***Cont../ Useful Information for Electricians & Apprentices***

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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


2392-10/ Domestic Installation Oven(s)

Ovenhas 4 Rings ( 2 x 1kW ) & ( 2 x 1.5kW ) & Grill ( 2kW ) & Oven (3kW )

-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

UsingDiversity allowance stated ↑↑ ( 43.48A sub 10A = 33.48A )

I= 33.48 x 30 ÷ 100 = 10.04A

Youradding the ( 5A ) for Socket outlet . I = 10A + 10.04 + 5A = 25.04A )- Asa Designer this is your Expected Current Demand .

Remember )- Supply Cables Rated to suit DesignCurrent ( Iz )

 

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O.S.G. - First Amendment . BS-7671:2008 – ( 2011 ) p/14

Basic Information Required .

132.16 .
For Additions & Alterations to existing installations .installers should SATISFY themselves asto the SUITABILITY of the supply . The distributor’sequipment & the earthing arrangements .

p/13 - For existing installations . Electricians should satisfythemselves as to the SUITABILITY of thesupply including the earthing arrangement .

Part P – Electrical Safety - Dwellings .

 

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O.S.G. - First Amendment . BS-7671:2008 – ( 2011 ) p/17

As the First Amendment . Reminds Us .

Function of Components .

2.2.1. Distributor’s Cut-Out . :svengo:

This will be sealed to prevent the fuse being withdrawn byUnauthorised Persons .
When the meter tails & consumer unit are installed in accordancewith the requirements of the distributor’s . The cut-out may be assumed toprovide fault current protection up to the consumer’s main switch .

As the cut-out is the property of the Distributor , installersMUST NOT CUT SEALS & WITHDRAW CUT-OUT FUES without PERMISSION .

When removal of the cut-out for ISOLATION is REQUIRED . the supplier of electricity shouldbe contacted to arrange DISCONNECTION & SUBSEQUENT RECONNECTION .

NOTE : The supplier of electricitymay NOT be the same Organisation as the Distributor .


As the First Amendment . Reminds Us .

2.2.2. Electricity Meter .

The terminals will beSEALED by the METER OWNER to prevent INTERFERENCE by UNAUTHORISED PERSON.S.

 

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O.S.G. - First Amendment . BS-7671:2008 – ( 2011 ) p/17

Meter Tails .

□ 521.10.1. Meter tails are part of the consumer’s installation & should be installed &sheathed or insulated & enclosed with “ CONTAINMENT “
For example (- Conduit or Trunking . meter tails are providedby the installer & are the RESPONSIBILITY of the OWNER of the electrical installation.

□ 514.3. “ POLARITY “ should be INDICATED by the COLOUR of the INSULATION & theminimum cable size should be 25mm[SUP]2[/SUP] .

The distributor may SPECIFY the MAXIMUM Length of meter tailsbetween the meter & the consumer unit in addition to the MIMIMUMCROSS-SECTIONAL AREA

( 2.2.4. ) In some cases .The distributors MAY REQUIRE an ELECRICITY ISOLATOR SWITCH .

2.2.4.
Electricity Isolator Switch .
Suppliers may provide & install an electricity isolator switchbetween the meter & the consumer unit . Labelled as Electricity Isolator Switch .
This Double-pole switch permits the supply to the installation to be interrupted withoutwithdrawing the distributor Cut-Out Fuse .

Note : An ELECRICITY ISOLATOR SWITCH may NOT always be installedby the Distributor . TT . TN-S . TN-C-S ( PME )


“Smart Electricity Meters “ is an electricity energy meter thatincorporates a communications unit .

Howlong can Meter Tails be . ??

Themeter tails should be as Short as possible .
Differentdistribution & metering companies have different policies but the length should always be lessthan ( 3 metres ) of cable from the Cut-Out through the meteringequipment to the Consumer Unit .

434.2.1 - 2011 . p/83 . p/75
(i) Not Exceed 3m inLength .

ElectricalSafety Council .

Isit permissible to install a consumer unit more than 3m from the distributorsservice head . ( Yes ) in certain circumstances
Distributorsgenerally accept a minimum of 3m from the service head .

Wherethe tails need to be longer . the distributor may require a means of Isolationto be provided within 3m of the servicehead . Any particular requirements should be ascertained in advance from thedistributor .

 

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O.S.G. p/24 . First Amendment

3.4.2. Other methods of protection against electric shock .

410.3.3. in addition toautomatic disconnection of supply . BS-7671 recognises other methods ofprotection against electric shock .

2008 First Amendment 2011 . p/51

410.3.3. in each part of aninstallation one or more protective measures shall be applied . taking accountof the conditions of external influence .

The following protective measures GENERALLY are permitted .

i) Automatic disconnection of supply .
ii) Double or reinforcedinsulation .
iii) Electrical separationfor the supply to one item of current-using equipment .
iv) Extra-low voltage ( SELV& PELV ) .

Note : in electrical installations the MOST commonly used protective measure is Automatic disconnection ofsupply . ( ADS. ) :rant:

 

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O.S.G. p/140 .

Voltage drop . ( Vd)

525 . To calculate the voltage drop in volts the Tabulated valueof voltage drop between ( mV/A/m ) has to be multiplied by the design current of the circuit ( Ib ) thelength of run in metres ( L ) & divided by 1000 ( To covert to Volts )

Voltage drop :- ( mV/A/m ) x Ib x L /1000 .

The requirements of BS-7671 are deemed to satisfied if the voltagedrop between the ORIGIN of theinstallation & a lighting point does NOT exceed 3 per cent of the nominal voltage ( 6.9V ) & for other current-using equipment orsocket-outlets does NOT exceed 5 per cent ( 11.5 single-phase ) Appx. 4 . 6.

525 . First Amendment . 2011 .

525 . Voltage Drop inConsumers Installation . p/130

525.1. in the absence ofany other consideration . under normal service conditions the voltage at theterminals of any fixed current-using equipment shall be GREATER than the LOWER limit corresponding to theproduct standard relevant to the equipment .

525.100 . Where fixed current-using equipment is NOT the subjectof a product standard the voltage at theterminals shall be such as NOT to impair the safe functioning of thatequipment .

525.101 . The above requirements are deemed to be satisfied if thevoltage drop between the ORIGIN of the installation ( Usually the supply terminals ) & a socket-outlet or the terminals of fixed current-using equipmentdoes NOT exceed that stated in Appendix 4 section 6.4.

525.102 . A GREATER voltage drop than stated in Appendix 4section 6.4. MAY be accepted for a motor during startingperiods & for other equipment with high inrush currents . provided that itis verified that the voltage variations are within the limits specified in therelevant product standard for the equipment or . in the absence of a product standard , in accordance with the manufacturer’s recommendation’s.

 

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O.S.G. . p/107

11.7. Multipole RCDs

As each LIVE conductor of the RCD is incorporated in the magnetic sensingcircuit it is not necessary to perform the test for poles ( L2 & L3 ) however .
If there is any doubt as to the Authenticity of the device inquestion – in terms of a FAKE orCOUNTERFEIT DEVICE – the advice would be to repeat the test for poles ( L2& L3 ) it goes without saying that such important devices . designed toprotect life & property . should be obtained from trusted sources &made by reputable manufacturers .

If a decision is made to test the RCD on all three lines .
There should be little on no discernable difference in operatingtimes as each pole is incorporated in the magnetic sensing circuit . if . forexample . the test performed on one pole did not meet the required disconnectiontime . yet tests on the other two poles were satisfactory . the device shouldbe considered faulty & replaced .

 

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Electrical Safety Council .

Appendix15 of BS-7671:2008 .

Givesadvice on Ring Final Circuits & sharing / spreading the load around the circuit . iii) suggests that cookers . oven & hobs over( 2 kW ) should be on their own dedicatedcircuit .

Whycan’t ovens of less than ( 3kW ) be connected to a Ring Final Circuit via a suitable connection point such as a socket-outlet or fused connectionunit .

Reminder :- Appendix 15 . isintended to guidance only . ( Informative )
Suchconnection is NOT prohibited . provided that NO part of the Ring Final Circuit will be OVERLOADEDas a result . 433.1.5.

 

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( T ) 514.1.2. Identification& Notices . p/114 .

So far as is reasonably practicable . wiring shall be so arrangedor marked that it can be indentified for Inspection . Testing . Repair or Alterationof the installation .

( Main protective bondingconductor )

 

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Current – Carrying – Capacity.

Currentrating are dependent on the method of installation . The insulation material affecting the maximumconductor temperature . Internal thermalrésistance & external

ambient conditions .

Current – Carrying – Capacity. Example .
Currentrating are based on continuous operation at an ambient temperature of 30°C - Maximum permissible ambient temperature 70°C

VoltageDrop .

Voltdrop ( Vd ) is dependent on theimpedance of the conductor . The load current . power factor & route length . in accordance BS-7671: 2011

MinimumBending Radii .
The minimum bending radii should be observed to ENSURE operatingreliability .

Avoid problems by taking appropriate care during Installation .

522.8.3. p/125
The radius of every bend in a wiring system shall be such thatconductors or cables do not suffer damage & terminations are not stressed .

Current – Carrying – Capacity. p/25 First Amendment

The maximum current which can be carried by a conductor underspecified conditions without its steady-state temperature exceeding a specifiedvalue .

□ The Guidance given in the O.S.G. is a Suggestion. NOT a regulation .

 

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UsefulJunk . ( Facts )

Bending Radius 2392-10 .

Installing T&E & Three-core cable(s)

Itis Important to be aware of certain Constraints .
When a cable is BENT . The Conductor Insulation on the inside of the BEND will COMPRESSED &that on the Outside STRECHED :gettree: .

 

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(Zs ) should be as Low as possible to allow enough fault current to flow tooperate the protection as Quickly as Possible

 

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Table A2 . Allowance for Diversity . 17[SUP]th[/SUP] 1B

Water – heater ( Instantaneous type )

In this context an (Instantaneous water heater ) is considered to be a water heater of any loadingwhich heats water ONLY while the TAP isturned ON & therefore uses Electricity Intermittently .

 

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Continued - Table A2 First Amendment . 17[SUP]th[/SUP] . 1B

Allowance for diversity .

Current demand to be assumed for points of utilisation current-usingequipment .

Reminder.

Purpose of the final circuit fed from the “Conductors “ or “Switchgear “ to which the diversity APPLIES .

Notes to table A2 : 2392-10 . :13:

† ) It is important to ensure that distribution boards or CONSUMER UNITS are of sufficient rating to take the totalload connected to them without the APPLICATION of any DIVERSITY .

 

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Declaration .

Regulation 631.4 .

The Certificate must be made out & signed by a competentperson in respect of the design . construction . inspection & testing ofthe work .

631.4.

Electrical Installation Certificates . Electrical Installation ConditionReport & Minor Electrical Installation Works Certificates shall be compiled& signed or otherwise authenticated by a competent person or persons .

 

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Electrical Installation Certificate . 2392-10.

Test Instruments’ will show different displays indicating “ Out ofRange “ e.g. + 299 or > 199.