Pair of ovens

[Dave Thornley]

Am about to install two ovens, one above the other. Both are rated at 16A max. Now am wondering about the feed and isolation needs, here are my alternatives, in my opinion.

1 Feed both off a 32A MCB using 6.00mm2 and a single 32A isolation switch by the ovens in the kitchen

2 As above but use 2 seperate 20A switches in the kitchen

3 Feed each oven seperately using 16A MCB x 2 and fed by a 4C 2.5mm2 cable

Opinions gratefully received.

 

[EFLImpudence]

Firstly, there is no requirement for isolation switches so it's up to you - whatever you want.

Just fit a standard cooker circuit.
32A MCB, 6mm² cable to 45A cooker switch, then 6mm² cable to dual cooker outlet, then two 1.5 or 2.5mm² heat resistant flex to ovens.

Then the ovens could be changed for any domestic cooking appliances without altering the circuit.

 

[AndyPRK]

Well 1. Is wrong using 2.5mm t&e on a 32a

The advantage of 2 isolation switches are that if the element goes in one and trips the rcd, you can isolate it and use the other oven.

A 6mm from the cu gives you flexibility in future. And you can still connect 2 isolation switches if you wish.

 

[Dave Thornley]

Yes made a right mess of my cable sizes have now edited the post.

 

[Dave Thornley]

Have had question answered to some degree by other requirements. Am also installing an induction hob max possible load 11.1KW. Now using 18th edition calcs I need it staes 16mm2 cable as the run is 14m.
I was hoping to use the present 10mm2 circuit for the hob. So now that will be used for the ovens and at some point near the ovens terminate it to run the seperate feeds.
Was thinking in the distant past of doing the hob in 3 phase but that got knocked on the head by my learned friends, not really sure why as I could use a 5 core 4mm2 which I think is less of a physical size then 16mm2 T&E

 

[EFLImpudence]

Dave, you seem to have some funny ideas through lack of knowledge.

Just fit a standard cooker circuit.
32A MCB, 6mm² cable to 45A cooker switch, then 6mm² cable to dual cooker outlet, then two 1.5 or 2.5mm² heat resistant flex to ovens.

That will be good for any cooking appliances up to 19kW (without socket in cooker switch).

 

[flameport]

Now using 18th edition calcs I need it staes 16mm2 cable

Other than some minor changes to tabulated values for various protective devices and installation methods, cable calculations haven't changed in decades.
There are no domestic cookers which require 16mm² cable. Whole houses are supplied with less.

 

[AndyPRK]

When people say they need 10mm cable for cooking, they get slapped down.
You seriously don't require 16mm!

Do you have 3 phase in the house anyway ?

 

[Dave Thornley]

Other than some minor changes to tabulated values for various protective devices and installation methods, cable calculations haven't changed in decades.
There are no domestic cookers which require 16mm² cable. Whole houses are supplied with less.

I was just putting in the possible load of up to 11.1KW and the distance into a calculator, found it on the TLC site referring to 18th edition and it comes up with 16mm2.

 

[Dave Thornley]

When people say they need 10mm cable for cooking, they get slapped down.
You seriously don't require 16mm!

Do you have 3 phase in the house anyway ?

To answer the last bit first yes I have a 3 phase supply. So do I deem you are saying that it is okay to feed this induction hob at the end of a 14m run with 10mm2 ?

 

[EFLImpudence]

For a start, 11.1kW @ 240V is 46.25A. 6mm² T&E can take 47A.

However for cooking appliances, which do not draw the full load at any one time, we use a diversity calculation to determine the design current.

That is the first 10A plus 30% of the remainder; 36.25 x 0.3 = 10.875 + 10 = 20.875A.

Therefore the circuit I have stated twice will be more than adequate for the hob (and the ovens as well).

 

[Dave Thornley]

Ah yes but the hob has an actual connected maximum load of 15KW but limits itself to a maximum of 11.KW so there could be a draw of 48 amps, assuming 230V not 240. I think the calculation was more concerned about the voltage drop.
Would be lovely if I could supply the hob and both ovens on the same ffed. Still waiting to receive from NEFF the csa of the flexible cables they supply looks like 4mm2 for single phase and 3 lots of 1.5mm2 for a 3 phase supply. Both to my a tad small
to my mind.

 

[flameport]

so there could be a draw of 48 amps,

There could, but only for a very short time.

Would be lovely if I could supply the hob and both ovens on the same ffed.

You can.
It's the 6mm² cable with a 32A protective device. The same as used in 99%+ of homes which have a hob and oven(s) or a freestanding cooker containing the equivalent.

Do not install the hob as 2 or 3 phase. It will add significant additional complexity, and if you want an isolator it will need to be a 3 phase one. There will be no benefit at all.

flexible cables they supply looks like 4mm2 for single phase and 3 lots of 1.5mm2 for a 3 phase supply. Both to my a tad small

They are not small, they are the correct size for the load.

 

[EFLImpudence]

The current and Wattage will be lower at 230V

 

[Dave Thornley]

The hob blurb from NEFF states 11100W 220-240V. So let me start again. What I will have is an induction hob of 11.1KW at 14m from the CU. Two ovens combined power 6.9KW, 3.45 KW each, at 11m from the CU.
So you are saying I am okay to use the existing 10mm2 T&E to feed all 3 appliances?