Cooker and hob wiring

2 Jun 2009
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United Kingdom
Hi - can anyone advise me on this. I am replacing a single undercounter oven with a double oven and an existing gas hob with new one. Under the worksurface is a double outlet 13A socket for the single oven and the gas hob ignition. The new oven is rated at 4.5Kw max so I will need a cooker outlet plate in place of the 13A socket, but can I connect the hob ignition circuit into this as well? I guess the answer is no as the fusing for the hob will then be 30A instead of 13A. Any ideas on how to convert the double 13A socket to somethng more useful - an outlet plate with a 13A single socket perhaps (if it exists)? The existing socket is wired in 6mm T&E to a double pole switch above the worksurface and to a 30A breaker at the consumer unit.
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If the existing socket has its own 30A supply as you say then replace the double 13A socket with a cooker outlet with built in socket for the gas cooker ignition (which will be just a few watts) such as:

Im curious why the double socket would have been wired to a 30A supply. If you look at the back of any double socket its rating is "13A" not "26A" or "2 x 13A".

Meaning if you connect two 13A loads to a double 13A socket then it will be overloaded by 100%

That said, i have seen some rated at 15 or 16A total across the two outlets.

I'm wondering if there used to be a single supply to a 30 or 45A switch which was removed and replaced with the double 13A socket at some point(?)


// Edit //

Whilst on the subject, Found this on MK's site::

All MK socket-outlets are manufactured to comply with BS1363 part 2: 1995 and are rated at 13A per unit. Double socket-outlets have been manufactured and tested to exceed this rating by margin that allows electrical safety and reduces the risk of heat and mechanical damage to components due to overloading. It should be noted that BS1363 part 2: 1995 does not allow double sockets to operate at twice the permissable maximum loading and it should be remembered that double socket-outlets are not manufactured to be able to withstand a 26A load for sustained periods of time. Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively shortperiod. Testing showed that a load of 22.3A was sufficientto cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-oulet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire.
Thanks for the quick reply Stuart. The socket is a standard MK 13A double. I guess the builders decided to put this on the end of the cooker cable so that the gas hob could be plugged in as well as the oven. The house is 6 years old by the way.

The old single oven presumably drew less than 13A and the gas hob current would have been negligable therefore the socket would have been OK for this purpose.
Stuart - just noticed your suggestion for a replacement socket. Would this have an outlet for the cable? I'm guessing not.
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It may have a knock out on the bottom, but most dont.

You would take the switched output from this switch to an outlet facia such as
which will have a knock-out on the bottom.

As for the cable size, you will need to maintain cable sized sufficiently to carry the ovens 20A current in a warm ambient environment.

PVC cable in 60C ambient requires a correction factor of 0.5, meaning you will probably need to stick with 6mm.sq for all wiring even although 2.5mm.sq can be rated at 24A and be enough for the oven in a room temp, but, at 60C it will be 12A
4mm.sq would be rated at 32A, but 16A at 60C
6mm.sq would be rated at 42A, but 21A at 60C

I do get worried when i see in B&Q and the likes, cable rated at its free air, 20C ambient rating. You will get people trying to squash too much down cables as they don't understand the effects of bundling, insulation, burring or high temperatures on the cable capacity.

Good point regarding the temperature effects. I'll stick to 6mmsq cable.

Would another possible solution be to replace the 13A socket along with its flush box and replace with 2 single boxes (side by side) and then mount a single 13A skt to one and a single cooker outlet plate to the other? Don't really need another isolator switch.
That would do the job, i was just thinking that it would be easier to replace the double socket with the switch & socket unit i suggested as that should fit in palace of the double socket.

That would do the job, i was just thinking that it would be easier to replace the double socket with the switch & socket unit i suggested as that should fit in palace of the double socket.

Why? He'll then have two switches, hidden behind his oven. The product is not designed for this. They dont have cable outlets. The cooker control unit is designed to be on show, and the socket on them is for conevnience only. Not for plugging a permenant appliance into.

@ the OP, a dual box with a cooker outlet, and a single unswitched socket on is what you need.
As I was suggesting in my last post? Single cooker plate / single socket over 2 single boxes in place of twin box. I just wanted to make sure this was kosher with the regs. A twin box with mounting screws for two single items would be better but I don't suppose this exists.
this question comes up quite regularly, a quick search would have pulled up several recent posts where this question ( or something very similar) was asked..


View media item 10929 View media item 10930
tada, job done..

dual back boxes are available in metal for sinking into walls, surface mount and (as shown) fast fix for plasterboard.

they are slightly wider than standard double backboxes so may need some extra cut out for the metal and fast fix versions..

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