New Oven & Hob on same supply ?

Mecoconuts

I had an old cooker with integrated hob on a Cooker Circuit with a 32 Circuit Breaker in the Mains Box.

I now have a new oven (20A - 3.3kW) and a new hob (30A - 5.8kW).

Can i connect them both to the original cable that the cooker was connected to ?

Thanks for any help !

Hunnymonster

I make the total a 50A draw if it's all active (unlikely I know) which is way OTT for the 32A breaker and probably the cable in the wall (unless it's 10sq mm cable - you'll be able to tell - you'll need a pipe bender to bend it ) - but a downer if the CB trips out as you start on the Xmas dinner....

And these days with part p being active that's an inspectable job

YorkshireBoy

There's a discrepancy with the electrical loadings you quote...

From Ohms Law, I = P/V (amps = power/volts), therefore...

I (oven) = 3300/230 = 14.35A, and
I (hob) = 5800/230 = 25.22A

I suspect your KW figure is the actual load and the current figure is the rating of the protective device required (ie, next size up).

With cooking equipment, you can apply something called "diversity" which basically involves an assumption that not all the load will be "on" at any one time. I can't remember the exact figures (my 16th ed regs are at work), but my initial recommendation would be...

1/ Cable required = 10sq mm
2/ MCB required = 40/45A

Now for the bad news. As this is an "additional circuit", it falls under the Part P umbrella which basically means you can't do it yourself unless you pay for an inspection on completion. As an indication of cost, I believe our our local Council charges £50 for this service.

If you employ your own (Part P compliant) electrician, and depending on length/type of cable route and consumer unit suitability, you will probably be looking at around £200-300.

Regarding the practicalities, I would probably run 10sq mm from consumer unit* to a 45A cooker switch. I would then run 2-off 6sq mm cables from the 45A cooker switch, 1 direct to the hob and 1 to the oven via a 20A DP switch mounted in an adjacent cupboard.

HTH
YB

* Be careful here as there are restrictions on the number of protective devices in excess of 40A you can fit into some consumer units. This restriction will probably affect you if you have a large (>7.5KW) shower installed.

Hunnymonster

YorkshireBoy wrote:

There's a discrepancy with the electrical loadings you quote...

From Ohms Law, I = P/V (amps = power/volts), therefore...

I (oven) = 3300/230 = 14.35A, and
I (hob) = 5800/230 = 25.22A

It's at variance because neither will be a purely resistive load - so there'll be the inductive element to account for too - which will add nothing to the power, but will add to the current flow (and hence the conductor size and protective device rating)

YorkshireBoy

Hunnymonster wrote:

It's at variance because neither will be a purely resistive load - so there'll be the inductive element to account for too - which will add nothing to the power, but will add to the current flow (and hence the conductor size and protective device rating)

Hi Hunnymonster, agree entirely with your theory. Would just add that the inductance would be negligible (and certainly would not add 5A to the "apparant" load), and thats why I didn't mention it.

I suspect the OP has quoted from the installation manual, and not the appliance rating plate.

YB

Hunnymonster

All those nice coils of nichrome wire to heat his cheesy beans from Asda..... inductance central mate

Have to say that my experience is that the oven part is usually perfectly happy on a standard domestic 13A socket - especially if the kW rating is given at 240V (not uncommon) and the supply is nominally 230v (-6+10%) as it is in this country, that 3.3kW becomes about 3.0kW and well within what a domestic BS1363 13A socket can cope with.

Then the hob goes on the cooker circuit and Robert's your father's brother - no part p inspection to mess about with (there's no wiring change) and everyone's happy.... probably