & an Exposed Conductive Part . [ it ismore serous than an Overload Current ]
Wherethe Earth Fault Loop Impedance for a circuit exceeds the maximum ( Zs ) for theOvercurrent device . is it permissibleto use an RCD .
Yes:- Regulation – 411.4.4. – 411.5.2.
Asthe Designer of an Installation . am I allowed to rely on the “ RCD element of an RCBO :49:“ to provide for Fault Protection in order toallow for Loop Impedance values greater than in table 41.3.
Yes:- so long as all the other ApplicableRequirements of the 17[SUP]th[/SUP] Edition ( asAmended ) are met . includingthose for Protection against Overload & Short Circuit .
Stillworking on an Electrical Installation that was designed before “ Amendment 1“ to BS-7671:2008 came into full Effect on ( 31 December 2011 ) to which requirements should theinstallation be ( Inspected . Tested . Verified & Certificated)
AnInstallation Designed before ( 31 December 2011 ) should be ( Inspected . Tested . Verified & Certificated) to BS-7671:2008 .That is to the Origin Version prior to the “ Amendment “
MotorWindings : :49:
A Motorcan be manufactured with the Windings Internally Connected. if this is the case & there are Three Terminal Connections in the Terminal Block labelled .
( U . V .& W . ) you wouldexpect the Motor Windings to be connected in ( Delta Configuration)
MotorWindings with Delta Connection :
Theremay be four connections in the Terminal box labelled ( U. V . W . & N ) if this is the case . The Windings would bearranged to give a ( Star Configuration)
MotorWindings with Four Connections :
Alternatively. the Terminal block may contain Six Connections . ( U1. U2 . V1 . V2 . W1 & W2 . ) This is used where both Star & DeltaConfigurations are required .
TheTerminal connections can then be reconfigured for either Star or Delta .
MotorWindings with Six Connections :
• U1 . U2
• V1 . W2 .
• W1 . V2 .
Cable Selection – Overview .
Requirements .
● The cable supplying the Load should be able to carry the current to the Load safety . After taking into account Diversity . without the cable overheating – ( 523 . App – 4 )
● Protective Devices should be able to provide protection for the cable from excess current ( 432.433. )
● The Length of the cable is Limited to ensure adequate voltage supplies the Load . ( 525 )
● Maximum Loop Impedance of a circuit is Low enough to ensure Disconnection within times specified by Table – 41.1.
● 0.4 – ( TN- ) 0.2 – ( TT ) for all circuits < 32A
5 sec . Disconnection time for Sub-mains distribution circuits
612.7. Earthelectrode résistance .
Wherethe earthing system incorporates an earth electrode as part of the installation. the electrode résistance to Earth shall be measured .
NOTE : Where a measurement of( Ra ) is NOT practicable the measured value ofexternal earth fault loop impedance may be Met . :13:
612.13. Functional testing :
Wherefault protection and/or additional protection is to be provided by RCD . theeffectiveness of any test facility incorporated in the device shall be verified.
612.13.2. Equipment . such as switchgear and controlgear assemblies . drivers . controls and interlocks. shall be subjected to a functional test to show that it is properly mounted .adjusted and installed in accordance with the relevant requirements of theseRegulations . :13:
2392-10-
612.14. Verification of voltage drop .
Whererequired to verify compliance with Section 525 . the following options may beused .
(i)The voltage drop may be evaluated by measuring the circuit impedance .
(ii)The voltage drop may be evaluated by using calculations . for example . bydiagrams or graphs showing maximum cable length v load current for differentconductor cross-sectional areas with different percentage voltage drops forspecific nominal voltages . conductor temperatures and wiring systems .
NOTE : Verification of voltage drop is not normally requiredduring initial verification . – Still the Same :13:
Certification& Reporting :
631.1.
Upon completion of the verification of a new installation orchanges to an existing installation . an Electrical Installation Certificate .based on the model given in Appendix 6 . shall be provided . Such documentationshall include details of the extent of the installation covered by theCertificate . together with a record of the inspection . the results of testingand a recommendation for the interval until the first periodic inspection . :rockon:
Certification& Reporting :
631.2.
Upon completion of theperiodic inspection & testing of an existing installation . an ElectricalInstallation Condition Report . based on the model given in Appendix 6 . shallbe provided . Such documentation shall include details of the extent of theinstallation and limitations of the inspection & testing covered by theReport . together with records of inspection . the results of testing and arecommendation for the interval until the next periodic inspection . :13:
631.3.
Where minor electrical installation work does not include theprovision of a new circuit . a Minor Electrical Installation Work Certificate .based on the model given in Appendix 6 . may be provided for each circuitaltered or extended as an alternative to an Electrical Installation Certificate. :13:
631.4.
Electrical Installation Certificates . Electrical InstallationCondition Reports and Minor Electrical Installation Work Certificates shall becompiled and signed or otherwise authenticated by a competent person or persons. :13:
631.5.
Electrical Installation Certificates . Electrical InstallationCondition Reports and Minor Electrical Installation Works Certificates may beproduced in any durable medium . including written and electronic mediaregardless of the media used for original certificates . reports or theircopies . their authenticity and integrity shall be verified by a reliableprocess or method . The process or method shall also verify that any copy is atrue copy of the original . :13:
560.9. Emergency Lighting Systems .
Emergency Lighting Systems . shall comply with the relevant partof BS-5266 series .
560.10. Fire Detection and Fire Alarm Systems .
Fire Detection and Fire Alarm Systems . shall comply with the relevantpart of BS-5839 series . :13:
Table41.1. .
411.3.2.2.
Themaximum disconnection time stated in Table 41.1 shall be applied to finalcircuits NOT exceeding 32A . :crazy:
Maximum disconnection times . ( No change on number ) 0.4 / 0.2 . Etc .
Bottom . Table 41.1.
Where . in a TT system . disconnection is achieved by anovercurrent protective device and protective equipotential bonding is connectedto all the extraneous-conductive –parts within the installation in accordancewith Regulation 411.3.1.2. the maximum disconnection times applicable toa TN system may be used .
Uo is the nominal a.c. r/ms or d.c. Line voltage to Earth .
Where compliance with this regulation is provided by an RCD . thedisconnection times in accordance with . Table 41.1 relate to prospectiveresidual fault currents significantly higher that the rated residual operatingcurrent of the RCD .
Note : Disconnection is not required for protection againstelectric shock but may be required for other reasons such as protection againstthermal effects .
416.2.4.
Whereit is necessary to remove a barrier or open an enclosure or remove parts ofenclosures . this shall be possible only .
(i) Still the same – 17[SUP]th[/SUP] Edition.
(ii)Still the same – 17[SUP]th[/SUP] Edition .
(iii)Still the same – 17[SUP]th[/SUP] Edition .
Note: This regulation does not apply to :
A ceilingrose complying with BS-67
* A Cord operated switchcomplying with BS-EN 60669-1 . FirstAmendment :sunny:
A bayonetlampholder complying with BS-EN 61184
AnEdison screw lampholder complying with BS-EN 60238.
* A Cord operated switchcomplying with BS-3676 . – 17[SUP]th[/SUP] Edition.
312.3. Deleted by BS-7671:2008 – Amendment no 1 . :sunny:
312.3. :- Type of Earthing Arrangement . 17[SUP]th[/SUP]Edition . 2008
411.4.7. No Change . “ First Amendedment“
Wherea circuit breaker is used to satisfy the requirements of regulation 411.3.2.2 or regulation 411.3.2.3. . Themaximum value of earth fault loop impedance ( Zs ) shall be determined by the formulain regulation 411.4.5 . Alternatively . for a nominal voltage ( Uo ) of 230Vand a disconnection time of ( 0.4s ) in accordance with Regulation 411.3.2.2.or ( 5s ) in accordance with Regulation 411.3.2.3. The values specified intable – 41.3. for the types and ratings of overcurrentdevices listed may be used instead ofCalculation .
BS-1361:1971( 1986 )
Specificationfor cartridge fuses for A.C. circuits indomestic & similar premises .
Replacedby BS-88-3: 2010 and withdrawn 1/3/2010 . First Amendedment
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