16.5kw Electric Cooker, What size Breaker? Pictures added

[Barney1686]

Hi Guys,

We have purchased a Ceramic Range Cooker from Britannia and some advice would be useful.

We are also currently having a new Consumer unit fitted and the Electrician who is doing the job thinks it may need its own consumer unit ( im sure there is a better word for it ) due to the huge power draw it is capable of, I think I remember him mentioning 100amp breaker and that 10mm t&e may not be big enough?

Thought I better clarify with Britannia and they are stating that it is fine going to a normal consumer unit and only needs a 40/45 amp breaker with 10mm t&e.

I must admit that the wire that comes out from the oven looks like something you would use on overhead power lines, but who is correct here guys?.

Just want the job to be safe and correct.

Cheers for any help offered.

 

[JohnW2]

We are also currently having a new Consumer unit fitted and the Electrician who is doing the job thinks it may need its own consumer unit ( im sure there is a better word for it ) due to the huge power draw it is capable of, I think I remember him mentioning 100amp breaker and that 10mm t&e may not be big enough? ... Thought I better clarify with Britannia and they are stating that it is fine going to a normal consumer unit and only needs a 40/45 amp breaker with 10mm t&e. ... I must admit that the wire that comes out from the oven looks like something you would use on overhead power lines, but who is correct here guys?.

That's a pretty massive cooker! Britannia are probably the more correct. If, as usual, the 16.5 kW is quoted at 240V, that represents a maximum current of 68.75A. However, it is usual to apply the concept of 'diversity' (which recognises that not all bits of the cooker will be on simultaneous), using a 'standard formula'. Appling that formula would give an 'after diversity' current of 30.625A - theoretically just about OK with a 32A breaker but, as Britannia said, 40A or 45A would probably be more sensible. As for the cable size, you'll see a lot of discussion about that here (some recently). Although 10mm² would certainly be OK, 6mm² almost certainly would as well.

Kind Regards, John

 

[Barney1686]

Thanks John, what do you think about not connecting it up to the new consumer unit?

As I say, he wants it on its own consumer unit.

 

[EFLImpudence]

 

[JohnW2]

Thanks John, what do you think about not connecting it up to the new consumer unit? As I say, he wants it on its own consumer unit.

Nonsense. He either has not heard of, does not understand or does not believe in (that one could be more of a problem!) the concept of diversity. I would suggest that you 'probe' him about that (maybe pointing out that Britannia have obviously heard of, and believe in, diversity).

Kind Regards, John

 

[mattysupra]

Reading with interest (im not a sparky so dont know)

This diversity thing is down to not using everything at once?

My mrs last year while cooking Christmas dinner was using every hod and both the ovens most of the day. Would this still be o.k ?

I presume that even tho she was using everything at the same time that the cooker would not be pulling full power as the ovens would be up to temperature for example. but what if she was turn every thing on at the same time?

 

[JohnW2]

Reading with interest (im not a sparky so dont know) ... This diversity thing is down to not using everything at once?

Well, everything not drawing current at once for long periods of time

My mrs last year while cooking Christmas dinner was using every hod and both the ovens most of the day. Would this still be o.k ?

Christmas day always gets wheeled out whenever this discussion arises. I'm not sure I've ever heard of anyone suffering on Christmas day as a result of 'diversity letting them down (and, even if they did, they'd just have to turn one or two bits off for a few minutes and reset the breaker) ...

I presume that even tho she was using everything at the same time that the cooker would not be pulling full power as the ovens would be up to temperature for example. but what if she was turn every thing on at the same time?

Exactly. Once they get going, everything cycles on and off per their individual thermostats, hence not 'synchromised'. There could, as you say, be an initial period of very high load if everything were to be switched on from cold simultaneously, but that situation would not last for very long at all and would not normally cause any problem. For example, a 32A breaker will tolerate a current of about 46A for an hour without tripping, and much higher currents for shorter periods of time.

Kind Regards, John

 

[Barney1686]

Thanks again John,

It would seem I am going to have to have one of those awkward conservations then.

He has good references but is very very cautious it would seem, a few other things he mentioned raised an eyebrow or two.
For example: He wants to replace my current 6 way consumer unit for a 21 way consumer unit, but im only adding 7 more circuits.

But I would prefer it that way than not caring at all so will not moan about him for that.

Before he will do any work I have to get the energy company to fit an isolator switch as he will not touch it until that.

Maybe get a second opinion as well.

 

[mattysupra]

Thanks Jon for clearing up.

In the case of a shower then (one heating element) the diversity rule wont apply then? only to items where multiple heating elements can be turned on etc?

 

[OwainDIYer]

what if she was turn every thing on at the same time?

This is so unlikely in practice in a domestic setting where a variety of dishes will be cooked that use different times and temperatures.

Different diversity factors apply to commercial kitchens.

 

[JohnD]

He has good references but is very very cautious it would seem

Ask which Competent Person Scheme he is in, and how long he has been a member.

He is surely unlikely to have forgotten the principles of diversity, even if he needed to look up the calculation.

 

[JohnW2]

Thanks Jon for clearing up. ... In the case of a shower then (one heating element) the diversity rule wont apply then? only to items where multiple heating elements can be turned on etc?

Indeed - you can't apply diversity to a single shower. If there are more than two (very rare domestically) it may then become possible to start applying diversity, on the basis that all are unlikely to be used simultaneously.

Mind you, there is 'diversity over time' as well as 'diversity over place' - in other words, even if a load only has, say, one element, if it cycles such that it is only 'on' for short periods, with large gaps in between, it may be possible to invoke a diversity concept - since the average load over any 'reasonable' period of time will be a lot less that the 'on' load.

Kind Regards, John

 

[JohnW2]

Thanks again John, ... It would seem I am going to have to have one of those awkward conservations then.

If I were you, I think I would simply 'blame Britannia' and tell him that when you expressed surprise at what they were telling you, they explained that there advice/instructions were based on applying the concept of diversity - then 'innocently' ask him what that concept is!! If he can't give you some sort of sensible answer (even if he personally feels nervous about relying on diversity), then I think you may have a problem - and perhaps should be looking for a different electrician!

He has good references but is very very cautious it would seem, a few other things he mentioned raised an eyebrow or two. ... For example: He wants to replace my current 6 way consumer unit for a 21 way consumer unit, but im only adding 7 more circuits. ... But I would prefer it that way than not caring at all so will not moan about him for that.

As you say, provided it's not taken too far, 'cautious' and (apparently) 'caring' is good - but it can sometimes be difficult to distinguish that from 'unnecessary work generation'! As you go on to say, if things get difficult (and maybe even if they don't), you could always tell him that you feel you need to get at least one other quote - which is a perfectly reasonable position to take.

Kind Regards, John

 

[Barney1686]

Will do,

I know you have only posted a few lines but it is people like you that can help jo public save money and time from possible mistakes,..So thank you for that.

 

[JohnW2]

Will do, ... I know you have only posted a few lines but it is people like you that can help jo public save money and time from possible mistakes,..So thank you for that.

You're welcome. Let us know how the conversation goes!

Kind Regards, John