2 x Ovens and a hob - can anyone help?

[Tattyt]

Hi,

I have had an electrician out to look at at what needs to be done to install two new ovens and a new hob.

Existing: 6mm cable which was used for a double oven & hob previously, with one isolating switch. 40A breaker (think it should be 32A)

Two new ovens: Neff 2 x 2.99KW 13A
New hob: 6.5 KW

I just want to confirm that his recommendations are correct as it involves running some new cables so carpet, floor boards up etc etc.

If anyone could advise that would be brilliant

 

[SparkyChick]

Hi,

I have had an electrician out to look at at what needs to be done to install two new ovens and a new hob.

Existing: 6mm cable which was used for a double oven & hob previously, with one isolating switch. 40A breaker (think it should be 32A)

Two new ovens: Neff 2 x 2.99KW 13A
New hob: 6.5 KW

I just want to confirm that his recommendations are correct as it involves running some new cables so carpet, floor boards up etc etc.

If anyone could advise that would be brilliant

Hi, welcome to the forums.

What has he recommended?

 

[telectrix]

you have a total load of 9.5kW. a 6.0mm cable on a 32A MCB can cope with 15kW, once you allow for diversity. running new/additional cables is just a waste of money.

 

[Tattyt]

Hi SparkyChick,

Thanks for a prompt reply.

To run two new 2.5 cables, 2 x new 20 amp breakers with two new isolation switches.

Regards, Tattyt

 

[Tattyt]

you have a total load of 9.5kW. a 6.0mm cable on a 32A MCB can cope with 15kW, once you allow for diversity. running new/additional cables is just a waste of money.

Would it not be 12.5kW in total? as its for 2 x new ovens (3KW each)

Regards, Tattyt

 

[telectrix]

Hi SparkyChick,

Thanks for a prompt reply.

To run two new 2.5 cables, 2 x new 20 amp breakers with two new isolation switches.

Regards, Tattyt

crazy. unless the appliances are in separate areas. and depending on installation methods, 2.5mm may not be up to it.

 

[SparkyChick]

I'm inclined to agree with @telectrix .

I'm guessing those two cables are for the two ovens... it's interesting that 20A breakers are specified for a 13A load (when 16A breakers are available)

 

[SparkyChick]

How far from the consumer unit are these appliances?

 

[Tattyt]

How far from the consumer unit are these appliances?

They are approx 4 metres from the consumer unit but I have no idea the path of the cables.

The ovens are on top of each other and the hob is about 35cm away from them.

 

[telectrix]

They are approx 4 metres from the consumer unit but I have no idea the path of the cables.

The ovens are on top of each other and the hob is about 350 away from them.

350 what? miles, yards, poles, furlongs?

 

[Tattyt]

350 what? miles, yards, poles, furlongs?

Apologies, I have corrected it to read 35cm.

 

[telectrix]

that's just over 1 foot. no reason not to feed all 2 ovens and the hob from existing 6.0mm (32A MCB/RCBO) via a 45A isolator and a dual connection unit. from the dual connection unit, feed hob in 4.0mm or 6.omm and each oven in 2.5mm (fixed loads do not require overcurrent protection for the 2.5mm).

 

[Octopus]

If you were having a rewire or refit I would recommend a 2nd supply ....

But as others have said your existing set up could be adapted .....

 

[Tattyt]

If you were having a rewire or refit I would recommend a 2nd supply ....

But as others have said your existing set up could be adapted .....

Thanks Murdoch, no rewire or refit so new cable(s) would require a lot of work and stress!. If it does need to be done then so be it but it would appear not by the replies I have had.

 

[robd]

I agree with above on face value. If it's in the onsite guide (as was) it's good enough for me...6mm cable 32a MCB up to 15kw...unless there's something else he is thinking of.

Edit..for cooker circuits obviously not showers

 

[Gavin John Hyde]

Has anybody else noticed the ever lower current demands for new ovens and hobs, fitted one last week, manual said put it on a 16amp breaker. was a nice fancy one with steam and other functions. all part of the new energy conscious world

 

[robd]

Had my double oven out today for the first time since we moved in..bit of 10mm behind there, goes into a one gang double pole isolator. Some people

 

[Tattyt]

Many thanks to everyone that has taken the time to reply. There is so much conflicting advise out there.

Another electrician has said:

"you will either need to upgrade your current circuit to 50amp and use 10mm cable, or put in an additional circuit using 4mm for a 32amp. Your current circuit is fine with the cable size and breaker but both your ovens have a max load of 26am
(together), and the hob on its own has a max of 28amps. Please bear in mind that these levels are the maximum, ie, everything all on at the same time at max, which I doubt will ever happen?

Taking Diversity into consideration, you should be fine with the current circuit and personally that is the approach I would take unless you begin to have overload tripping issues. And then review the idea of upgrading or adding an additional circuit."

You try to do the right thing by getting an electrician in but it feels like the 1st one was trying to make it a bigger job than it probably is.

Special thanks to telectrix, I will be following your advice.

 

[Wilko]

Had my double oven out today for the first time since we moved in..bit of 10mm behind there, goes into a one gang double pole isolator. Some people

One place I was at, the cooker had 10mm and the shower 6mm. You don't have to guess why I was called ...
Re the Kitchen - I'd get another Electrician out .

 

[johnduffell]

I think the first electrician has forgotten about diversity in cooking appliances. And the second shouldn't be suggesting to wait until things trip.
they should confirm that on site in accordance with the regs

 

[telectrix]

just as an aside, i recently came across an installation where a 6.0mm cable on a 30A 3036 fuse had happily been supplying a sub-main feeding a free standing cooker and a 8.5kW shower. been fine for over 30 years. no sign of cable damage.

 

[robd]

It always was in the onsite guide they really should have that kind of thing to hand. Makes it pretty clear really, 32a MCB 6mm cable good for 15kw of cooker

 

[multimick]

fiitted a 6 ring hob last week,came with a plug top ,super intelligent thing, knew when it was going to pull too much apparently ? and shut rings down temp ? before it happened

 

[Octopus]

I think the first electrician doesn't know about diversity in cooking appliances. And the second shouldn't be suggesting to wait until things trip.
they should confirm that on site in accordance with the regs

edited that for you ............

 

[bigspark17]

Think the comments are slightly unfair as no member has seen the job. If its only 3m away how hard isit going to be to wire 2x radial circuits to the ovens and put 20A dp switch above in the cupboard (assuming its larder unit). Could be easier/cheaper than faffing around with the old 6mm supply, and yes diversity proves it could take it but there is the chance you could overload it and guidance is for any fixed load appliance >2kw to be on a dedicated circuit.
Just saying

 

[BruceBanner]

Thought diversity only applied to max demand, not design current. I know in the real world its another thing. I would try to separate supplies to some degree purely to ensure continuity of supply in case of a fault. One out all out, no good?!?

 

[Tattyt]

Think the comments are slightly unfair as no member has seen the job. If its only 3m away how hard isit going to be to wire 2x radial circuits to the ovens and put 20A dp switch above in the cupboard (assuming its larder unit). Could be easier/cheaper than faffing around with the old 6mm supply, and yes diversity proves it could take it but there is the chance you could overload it and guidance is for any fixed load appliance >2kw to be on a dedicated circuit.
Just saying

Hi bigspark17, to get the new cables would require either unsightly trunking along the entire length of the hall way or taking up the new carpet/chipboard upstairs to hide the cables. Neither ideal tbh. This is why I came on here to get a second opinion. It would seem that everyone has a different opinion

 

[johnduffell]

It would seem that everyone has a different opinion

The regs are concerned about safety, not standardisation, so there's more than one way to skin a cat. Design involves more than pulling a standard circuit out of your back pocket, you have to look at what's there and make a suitable design for the situation in front of you.
Your original sparky hasn't done that. However if you want 4 opinions then ask 2 people! And only 3 of them will comply with the regs, but everyone will swear blind theirs is the only one that complies.

 

[Deuce]

It's a funny thing, getting professional guidance... In my experience some sparks over rate what is needed to be safe because they don't understand what is really required to be safe (fear of falling short of complex and somewhat vague regulation). Then you have another group that over exaggerate simply to line their own pockets. Together these two groups seem to account for a worryingly high % of sparks.

Then of course you have the other type that has the knowledge to confidently calculate what is required, and as a professional will offer to sell you nothing more or less than what they calculate is correct. I use this forum as I know that the sparks on here are driven predominantly by passion over profit - otherwise they wouldn't be on here talking about their work for free, after having already been at work all day! They still won't agree about method of course.. But generally there is collective agreement if something is definitely not right. It seems your local sparks plan was a bit ott... I'd go for a couple more quotes and consider how much confidence the person inspires, alongside whatever price/solution they give

 

[Phillip]

6mm cable feed for all is fine, I agree.

 

[Wilko]

I've not had problems following the 6mm 32A approach myself, but I've one to do that's given me pause for thought. Biggest fully electric range (for household use) I've seen and says 14.5kW on specs. I thought, I know - I'll check with their tech department. They emailed advice of 45A OCPD and RCBO as it has 8mA leakage. . I felt like asking if that would improve if I cooked the elements for a while, but chickened out.

 

[EalingBadger]

14.5KW on a 45A OCPD?

Diversity is one thing, but surely there must be a (considerably) greater than zero chance of everything being turned on all at once from time to time?

One only has to imagine Christmas dinner with a few of the relis to see how.

Even though the oven with the bird and the pigs-in-blankets in it will likely be up to temperature and thus only clicking in and out relatively infrequently as the crisis peak approaches just before the critical moment when dinner is ready to be served there are still going to be times when this will happen when you have the plates, stuffing, parsnips, beef (for those weirdos in the family that don't like turkey), and the roasties keeping warm in the second oven, and then the hob rings are being used to cook the carrots, peas (for those weirdos in the family that don't like mushy peas), sprouts (which have been on since the 1st of November just to make sure that they are properly cooked), mushy peas, cauliflower cheese (my sister-in-law does a stunning Christmas lunch but this is just plain weird of her), whilst the bread sauce (s-i-l weirdness again! ) and Xmas pud are slowly simmering away at the back.

I mean surely, this has got to test the endurance of the poor old 45A OCPD hasn't it?

 

[MFS Electrical]

just as an aside, i recently came across an installation where a 6.0mm cable on a 30A 3036 fuse had happily been supplying a sub-main feeding a free standing cooker and a 8.5kW shower. been fine for over 30 years. no sign of cable damage.

I’ve seen that before shower piggy backed from cooker switch how the hell they fitted two 6mms in I’ll never know none of them even had cores chopped to fit I got the call because the cooker isolator smelled like fish when the shower was on

 

[freddo]

A problem with many newer cooking appliances is that the instructions demand a maximum fuse/MCB rating of 16A or 20A.

 

[FatAlan]

14.5KW on a 45A OCPD?

Diversity is one thing, but surely there must be a (considerably) greater than zero chance of everything being turned on all at once from time to time?

One only has to imagine Christmas dinner with a few of the relis to see how.

Even though the oven with the bird and the pigs-in-blankets in it will likely be up to temperature and thus only clicking in and out relatively infrequently as the crisis peak approaches just before the critical moment when dinner is ready to be served there are still going to be times when this will happen when you have the plates, stuffing, parsnips, beef (for those weirdos in the family that don't like turkey), and the roasties keeping warm in the second oven, and then the hob rings are being used to cook the carrots, peas (for those weirdos in the family that don't like mushy peas), sprouts (which have been on since the 1st of November just to make sure that they are properly cooked), mushy peas, cauliflower cheese (my sister-in-law does a stunning Christmas lunch but this is just plain weird of her), whilst the bread sauce (s-i-l weirdness again! ) and Xmas pud are slowly simmering away at the back.

I mean surely, this has got to test the endurance of the poor old 45A OCPD hasn't it?

Especially with two lots of mushy peas

 

[Wilko]

The Tech Person stated 45A was their advised minimum OCPD rating after diversity was taken into account. I'm quoting for 10mm and 50A rcbo and fittings. I'll report back with max current and leakage and we'll see if the Customer's money was well spent. But that may not be till January the speed these guys are moving.