Cooker/Oven circuit

[ldoodle]

Hey,

The house we're buying has a 32amp breaker for the cooker (currently freestanding all-in-one with hob). We're gutting it and the oven we're looking at is 20amp (will be a separate 3amp gas hob not on the same circuit).

Does an accessory need to be rated at what the breaker is 'pushing', or what the appliance is pulling. i.e. in this scenario would a 20amp DP wall switch suffice as the oven is 20amp, or would it not suffice as the breaker is rated at 32amp, requiring a 32amp or higher wall switch.

Or would it be sensible to change the breaker for a 20amp one as that's all the oven needs? I can keep the current 32amp safe in case I, or any future buyers, require it.

Thanks

 

[Taylortwocities]

The fuse/breaker in the consumer unit is there to protect the CABLE that runs from the consumer unit to the cooker.
It will trip if too much current is drawn from that circuit.

Any switch will also need to be able to carry the maximum current.

So your circuit is fine as it is if the load is 20amp. The isolation switch will need to be >32amp. Cooker switches tend to be 45amp or more, so get one of those.

You should not need to reduce the fuse/circuit breaker unless the maker of the oven specifies this.

 

[ericmark]

For portable items any fusing required is built into the appliance but with fixed items the manufacturer can stipulate the protection required on the supply.

Since 32 amp is the standard supply for cookers I would think it unlikely a manufacturer would stipulate a smaller protection device. However when using a 45 amp supply they may.

So you do need to read the instructions but likely it is OK.

 

[JohnW2]

For portable items any fusing required is built into the appliance but with fixed items the manufacturer can stipulate the protection required on the supply.

It does seem very reasonable for a circuit's OPD to be used as the means of protecting a 'fixed' load which is hard-wired to a dedicated circuit. I therefore wonder whether electricians should perhaps move a little away from the often-heard generic assertion that a circuit's OPD is always there only to protect te cable?

Kind Regards, John

 

[ban-all-sheds]

I think that electricians should write to the manufacturers of such equipment, and ask them to confirm that they cannot design equipment which has its own integral protection but instead have to rely on the circuit protective device.

 

[JohnW2]

I think that electricians should write to the manufacturers of such equipment, and ask them to confirm that they cannot design equipment which has its own integral protection but instead have to rely on the circuit protective device.

That's one approach but, as I suggested, I don't think it unreasonable for equipment intended to be run on dedicated circuits to have a single protective device for both equipment and cable.

Not only does that avoid the need for an 'unnecessary' protective device but if the equipment has integral protection, it would usually be impossible to get reasonable discrimination between that and the circuit's CPD, unless the circuit were seriously over-specified.

Kind Regards, John

 

[ldoodle]

Any switch will also need to be able to carry the maximum current.

Thanks... that's the only bit I wasn't sure about.

The reason for my post is MK do a 32amp square, but with neon, or a 45amp oblong one... neither of which I really like.

GET (or now Schneider) do a 45amp square with no neon, but it's been Pavarotti'd compared to GET's other accessories!

Might just start my own accessories range, where absolutley everything looks EXACTLY the same

 

[ban-all-sheds]

I don't think it unreasonable for equipment intended to be run on dedicated circuits to have a single protective device for both equipment and cable.

On the contrary, we see all the time the unreasonable difficulties which arise when manufacturers decide to rely on the external circuit device. 16A ovens which cannot be connected to 32A cooker circuits. Extractor fans which cannot be connected to 6A lighting circuits.

There is nothing reasonable about choosing to make equipment which constrains the circuit designer.

The circuit protective device ought to be for the circuit cable and only the circuit cable. I see no reason why equipment makers cannot stick to that, and no reason why they could not be forced to by legislation.

Not only does that avoid the need for an 'unnecessary' protective device but if the equipment has integral protection, it would usually be impossible to get reasonable discrimination between that and the circuit's CPD, unless the circuit were seriously over-specified.

The discrimination problem also applies to 13A BS 1362 fuses and 20/32A MCBs.

 

[JohnW2]

I don't think it unreasonable for equipment intended to be run on dedicated circuits to have a single protective device for both equipment and cable.

On the contrary, we see all the time the unreasonable difficulties which arise when manufacturers decide to rely on the external circuit device. 16A ovens which cannot be connected to 32A cooker circuits. Extractor fans which cannot be connected to 6A lighting circuits.

As you correctly quoted, I referred to "equipment intended to be run on dedicated circuits", in relation to which I don't think it's particularly reasonable to unnecessarily duplicate non-discriminating overcurrent protection. Things like extractor fans obviously don't come into that category. Cookers might, although a designer might choose not to use a dedicated circuit (i.e. by using the circuit to also supply a socket).

Do immersion heaters and showers have integral overcurrent protection? Maybe they do.

Kind Regards, John

 

[ban-all-sheds]

As you correctly quoted, I referred to "equipment intended to be run on dedicated circuits", in relation to which I don't think it's particularly reasonable to unnecessarily duplicate non-discriminating overcurrent protection.

I submit it is unreasonable to force the circuit to provide protection for the internals of your appliance.

Things like extractor fans obviously don't come into that category.

Correct - sorry.

Cookers might, although a designer might choose not to use a dedicated circuit (i.e. by using the circuit to also supply a socket).

But he can't if that means that the circuit OPD is higher than the maker specifies.

If we take the separate hob & oven combination, which is very common, if the oven maker insists on a 16A circuit, he is insisting on a separate circuit just for his appliance. More cabling, more switching, another way in the CU gone....

That is not reasonable.

 

[JohnW2]

I submit it is unreasonable to force the circuit to provide protection for the internals of your appliance.

Fair enough. I understand your viewpoint.

Do you know the answer about immersion heaters and showers?

Kind Regards, John

 

[EFLImpudence]

Do immersion heaters and showers have integral overcurrent protection? Maybe they do.

Why would they need it?

Showers have thermal cut-outs.

 

[JohnW2]

Do immersion heaters and showers have integral overcurrent protection? Maybe they do.

Why would they need it?

They wouldn't if they were (as is commonly the case) on a dedicated circuit with an appropriate size of CPD - that was my point.

Showers have thermal cut-outs.

Do I take it that you mean 'thermally-operated thermal' (rather than electrically-operated thermal'), if you understand what I mean? [i.e. in wouldn't operate in response to electrical overcurrent until the whole thing had got very hot]

Kind Regards, John

 

[ban-all-sheds]

Do you know the answer about immersion heaters and showers?

No.

Throwing it open to all - has anybody ever heard of an IH maker mandating a maximum circuit OPD rating? There isn't really any internal wiring - I suspect that it's penny pinching there which leads appliance makers to need to rely on external protection. And probably a healthy amount of misinterpretation by the people who write the manuals and end up changing "needs an X amp supply" to "must have an X amp supply".

I can't see it ever happening with showers - 80/90A circuits are uncommon.

 

[JohnW2]

And probably a healthy amount of misinterpretation by the people who write the manuals and end up changing "needs an X amp supply" to "must have an X amp supply".

... and, in the examples you give, maybe also some misinterpretation on the part of readers. If a manufacturer literally wrote either of the things you suggest, would it not be reasonable to interpret it as saying that the equipment needed a supply capable of providing at least X amps, not a supply with an X amp OPD?

Kind Regards, John