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
HBC fuse link . BS-1361 . ( House Service &Consumer Unit fuse ) Notpopular for use in Consumer Unit(s) . gives good Short-circuit currentprotection / & does not result in cable de-rating . ranges from . 5A – 100A .
2392-10:Total Loop Impedance ( Zs ) What’s the main reason behind this- ??
:icon_bs:This has to be measured in order to ensure that the protective device will operatein the specified time Under Fault Condition(s) . You’ll be coning for your 2391-10 .
2392-10)- Indicates residual current ratings& Uses as Mentioned in BS-7671:2008 –Red Cover .
30mA – RCDs . …. ( a Break down forYou ) :icon_bs:
• Allsockets outlets rated at no more than ( 20A )& for Un-supervised : General Use. • Mobileequipment rated at NO More than ( 32A ) for use Outdoor(s) • Allcircuits in a Bath/ Shower room • Preferredfor all circuits in a TT System • Allcables installed Less than ( 50mm ) from thesurface of a Wall or Partition [ in a Safe Zone] if the installation is Un-supervised . & also at any depth if theconstruction of the Wall or partitionincludes Metal Parts . • Inzone ( 0 . 1& 2 ) of Swimming pool locations • Allcircuits in a location containing Saunas . Etc •Socket outlet final circuits NOT exceeding ( 32A ) in Agricultural Locations . • Circuitssupplying ( Class II ) equipment in Restrictive Conductive Locations •Each socket outlet in caravan parks & marinas & final circuits forhouseboats •All socket outlet circuits rated NOT MORE than (32A ) for show . Stands . Etc •All socket outlet circuits rated NOT MORE than (32A ) for construction sites [ Where Reduced Low Voltage . Etc – is NOT USED ] •All socket outlets supplying equipment Outside mobile or transportable units •All circuits in Caravans •All circuits in Circuses . Etc •A circuit supplying ( Class II ) heating equipment for floor & ceilingheating systems
500mA– RCD •Any circuit supplying One or More outlets of rating EXCEEDING( 32A ) on a Construction Site
300mA– RCD •At the ORIGIN of a TEMPORAYSUPPLY to circuses . •Where there is a ( RISK OF FIRE ) due to storageof combustible materials •All circuits [ Except Socket Outlets ] in Agricultural Locations
100mA– RCD •Socket outlets of rating EXCEEDING ( 32A ) in AgriculturalLocations
WhereLoop Impedance values CANNOTbe MET . RCDsof an appropriate rating can be Installed . Their rating can be Determined from( I∆n = 50/Zs ) Where ( I∆n ) is therated operating current of the device – ( 50 )is the Touch Voltage & ( Zs ) is themeasured loop impedance
Apprentices)- Electrical - Calculation(s) Basics
:38: Alternating Current Circuit Impedance:
i)in D.C. circuit(s) - The current is limited by Résistance . ◄◄ ii)in A.C. circuit(s) - The current is limited by Impedance ( Z ) – (Résistance& Impedance are measured in Ohm’s. )◄◄
U/Z= I . or voltage ( U ) ÷ Impedance ( Ohm’s ) = current ( Amperes )
• The voltage applied to a circuit with an ( Impedance ) of ( 6Ω is 200 volts ) Current in the Circuit [ U/Z = I ] 200 ÷ 6 = 33.33A ← Round off to4 •The Current in a 230V – single-phase motor is (7.6A ) Impedance of the Circuit . [ U/I = Z ] 230 ÷ 7.6 = 30.26Ω . •A discharge lamp has an Impedance of ( 265Ω )& current by the lamp is ( 0.4A ) [ Z x I = U ] 265 x 0.4 = 110 Volts . • Thecurrent through an Impedance of ( 32Ω . is 8A ) Voltage drop across the Impedance . [ U = I x Z] 8 x 32 = 256V
• Thecurrent through an Electric Motor is ( 6.8A )at ( 230V ) The Impedance of the motor . [U = I x Z ] Transposefor Z ] Z = U/I . – 230 ÷ 6.8 =33.82Ω . ….. 33.82352941 / Roundoff to → ( 33.82 )
•An coil has an Impedance of ( 430Ω ) Voltage ifthe coil draws a current of ( 0.93A ) [ U= I x Z ] Transposefor U ] 0.93 x 430 = 400V . ….. round of 399.9 / 400
Apprentices: “ Meaning “ ( PSCC ) 612.11
:icon_bs: (PSCC ) - Prospective ShortCircuit Current –The maximum current which could flow ( Between )Live Conductor(s) ? L/N . for thesake of -&-s . 2 live conductor(s) (PFC ) - Prospective FaultCurrent – The ( Highest) current which could flow in a Circuit due to a Fault. this will come up on 2392-10 .Exams ◄
UsefulJunk . Yeah Transpose )- “ Meaning “ Change order to calculate a Value .
UsefulJunk . ► Thermosetting )- “ Meaning “ Cable Insulationwhich becomes “ SOFT “ when “ HEATED “& is “ RIGID “ when Cooled Down .
Scenario/ Exercise / Electrical Calculations ( I don’t know if you still get them in 2391-10 . Exams ?? ) ◄◄
:86: i). Shower circuit has a measured ( Zs ) value of( 2.2Ω ) ii). Previously the circuit ( R1 + R2 ) value was measured as ( 1.8Ω) iii). The temperature factor is ( 1.2 ) & cablefactor is ( 1.04 ) iv). if the maximum tabulated ( Zs ) value forthis circuit is ( 2.6Ω )
► Show by Calculation if the measured ( Zs ) value is Acceptableor Not .
Whencarrying out an Insulation Résistance Test . on a Consumer Unit it is often easyto forget that ( ALL ) circuits basically are connected across Line & Neutral .Whatever they are .
Thismeans that when ( ALL ) of these circuits areconnected together & an Insulation Résistance Test is done . “The overall reading may well be Unacceptable . “
Back to Basics . Becausethe circuits ( ALL ) possess Résistance & Resistorsin Parallel have the effect of Reducing theOverall Value .
BS-7671:2008 TheRegulations allow us to ( Sub-divide ) Thesecircuits to get ( Around ) this problem .
AsElectricians’ we must keep our Fundamental Principle in Mind .
p/38- As GN-3 rightly put it .
2392-10– IR . You do not want . a Low Résistance on your readings . ( Which would indicate defective insulation )
GN-3. p/38 InsulationRésistance value of Not Less than ( 1.0MΩ ) complieswith the Regulation(s) where an Insulation Résistance of Less than ( 2MΩ ) is Recorded the possibility of a latent defectExists .
p/39- As GN-3 rightly put it . where a LOW READING is obtained ( Lessthan 2MΩ ) it may be necessary to test EACHCONDUCTORSEPARAETLTY to EARTH . (After ensuring that all Equipment is Disconnected)
2392-10. Résistance Readingsobtained should be Not Less than the minimumvalues referred to in . Regulation(s) Table 61 . p/158
TheRegulations are tell us . The Minimum Insulation Résistance ( MΩ .≥ 0.5 / ≥ 1.0MΩ )
General Information about ( Prospective Fault Current ) :icon_bs:
BS-7671:2008. requires the following . Prospective FaultCurrent to be determined for each installation by “ Calculation “ or “ Enquiry “
•The Prospective Short – Circuit Current at the Origin . Regulation 313.1. /refers . & •The Prospective Short – Circuit & the Prospective Earth Fault current at every point of the installation . Regulation . 434.1. refers
Thiscovers the determination of the Maximum ProspectiveShort – Circuit Current at the Origin of an installation by means of Enquiry toa distributor . Where the installation is supplied at ( 400V three-phase / Similar. for an installation having 230V . single-phase ) supply of up to 100A
►►Example Only . ( kW ) Making you Aware of Diversity :uhoh2:
Conveyorbelt made up of ( Six ) sections . – Eachdriven by a ( 2kW/ Motor ) Materialis Transported along this belt – it is first carried by section ( 1 ) Then each section in succession until the finalsection is reached .
SimpleExample Only( One ) section of conveyer is carryingmaterial at any point in time . Therefore( Five ) Motors are Only handling – No-Load mechanicallosses ( ? 1 kW )
Keepingthe belts moving whilst ( One Motor ) is handling the Load. ( ? 1kW) The Demand presented by ( Each Motor ) when it is carrying it’s Load is ( 1 kW )
Demand Load(s) – is ( 6kW ) but the Maximum Loadpresented by the System at any time is Only ( 1.5 kW )
TheDiversity factor for this system is ?? TheDemand Load(s) – 6kW Maximum Demand – 1.5kW
ElectricalTest Certificates are used to record what has been done & confirm that theinstallation meets the required standard .
2392-10: Withinthis Standard . Regulation - 610.1. State that . Everyinstallation shall . during erection & completion before being put intoservice be Inspected & Tested to verify . so far as reasonably practicable. that the requirements of the regulations have been met .
2391-10PIR ) Regulation. 621.1. State that . Whererequired . Periodic Inspection & Testing of every electrical installation shall be carried out in accordance withRegulations . 621.2. to 621.5. in order to determine as far as is reasonablypracticable . whether the installation is in asatisfactory condition for continued service .
Design& Installation . from ( Part P ) with respect Workshould Comply with BS-7671:2008 . Electricalwiring Regulation(s)
( Part P ) with respect Inspection& Testing before taking into Service . p/79. 6.2.1. General – Every installation must be inspected During Erection asnecessary & on Completion & before being put into Service to provide a Visual Check that theinstallation including the ( Installed equipment complies with the requirementsof BS-7671:2008 )
( Part P ) BS-7671:2008Installation Certificates . Compliancewith Part P can be demonstrated by the Issue of a correct Electrical InstallationCertificate
2392-10: Compliancewith Building Regulations is a ( Legal Requirement ) electrical work carried out in DomesticSector is now in the Building Regulations . Itis a Criminal Offence “ NOT “ to “ Comply “ withBuilding Regulations .
Justa gentle reminder . 2392-10 . BS-7671:2008 . does NOT recognize a “ Kitchen asa Special Location “ ( Document P ) p/60 – 5.2. ▼
Kitchen is defined in the Building Regulation(s) as a “ Room or part of a Room “ which contains asink & food preparation facilities .
BS-7671.requires . ? 2392-10: under Part P . The Electrical Installation Certificate. may be used together with Schedule of Inspections. & Schedule of Test Results . Hint . ►► this will come up inyou -&-s EXAMS / 2392-10 . ( 1 x 1 x1 ) ??
Remember . Approved Document P– Electrical Safety . AsPart P . reminds us . This Safety Certificate has been issued to confirm thatthe Electrical Installation Work to which it relates has been Designed .Constructed & Inspected & Tested in accordance with British Standard7671
Ifan Electrical InstallationCertificate is required . then the Earthing arrangements must be Upgraded to complywith the current Edition of BS-7671 .
UsefulJunk : Asits not in the Regulation(s) -Table 61 .Insulation Résistance. it may never come up . -&-s . Q/As – FELV. circuit(s) are tested as ( LV ) circuit(s) at ( 500V . d.c. )
2392-10. Q/As -&-s . Your testing your self . PS. This one is still on the books . ▼▼
Asa Tester ( 100mA) general purpose . RCD to BS-EN 61008 is to be Tested to ensurethat it operates within Speciation . ( You should bedoing Handstands at this Stage . Yeah )
- TTsystem should preferably use a Slit – Consumer Unit . with RCD rated at ( 100mA) for equipment . & ( 30mA ) for socketoutlets – O.S.G. p/24. fig 3.2. -Where a circuit has ( High Loop Impedance ) a 100mA RCD issuitable providing it is NOT for socket outletsthat could be used outside & that the circuit is NOTin a special location .
2392-10– as a Tester . S Type 100mA RCD does not normally trip ( Without Reason )
( Firstly ) → TheInspections Schedule provides CONFIRMATION that a VISUALINSPECTION has been carried outas required by Part 6 of BS-7671 .
2392-10. don’t worry You will not get this in Exams . 2391-10 / may Thesum of the Résistance of the Line conductor &the Protective conductor ( R1 + R2 ) should be recorded & . after appropriate correction for temperaturerise . Maybe used to determine Zs – ( Zs = Ze + ( R1 + R2 )
Where Test method 2 is used .The maximum Value of ( R2 ) should be recorded.
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