Installing new oven ring main without making a mess. Possible?

Taylortwocities · 10 Nov 2019

The breaker is there to protect the cabling, not the appliance. The breaker size is selected once the cable size is known. The cable size is selected once the load is known (plus other factors, like cable run inside insulation, etc).

mind you, the regulations say that one should take account of the Manufacturer’s Instructions, so it may be prudent to install a (for example) 16A breaker if that is what the MIs mandate.

winston1 · 10 Nov 2019

MugabesDeadCat said:
Do you only ever fit a breaker to suit the rating of the appliance? I.e. current oven is 4.4kW, which I believe is about 18A, so you fit a 20A breaker

No. The breaker is to protect the cable not what is on the end of it.

winston1 · 10 Nov 2019

Taylortwocities said:
The breaker is there to protect the cabling, not the appliance. The breaker size is selected once the cable size is known. The cable size is selected once the load is known (plus other factors, like cable run inside insulation, etc).

mind you, the regulations say that one should take account of the Manufacturer’s Instructions, so it may be prudent to install a (for example) 16A breaker if that is what the MIs mandate.

Manufacturers instructions are often wrong.
So take account of but don’t blindly follow.

Taylortwocities · 10 Nov 2019

That’s what I said. Take account of.

EFLImpudence · 10 Nov 2019

EFLImpudence said:
Maybe someone fitted the 20A MCB for the present oven and it is a 'standard' cooker circuit.

I didn't say it was necessary or that he was correct to do so.

MugabesDeadCat · 10 Nov 2019

So if it's say 4mm cable, and the oven is either 5.9 or 6.4kW depending on what we get. Would that require a 32A breaker?

EFLImpudence · 10 Nov 2019

Not mandatory - but most people would fit a 32A.

Your 20A will be acceptable using what we call 'diversity' for cooking appliances.

That is the first 10A plus 30% of the remainder.

6.4kW @ 240V = 26.7A.
so 10 + (16.7 x 0.3) = 15A.

MugabesDeadCat · 11 Nov 2019

Spoke to an electrician earlier, he's coming to have a look tomorrow. But he says it needs a 6mm feed.

Am I doing to get the same response from all electricians?

John D v2.0 · 11 Nov 2019

I think the guidance notes say 6mm for cooker, so i guess many would include an oven. But the people on here have designed the specific circuit according to the load so those rules of thumb are overly conservative in that case.

EFLImpudence · 11 Nov 2019

MugabesDeadCat said:
Spoke to an electrician earlier, he's coming to have a look tomorrow. But he says it needs a 6mm feed.

Am I doing to get the same response from all electricians?

You very well might.

6mm² had to be used for 30A cooker circuits in the past with rewirable fuses.
People still use it because it has always been used so people still use it because it has always been used.

See if you can find an electrician who knows what he is doing.

MugabesDeadCat · 11 Nov 2019

He says it's 6mm cable, so will provide a new breaker

EFLImpudence · 11 Nov 2019

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Installing new oven ring main without making a mess. Possible?

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