Constraints on use of a 3.7kW induction hob?

itm2

Risteard said:

I have a 7kW+ induction hob and an oven on a standard 32A cooker circuit. It's not an issue. Diversity allows 15kW of cooking equipment on a standard 30/32A cooker circuit. I have never limited what I use at a time with it. Electrical competence means I understand that I don't have to.

That's very interesting. Do you have an idea of what the largest load is that you would have placed on your hob and cooker? For example, have you ever had the oven @200 degrees while boiling/simmering vegetables on 2 or more rings of the hob?

Rodders53

I really, really doubt that the kitchen in a modern town house has only one 32A feed...  Almost certainly 1 x 32 A mcb for 'Cooker' and 1 x 32 A mcb for 'sockets'.  OP needs to check and clarify if that is the case.

For Cooker circuits: Diversity is based on the practical truth that all heating elements will not all be in use at the same moment in time (or long enough to cause an issue wrt cable current rating heat, and fuse/MCB tripping).
The calculation is:
The first 10A of the load + 30% of the remaining load, plus 5A if the cooker switch has a 13 A socket 
This calculation has been tried and tested for probably hundreds of millions of domestic Christmas dinners over the decades and has yet to be found wanting. (from the IET forum)

So maths time:
Oven/Grill =  3.35 kW = 16 Amps
Hob = 7.2 kW = 30 Amps
10 + (0.3 * 36 = 10.8) + 5 = 25.8 Amps.  So well under the MCB (and cable) rating of 32 A
No problem having both on a dedicated 32A cooker switch circuit.  That is probably not so if all the kitchen sockets (washing machine, dryer, dishwasher) are fed from the same 32 A circuit, though.

I have a Siemens/Neff/Bosch induction hob and it allows for the electronics to limit current draw to 13, 16, 20 if required.  Even on the unlimited setting the four 'rings' cannot all be used on their highest 'boost' power setting at the same time.

My son uses a 13A plug-in 4 'ring' induction hob quite successfully, with all 4 in use simultaneously.  
Think about it: not all items need the same cooking time, so most rings are 'simmering' while another is bringing water up to the boil for the <insert vegetable of your choice>.

itm2

Rodders53 said:

I really, really doubt that the kitchen in a modern town house has only one 32A feed...  Almost certainly 1 x 32 A mcb for 'Cooker' and 1 x 32 A mcb for 'sockets'.  OP needs to check and clarify if that is the case

Our townhouse isn't exactly "modern" - it was built in 1970 - and actually didn't have a single 32A feed until about 12 years ago, when we had an electric shower fitted in the room adjacent to the kitchen. Since that shower is no longer used we plan to use the 32A supply for the oven/hob/whatever.
Prior to that we had an electric oven plugged into a 13 amp socket (and a gas hob).

Risteard

onomatopoeia99 said:

Mickey666 said:

Diversity is an important factor when designing kitchen circuits and is best left to a qualified electrician to work out what’s really required in practice.

It's a really simple calculation that anyone that passed their maths GCSE could do (and probably anyone that failed it could do as well, to be honest).

The only magic is the cost of buying a copy of BS 7671 where the calculation is printed.

No such formula appears in BS 7671. It merely states that diversity should be taken into account.

Risteard

itm2 said:

Risteard said:

I have a 7kW+ induction hob and an oven on a standard 32A cooker circuit. It's not an issue. Diversity allows 15kW of cooking equipment on a standard 30/32A cooker circuit. I have never limited what I use at a time with it. Electrical competence means I understand that I don't have to.

That's very interesting. Do you have an idea of what the largest load is that you would have placed on your hob and cooker? For example, have you ever had the oven @200 degrees while boiling/simmering vegetables on 2 or more rings of the hob?

I just cook normally. I'll use multiple (if not all) zones) and the oven. Not a problem.