Cable size

Stevec1999 · Aug 28, 2021

My electrician assures me that a 10.6kw freestanding cooker is fine to have on a 6mm cable, 32a breaker. Could anyone out there give me a 2nd opinion.

pc1966 · Aug 28, 2021

The thing with cookers is they rarely have all heaters on at once, and even if they do they don't stay on that long until they start cycling to maintain a set temperature and so reduce the average power used. This is referred to as "diversity" here.

So while your cooker is rated at 46A & 230 V = 10.6kW, the usual formulae for estimating domestic cooking loads is 10A plus 30% of the remainder, and 5A more if a 13A socket outlet is provided.

So in your case it would be 10 + 0.3* (46-10) + 5 = 25.8A so under 32A.

The 6mm cable is fine for at least 32A under most installation methods, except for 101 and 103 where it is extensively covered in thermal insulation, so a combination of 6mm and a 32A MCB is usually safe no matter what, though if you really push the cooker to all on at max at once (as a commercial chef might do at the start of the evening) you might just trip it.

Dustydazzler · Aug 28, 2021

6mm covers 99.999% of all domestic cooker installations

pc1966 · Aug 28, 2021

Dustydazzler said:
6mm covers 99.999% of all domestic cooker installations

Yes, working backwards 32A is fine for a 15kW cooker and socket outlet, the only restriction for 6mm being methods 101 and 103 having lower limits due to heating (27A / 23A) but if running in a new cable I relly doubt you would end up with it in such thick insulation.

Deleted account · Aug 28, 2021

Stevec1999 said:
My electrician assures me that a 10.6kw freestanding cooker is fine to have on a 6mm cable, 32a breaker. Could anyone out there give me a 2nd opinion.

Second opinion. I agree with your electrician. In fact 4mm might be big enough.

Stevec1999 · Aug 29, 2021

Paignton pete said:
Second opinion. I agree with your electrician. In fact 4mm might be big enough.

Thanks for your time

Stevec1999 · Aug 29, 2021

pc1966 said:
The thing with cookers is they rarely have all heaters on at once, and even if they do they don't stay on that long until they start cycling to maintain a set temperature and so reduce the average power used. This is referred to as "diversity" here.

So while your cooker is rated at 46A & 230 V = 10.6kW, the usual formulae for estimating domestic cooking loads is 10A plus 30% of the remainder, and 5A more if a 13A socket outlet is provided.

So in your case it would be 10 + 0.3* (46-10) + 5 = 25.8A so under 32A.

The 6mm cable is fine for at least 32A under most installation methods, except for 101 and 103 where it is extensively covered in thermal insulation, so a combination of 6mm and a 32A MCB is usually safe no matter what, though if you really push the cooker to all on at max at once (as a commercial chef might do at the start of the evening) you might just trip it.

Thanks for your time.

Stevec1999 · Aug 29, 2021

Dustydazzler said:
6mm covers 99.999% of all domestic cooker installations

Thanks for your time

Stevec1999 · Aug 29, 2021

pc1966 said:
Yes, working backwards 32A is fine for a 15kW cooker and socket outlet, the only restriction for 6mm being methods 101 and 103 having lower limits due to heating (27A / 23A) but if running in a new cable I relly doubt you would end up with it in such thick insulation.

Thanks for your time

pc1966 · Aug 29, 2021

Just to add that if the run is very long you might need a thicker cable to reduce the voltage drop. However, 6mm at 32A is usually fine for 45m, often up to to 63m, so it would be an unusually large property (or convoluted run) to reach that limit.

pc1966 · Aug 29, 2021

Paignton pete said:
Second opinion. I agree with your electrician. In fact 4mm might be big enough.

Yes 4mm might be, if clipped direct (no conduit or thermal insulation) and not too long (max 43m on VD, 28m for Zs on typical TN-S supply, from OSG table).

But for the fairly small cost difference 6mm would make it the margins that much more comfortable!

Stevec1999 · Aug 29, 2021

pc1966 said:
Just to add that if the run is very long you might need a thicker cable to reduce the voltage drop. However, 6mm at 32A is usually fine for 45m, often up to to 63m, so it would be an unusually large property (or convoluted run) to reach that limit.

About a 10m run. Thanks for your time.

Stevec1999 · Aug 29, 2021

pc1966 said:
Yes 4mm might be, if clipped direct (no conduit or thermal insulation) and not too long (max 43m on VD, 28m for Zs on typical TN-S supply, from OSG table).

But for the fairly small cost difference 6mm would make it the margins that much more comfortable!

New 6mm cable. Thanks for your time.

Stevec1999 · Aug 29, 2021

pc1966 said:
Yes, working backwards 32A is fine for a 15kW cooker and socket outlet, the only restriction for 6mm being methods 101 and 103 having lower limits due to heating (27A / 23A) but if running in a new cable I relly doubt you would end up with it in such thick insulation.

I was never aware of 101 and 103. All of my cables run through or along the joists of a warm deck flat roof (120mm celotex laid on plywood fixed to the top of joists). In all of my ignorance, do either 101 or 103 relate to my situation? Do 101 and 103 relate to cable that is either in contact with insulation or through insulation?

pc1966 · Aug 29, 2021

Stevec1999 said:
I was never aware of 101 and 103. All of my cables run through or along the joists of a warm deck flat roof (120mm celotex laid on plywood fixed to the top of joists). In all of my ignorance, do either 101 or 103 relate to my situation? Do 101 and 103 relate to cable that is either in contact with insulation or through insulation?

They apply when cable is well insulated. The following pages from the IET's On-Site Guide is the best explanation