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
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
If you Know → Need to know. Yeah
Volts÷ Ohm’s → Need to know =Amps Volts÷ Amps → Need toknow = Ohm’s Voltsx Amps → Need toknow = Watts Watts÷ Amps → Need toknow = Volts Watts÷ Volts → Need toknow = Amps Ampsx Ohm’s → Need toknow = Volts
Resistanceof the Length of Cable ….. Ohm’s x Current Drawn….. Amps = Volt Drop … Vd
FlexibleCables ?
Ifwe are “ Overloading “ a Cable : Keep inmind that the cable . Has a running current . by using more it will get Hot& eventually Melt the PVC coating . ( Plain English – Use the Right Size ) TheRegulations . my be a pain in the But !!There for a reason some kind person sitting at a desk has done the Work for us
Definitions/ p24 – Flexible Cord . A flexible cable in which the Cross-sectional area ofEach Conductor does Not Exceed 4.0mm[SUP]2[/SUP] ( PS. You will get this on CoP -&- ) 2011
BritishStandard BS-7671 : is set of Electrical Standards published by the IET in the UK . TheStandards are NOT a LEGAL REQUIREMENT but a set of Standards which will ensurea Safe & Proper Electrical Installation
Aswe Say in the Trade ?? Some Contracts Specify that the Electrical Equipment ofthe “ Installation “ will CONFORM to BS-7671 & so at this Point they become( LEGALLY BINDING on the INSTALLER )
Fora Designer point of View .
Definition)- MechanicalProtection
522.6.5.(v) A cable installed under a floor or above a ceiling shall be run in such a positionthat it is NOT liable to be Damaged by contact with the floor or ceiling ortheir fixings . PlainEnglish ) Be mechanically protectedagainst Damage . Prevent penetration of the Cable by Nails & Screws . & Like ( Keep Cables Out of Harms Way )
2392-10. We will use this on Part P . also
iii)&& (v) require Conduit & Trunking to be Earthed
• Whatis Mechanical Protection !!
Example : FP-200 is Fire Résistance? say 30 mins
Pyro: Mechanical Protection & Fire Résistance (2/1 ) i)Protection of cables against Mechanical Protection ii)Protection of cables against Damage by Fire …( Long history of performing extremelywell in Fire(s) - Beyond the duration necessary to ensure theObjectives !!
MostDesigners specify either MICS → ( Pyro ) orProprietary Fire-resisting Cable(s) Asa young Designer . ?? What would you Use .
?Mechanical Protection – running the cables on Cable Tray .
CableTypes ?? Twomost Important thing about Cable(s)
i)Insulation Properties’ are One of the Most Important things to consider whenselecting a Cable for a Circuit . (if the Insulation is not rated for the Environment the circuit is installed intit can have a number of Detrimental Effects on its operation & Safety )
ii)Mechanical Protection . for cables is probably as Equally as Important as itsInsulation if the circuit with limited Mechanical Strength . ( Installedin an Environment where there is a risk of it coming into contact with Heavy Objects. as for our point of view ? )
522.6.5.(v) A cable installed under a floor or above a ceiling shall be run in such a positionthat it is NOT liable to be Damaged by contact with the floor or ceiling ortheir fixings . PlainEnglish ) Be mechanically protectedagainst Damage . Prevent penetration of the Cable by Nails& Screws . & Like ( Keep Cables Out of Harms Way )
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
SeparatedExtra Low Voltage ( SELV ) Isthe most common method of providing protection . ElectricalSeparation ( Which means NO Electricalconnection between the SELV circuit &higher voltage systems )
* Regulation 610.1 - Theseare Hand & Glove with Q/As -&-s Everyinstallation shall during Erection & on Completion before being put into Service. be Inspected & Tested to Verify . So far is reasonably practicable . Thatthe regulations have been met .
( Precautions’shall be taken to avoid Danger to persons . Livestock & to avoid damage toproperty & Installed Equipment during Inspection & Testing )
Certification& Reporting –
* 632.4 . Defects or omissions revealedduring Inspection & Testing of the Installation Work covered by theCertificate shall be made good before the Certificate is issued .
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
All cable(s) have Electrical Résistance. So !
Therewill be Heat loss ( Energy loss ) when they Carry Current . This loss appearsas Heat & the Temperatureof the cable rises. i)The rate of Heat loss is a function of the difference in Temperature between the Conductor & thesurroundings . ii)“ Making it “ As the conductor Temperature rises – so does its rate of Heat Loss
Backon to Cable(s) . Cablesare designed to be able to withstand a certain amount of Heat Copperis a very good Electrical Conductor ( 300mm[SUP]2[/SUP]) Thismeans that the Résistance of a length of Copper Cable is relatively low .
Aluminiumcable would have Nearly Twice the Résistance of Copper Cables with the sameDimensions . ( 500mm[SUP]2[/SUP]) That’sthe reason why we stop using them / partly Cost
- Therésistance of the cable )- A higher résistancecable will get hotter at a given Current . -The Insulation on the cable )- This will tend to keep it warm like a quilt . - TheEnvironment of the cable )- were it is situated .
DesignCurrent ( Ib )
i)The first stage of the Design Current is to determine how much current will flowin the Circuit . ii)This Current is known as the Design Current & is the FULL LOAD CURRENT of the CIRCUIT. iii)Depending on Load ????
Singlephase . 230V resistive . I= P/V . at this stage you areCalculating the Design Current )- I = 2000 ÷ 230V = 8.70A
Three-phaseInductive Load . power consumption of 30.000Watts – 30kW Powerfactor – 0.95
atthis stage you are Calculating the Design Current )- I = P --- √3 x V cos Ø
UsefulJunk . Ambient Temperature( Ci ) RememberCables must give off Heat … ( Surroundings’ ofthe cable . the more difficult it is for the cable to get rid of Heat )
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Example. “ it still forms part of Designing “
Cable Calculations ( The Whys & How’s ) it’s a Start
- Workout the design current ( Ib ) … I = P/V -Select the Protective Device size ( Ib ≤ In ) - if we need to . Obtain all correction factors . Ca .Cc . Cg . Ci . -Calculate ( Iz ) … Iz = In ----- Ca x Ci x Cg x Cc -Select Conductor sizes . With ( Iz ) use the tables Appendix 4 & choose . ( Iz ≤ It ) -Calculate Volt-drop . Use design current ( mV/A/m ) value from cable table .The circuit length then ÷ 1000 [ Volt-drop Ib x ( mV / A / m ) x L --- 1000 -Calculate ( R1 + R2 ) Using table ( 9A / 9B & 9C ) find the mΩ/m value ÷1000 then apply multipliers . ▼ (R1 + R2 ) = 9A --- 1000 x 9B x 9C = Ω - Calculate( Zs ) ……. ( Zs = Ze + R1 + R2 ) = Ω -Verify ( Zs ) values with BS-7671 – using the tables in section 41 ensure calculatedvalues is less than the Tabulated values . ETC - Calculatethe Fault Current .. Using nominal voltage & ( Zs ) . I = Uo/Zs = A . PS – Usefuljunk Regulations p/35 . Symbols (If ) fault current ( A ) 442.2.1 -Establish the disconnection time . Usingthe fault current . device type & time / current graphs in Appendix 3 obtainthe Expected Disconnection Time . - Calculateminimum size of CPC . Using the Adiabatic formula . Input all values ( Including k factor ) & work out minimum size ofCPC . Then compare with our chosen CPC size .
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
559.6.1.5. Fixing of the Luminaries.
Thevast majority of light fittings are installed above head height . so clearly itis Important that the fittings are secure BS-7671 requires that the fixing for somethingas Light as a Pendent Set has to be capable ofsupporting a Mass of 5kg .
► Just a Point to Note here . The RCD is not just a Manually OperatedInsolating Switch – Sensitive Safety Device which cuts OFFin fraction of a second if it Senses an Earth Fault. ► Question ? it is NotPractical to fit One RCD to protect the Whole House . !! Why Tripping . Ido want to open a mine field here . “ Division of Installation “ 314.Every Installation shall be divided into Circuits . as necessary to ? (i) Avoidhazards & minimize inconvenience in the event of a Fault . “ So “ One RCDat the Main incoming does not meet this criteria . ( iv)
Example)- 8 – Way 30mA DPRCD … ( 1 x RCD) IP2X . BS-EN 60439-3……(British Standards )The country hasStandards for & reasonNOT made in China 100 Amp . Example)- 6A ( SP) type B / MCB …. 40A ( SP ) type B / MCB → This could be used for a Shower& Power Circuit ( SP ) meaning -Single – Pole ( Line Only ) ( DP ) meaning -Double – Pole ( Line& Neutral Only ) with ( L & N – Earth must be Added )
Asa Young Designer this must seem daunting . Don’t Worry gointo the Forum& Ask Questions . We wereApprentices at one Time . Yeah .
Meaning!! BS-EN 60439-3 Regulation530.3.4. ( Consumer’s Controlgear ) Learning Curve . Foran Installation with a 230V Single phase supplyrated up to 100A that is under the control of Ordinary Persons . Switchgear & Controlgearassemblies shall either comply with BS-EN 60439-3& Regulation 432.1. or be a Consumer Unit incorporating components &Protective devices specified by the Manufacturer complying with BS-EN 60439-3 . including the conditional Short-circuit testdescribed in Annex ZA of BS-EN 60439-3 .
Asa young Designer . if we look in O.S.G. p/17 – 2.2.5 Consumer’sControlgear AConsumer Unit ( to BS-EN 60439-3- Annex ZA ) is for use on Single-phase Installation’s up to ( 100A ) itincludes . 530.3.4 •A Double pole isolator . Fuses. circuit breakers or RCBOs for protection against Overload & Faultcurrents . & •RCDs for Additional Protection against Electric Shock . ( Anything that moves . RCD it & Earth it )RCD / RCBO – remember that an RCBO is RCD/MCB .
Designer/ Electrician : Whenspecifying Enclosures & their Accessories . it is Important to bear in mindExisting Standards to which the Products are Manufactured&/or Tested . TheStandards are Written to Ensure CONFORMITY .Integration with other Products & Safety ofPersons & Equipment.
Thisto keep in Mind - Overload. ShortCircuit ↔ ( Fault Current ) EarthFault . Wewill go there an other day { PS am not asking you to take this in all in One .am opening your eyes to things as a Young Designer }
IP4X . Rating’s on Consumer Units . “ Meaning “ RedCover - The Only Requirement of the Regulations ( BS-7671:2008) – 416.2.2. forthe Initiated ↔ ( is the TOP SURFACE of theEnclose ) IP4X/ IPXXD (with Apertures Intended to exclude Particles of Greater than ( 1mm diameter ) To stop Dirtfalling into the Enclosure
IP2X . Rating’s on Consumer Units . “ Meaning “ TheBottom & Sides ofthe Enclosures Only need to be IPXXB or IP2X ( The Testis made with a Metallic British Standard finger Test – 12.5mm diameter . “Plain English “ FullPenetration into the Enclosure is NOT Allowed . Let ask you this ??
[Both Joints of the finger may be Bent through 90° degrees with respect to theAxis of the Finger but in ONE & the SAME direction ] AmUsing the Wording - Finger is PushedWithout UNDUEFORCE . So there you have it . in One Young Apprentices this is Only Guidance
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
ConsumerUnit(s) MCBs/ RCBOs are sitting on the bottom off Buzz Bar “ Copper Bar “ Feeds Mainspower to MCBs / RCBOs MCBs/ RCBOs are Clipped onto a DIN rail
Justa point to Note : Wecan get – MCBs Colour coded dolly’s allow quick Visual Identification of Ratings .now – BS-EN 60898
Whatis a Split Load . 100A Main Isolator → outgoingways ?? MCB / RCBOs ( 4) Non-RCD side RCD30mA – 80A → MCBs ( 4 ) RCD side - ( Additional Protection ) 30mA RCD Basic Protection / Touching Live Parts . ARCD is a Fixed Equipment RCD30mA – 80A → MCBs ( 4 ) RCD side
TestingRCD buttons – Do Not Hold the button more than 2 seconds [ You are crating aFault in the RCD for Testing Purposes]
RCDs- 0° & 180° deg ( ½ - 1x – 5x )times ( This sign is for Alternating Current ≈ A.C. ) Marked on the RCD - 230V . SinglePhase
Donot Overlook – as a Tester that ( When all the Tests are Complete the Testbutton to Ensure this Functions Correctly )
Pointto Note . The 17[SUP]th[/SUP] Edition tells usto test the Button on an RCD “ But Not “Before or After Testing RCD .
Megger1552 )- an RCD Tester is an ElectronicDevice which draws current from the Supply for it’s Operation . Thiscurrent is usually of the Order of a few mA s which is taken from Line & Neutral of the Supply under Test(s) Single-phase
For-&-s Purposes Exams’ ?? TestingResidual Current Devices ( RCD )
RCDto Achieve Automatic Disconnection in the case of a Fault . ( If )
411.3.2.1. Requires. “ in most cases “ that a Protective Device ( MCB ) shall Interrupt the Supply to a Line Conductor of a Circuit or Equipment in the eventof a Fault of Negligible Impedance between / Line Conductor& part or a Protective Conductor for the Circuit or Equipment within theAppropriate Required Disconnection Time .
“Plain English “ 2392-10- TN- 0.4 seconds 41.1 – 411.3.2.2. tells us The maximum Disconnection – 41.1. shallb e applied to final circuits NOT EXCEEDING 32A [Domestic Installation(s) ]
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Working my way Around the 17[SUP]th[/SUP] Edition :
555)- Transformers .
Thereare Only three Regulation(s) . 555.1.1. to 555.1.3. relating to Transformers asItems of Equipment . Throughtheir Installation . subject to the generality of BS-7671:2008
Thefirst > Autotransformers & Step-up-Transformers Autotransformers& requires where such transformer is employed & is connected to acircuit with a Neutral conductor that conductormust be connected to the common terminal of the Winding
Regulation555.1.2. Precludes . Theconnection of Step-up Autotransformers to an ( IT ) system . in all cases wherea Step-up Transformer is used - Regulation555.1.3.calls for a Linked Switch to disconnectall Live Conductor(s) Line & Neutral – Simultaneously fromthe Supply ( DP )
Working my way around the 17[SUP]th[/SUP] Edition .
Principal Requirements for Devices for General Emergency Switching
Regulation537.4.2.3. ( Requirement )- Where practical . non-automatic device Regulation537.4.1.2. ( Requirement )- Switching of all the live conductors( Except the Neutral where excused by Regulation 537.1.2. ) is required if there is a Risk of Electric Shock Regulation537.4.2.1. ( Requirement )- Capableof Switching Load Current . Regulation537.4.2.1. ( Requirement )- In the case of Motor(s) . Must be capable of switching stalled-rotor current . Regulation537.4.1.3. ( Requirement )- To be Single-ActionDevice . Regulation537.4.2.7. ( Requirement )- Identified as to purpose ( Appropriately Labelled ) Regulation537.4.1.3. ( Requirement )- Device to act as directly as Possible onCircuit concerned Regulation537.4.2.5. ( Requirement )- Suitably Located Regulation537.4.2.3. ( Requirement )- If device is used to operatecontactor controlling the circuit . Switching is requiredto de-energize coil . or another technique of suitable reliability mustbe used Regulation537.4.2.6. ( Requirement )- If Push Button. must be the Latching OFF TYPE Regulation537.4.2.8. ( Requirement )- Plug &Socket-outletNOTACCEPTABLE Regulation537.4.2.4. ( Requirement )- Operating Knob . Lever or Button . PERFERABLY Colour RED .
Emergency Switching )- devices must “ Regulation 537.4.2.1. “ must be capable of Interrupting the Supply ON LOAD Plain English – The Full Load Current )
Emergency Switching )- requirements apply to ALL EQUIPMENT where a HAZARD may be EXPECTED in NORMAL USE. Plain English – Located in a ReadilyAccessible Position & Operator is not put in DANGR - that could be you one day
Regulation 537.4.1.3. – Demands that an Emergency Switch Arrangement is such that onesingle action will Interrupt the appropriate supply . Regulation 537.4.1.3. – Means for Emergency Switching shall act as directly as possible onthe appropriate supply conductors .
Regulation(s)Table 53.2 ( Restriction on Use as Isolator ) Note 3 bottom of page – read
Fused ConnectionUnit : ( FCU ) Yes / Note 3 Whatthe Regs are saying – Suitable for OFF LOAD operation Only You will be . Isolationof current using equipment . ( Fuse in Pocket ????? )
2392-10)- keep in mind you may have a TT System Except where Neutral requiresIsolation . PS – I have been known to use lock off Spurs Unit / padlock
TN-C ( Number of Phases – Single – Phase ↔ ( Isolation required for ) Line Only TN-C ( Number ofPhases – Three – Phase ↔ ( Isolationrequired for ) Three Line(s) Only
TN-C–S ( Number of Phases – Single – Phase ↔ ( Isolation required for ) Line Only TN-C–S ( Number of Phases – Three – Phase ↔ ( Isolation required for ) Three Line(s) Only
TN-S ( Number of Phases – Single – Phase ↔ ( Isolation required for ) Line Only TN-S ( Number of Phases – Three – Phase ↔ ( Isolation required for ) Three Line(s) Only
TT( Number of Phases – Single – Phase ↔ (Isolation required for ) Line & Neutral TT( Number of Phases – Three – Phase ↔ (Isolation required for ) Three Line(s) & Neutral
IT( Number of Phases – Single – Phase ↔ (Isolation required for ) Line& Neutral IT( Number of Phases – Three – Phase ↔ (Isolation required for ) Three Line(s) & Neutral
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