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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Which electrician to believe https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1257507808 Message started by mikeidge on Nov 6^th, 2009, 11:43am

Title: Which electrician to believe
Post by mikeidge on Nov 6^th, 2009, 11:43am

Hi,

I've just moved house into a property that currently has a Halogen hob drawing 6.6kW. This is connected to a 6mm2 cable to a 32-amp MCB on the consumer unit, and the isolation switch for the hob in the kitchen also has a standard 13-amp socket on it.

Having just bought an oven, I'd like to get it installed. It draws a maximum of 2.35kW. I've had a number of electricians around, and I've been told they'd do one of two things:

1) Connect the oven to the existing switch and run the hob and oven off the same 32-amp MCB,
2) Give the oven its own MCB and route it straight to the consumer unit, as it's likely to trip all the time, and/or overheat.

I can't see where the existing 6mm2 cable is chased, though I'd imagine it's probably going either under the floorboards or above the ceiling. It's an older property (built in 1903), so there's solid brickwork throughout.

I'm not an electrician, so the thing I'm most wary of is how much load the existing 6mm2 cable can take given the way it's been chased. From having read about this online, it seems that at best it can take 45A, but at worst, about 35A. Surely that's a significant difference, because the hob's drawing over 28A on its own. Stick the oven into the equation, and that jumps up to 38-39A.

What also worries me is that most of the electricians failed to mention the existence of the 13-amp socket. Even without the oven, if I were to plug in a 13-amp device and use it at the same time as the hob, it'd already be drawing over 40A. That's 50A if the oven's on as well, which is definitely going to cause the circuit to trip.

My own prefered solution is to change the existing isolation switch such that it no longer has a 13-amp socket on it. It means I'll lose a socket in the kitchen, but it also means the maximum load on the cable will never exceed 39A.

What do people think about this? Would it be safe and reliable to stick the oven on the existing circuit, or should I route it straight to the consumer unit on its own cable?

(When I say "I", I mean which electrician should I go with?)

Thanks!

Title: Re: Which electrician to believe
Post by big_all on Nov 6^th, 2009, 1:43pm

thats where diversity comes in it says somthing like you can allow for appliances and circuits to not be fully loaded all the time and somthing like 60% load is reasonable

after all your not going to have 4 rings a grill and oven on full blast at the same time ;D ;)

any way wait for a spark to give you the correct answer before you form an opinion

Title: Re: Which electrician to believe
Post by CWatters on Nov 6^th, 2009, 2:22pm

Did the oven come with a plug on it?

Title: Re: Which electrician to believe
Post by londonman on Nov 6^th, 2009, 5:25pm

Being pragamatic for a moment. It's your house. You know that you might exceed the capacity of the MCB if you stick a 2kW fire into the socket ...at the same time as all the hobs on and at the same time as the oven going full blast...as the others have suggested. So don't do it! Stick one of those child-proof covers in it if you're worried. A lot easier than replacing and making good.

Title: Re: Which electrician to believe
Post by sparky415 on Nov 6^th, 2009, 6:11pm

Go with Number 1

It might trip on Christmas day and thats about it

(Ding, Im not even going to ask how long the run is ;))

Title: Re: Which electrician to believe
Post by dingbat on Nov 6^th, 2009, 6:18pm

big_all wrote on Nov 6^th, 2009, 1:43pm:

any way wait for a spark to give you the correct answer before you form an opinion

Isn't that part of the problem? ;D

Title: Re: Which electrician to believe
Post by sparkyjon on Dec 3^rd, 2009, 9:48pm

unless your oven came with a 4mm cable you will have to fuse it down to 13A anyway either by a a switched fused spur or 13A socket outlet (warranty will be viod if plug removed) and upping braker to 45A will be cheapest way bare in mind local isolation (switch) needs to be present.

Title: Re: Which electrician to believe
Post by supersparky on Dec 7^th, 2009, 8:28am

wrote on Dec 3^rd, 2009, 9:48pm:

Depends on the calcs ;)

If the flex is 2.5 on the oven, maybe even 1.5 the short circuit protection will be provided by the mcb and the over current will be provided by it being a fixed appliance with fixed loading!