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
Instantaneouswater heaters heat Only the water that is needed . Thisis done by controlling the flow of water through a small water tank which hasheating elements inside it Themore restricted the flow of water then the hotter the water becomes . Thetemperature of the water can therefore be Continuously Altered or Stabilisedlocally at whatever temperature is selected .
TheShower-type water heater must be supplied via its OWN MCB in the ConsumerUnit - Double pole isolator “ as a rule“ located near the shower .
Thereare Two-main methods of heating Water Electrically Eitherheating a large quantity stored in a Tank or Heating only what is required whenit is needed .
•Non-pressure . Non-pressurewater heaters . which are typically rated at ( Less than 3kW & contain Lessthan 15 litres of water ) Heat water ready for use & are Usually situateddirectly over the sink
WaterHeating Control . ( must have a Functional Switching Device for Convenience )
BS-7671some references Regulations554.3.3. )- An Immersion Heater must be connected to the supply by Double-polelinked Switch Only . The use of a plug top & socket outlet is Not permitted Note: No change for 16[SUP]th[/SUP] Edition to the 17[SUP]th[/SUP] Edition 2008 –Red Cover
Regulations554.2.1. )- An Immersion Heater must be Provided with a Thermal Cut-Out toprevent the water from boiling if the thermostat fails .
ImmersionHeaters should be supplied through a Switched Cord-Outlet Connection Unitcomplying with BS-1363-4 . BS– 1363-4 )- Specification for 13A FusedConnection Units – Switched & Unswitched .
TheRing Final Circuit : RedCover . BS-7671:2008. makes the following reference to Ring Final Circuits .
RingFinal Circuit must Not supply an Immersion Heater . Storage Heaters etc . 433.1.5. TheRing Final Circuit Arrangements . p/362 . (ii)Not supplying ImmersionHeater(s) . comprehensive Electric Space Heatingor Loads of a Similar profile from the Ring Circuit
Regulations314.2 )- All Final Circuits must be wired Separately from all Other Final Circuits
Re: Continued Useful Information for Electricians’ & Apprentices
Earth Loop Impedance ( EL-Z ) Test
This is a Live Test:
The Main Power has to be Energised to carry outthis procedure . There a certain amount of information required .as a rule thisTest is straightforward { Three-prong Test } if was carried out on alighting circuit you would be required to connect to the Line . Neutral . Earth.
Example : were Testing on the Ring Final circuit .What will be measured is called the Maximum ( Zs ) or the Measured ( Zs ) itshould be compared to the Maximum ( Zs ) in BS-7671:2008 . • so Prior to Testing it is Important to known whichCircuit-breaker is protecting the circuit to be Tested . { in this case it willbe an RCBO to BS-EN61009-1 Rated at 32A }
Look in the Regulations BS-7671 page 49 table 41.3– the maximum ( Zs.s ) you must obtain a reading which is a reading less thanin this case it is 32A - 1.44Ω . it is Important to Note when Testing youshould obtain less than 80% of the figure . Sousing a calculator 1.44Ωs x .8 = we are looking for 1.15Ω
► We are looking for LESS THAN [ 1.15Ω < ] With the Instrumentplugged into the furthest socket ↔ The Loop Scale . Test is taken & a reading of [ 1.1Ω ] → Less than the Maximum value .
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Symbol \ : Therefore. ◄ Electrical Therefore [\Sometimes used in proofs beforeLogical ] – Therefore : so : hence . Therefore : it follows –that . Symbol ¥ : What is it ? Infinity – as a Tester you will use this a lot
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
The Basics .
Ib)– term used to describe a circuit’s design current in Amp’s . ( TheLoad ) In)– term used to describe a circuit’s Protective size in Amp’s ( MCB ) orfuses . Iz)– term used to describe a circuit’s value . in Amp’s once all de-rating factor have been considered . It)– term used to describe the tabulated current rating of a cable in Amp’s .( The Current a cable can Safety Carry )
[ Ib ≤ In ≤ Iz ≤ It ]
The formula above states the Underlying principle of the calculation of a circuitscable size . The first factor you need to consider is Design Current. ( Ib )
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Inspection& Testing – 2391-10 / Designer
TheCertificate couldbe used in a Court of Lawto prove the competence of the Electrical Tester should anything happen at alatter date . if we were to certify an Electrical Installation that would laterresult in damage or harm to persons or property we would Require Proof that we carried outa Full Inspection & Test in accordance with BS-7671:2008 which would satisfythe Electricity at Work Act . The legalities ofour responsibilities are that we are guilty until proven innocent . So havingcorrect paper work & Test Records could save your neck .
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Remember . if any of the Initial Verification Checks require you to Remove Covers then you will need to Carry Out Safe Isolation . Otherwise you will CONTRAVENE the ELECTRICITY at WORK ACT
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Keeping Circuits inOrder .
BS-7671:2008. Regulations314.1. (i) & (ii) states that every Installation shall be divided intoCircuits to avoid Danger & minimise Inconvenience & to facilitate safeoperations . Inspection . Testing & Maintenance .
( T ) Regulation 514.1.2. Statesas far as reasonably practicable . wiring shall be arranged or marked that itcan be Indentified for Inspection . Testing . Repair or Alteration of theInstallation .
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
BS-7671:2008. Makes the following reference to Ring Final Circuits .
Regulation132.12 )- All Electrical Equipment must be )- Accessible for Operation . Inspection & Testing . Fault detection. Maintenance & repair . Regulation 411.3.3. )- Unlessspecifically labelled or suitably Indentified . All 13A socket outletsmust be 30mA – RCD protected . Regulation 543.2.9. )- Except where the Circuit Protective Conductor is formed by a MetalCovering or Enclosure containing all of the Conductors of the Ring .The Circuitprotective conductor of every Ring Final Circuit shall also be run in the formof a Ring having BothEnds connected to the Earthing Terminal atthe Origin of the Circuit.
Apprentices. Top Page Note : “ Wording “ Informative . ◄◄ Apprentices. Read the Wording ) p/362 . Ring FinalCircuit Arrangements . Regulation 433.1.5. TheLoad current in any part of the circuit should be unlikely to EXCEED for LONG PERIODS the Current-Carrying-Capacity of the cable . Regulation433.1.5 – refers )- This can generallybe Achieved BY
Regulation 433.1.5. )- Appendix 15 p/362 . Note : Informative . Cookerrated more than 2kW .
ARing Final Circuit must not serve a floor Area Greater than ( 100m[SUP]2[/SUP]) p/362 .. PS Ring – 100m[SUP]2 -[/SUP]32A Regulation 433.1.5. p/362 )- A Ring Final Circuit mustStart & Finish in the Consumer Unit & be connected to ( 30A / 32A ) MCB etc . Regulation 433.1.5. p/362 )- The minimum C.S.A. of theLine & Neutral conductor is 2.5mm[SUP]2 [/SUP] . The minimum C.S.A. of the CPC is 1.5mm[SUP]2 [/SUP] Regulation 433.1.5. p/362 )- An Unfused Sur can feedeither One Single or One Double outlet only & can be taken from the MCB inthe Consumer Unit . Regulation 433.1.5. p/362 )- The number of Spurssupplied from a Fused Spur connected unit ( a Switched Fused Spur ) depends on the size of the Fuse in the Fused connection unit . Regulation314.4. )- All FinalCircuits must be wired separately from all other Final Circuits . Note : O.S.G. IB )- Top of the Page. Purpose of the Final Circuit fed from theconductors . ETC.
O.S.G.p/18 )- Socket Outlets must be spaced at least 150mm away from Gas-pipes unlessthere is a plane of Non-combustible Insulating Material Separating them . O.S.G.p/54 )- Lengths of Unfused Spurs off a Ring Final Circuit should not generallyExceed ( 1/8 ) the cable length from the Spur to the furthest part of theRing O.S.G.p/54 )- The Wording : As a Rule of Thumb for Rings . Unfused Spur lengths ETC. ( 1/8 )
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Conduit Capacities . Basics
To calculate the number of Cables that may be draw into a Conduit .
O.S.G.You make use of the FOUR Tables
Table5A – Cable factors – conduit for short straightruns up to ( 3m ) Table5B – Cable factors – Use in short straight runs up to ( 3m ) Table5C – Cable factors – for long short straight over ( 3m ) or runs of any lengthincorporating bends . Table5D– Cable factors – conduit factors for conduit incorporating bends & long straightruns
AllCables are Stranded . ( there are Two types of Cables in use Solid or Stranded )
Example: Conduit25 metres long without bends with ( 3 x 1.5mm[SUP]2[/SUP]& 3 x 2.5mm[SUP]2 [/SUP]Stranded conductors )
a) Select the correct table for the cable factors & conduit ( 5A ) b) Obtain the cable factors for each size of cable ( 1.5mm[SUP]2 [/SUP] = 31 & 2.5 mm[SUP]2 [/SUP] = 43 ) → ( 5A ) c) Multiply the number of cables by the factor ( 3 x 31 ) +( 3 x 43 ) = 222 d) Select the correct table for the conduit factor & length of run ( 5B ) e) Obtain the factor which is greater than the sum of cable factor(s) ( 20mm = 460) f) The conduit size is 20mm .
O.S.G.Trunking Capacities : & Tables from “ BS-7671 “
Minimum trunking size is calculate in much the same way conduit although trunking hasits own Table . O.S.G.– No consideration is paid to the Length of Run .
Firstlyf or Exam - &- maximum allowable 45%space factor .
Table 5E O.S.G. - Cable factors for Trunking . Table 5F O.S.G. – Factors for Trunking .
Trunking with 100 x 1.5mm[SUP]2[/SUP] & 100 x2.5mm[SUP]2[/SUP]
a) Obtain the cable factors for each size & type of cable ( 1.5mm[SUP]2[/SUP] = 8.6 & 2.5mm[SUP]2[/SUP] = 12.6 … ( P.V.C. Cable factor ) → Stranded Cable b) Multiply the number of cables by the factor ( 100 x 8.6 ) + ( 100 x 12.6 ) = 2120 c) Obtain the factor which is greater than the sum of cable factor(s) ( 75 x 75 =2371 ) d) The Trunking size is ( 75mm x 75mm )
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
O.S.G.
Apart from Indicating that Diversity & Maximum Demand must be assessed . The Regulations themselves gives little help on calculations’ .
In BS-7671:2008 ( 17th Edition ) Regulation 311.1 gives requirements for the assessment of requirements of Maximum Demand . etc. determining the maximum demand have to consider Diversity .
• Water Heater(s) Thermostatic
( 2 x 6kW & 7 x 3kW ) Table 1B states “ No Diversity Allowable “
Small Shop ??
So the Total load will be .
P = ( 2 x 6kW ) + ( 7 x 3kW ) = 12 + 21 = 33kW → I = 33.000 ÷ 230V = 143.47A ( Unit in Amps )
( 2 x 6kW ) = 12
( 7 x 3kW ) = 21
• Ring Circuit(s) 8 x 32A
O.S.G. Table 1B states “ 100% of the largest & 50% of remained “ The Total Load ??
Table 1B Colum 9 ( Next column across 100% / 50% )
First Ring ( I – 32A ) PS … Not Domestic Installation(s)
Remaining Ring Final Circuit(s) ( I = 7 x 32A = 224A x 50% ÷ 100% = 112A ( Total for Ring Final Circuit(s) = 144A
Table 1B Colum 9 ( 100% / 40% - for Domestic Installation(s) 2392-10 Domestic Installation(s)
Ring Final Circuit – Full Demand on First Circuit → MCB is 32A . ( Then add 40% of remaining ) The two Ring Final Circuits are on 32A MCBs
After Diversity = 32 + ( .4 x 32 = 12.8 ) = 32 + 12.8 = 44.8 Amps . [ 40% for rest of Socket Outlets ]
The Term → ( MD ) Maximum Demand . is self-explanatory . it simply the sum of all the Individual Loads to be connected for a Simultaneous & Significant period .
Re: ***Cont../ Useful Information for Electricians’ & Apprentices***
Inspection& Testing “ Overview “ 2392-10
Youwill need to demonstrate “ Assessor “
- Carryout an Initial Inspection of the Installation . - Selectcorrect Instrument(s) to carry out Tests . - Completethe Correct Sequence of Tests . - Record the Test ResultsObtained . - Carryout Functional Testing of an Installation . - Fill in recognised Certificatesof Completion .
KnowledgeRequirements – 2392-10
• Howto Carry out an Initial Inspection . • Howto Correct any Deviationsfound during Inspection . • Howto use Various Test Instruments . • The Importance of the Sequence of Tests . • Howto carry out Functional Testing • Howto Document Inspection & Testing .
Whatwould you do if you Discover Unsatisfactory Test Results . ??
ThePurpose of Inspection & Testing is to PROVIDE . So far is reasonably practicable.
• Thesafety of Persons & Livestock . 132.1. Design – The Electrical Installationshall be designed to prove . i)The protection of Persons . Livestock & Property . ETC. ii)The proper Functioning of the Electrical Installation – for the Intended USE .
•Protection against Damage to Property by Fire &Heat arising from an InstallationDefect . •Confirmation that the Installation is NOT Damaged or Deteriorated so far as to ImpairSafety . • TheIdentification of Installation Defects & Non-compliance with the Requirementsof the Regulations which may give Rise to Danger .
Inspection& Testing . 2392-10 During & or on Completionof a New Installation
Withthat in Mind ? 2392-10 Youhave to Satisfy the Requirements of Part P of the Building Regulation(s)
Best EV Chargers by Electrical2Go! The official electric vehicle charger supplier.
OFFICIAL SPONSORS
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc
