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
Therequirements are :- Thecable supplying the Load should be able to carrythe current to the Load safety . after takinginto account Diversity . without the cable Overheating– 523 . App 4
Protective Devices should beable to provide protection for the cable from Excess Current – 432. 433 .
TheLength of the cable is Limited to Ensureadequate voltage supplies the Load . 525.
MaximumLoop Impedance of a circuit is Low enough to ensure disconnection within timesspecified by Table 41.1.
( 0.4 - TN ) & (0.2 sec - TT ) for all circuits 32A ( FinalCircuits Not Exceeding 32A ) P/46 (5 sec disconnection time ) for Sub –main distribution circuits . Etc .
Two Important Measurements mustbe taken to prevent this hazard . :50:
i) Impedance of acircuit conductors is kept to a minimum . The Earth Fault LoopImpedance under Fault Conditions . ii) Overcurrent device protecting the circuit isselected to rapidly disconnect an Earth Fault .
Room Thermostat should belocated in the part of the house where people spend the most time . it shouldbe ( 1.5m. ) above floor level . ( 0.5m away from an outside wall ) :aureola:
Relevanttests of Regulation – 612.2. to 612.13 .Example Continuity of Protective conductors & Earth Fault Loop Impedance .Applicable to parts of the system(s) such as room & cylinder Thermostats .motorized valves & programmers .
( YES ) Automatic Disconnection of Supply ( ADS ) is acommonly – used protective measures against Electric Shock in such systems .The Continuity of the protective conductorsto each point should be confirmed . This value of ( R2 ) or ( R1 + R2 ) may be used to estimate the Maximum EarthFault Loop Impedance of each control circuit for Verification Purposes . Insulation Résistancetests should also be carried out . precautions having been taken to avoiddamage . to any Electronic Components . The test results should be recorded on a Schedule oftest results .
DoesBoiler pipework need to have Main Protective Bonding Conductor for ElectricalSafety Reasons . :dupe:
Thereis “ NO SPECIFIC “ requirements for Boiler pipework to be SupplementaryProtective Bonding Conductors . However:- Such bonding may called for in the Boiler Manufactures . in which case BS-7671:2008 .requires those Instructions to be followed ( Regulation 510.2. refers ) Anystated requirements for Additional Bondingthat is considered to be Unnecessary should be queried with the ManufacturesConcerned. & Amended Installation instruction requested .
Isan RCD Main Switch . ( Such as a 100mAtime – delayed device )still required in the Consumer Unit of a New Domestic Installation forming partof a TT System . :dupe:
Fora Domestic Installation complying with the 17[SUP]th[/SUP] Edition where allthe Final Circuits are RCD – protected . AnRCD Main Switch. is NOlonger required . Provided that the Consumer Unit is of all Insulated Construction .
2392-10:- Asthe Designer of an Installation . Am I allowed to rely on the RCD element of an RCBOto provide for Fault Protection in order to allow for ( Loop ImpedanceValues ) Greater than given in Table 41.3 .
Yes) . So long as all the other Applicable requirements of the 17[SUP]th[/SUP] Edition ( as Amended ) are met .Including those for protection against Overload & Short – Circuit . Regulationnumber(s) 411.4.4. - 411.4.5. - 411.4.9. :aureola:
Wherethe Earth Fault Loop Impedance for a circuit Exceeds the Maximum ( Zs) for the Overcurrent Device . is it permissible to use an RCD . Yes:- Regulation . 411.4.4. - 411.5.2.
CanI use an ( Electrical Connector ) having “ push fit “ connections that the Manufacturer claims areMaintenance free in an area that will be inaccessible when the installation iscomplete .
NotNecessarily . Not all types or designs of Push Fits ( Screw less – type ) Clamping with the requirements ofRegulation - 526.3. ( vi )
Ifthe connector will be inaccessible when the Installation is complete . it mustComply with BS-5733 for a Maintenance – free accessorywith the Manufactures Instructions .
BS-5733 Requires . Example . Tests for Résistance to ageing .Cyclic loading . Overload . Fault current & Vibration .
Workingmy way around the 17[SUP]th[/SUP] Edition . 2392-10
Regulation. 544.1.2. Main ProtectiveBonding Conductor . ( Gas / Water ) :rant:
Positioningof Bonding Connection . ( Apprentices –look at the drawings – p/32 – Regulations )
17[SUP]th[/SUP]Edition . The main equipotential bonding connection to any . Gas . Water . orother services shall be made as near as practicable to the point of entry ofthat “ Service “ into the premises . Where thereis an Insulating section or insert at that point . or there is a ( Meter ) Theconnection shall be made to the Consumer’s hard ( MetalPipework ) & before any branch pipework . Where practicable theconnection shall be made within ( 600mm ) of themeter outlet union or at the point of ( Entry ) to the building if the meter isExternal .
Workingmy way around the 17[SUP]th[/SUP] Edition . 2392-10
Definitions. p/24 .
Extraneous-Conductive-Part. Conductive part liable to introduce apotential . generally Earth Potential . & not forming part of theElectrical Installation .
( A Metallic Fixture notassociated with the Electrical Installationthat could become Live under Fault Conditions ) :icon_bs:
Selectcable size from Appendix 4 . • Cableselection for type should have already been considered due to initial characteristicsof purpose . Environment . Maintainability . part 3 & 4 . Appendix 5 – External Influences .
• Appendix4 – table 4A1 provides methods of Installation which are cross referenced whenselecting the maximum Current Carrying Capacity ofthe circuit cable . p/260 .
• 2392-10 . DomesticInstallation cables are to be used the Appendix 4 – Table 4D5 . ( Sheathed flat cables) T&E.
525.1– Requirements for volt drop inbuildings .
Table 12 – Voltage Drop . Regulation - p/358
Making you Aware .
(i) Low voltage Installations supplied directly from apublic Low voltage distribution system ( lighting – 3% ) – ( Other uses 5% ) (ii)Low voltage Installations supplied from private LV supply – ( * ) ( lighting – 6% ) – ( Other uses 8% )
( * ) The voltagedrop within each final circuit should not exceed the values given in ( i )
Wherethe wiring systems of the Installation are longer than ( 100m ) .the voltage drops indicated above may be increased by ( 0.005% ) per metre of the wiring system beyond ( 100m ) without this increase being greater than ( 0.5% )
Thevoltage drop is determined from the demand bythe Current-using Equipment . applying Diversity factorswhere Applicable. or from the value or the Design Current of the Circuit .
Current– Using Equipment :17:
554.1.Electrode water heaters & boilers .
554.1.4. RCD tooperate in Excess of 10% of rated current but can be extended to 15% dependant upon machine . Time Delay RCDs maybeUsed .
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