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
MainElements of Circuit design for conventional Circuits . :juggle2:
•Determine Design Current . actual flow of current through the cables ( Ib )less diversity where appropriate . •Select type & size of protectivedevice ( In ) •Apply any correction factors to reduce self heating of cables ( It ) •Select type & size of cable fromAppendix 4 ( Iz ) •Determine whether volt drop is satisfactory for Length . Loading & routingof cables .
Note (- 2392-10 Inmost practical applications where an Installation already exists you may havethe choice of Type but only Size .
ApplyingElectrical Design . Cable Sizing .
LoadCurrent ( I ) & design current ( Ib ) Effectivecontinuous current flow through a circuit -Basic Calculation : P = V . I or I = P/V
Whencalculating Design Current with inductive loading & where there isinsufficient information available apply a factor ( 1.8 ) to the power consumption . App 1 – Table1A O.S.G. note 2 - I = P x1.8 / V
Alternatively. if the powerfactor is known then apply ( P = V x I x Cos Ø or P = √3 x V[SUP]L [/SUP]x I[SUP] L [/SUP] x Cos Ø )
ApplyingElectrical Design . Cable Sizing .
DesignCurrent ( Ib ) Maximum Demand 311.1. ( MD )
Diversitymay be taken into account when determining MaximumDemand Diversity– O.S.G. Appendix 1 . Table 1A . 1B .
Point to Note : Not all circuits run at their full powerrating . CookerCircuit - Minus first ( 10A ) then 30% of the rest add( 10A ) to the Total + 5A for Socket / Outlet .
LightingCircuits : Domesticlighting ( 66% ) is assumed to be on Continuously .
PowerCircuits : 1[SUP]st[/SUP] Circuit = Full Rating . 2[SUP]nd[/SUP] Circuit 40% & all Other Circuits . ◄◄
Diversity applies to groups of circuits or / & cables supplying groups of circuitssuch as a Sub-mains distribution boards .
AppropriateBritish Standard or do a “ Risk Assessment“ :35:
• SafetyServices to be Installed to allow adequate duration equipment to be suitable tolast for the duration of Escape . •560.5.3. – Continual ( IT ) insulation monitoring devices that give an Audibleor Visual indication of the first fault in the System .
Ido fell the Humble MCB is in theBackground now . The RCD has taking Front Row . :aureola:
TimeDiscrimination :
Isachieved by delaying the Opening of the ( RCD or MCB ) upstream ( RCD or MCB ) untilthe downstream ( RCD or MCB ) has Opened & cleared the Fault . Thetotal clearing time of the downstream ( RCD or MCB ) MUSTbe LESS than the time setting of the upstream ( RCD or MCB ) & the upstreammust be able to withstand the Fault Current for the time setting period .
Thereforethe upstream ( RCD or MCB ) must be acategory which has been designed & tested for this purpose .
MCBs- To determine timediscrimination it is only necessary to compare the Time / Currentcharacteristic curves of the Two Devices to ensurethat NOoverlap Occurs .
RCBOs – have taking a primaryrole in Industry now - RCD/MCB . ( B & C . curves ) C forLighting . B forPower .
2392-10: Your first role is a Designing . second is Electrician . :aureola:
Forthe Protection of Lighting Circuits the “ Designer “ must select the CircuitBreaker with the Lowest Instantaneous trip current compatible with the inrushcurrents likely to develop in the circuit
Whatis an Insulation RésistanceTest ( IR ) :aureola:
AnInsulation Résistance Test measures the total Résistance of a products’ ( Cable) Insulation System(s) Itis also useful test to perform when doing preventative maintenance on ( Cable ) overtime .
Whatis an Insulation RésistanceTest ( IR ) Measuring& Recording long term Stability of Insulating Materials over time .
InsulationRésistance Testing . as a Tester . – The Test results can provide usefulinformation about a ( Cable Integrity ) & can yield clues when itsInsulation should be Replaced .
InsulationRésistance (- 2392-10 . from -&-s point of View . :aureola: InsulationRésistance measurement is preformed inorder to ( Assure Safety ) against ElectricShock through Insulation .
Apprentices(- ParallelRésistance Paths - Interferingcurrent in measured circuit will influence the TestResults.
From-&-s point of View (- “ Nulling“ / Test Leads Résistance beforeperforming Continuity Measurement
When measuring Insulation Résistance betweeninstallation conductors all Loads must bedisconnected . ( & all SwitchesClosed ) Mains Voltage Switched OFF
“Functionality “
Regulation 612 – BS-EN 61557.
ElectricalSafety in Low-voltage distribution systems up to 1000V. A.C. & 1500V . D.C. . Regulationsp/31 ( Low . Exceeding extra-low voltagebut not Exceeding 1000V . A.C. & 1500V . D.C. . between conductors. Equipmentfor Testing . Measuring or Monitoring of Protective Measures .
Thecircuit under test must be Switched OFF .de-energised & Isolated before test connections are made when carrying outInsulation & Continuity Tests .
612.2. & 612.2.1. Continuityof Protective Conductor(s) & Main Protective Bonding Conductor of New orModified Installation(s) must be verified before carrying out an Earth FaultLoop Impedance . or RCD test .
Isa Live Test. which is carried out on a circuit to check the Résistance of the Line conductor to Earth.
Thisshows if the current created under Fault Conditions will trip the MCB .
Apprentices: Refered to as Earth Fault Loop Impedance . -&-s . Extremely Important Test to verify the System is Safe.
TheEarth Loop Impedance test measures therésistance of the path that a ( Fault Current ) would take between Line & Protective Earth Thismust be low enough to allow sufficient current to flow to trip a MCB
InterpretingResults & taking Remedial Action . “Remember “ that it is NOT sufficient just to carry out TESTS & Record the Results .
Knowledge of Regulations . & of how to Interpret results . is alsorequired to ( Ensure the Installations ) Safetycharacteristics are within the prescribed limits . Example(- An excessive Earth Loop Impedance value should . (Prompt an Investigation ) into its CAUSE
Asa “ Inspector “ Remedial Action should then be carried Out .& the Installation Retested .
Inspectionis the Vital Initial Operation . Testingsupports the Inspection :dupe:
531.2.1.– A residual current device shall be capable of disconnecting all the Lineconductors of thecircuit at substantially the same time .
531.2.2.– The Magnetic circuit of the transformer of a residual current device shallenclose all the Live conductors of the protectedcircuit . The associated conductor shall be outside the Magnetic circuit .
531.2.3.– The residual operating current of theprotective device shall COMPLY with therequirements of Section 411 as appropriate to the type of System Earthing.
531.2.4.- A residual current device shall be so SELECTED & the ELECTRCALCIRCUITS so SUBDIVIDED that any protective conductor current whichmay be expected to OCCUR during normal operationof the Connected Load(s) Will be Unlikely to Cause unnecessary tripping of the Device .
531.2.5.– The USE of a residual current device associatedwith a circuit normally expected to have a protective conductor shall NOT be considered SUFFICIENT for Fault protection if there is NO such conductor . EVENif the rated residual operating current ( I∆n ) of the device does not EXCEED 30mA .
Workingmy way around the 17[SUP]th[/SUP] Edition – Selection & Erection / Part 5
Making you aware of Effects of External Influences - ( HEAT ) :66:
Protectionof Wiring Systems by :- -Shielding . - Distance. -Type of Wiring . -Changing or Reinforcing type of Insulation .
522.2.2.– Extra insulation – ( Lighting ) 522.3.- ( IP )rating for Ingress of Water . 522.4.- ( IP )rating for Ingress of Dust & Particles . 522.5.– ( Corrosion) from liquids . Electrolytic Action from dissimilar metals .
Workingmy way around the 17[SUP]th[/SUP] Edition – Selection & Erection / Part 5
Making you aware of “ Methods& Selection of Connection(s). :yawn:
“ ElectricalConnections “ :aureola:
- Conductor& Insulator materials . -Number & Shape of wires forming the Conductor . -C.S.A. of conductor . -Number of conductors Connected Together . -Temperature of Joint for normal Operation . -Prevent mechanical movement under Vibration .
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