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
-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
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.
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 .
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. )
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 .
(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 .
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 .
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.
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 ) RCDsSHALLNOT be USED . this is what -&-s are looking . Q/As .2011 .
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 .
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 )
• 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 .
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 - LineConductor )
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)
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 .
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 )
Best EV Chargers by Electrical2Go! The official electric vehicle charger supplier.
OFFICIAL SPONSORS
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
