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Cooker rating and wiring

I'm having a new kitchen installed and have purchased a new range cooker which has a Max. Elec load @230v 10.8kW. I've had quotes from a couple of electricians as the cooker socket needs to be moved and have had conflicting advice regarding the wiring.
One thinks that the existing wiring is ok (current cooker has a max load of c.6.5kw) and he can just utilise the existing to move the socket.
The other wants to install 10mm wiring (I'm not sure the size that is there currently) and change the circuit breaker to 50A (current is 32A).
Obviously there is a big cost differential between the two approaches! Anyone have any views on which sounds most sensible?

7 Answers from MyBuilder Electricians

Best Answer

Be very, very careful here. Especially those of you giving wrong advice.

Diversification is used to calculate maximum load within a system, it should not be applied to an individual circuit.

The cable should be selected to cater for the Maximum load of the circuit, the MCB is selected to protect the cable. You should NEVER do it the other way round.

Diversification in this context allows for thermostatic controls randomly bringing on the heating elements, AND ASSUMES THAT NOT ALL ELEMENTS ARE SWITCHED ON AT THE SAME TIME, ALL OF THE TIME. So full load is unlikely to be met for the majority of the time, but can and does happen.

MCB's do not trip on over current for a long time and though every device has a fusing factor, a common factor for MCB's is 1.45 x In, so in this case 46A. Now the regulations allow for a 145% increase in current carrying capacity for 1 hour to allow for the MCB tripping so using a 6mm for a maximmum load od 32A with a 32A MCB is acceptable. Using a 32A MCB to protect a 6mm cable with a maximum load of over 50A is not.

So if you install a 10Kw cooker on a 32A MCB, it will happily sit not tripping up to 46A WHICH IS FAR IN EXCESS OF THE CABLE CARRYING CAPACITY. And if run within insulation = puff of smoke syndrome.

Plain and simple you need a 10mm cable, 6mm is not correct, it may work but may also burn your house down, you take the risk.

What are we teaching people these days that so many get it wrong!!! Okay off my soap box now.

2015-10-06T15:50:01+01:00

Answered 6th Oct 2015

The electrician that says the existing circuit will suffice is correct as per diversification tables in the electricians on site guide. All electricians are supposed to have this on hand so if in doubt ask to see it. A short reference to this is in appendix H4 page 184 in the latest on site guide. It says a circuit of 30 or 32 A is usually appropriate for household or similar cookers of rating up to 15KW.
I would follow this advise unless manufacturers installation instructions say otherwise.
DIVERSITY TABLE A1
HOUSEHOLD COOKING APPLIANCE
THE FIRST 10A OF THE RATED CURRENT PLUS 30% OF THE REMAINDER OF THE CURRENT PLUS 5A IF A SOCKET OUTLET S INCORPORATED IN THE CONTROL UNIT. (page 116 appendix A BS 7671 on site guide)

2015-10-04T18:05:01+01:00

Answered 4th Oct 2015

I agree with Kevin Cassidy here. By using diversity, and even assuming a socket outlet on the circuit, the maximum load would calculate as 26.08 Amps @230v. Depending on the installation method and length of run, a 6mm or 4mm T + E should be sufficient. (Even 2.5 has a CCC of 27 amps when clipped direct)

EDIT - Re- Proman

Diversity is a perfectly acceptable way of assessing the total current demand of an individual final circuit. The on site guide (appendix A) states-

"The current demand of a FINAL CIRCUIT is determined by adding the current demands of all points of utilisation and equipment in the circuit and, where appropriate, making an allowance for diversity"

Allowing for the manufacture's stated MAXIMUM OUTPUT, not MAXIMUM LOAD, when this is not only unlikely but impossible, due to the way the thermostatic controls work it just overkill.

Anybody who says a 10mm cable is required for a 10.8kw domestic cooker does not understand the basic principles of circuit design

2015-10-07T09:10:01+01:00

Answered 7th Oct 2015

Yes do not listen to 3rd answer, first answer correct

2015-10-06T14:10:01+01:00

Answered 6th Oct 2015

Hi,
The electrician who has said that you need to upgrade your MCB to a 50amp breaker has done his maths correctly as when you divide 10.8kW by 230v you have 46.95....meaning the only breaker big enough to operate safely will be a 50a one.
As for the cable, it depends on the distance of the run, but 10mm sounds about right for the load it will be pulling.
Hope this helps!

2015-10-04T14:55:02+01:00

Answered 4th Oct 2015

The third answer has applied no diversity whatsoever so would disregard that answer. The other two are spot on.

2015-10-05T17:20:02+01:00

Answered 5th Oct 2015

The right answer is you always go by the manufactures installation manual which I would have a guess would say 10mm. My guess is the guy saying 10mm is either playing safe or has read the manual, going against the manual will invalidate your warranty on your appliance and put you at risk of a fire.
Regards
Kelvin
Iconnect Electrical Solutions

2015-10-06T19:15:01+01:00

Answered 6th Oct 2015

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