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
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 .
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 .
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 .
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 .
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 )
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.
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.
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 .
Thisis a Live Test . ◄◄ for-&-s 2392-10 - ( At Socket Outlets)
“ Simple“ What is required . The Instrument is pluggedinto 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 .
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:
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