Cooker Cable requirements

DJM · 2 Jan 2007

We are thinking of updating the kitchen and with Part P etc, and the shape of the kitchen we were going to simply replace old units for new and leave all electrical installations as is.

However, we would like a new cooker and currently have a cooker switch with single outlet adjacent run on 6mm cable from a 30A (don't scream too loudly) rewirable fuse.

The cooker SWMBO wants says it is nominal power of 13.1KW and requires 45 amp power supply which seems to force me into minimum 10mm cable. Even then this seems a bit thin based on the run being completely enclosed for most of it's length and worse bundled near the consumer unit.

Can you confirm or deny my worst fears and offer any sage advice

kevnurse · 2 Jan 2007

Is SWMBO likely to change her cooking habits as a result of this "new for old" change? If so, then you need to take advice from an electrician, but I would be very surprised if you need more than 10mm2 cable

Mosez · 2 Jan 2007

DJM said:
We are thinking of updating the kitchen and with Part P etc, and the shape of the kitchen we were going to simply replace old units for new and leave all electrical installations as is.

However, we would like a new cooker and currently have a cooker switch with single outlet adjacent run on 6mm cable from a 30A (don't scream too loudly) rewirable fuse.

The cooker SWMBO wants says it is nominal power of 13.1KW and requires 45 amp power supply which seems to force me into minimum 10mm cable. Even then this seems a bit thin based on the run being completely enclosed for most of it's length and worse bundled near the consumer unit.

Can you confirm or deny my worst fears and offer any sage advice

What is the length of the cable?

DJM · 2 Jan 2007

I haven't yet traced the cable route end to end yet and we have solid floors so I think it goes up and over the kitchen in the false ceiling which would add a few metres. I am at work so my estimate from memory is

consumer unit to cooker switch approx 8 - 10 metres
cooker switch to cooker approx 4 metres.

current cable is 6mm2 so for the new cooker (and possibly for current cooker now come to think of it) not sufficient I think

DJM · 3 Jan 2007

Routing of cable is a bit strange, but the lengths given in my previous post are about right and it is definitely 6mm2.

So anybody like to confirm I will need to upgrade to 10mm2?

securespark · 3 Jan 2007

Allowing Reference Method 4 (the lowest current rating for any given size of conductor, if you like), then if you also allow diversity for your cooker, you can run it on 6mm² for 14m OK.

45A? If you want to upgrade the circuit to allow flc, then you need a 60A breaker (not many mfrs do these) and the hardware to support it. Oh, and 16mm² cable, too.

You could go for a happy medium (ie 45A), but that would still have some allowance foir diversity on the circuit.

If you did that, then (still using RM4) 16mm² is still applicable.

Some will say RM4 is too harsh, but it allows for the bunching.

DJM · 4 Jan 2007

Thanks for the reply securespark, but could you clarify something for me.

1) You say 6mm2 is OK using diversity and RM4 for the suggested 13.1kW cooker (and I checked last night and our current cooker is 13.115kW and has been running fine for many years so I have no reason to doubt that) but how did you calculate that? Are the following calculations are correct then 13.1KW gives about 57A and using Diversity 10A + 30% + 5A for socket, the figure is 20A which appears to be fine for Installation Method 6 (I don't have access to the full tables, just the updated table in Amendment 1 of the BS)

2) Can you think of a reason why the manufacturer (Smeg) would state in their literature "45 Amp power supply required"

3) Am I correct in assuming if I went for 45A then I am forced to 16mm2 as even with IM6 it would appear 10mm2 is insufficient, and even after re-routing, there will be a short stretch from the CU where the cables would be bunched..

DJM · 4 Jan 2007

Just for interest, what does RM4 state for 10mm2

Adam_151 · 4 Jan 2007

DJM said:
Just for interest, what does RM4 state for 10mm2

Deleted: I've learnt to read the question properly now!

Adam_151 · 4 Jan 2007

DJM said:
Just for interest, what does RM4 state for 10mm2

46A

DJM · 5 Jan 2007

DJM said:
....I checked last night and our current cooker is 13.115kW and has been running fine for many years so I have no reason to doubt that) ...

Woops, I managed to translate one half of a figure on one line and the scond half from the next.
Current cooker is actually 11.115KW

slider45 · 5 Jan 2007

Sorry to jump in on this thread - I'll start another if this question warrants more than a yes/no answer.

We've just inhereted a nice Bosch halogen combined hob/oven/grill rated at 9.6Kw.

Our Cooker connection switch is I believe wired with 4mm cable to the CU (only about 2m away) where it is fused at 20A.

9.6Kw = approx 41.74A
Applying 'diversity' gives
10A + 9.52A + (no socket) = 19.52A

Is using this cooker on the existing circuit feasible or will the electrician (who is coming tomorrow) be right if he suggests an upgrade?

Again - sorry to interrupt!

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Cooker Cable requirements

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