Two ovens and induction hob wiring?

[EFLImpudence]

After diversity 18.4kW comes to 30A.

 

[JohnW2]

While 4mm maybe adequate for B32 everyone uses 6mm, and it seams a little silly to install smaller than average when you know you are having an induction hob and 2 ovens on the end. Not exactly future proof

The future against which you want to 'proof' will hopefully be a future in which there is a more sensible approach to energy utilisation, not an increase in energy usage for the same tasks. In any event, unless people start cooking and eating a lot more than they do today, why should they ever need more energy for cooking than they do today?

From the point of view of cables and OPDs, what matters is 'average current' over appreciable periods of time (i.e. 'diversity'). Quite apart from 'green' considerations, there's also the matter of cost. If cooking facilities really ever needed more than an average of 32A, then that would (at today's prices) correspond to a cost of probably about £400 per year for each average hour-per-day of usage, and I wonder if people would want to pay that much for cooking?

Kind Regards, John

 

[ericmark]

Aside from what has already been talked about, be aware of the problems with touch controls, with the halogen hob touch controls made for easy cleaning and since they retained heat, speed of operation was not important, however with induction the speed it can respond to controls is very like gas, no need to lift a pan, simply turn it down, however many touch controls need multi touches to alter output which is too slow to make use of the instant response that the induction is capable of, so in the main knobs are far better with induction hobs.

 

[ban-all-sheds]

After diversity 18.4kW comes to 30A.

Depends on

1) At what voltage the load is 18.4kW.

2) Which table in the OSG you look at.

 

[EFLImpudence]

You really are tiresome these days.

 

[ban-all-sheds]

Please explain how I am in any way responsible for this:

 

[flameport]

ovens at around 5.5kw

Doubles or singles?
Most double ovens are around 5kW - are you really looking at having two double ovens? As in 4 cooking boxes.
Singles are typically 3kW or even less.

 

[ChrisZx]

After diversity 18.4kW comes to 30A.

Depends on

1) At what voltage the load is 18.4kW.

2) Which table in the OSG you look at.

Doesn't make sense to me to only apply 10A to all three loads. Common sense to me dictates applying 30A + 30% remaining.

Doubles or singles?
Most double ovens are around 5kW - are you really looking at having two double ovens? As in 4 cooking boxes.
Singles are typically 3kW or even less.

Not my decision is it, it's hers

I must admit I'm back to the idea of 45A circuit, I don't really see why not...looking at forums, doesn't seem so unusual to me.

 

[ban-all-sheds]

Doesn't make sense to me to only apply 10A to all three loads. Common sense to me dictates applying 30A + 30% remaining.

Imagine you were skilled at metal bashing, and you made a free-standing enclosure for the ovens and the hob, with a single electrical connection for them all. Would they use less power than if they were installed and supplied separately?

Imagine if you bought a range cooker, with a hob and multiple ovens, and you had at it with angle grinders and hacksaws and separated out the hob and ovens, and installed and supplied them separately. Would they start to use more power than they did when combined into the cooker?

 

[JohnW2]

I must admit I'm back to the idea of 45A circuit, I don't really see why not...looking at forums, doesn't seem so unusual to me.

You're right - provided that one pys adequate attention to 'what happens at the ends' (and that's not much of an issue with cooking appliances, there's never an (electrical) reason why one can't have a circuit with greater current-supplying capabilities than one needs. However, that does not mean that it is necessary, nor that one gains anything by doing it. ... but, if it makes you more comfortable, there no reason why you can't do as you wish

As for "doesn't seem unusual', it would certainly not be unique - but I would say that it would be pretty "unusual" in terms of what is installed these days. In the past, all sorts of things were done, perhaps because people thought even less back then (if such is possible!) about what they were doing in those days, and did things "because other people did them". I inherited a particularly odd (unused) cooker circuit - wired in 10 mm² cable (Imperial equivalent) but protected by a 30A fuse - that did seem a bit daft!

Kind Regards, John

 

[ChrisZx]

Imagine you were skilled at metal bashing, and you made a free-standing enclosure for the ovens and the hob, with a single electrical connection for them all. Would they use less power than if they were installed and supplied separately?

Imagine if you bought a range cooker, with a hob and multiple ovens, and you had at it with angle grinders and hacksaws and separated out the hob and ovens, and installed and supplied them separately. Would they start to use more power than they did when combined into the cooker?

I get that completely, but just because that's the outcome of the regs doesn't mean it's logical. Theoretically if you had infinite appliances the regs would be ridiculous, so at some number of applicances it becomes stupid...if you get what I mean. So I don't think blindly following your logic is a good idea.

At 80A total load each would only have to be at 40% to max out the circuit. Am I the only one that thinks that doesn't sound so unlikely?

You're right - provided that one pys adequate attention to 'what happens at the ends' (and that's not much of an issue with cooking appliances, there's never an (electrical) reason why one can't have a circuit with greater current-supplying capabilities than one needs. However, that does not mean that it is necessary, nor that one gains anything by doing it. ... but, if it makes you more comfortable, there no reason why you can't do as you wish

As for "doesn't seem unusual', it would certainly not be unique - but I would say that it would be pretty "unusual" in terms of what is installed these days. In the past, all sorts of things were done, perhaps because people thought even less back then (if such is possible!) about what they were doing in those days, and did things "because other people did them". I inherited a particularly odd (unused) cooker circuit - wired in 10 mm² cable (Imperial equivalent) but protected by a 30A fuse - that did seem a bit daft!

Kind Regards, John

I keep going back and forth (bearing in mind I won't be starting the install for weeks at least so no urgency!) but maybe I should hedge my bets in a similar fassion... 6 or 10mm depending on installation that could handle 45A and a 32A MCB. At least that way I wouldn't have to rip out all the plaster if 32A kept tripping. AFAIK there's no problem with that?

 

[AndyPRK]

The only real downside of 10mm is terminating the big cables at the kitchen end.

So maybe consider a back up plan.

 

[AndyPRK]

Or if things trip on a 32A you could move one oven into the ring circuit.

 

[JohnW2]

I get that completely, but just because that's the outcome of the regs doesn't mean it's logical.

I would personally say that it's totally logical. As BAS has said, why on earth would several 'smaller' cooking appliances use less electricity if put together into one case, or one 'larger' cooking appliance use more electricity because it was split up into several different bits?

Theoretically if you had infinite appliances the regs would be ridiculous, so at some number of applicances it becomes stupid...if you get what I mean.

Don't forget that the diversity guideline we are talking about is the one for domestic installations - and the amount of cooking one does domestically will not differ according to how many or few #cases' one's cooking appliances are housed in. There are different guidelines in relation to commercial kitchens.

So I don't think blindly following your logic is a good idea.

It's not just BAS's logic - it's the same logic that most people apply.

At 80A total load each would only have to be at 40% to max out the circuit. Am I the only one that thinks that doesn't sound so unlikely?

Don't forget that what matters is 'average current for appreciable periods of time'. If absolutely everything were 'turned on full' from cold simultaneously (which is virtually never going to happen) then yes, the full 80A would initially be drawn, but only for a very short period of time. Even if you continued using every single bit of the cooking appliances, the thermostats would rapidly start turning things on and off, and you would soon reach the situation in which the average current over any appreciable period of time would be a small fraction of 80A.

I keep going back and forth (bearing in mind I won't be starting the install for weeks at least so no urgency!) but maybe I should hedge my bets in a similar fassion... 6 or 10mm depending on installation that could handle 45A and a 32A MCB. At least that way I wouldn't have to rip out all the plaster if 32A kept tripping. AFAIK there's no problem with that?

Well, you'd then be getting close to the 'usual' situation for a domestic cooker circuit - which I would say is probably 6 mm² cable (although 4 mm² would theoretically often be adequate) on a 32A MCB.

Kind Regards, John

 

[EFLImpudence]

I get that completely, but just because that's the outcome of the regs doesn't mean it's logical.

It's nothing to do with the regulations.
It is standard practice which has been followed satisfactorily for decades.

Theoretically if you had infinite appliances the regs would be ridiculous, so at some number of applicances it becomes stupid...if you get what I mean. So I don't think blindly following your logic is a good idea.

No - the more appliances the better.
The hobs and elements will be cycling on and off the whole time.
When you have installed whichever cables and devices you decide, buy a current clamp meter and look at the actual current being used.

At 80A total load each would only have to be at 40% to max out the circuit.

Then that must be how it works out.
Don't forget that time is also a factor.

Am I the only one that thinks that doesn't sound so unlikely?

Amongst those in the discussion - yes.

I keep going back and forth (bearing in mind I won't be starting the install for weeks at least so no urgency!) but maybe I should hedge my bets in a similar fassion... 6 or 10mm depending on installation that could handle 45A and a 32A MCB. At least that way I wouldn't have to rip out all the plaster if 32A kept tripping. AFAIK there's no problem with that?

I am talking about method C - clipped direct or buried in masonry.
Obviously if you run the cable in thermal insulation it affects the current carrying capacity of the cable but that goes for any circuit so don't do it.

6mm² cable is traditionally used with a 32A MCB for cookers because it is traditionally used. 4mm² is adequate with a 32A MCB.
6mm² cable was required with 30A rewireable BS3036 fuses because they take longer to trip than MCBs.

So, 4mm² cable is good. It has a maximum CCC of 37A.

If you want to use a 40A or 45A MCB (not all manufacturers make 45A ones), then you will require 6mm² cable as it has a maximum CCC of 47A.

If you want to use 10mm² cable which has a maximum CCC of 64A (note this is frequently used as the supply cable for entire flats) then you could use a 63A MCB.