Wiring for 3 Domino Hobs 3/3/3.7kw

MickeyT

MickeyT

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Hi I am fitting 3 electric hobs (domino hobs so 30cm induction/30cm grill/30cm teppanyaki) on an island with them being 3kw/3kw/3.7kw loads and each has 1.5m flex cable. Do I need to take 3 x 6mm T&E from CU to each one via separate cooker switches or can I do with less cabling e.g. 1 x 10mm T&E and only 1 cooker switch on basis they are 1 conjoined hob unit. I suspect I need 1 x 10mm to service the 2 x 3kw = 6kw from 1 point and 1 x 6mm for the 3.7kw as all 3 hobs could be on at the same time?
 
Well, 9.7kW @ 240V is 40.42A therefore with installation method C (clipped or buried in masonry) 6mm² T&E will be adequate for all three.
Using diversity the design current will be 19.12A so you could theoretically have one 2.5mm² or even one 1.5mm² circuit.

You say each is wired in 1.5mm², therefore you could have three 1.5mm² circuits or one 6mm² (or 4mm² circuit with a 32A MCB).

It is up to you whether you want three switches or none.


Is this a domestic or commercial premises?
 
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There is no requirement for cooker isolation switches in the regs. You can isolate at the CU for maintenance.
 
Domestic kitchen. I'm just laying the cable to the island now before laying the concrete floor so have to guess what I may need in future. This 3 electric hob option is what I thought would be the most loaded of the options with the basic option being just a 5 ring induction hob 7.2kw. Sorry just to be clear each hob apparently has a 1.5m long flex cable (don't know thickness but presumably 1.5mm - I remember 2.5mm 90°C was for the 7.2kw hob). In which case I think I'll wire up a 6mm to just one cooker switch and that will work on both options.

Thanks all
 
Yes, the standard cooker circuit is a 32A MCB with 6mm² cable and is good for any cooking appliances likely to be installed in a domestic kitchen.

The 6mm² cable is actually over-sized (clipped or buried) for 32A but is still installed (for historic reasons to do with fuses).
 
MickeyT said:
Hi I am fitting 3 electric hobs (domino hobs so 30cm induction/30cm grill/30cm teppanyaki) on an island with them being 3kw/3kw/3.7kw loads and each has 1.5m flex cable. Do I need to take 3 x 6mm T&E from CU to each one via separate cooker switches or can I do with less cabling e.g. 1 x 10mm T&E and only 1 cooker switch on basis they are 1 conjoined hob unit. I suspect I need 1 x 10mm to service the 2 x 3kw = 6kw from 1 point and 1 x 6mm for the 3.7kw as all 3 hobs could be on at the same time?
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Will there be anything else on the island, such as 13A sockets?

I'd suggest [from experience of alterations later] to lay a 10mm² and fit a 4w, or possibly 6w, CU in the island so each appliance can have its own circuit. I'd even suggest using DP MCB's to act as an isolator.
 
MickeyT said:
Domestic kitchen. I'm just laying the cable to the island now before laying the concrete floor so have to guess what I may need in future. This 3 electric hob option is what I thought would be the most loaded of the options with the basic option being just a 5 ring induction hob 7.2kw. Sorry just to be clear each hob apparently has a 1.5m long flex cable (don't know thickness but presumably 1.5mm - I remember 2.5mm 90°C was for the 7.2kw hob). In which case I think I'll wire up a 6mm to just one cooker switch and that will work on both options.

Thanks all
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Put in a duct to future proof.
 
Sunray those are great suggestions. I really like the idea of a CU on the island - I guess the DP MCB fuses will just act of the switch within 2m requirement as DP?
 
All this talk about not needing to fit isolator switches for things like cooker and shower circuits, and yet every one I've ever encountered has had an isolator, even the shoddiest of jobs.

(Can't say the same for washing machines, fridges, freezers, dishwashers, where there has been a socket, but fitted directly behind the appliance.)
 
That is probably because people think they are a requirement.

Perhaps understandable with showers and cookers, but now it has spread to appliances.

However, the fact remains that the regulations do not require a local isolator for anything.
 
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