13 Amp Single Oven connection with ceramic hob

[adrianpaulwood]

I am replacing an existing standalone cooker, that connects on a cooker radial circuit via a cooker connection unit behind the cooker, and is isolated by a cooker control unit above the worktop to the right of the cooker. All cabling is all 6mm, and protected by a 30 Amp type B MCB (fitted by myself to replace a rewireable fuse holder).

This cooker is being replaced by a ceramic hob (5.4kw) and single oven (3.0kw). The hob will be hardwired with 6mm cooker cable into the cooker connection unit) and the 3.0kw single oven could either be hardwired to the connection unit (with 6mm cooker cable) or I could fit a 13 amp plug (with 2.5mm cable).

The kitchen is on the same ring main as the rest of the house, so given other kitchen appliances on the ring main, it wouldn't be a good idea to plug in the single oven to the ring main.

I would like to use the existing kitchen wiring in such a way that I don't have to notify the work or employ an electrician in order to fit this single oven and hob.

Ideally I would like to connect the oven to the cooker connection unit, along with the hob, so both can then be isolated via the cooker control and both are connected neatly behind the oven / hob. However, if I do this the instruction manual recommends that the cooker is protected by a fuse rated between 15 amp and 20 amp (or 13 amp if plugged in). That presumably can only be done by fitting a fused connection unit or single unswitched 13 amp socket between the cooker connection unit and the oven. I guess I'm not allowed to do that, because such changes would be notifiable?

I could solve this by plugging the cooker into the 13 amp socket in the cooker control unit - but this would be rather unsightly.

Would it be permissable (without notification) to replace the cooker connection unit (behind the cooker) with a 2nd cooker control (ccu) including socket? I could then connect the hob and oven to this 2nd ccu (the oven being plugged into the 13 amp socket on the ccu). Both could be isolated by the existing cooker control unit that is above the worktop to the right of the cooker. I've never heard of anyone doing this so I guess its not allowed, and it might be notifiable, but it would be a neat solution.

Note - unless I end up plugging the single oven into the 13 amp socket on the existing ccu (above the worktop), I will replace the existing ccu with a new ccu that has no socket, so as to avoid overloading the circuit and for general safety reasons.

Can anyone think of any other solution that would not be notifiable, would not require an electrician and would not mean connecting the oven to the ring main?

Given diversity calculations, the 30 Amp MCB and 6mm cabling should be sufficient I think, for the oven and hob (from what I have read). There is a small risk of nuisance MCB trips because if the oven and 4 hobs were run at full power, they would exceed 30 Amps. However, this is unlikely to be an issue for the way we use the oven and hob.

Thanks for any help and advice.

 

[adrianpaulwood]

I posed the same question above on another forum, and the electricians there were unwilling to help - since they felt that would be doing them out of work. (Note I have employed a part-qualified electrician to check the existing circuits for earthing etc, and plan to use him in 2 or 3 years to rewire) - but currently he has more to learn and doesn't have the necessary practical experience to fully answer my question here.

Anyhow, on the other forum, someone mentioned I shouldn't be using a type B, MCB, but then didn't explain - told me to go an look at the regs. I wouldn't know where to start looking (or how) ...

Everything I have read suggest that for domestic installations, type B MCBs are appropriate, and in the places I've looked, they only sell type B. The above electrician suggested I get an MCB to allow quicker tripping (also mentioning a few other technical reasons that I can't exactly recall), but he didn't notice anything wrong with the MCB I had installed when he did his checks.

Can anyone help me understand about this MCB question (the other electrician is on holiday at the moment).

 

[flameport]

Would it be permissable (without notification) to replace the cooker connection unit (behind the cooker) with a 2nd cooker control (ccu) including socket? I could then connect the hob and oven to this 2nd ccu (the oven being plugged into the 13 amp socket on the ccu).

Unusual, but nothing wrong with it. Doesn't look to be notifiable either, as you would just be replacing existing accessories.

Given diversity calculations, the 30 Amp MCB and 6mm cabling should be sufficient I think, for the oven and hob (from what I have read).

6mm should be ok - how long is the cable, and how is it installed (surface, in the wall, etc.)?

There is a small risk of nuisance MCB trips because if the oven and 4 hobs were run at full power, they would exceed 30 Amps. However, this is unlikely to be an issue for the way we use the oven and hob.

8400W = 36A. In reality, the current will be much less than 36A due to the various thermostats in the oven and hob.
Even at the full 36A, the MCB won't trip for a very long time, if ever.

As for the types of MCB - other than the B type you have, there is only C or D. Highly unlikely that either would be required in a domestic situation, and it is quite possible that you can't have them anyway.
More info here:
//www.diynot.com/wiki/electrics:fuses_and_miniature_circuit_breakers:mcb

 

[pompeygit]

Seems pretty reasonable approach as you will be able to isolate both appliances from the single CCU above the worktop. I would however change the 'main' switch to 1 without a socket. You could have the the oven and hob both running and then someone comes along and plugs in a 2.5Kw kettle for a cuppa...........