De-rating of cable for cooker?

[SparkusMaximus]

Hello,

My mate has just brought a new gas oven from B&Q and there fitters said something about they can't fit it as the cable supplying it is too large I presume 6mm or maybe more.

What are the regs on this surly you can never have to big a cable as long as it is fused correctly?.

Also said something about flex but I presume they were talking flex outlet, but that could be installed, he asked my opinion but we don't do much domestic work and to be honest its only lately I have been thinking about regs and do's and don'ts rather than just doing what the gaffer says.

So does it sound like these guys don't know there bums from the elbows?

 

[bugsy]

It's proberbly 6mm from the cooker outlet plate , change the outlet plate to a fused spur with flex outlet and run a suitable flex ( 1.0 / .75mm if its only for the ignition ) and fuse to 3a

 

[SparkusMaximus]

Thats what I told him, however he thinks they are saying the whole cable needs to be changed, but maybe he misunderstood what they are talking about.

Cheers.

 

[Dunc]

Knowing B&Q and other DIY places they probably would mean a whole new cable needs installing. If it's an all gas unit do as you thought and fit a spur in place of the outlet, if it's an electric oven/gas hob combined unit that is rated at 3.4kW for example just fit a 2.5mm flex (what the manufacturers usually recommend from experience if one isn't already fitted) and fit a smaller MCB (16A). This work would probably be notifiable though and would require Minor Works Certificate.

 

[Engineer54]

Most single ovens come ready wired with 1.5mm cable and plug top these days...

 

[PC Electrics]

Thats what I told him, however he thinks they are saying the whole cable needs to be changed, but maybe he misunderstood what they are talking about.

Cheers.

OR
maybe they misunderstood what they were talking about

 

[SparkusMaximus]

Popped round there today to have a look, its a separate hob and the current one is on its own circuit, 40a mcb 10mm cable which must be way over the top for a single hob.

New hob to go in is rated at 6400-7200w I am thinking just keep the 10mm and fuse the mcb down to a 20a, how does that sound, and that would be a minor works? although its like for like but am changing the protective device as 40a is too high.

 

[telectrix]

the 40A MCB is there to protect the cable, irrespective of whatever is connected to it.

 

[SparkusMaximus]

so its ok to put this new hob that I caculate to be drawing 16.3a on the 40a and not bother putting in 20a?

 

[telectrix]

you can fit a 20A MCB. but just imagine a ring final 32A MCB, might only have a 5A load for a couple of small appliances. you wouldn't fit a smaller MCB .

 

[SparkusMaximus]

So the fitter guys were talking tosh then. I can just put the 10mm into the new hob and all will be well. Just want to sort it out for him.

Cheers guys for you help, I really appreciate it.

 

[Martin Bradley]

Down rate the protective device and this will give you peace of mind. but check you calculations.
The B&Q chaps mite have been in a rush and did not want to do the job, it happens, if you can't do it Blag & Q it. Next.

 

[SparkusMaximus]

Are my calcs wrong,

6400-7200w so I take 7200w / 230 gives me 31.3 diversity calls for 10a of that plus 30% of the remaining 21.3 so 21.3 x 0.30 = 6.3 so the original 10 + 6.3 gives 16.3.

Please let me know if I have done something horribly wrong.

Thanks.

 

[Martin Bradley]

Sorry my input was inc a socket out, you are correct. extra 5amp.