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Topic Title: Domestic cooker diversity.
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Created On: 09 December 2013 07:18 AM
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 09 December 2013 07:18 AM
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alanblaby

Posts: 345
Joined: 09 March 2012

I'm currently having an argument with a kitchen designer who wants a new feed putting in for an induction hob, but the customer doesnt want the disruption caused by fitting a new cable.

There is currently a 6mm cable, protected by a 32A CB supplying a standalone cooker.

He wants a 20A supply for a new oven and a 32A supply for the hob.
Rated wattages are 3700 and 6900w.
So total wattage of 10.6kW, 46A.
With diversity,I think a supply of 21A is required (46A -10A +(30% of 36A) for both of them.

When I explained this, he didnt believe it, and says the appliances require the full rated current. I think he doesnt know what he is talking about, but, before I re-start the argument later, could someone confirm / deny my thoughts?
Thanks
Alan.
 09 December 2013 07:26 AM
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dickllewellyn

Posts: 1150
Joined: 19 March 2010

Your calculation appears to be correct for cooker diversity, I would say thought hat with an induction hob I don't think there is quite so much allowance. It's a question that has often come up, but I've never really had an answer for. That said, I think I would be happy for both appliances to run on a 32A supply.

Perhaps you could ask the kitchen fitter to show his credibility to be able to design a circuit as you have?

Is the kitchen fitter paying you, or the client? Is there a problem that means additional circuits can't be installed? It generally doesn't hurt to have a couple of spare 20A radials to a kitchen these days with all the fancy new appliances being invented. If I had a pound for every integrated microwave that said it needs a 20A supply at the end of the job I'd have at least a fiver now!

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 09 December 2013 07:41 AM
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alanblaby

Posts: 345
Joined: 09 March 2012

My first thoughts on being given the details were a new circuit, but on seeing the property, it would be major disruption. Fitted wardrobes and tiled floors upstairs to impede access from above, Cannot really run it on the outside as it is a really old white painted house that just wouldnt be right with a length of white conduit running around, as well as garage and porch sticking out to make a difficult, and ugly run.
Buried is no good as it is tarmacced up to the walls.

So I went with using the existing cable as the best solution.
 09 December 2013 07:52 AM
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dickllewellyn

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You will be fine! Realistically the oven is unlikely ever to draw more than 3kw, the rating plate will be all the elements added together, but realistically they probably can't even be physically turned on at the same time! The hob will probably only ever see a pan or two at a time, and even fully loaded I think the induction aspect is pulsed rather than constant so there will probably be some kind of allowance. Not quite as much as thermostatically controlled resistive plates, but I've installed a few as like for like replacements and never had to return due to overloading a standard cooker circuit.

My suggestion would be to stick to your guns, show written calculations and evidence of diversity allowance if need be (on site guide has diversity in the back), and explain the problems associated with installing a new circuit and give a price for it allowing a day or two or whatever you think, explaining that there may be untold making good to follow that is not included in your price, and let the client decide!

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 09 December 2013 10:52 AM
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AJJewsbury

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When I explained this, he didnt believe it, and says the appliances require the full rated current. I think he doesnt know what he is talking about, but, before I re-start the argument later, could someone confirm / deny my thoughts?

I agree with you. If you want some extra ammo though, try to get the make/model of the induction hob - some are programmable to limit their maximum current draw, so you may well be able to configure it to operate on say a 20A supply anyway.
- Andy.
 09 December 2013 04:39 PM
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alanblaby

Posts: 345
Joined: 09 March 2012

Thanks for the confirmations, the customer is happy, I am too, as it will be a major pain to put in a new circuit.
Thanks
Alan.
 09 December 2013 07:39 PM
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breaker

Posts: 280
Joined: 05 October 2006

How about a spur of a spur feeding a 6KW induction hob via a 1362 13A fuse, it's what I found last Friday!
 09 December 2013 08:17 PM
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psychicwarrior

Posts: 220
Joined: 18 October 2010

and take note of the manufacturers installation instructions for the cooker/hob...sometimes they detail the required protective device (as it was with my induction cooker - 40A required!)
 09 December 2013 08:37 PM
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ady1

Posts: 766
Joined: 19 April 2005

Hey Breaker
Why not ! It can theoretically only draw over 13A max for a short period, certainly won't melt the 2.5
Regards
Ady
ps. this is a theoretical dabate only !!

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 10 December 2013 07:41 PM
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breaker

Posts: 280
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So ady1 theoretically would you put your name to it ?

Bearing in mind the manufacturers instructions state a minimum 32A supply.
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