Wiring 13 amp single oven and ceramic hob to cooker radial

[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.

 

[Had8Lives]

I'm guessing you are not a qualified electrician. You have made a simple (to an electrician) mistake in the type of MCB you have selected, this is if the cooker is in a downstairs room. Get a Regs book or onsite guide and you will find out the answer. There is a way to get round notifying the works or employing an electrician but as this forum is for electrcians I don't see why we should give you the answer and do ourselves out of some work.

 

[MacSparky]

Well put Had8lives.....fella's got a cheek!

 

[Cirrus]

Cmon chaps. we've all wanted free advice on something at some point. Can't blame him for trying?

 

[adrianpaulwood]

Thanks for looking. I'm not trying to do an electrician out of work, just don't want to pay a lot of money for what should be a relatively simple job. I'd rather not waste money that could better, for example, be given to charities.

I'll check about the MCB - though I'm rather suprirsed, I've read lots of advice that suggested only Type B is appropriate, in fact most places I've seen only sell type B. I did have the cooker radial circuit checked by an electrician (part qualified) who also did various tests on the earthing, impedance etc (so I have employed an electrician to a certain extent).

I'd guess if type B isn't appropriate, it must be type C that is. Is it too much to ask for even that advice?

Note, when my system is a little older, and I've more money available, I intend to employ the electrician mentioned above to rewire the kitchen circuit fully. (Once he is fully qualified and looking for his first proper job).

I have asked him about this question, but wanted advice from someone with more practical experience and knowledge.

 

[danzor]

I'd rather not waste money that could better, for example, be given to charities.

oh the charity card is played

 

[Shakey]

I'm guessing you are not a qualified electrician. You have made a simple (to an electrician) mistake in the type of MCB you have selected, this is if the cooker is in a downstairs room. Get a Regs book or onsite guide and you will find out the answer. There is a way to get round notifying the works or employing an electrician but as this forum is for electrcians I don't see why we should give you the answer and do ourselves out of some work.

C'mon then, what is this simple mistake he has made?

And this forum is not just for 'electricians', a good number of the people on here are either considering becoming sparks or are under training

there is a fine line between people we help and people we dont - and I draw that line at wether or not the chap is trying to do something properly and safely and asking for advice (in which case advice is reasonable)

or if he has already done something improperly and unsafely and wants a soltion to the sh*t he has got himself into to (in which case he can go swivel)

So, in answer to the original question, no, dont plug it into the existing ring or CCU

Fact is, this is almost certainly notifiable work, because there are a number of solutions, and they all come under that category

Have to bite the bullet i'm afraid

 

[Had8Lives]

Good points Shakey, I'll keep them in mind. Adrian, I see you intend to spend and have spent some money with a electrician, so I take back the bit about doing us out of work, Apologies.

Is there a possibility of plugging portable equipment into the existing CCU? That should give you a clue as to the mistake in the choice of breaker (unless you change the exisiting CCU). If you look in the Regs book the answer is obvious ;-)

 

[Shakey]

Good points Shakey, I'll keep them in mind. Adrian, I see you intend to spend and have spent some money with a electrician, so I take back the bit about doing us out of work, Apologies.

Is there a possibility of plugging portable equipment into the existing CCU? That should give you a clue as to the mistake in the choice of breaker (unless you change the exisiting CCU). If you look in the Regs book the answer is obvious ;-)

no mate, the answer isnt obvious

He has chosen a Type B, and you are saying he has made a mistake

the chap is quite reasonably asking if he should be using a type C then, and i have to admit you had me stumped as well

now it seems you are 'hinting' at RCD protection

Why?

This is a requirement for sockets 'reasonably expected to feed portable equipment outdoors' (not just portable equipment as you have said)

There is no requirement for all downstairs sockets to be an RCD, and certainly not the auxilliary socket on a CCU

My house for example, I have an outside socket, RCD protected, so I would not 'reasonably' need to use any sockets inside the house, and hence they dont need RCD protection.

We dont know this chaps circumstances, he may already have his downstairs ring RCD protected, so why would he need to RCD protect his cooker CCU?

truth is, there is nowt wrong with his type B MCB. Whether or not he needs supplemntary protection from an RCD is irrelevevant to what he is asking

Now if he had put a type C or type D in, then THAT would be wrong

 

[wayne]

figured you'd be hinting towards rcd protection

 

[Had8Lives]

My apologies Shakey and Adrian, I had remembered a table in the Regs book that outlines disconnection times for a CCU with and without a Socket(can't Bl**dy find it now). Somewhere in my brain I had crossed over disconnection times and RCDs. A Type B breaker is fine as long as the Earth Loop impedance of the cooker circuit will allow a disconnection time of 0.4 Secs if the CCU has a socket, or 5 Secs if there is NO socket.

 

[Shakey]

My apologies Shakey and Adrian, I had remembered a table in the Regs book that outlines disconnection times for a CCU with and without a Socket(can't Bl**dy find it now). Somewhere in my brain I had crossed over disconnection times and RCDs. A Type B breaker is fine as long as the Earth Loop impedance of the cooker circuit will allow a disconnection time of 0.4 Secs if the CCU has a socket, or 5 Secs if there is NO socket.

no probs mate, but if its on a 60898, there is only one table of Zs values for 0.4 or 5 seconds, so unless its on a fuse (which it isnt) the Zs would surely be the same with ot without a socket