Electric hob and oven

[GB]

Sorry, more noob questions!

I'm planning a new kitchen. The present electric cooker runs off a 32A spur. I could just replace it with a new one, but would prefer a separate hob and oven. The cooker incorporates a 13 amp socket and I can find an oven that uses 13A or less. That leaves just under 20A available for the hob, ie about

5kw. Amazingly, I am struggling to find the power consumption of many hobs, and those I have tracked down seem to be a bit higher, more like 6-7kw. Any suggestions, please?

[cynic]

In a word DIVERSITY - "The first 10A of the rated current plus 30% of the remainder of the rated current plus 5A for an integral socket ".

[GB]

Well, I agree that **in practice** a 32A socket will run cooking appliances with a much higher load. The rings switch themselves on and off all the time, so even with the oven and all 4 rings on, nearly all the time you'll be running at much less than the rated current. I just didn't think you were allowed to bank on that.

[ARWadsworth]

I'll bet if you find the load plate for your existing cooker you will find out that is exactly what you have been doing.

The OSG gives a maximum of 15kW for a household cooker with a 32A supply.

[John Rumm]

In practice (for domestic use) a 32A supply is more than adequate for even a fairly large cooker. To work out what your design current for the circuit is, take 10A plus 30% of the remaining load. Add on another 5A if you have a general purpose socket on the cooker point as well.

So for a 6.5kW hob, and a 3.2kW oven that is a 42A peak load. So if you provision a circuit to supply 10 + 30% x 32 = 19.6A

[GB]

I could see that working in practice - I just hadn't expected it to be allowed by the regs. Thanks.

I've seen overloading quite recently. I lent my extension lead to a builder to run his steam stripper off. He did not think to wind it all off the drum, and the first I knew about it was when my PC went off. He had melted the drum completely as well as enough of the cable sheath to cause a short circuit. Even 5 minutes later the cable drum was too hot to touch.

[Tabby]

So how much can I run on bellwire in conduit with fan cooling? And neutral earthing :)

NT

[John Rumm]

Diversity plays a part in quite a number of places in the regs, from the number of sockets you stick on a circuit, to the way you count the total load of circuits at a CU etc. There is a whole appendix on it in the OSG...

(might be worth doing a wiki page on it in fact)

Yup, heat when it has no escape path can soon pose a real problem in circumstances like that. That's why calculating the current carrying capacity of a cable can be so complicated in some installation conditions.

[John Rumm]

As much as you like... just can't tell you for how long ;-)

[Windmill]

That's an interesting and useful warning. I've been trying to dry out after a huge water leak from the flat above, with the usual level of help from the inusurers [I swear that typo was an accident; the subconscious in action again] who still haven't got dehumidifier etc. in place.

My home-brew extension cord works well, but the drum unit I use for outdoor work overheats. Not to the point of melting, and I've been assuming that it was a flaky socket rather than the tightly-wound cable which was responsible, but now I'm wondering. Cable diameter suggests rather thin conductors so fairly high resistance, despite the claim of a 13A. rating.

[John Rumm]

Usually they contain warnings saying 13A fully unwound or 5A wound etc,