Electric Oven

  rawprawn 10:59 27 Dec 2010

My son and his wife have just renovated an old barn. They got a kitchen designed and fitted by a specialist company, however the oven they chose turns down all the lights in the house if everything is turned on,and they are told that it will have to have special wiring,
I have never heard of anything like that, I thought all domestic ovens would work perfectly on ordinary 32 amp domestic wiring circuits.

  Forum Editor 13:05 27 Dec 2010

the new incoming electricity supply cable was installed by the electricity company, or the National Grid contractor?

Whenever a new main and meter are installed the electricity supplier needs to be satisfied that the house installation is safe, and that includes an earthing test - they won't connect a supply until/unless this has been done.

Your son and his wife would have needed building regulations approval (and planning consent) for the conversion, and the local authority would have required an electrical installation certificate from an approved installer.

The cooker control box should be supplied on its own radial circuit direct from the consumer unit. For distances up to 12 metres of run a 4mm conductor cable can be used; any distance over 12 metres needs a 6mm conductor size.

If the cable supplies a cooker only, a 30Amp fuse is sufficient for a 7.2KW load. If the control unit has a combined socket outlet you'll need a 45Amp fuse.

The lights are dimming when the cooker is running because these rules haven't been complied with; your son should get a qualified and local authority approved electrician to make an urgent inspection and report.

  rawprawn 13:22 27 Dec 2010

Thanks for the replies, I think I may have misled you all through my lack of knowledge.
There is nothing wrong with all the electrics, they have been all installed passed and certified.
Apparently the cooker they have bought needs more electricity? amps? than a normal cooker which is how it was wired up.although I haven't seen it but apparently it is one of those big "Old fashioned style" range types, similar in size to an AGA

  rawprawn 13:40 27 Dec 2010

Hi, I am going over to have a look at their new home on Wednesday so I can have a proper look. They have called the electrician back, but I don't know whether he will have been by the time I get there.
It just seemed very strange to me, they say that they can use it OK as long as they don't turn everything on at once.
I will try and let you know the outcome.

  namtas 14:20 27 Dec 2010

Your large cooker will have been connected taking diversity into account. The IEE Regulations 15th Edition gives a simple method of diversity calculation for household electric cooking appliances.

Take the full load of the cooker, then deduct the first 10 amps.

Take 30% of the remainder and add the first 10 amps originally deducted.

If an electrical socket outlet is incorporated into the cooker switchbox, add 5 amps to the total load.

  rawprawn 15:04 27 Dec 2010

Thanks namtas, I have made a note and I will take it with me.

  Diemmess 15:12 27 Dec 2010

Was the barn conversion connected by the appropriate supply authority to its own meter or is it dependant on a supply extended from another building?

If it is merely an extension then my guess is that the cable used was not of the correct capacity or is of considerable length or both.

If the connecting cable is too 'thin' there is a risk of fire and in both circumstances the voltage drop in the barn conversion on full load would account for the dim-out.

This is assuming that all lights and appliances suffer under added load.

If it is only parts of the conversion, then it will be the result of faulty domestic wiring and not the supply cable.

In either case it would be wise to seek certificated help forthwith.

  rawprawn 15:38 27 Dec 2010

Thanks Diemmess, I can't answer your questions because I don't know.
The barn in question is part of farm building complex all of which has been converted. I have not heard that any of the other buildings (Three of them)have had a problem.
I will learn more on Wednesday.

  Forum Editor 23:51 27 Dec 2010

as if they have bought one of the big Rangemaster ovens, in which case they could be looking at a 15KW load when everything is switched on.

They're in for some hefty electricity bills if they like cooking, and with a cooker like that I assume they do.

Nonetheless, it shouldn't cause a problem on a properly installed system.

  robin_x 05:01 28 Dec 2010

From memory, 4mm is way too small (4mm is actually 4mm squared, commonly referred to as "4 mil")
OK for a 32A radial circuit.

I was at the back end of 16th Ed., Part P 17th Ed. coming in. I never took the course, but differences are minimal.

New showers and cookers are frightening in their Amperage.

Read the instructions and Google your Range/Model Number/UK Installation .pdf etc etc.

I believe even 6 mil is not enough, maybe 10 mil now. Deep box for the Cooker Switch. Definitely 45A MCB in the Consumer Unit, on the RCD side.

Have fun.

  The Old Mod 08:48 28 Dec 2010

Hi Rawprawn, it sounds as if the property is on an overhead supply, if it is somewhere near the end of a run then the voltage will be not at full 230v, so when drawing high current it can dim lights etc, you will need to have the supply company check out the supply.

I hope this helps.

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