Is this right for domestic oven supply?

[milbo1990]

Hi,

I was just wondering if you knowledgable folks would be able to check that what I'm planning to do for my oven supplies is correct...

I'm fitting 2x3.5kw ovens side-by-side and am planning to supply them as follows;

40A MCB > 6mm twin and earth > 20A cooker switch > oven connector & 2nd 20A Cooker Switch > oven connector.

My only concern is that 6mm cable is only rated to 38A I believe?

 

[OwainDIYer]

cable rating depends on your mounting method.

However an oven, once it's heated up, is an intermittent load controlled by the thermostat.

7kW on 230V is only about 30A anyway. That's before taking diversity into account.

My concerns would be 20A switches on a 40A circuit and the size of the terminals looping 2 x 6mm conductors in the supply terminals.

For that reason I'd use 30A / 40A switches, double faceplate size on deep back boxes, to give plenty of space for wiring.

 

[deadshort]

Hi, why do you require 2 switches ?

I would use a 45a switch and a dual appliance plate to connect my ovens.

Regards,

DS

 

[JohnW2]

7kW on 230V is only about 30A anyway. That's before taking diversity into account.

Indeed. In fact, if (as almost always the case) the 7kW is quoted at 240V, that would equate to about 28A at 230V, which is about 15.4A after application of diversity. As far as cable is concerned, virtually any would be adequate for that - although I'm not offering it as a serious suggestion, even 1.5mm² cable (with 20A MCB) would theoretically be adequate if 'clipped direct' !!

The point is that 6mm² cable would clearly be more than adequate for the OP, no matter what the installation method. If it were 'clipped direct' it would be OK on a 40A MCB. However, with other installation methods it might not be, in which case the MCB could be reduced to 32A. A 6mm² cooker circuit on a 32A MCB must be about the most common we see - and is adequate to serve virtually any future cooking load (up to about 19kW total, after application of diversity).

My concerns would be 20A switches on a 40A circuit and the size of the terminals looping 2 x 6mm conductors in the supply terminals. ... For that reason I'd use 30A / 40A switches ...

Agreed. It actually sounds as if the ovens may be designed for use with 13A plugs. 3.5kW at 240V translates to about 11.2A at 230V after application of diversity. The one issue the OP may have, if it concerns him, is the matter of what the manufacturer's instructions say - it's possible that vthey say, for example, that each oven should be protected by a 13A fuse (in plug) or 16A MCB. milbo1990: what do the instructions say?

Kind Regards, John

 

[EFLImpudence]

Standard cooker circuit is good for up to 19kW of appliances (no integral socket on cooker switch).

32A MCB >>
4mm² cable clipped to surface or buried in masonry (6mm² if in any conduit, larger if in thermal insulation so don't) >>
45A cooker switch >>
same size cable >>
45A double cooker outlet >>
4mm² flex to each oven.

Clipped or buried:
4mm² - 37A
6mm² - 47A

If you want two switches that's up to you.

Gas hob ?

 

[JohnW2]

Hi, why do you require 2 switches?

Perhaps so that if one became faulty, it could be isolated and the other still used, pending repair of the faulty one?

Kind Regards, John

 

[Iggifer]

You can get grid modules that are 32A DP switches, so I'd stick a couple of those on a 32A circuit, and it would at worst, take up the same amount of space as a normal cooker switch

 

[deadshort]

Interesting, i have never seen 32a grid switches, who make them ?

Regards,

DS

 

[milbo1990]

Standard cooker circuit is good for up to 19kW of appliances (no integral socket on cooker switch).

32A MCB >>
4mm² cable clipped to surface or buried in masonry (6mm² if in any conduit, larger if in thermal insulation so don't) >>
45A cooker switch >>
same size cable >>
45A double cooker outlet >>
4mm² flex to each oven.

Clipped or buried:
4mm² - 37A
6mm² - 47A

If you want two switches that's up to you.

Gas hob ?

Fantastic, thanks.

The only reason I'd suggested 2 cooker switches is because I've not seen 45A cooker switches. Do you know where I can get those and the 2G Cooker Outlets from? I've not seen them at Screwfix.

And yes, I'm having a gas hob - I'm presuming they don't usually require a power supply (thinking about ignition).

I've not actually bought the kitchen or any appliances yet, I'm just getting ready for a plan I've had done, so don't know about any manufacturer instructions.

 

[JohnW2]

Interesting, i have never seen 32a grid switches, who make them ?

You just beat me to it. Nor have I seen any 32A ones (only 20A) - so I'd be interested to hear about any which do exist. I would add that 32A would be a very unusual rating for a switch of any sort.

Kind Regards, John

 

[JohnW2]

And yes, I'm having a gas hob - I'm presuming they don't usually require a power supply (thinking about ignition).

They often/usually require a (very small) electricity supply for the ignition - usually 'plugged in' with a 3A fuse in plug.

I've not actually bought the kitchen or any appliances yet, I'm just getting ready for a plan I've had done, so don't know about any manufacturer instructions.

Fair enough but watch out for what I said - it could be that the instructions say that each oven requires protection no greater than a 16A MCB - in which case, if you wished to comply with those instructions, a bit of re-thinking would be required.

Kind Regards, John

 

[flameport]

The only reason I'd suggested 2 cooker switches is because I've not seen 45A cooker switches. Do you know where I can get those and the 2G Cooker Outlets from?

Double outlet: https://www.tlc-direct.co.uk/Products/AA45DCOP.html

45A cooker switches - that would be all of them except the unusual 32A MK effort:
https://www.google.co.uk/search?hl=...q=45A+cooker+switches&hl=en&tbs=vw:g&tbm=shop

 

[Iggifer]

Interesting, i have never seen 32a grid switches, who make them ?

You just beat me to it. Nor have I seen any 32A ones (only 20A) - so I'd be interested to hear about any which do exist. I would add that 32A would be a very unusual rating for a switch of any sort.

Kind Regards, John

MK make a 32A rated isolation switch, as do others, 32A is a pretty logical rating to make a switch at.

Click make 32A grid switches, they are double width, but two is going to work out no bigger than a standard 45A cooker switch

http://www.electricbase.co.uk/click-scolmore-md032wh-250v-125-1704992

They're not 'typical' grid switches, but the concept is the same

 

[JohnW2]

MK make a 32A rated isolation switch, as do others, 32A is a pretty logical rating to make a switch at.

As you say, a pretty logical rating but, IME, a very unusual one.

Click make 32A grid switches, they are double width, but two is going to work out no bigger than a standard 45A cooker switch

Interesting, although not quite what I would personally call a 'grid switch'. AFAIAA, Click do 'modular everything'

Kind Regards, John

 

[EFLImpudence]

Everywhere will have 45A cooker switches - that's what they are.

Can't see any duals at Screwfix.
CLICK HERE