Wiring a new Electric Oven

[c0wb0y]

Hi there,

This is my first ever post so will appreciate comments from all the good folks here.

I have a Electric Oven (Bosch rated at around 6kW). The hob is gas.

Starting at the MCB and leaving a 30cm overhang (ready for when the sparky arrives), a 9meter length of 10mm electric cable was channeled through floorboards directly into a 45amp Cooker+Socket switch.

Question 1: Probably a daft question but is the 10mm cable fine? or should I have used 4/6mm? i.e. its not dangerous is it? 10mm cable was used as it was a spare reel I had left over.

Some suggest simply connecting the cooker directly into the 45A socket - others say install a CCU and wire the cooker into that. For now, the oven is connected directly into the socket with a generous slack for when pulling the oven out in the future.

Question 2: Is this done correctly or is it advised/law to have a CCU in-between the 45A and oven? Is it really dangerous to not have one?

Question 3:I'm no electrician but at 6kW, isn't a 45A cooker socket 'over fused' for this setup? It has a 3pin UK plug fitting on it too but I doubt that would ever be loaded more than 1kW. Any advice on this?

Question 4:What should I expect the sparky to do at the MCB? Would he use a 32A fuse dedicated to this oven? I have a new Wylex MCB with numerous new fuses I purchased recently so he can take his pick from 16A, 32A and I believe a 40+ Amp too (I do have a shower upstairs so I guess he'll be needing dedicated fuses for both the shower and cooker?)

Interestingly, I've discovered this and seeing the images, its very similar to my own setup.

 

[ericmark]

Easy bit first 10mm cable is fine no problem there.
As to cooker connection unit may need one to get cable into oven as terminals in oven may be too small to take 10mm cable.
It will need local isolation if the CU is not in kitchen personally I would always fit a local isolator.
45A is the max the switch can carry nothing wrong with using it for a smaller supply.

Now the bits which don't seem right. 6kW will not run from a 13A plug. Max for 13A plug is 3kW.
When one alters the power setting on a cooker it does not reduce the power being used it just switches it off and on. So even with low setting if rated 6kW you still need 6kW supply.
Much depends on manufactures recommendations they can stipulate the largest fuse/MCB/RCBO to use.
Ovens are rarely 6kW as in the main they are designed to run on a Europe 16A supply but often are bigger than can be used with 13A supply.
Oddly the oven in a stand alone cooker can be 6kW in fact mine is having elements top bottom and back (fan) which can all be used together. However most ovens built in time share so don't need such a large supply.

So size of MCB is all down to manufacturers and it just needs some reading of the manual.

 

[riveralt]

Question 4:What should I expect the sparky to do at the MCB? Would he use a 32A fuse dedicated to this oven? I have a new Wylex MCB with numerous new fuses I purchased recently so he can take his pick from 16A, 32A and I believe a 40+ Amp too (I do have a shower upstairs so I guess he'll be needing dedicated fuses for both the shower and cooker?)

If the electrician is a member of a competent persons scheme he will walk away and leave you to it - because unless he is involved in each of the three stages of design, installation and testing he cannot complete and sign off the Electrical Installation Certificate.
Also given your obvious lack of knowledge (Wylex MCB and fuses - no mention of RCD protection - cable derating factors etc) and an assumption, given your comments, that you fitted the CU yourself - would be another reason to steer well clear of you and your installation.

 

[c0wb0y]

may need one to get cable into oven as terminals in oven may be too small to take 10mm cable.

I've managed to get the 10mm cable into the cooker and your right, it was tricky. But that's done.

6kW will not run from a 13A plug. Max for 13A plug is 3kW.

Just to clarify, the cooker is connected to the rear of a 45A switch with the usual large red on/off switch labelled 'cooker'. The 3pin UK plug next to the cooker switch isn't currently being used. Even if the plug side was loaded to e.g. 1kW, isn't 45A for both cooker + socket overkill? isn't it dangerously over fused?

 

[c0wb0y]

If the electrician is a member of a competent persons scheme he will walk away and leave you to it - because unless he is involved in each of the three stages of design, installation and testing he cannot complete and sign off the Electrical Installation Certificate.
Also given your obvious lack of knowledge (Wylex MCB and fuses - no mention of RCD protection - cable derating factors etc) and an assumption, given your comments, that you fitted the CU yourself - would be another reason to steer well clear of you and your installation.

I can't see why a sparky would walk away: all I've done so far is channeled a cable from MCU to Cooker and stripped cable for insertion into socket + rear of cooker. Everything is looose fitted for when the sparky arrives. The MCU is new and hasn't been fitted yet: it will replace an old one which looked tatty with the cover broken etc. There's loads more this sparky will have to do in this house which isn't mentioned in this post. I'd like to think I've helped him by doing what I've done so far (which may mean he'll knock off £30 odd quid from the job). I've even purchased the earth sheathing and left it longer than the + and - cables by 10cm: how professional of me

 

[sparkiemike]

with a use name of cowboy, do you really expect help - got to be a wind up

 

[Taylortwocities]

Just to clarify, the cooker is connected to the rear of a 45A switch with the usual large red on/off switch labelled 'cooker'. The 3pin UK plug next to the cooker switch isn't currently being used. Even if the plug side was loaded to e.g. 1kW, isn't 45A for both cooker + socket overkill? isn't it dangerously over fused?

Just to clarify things for you.

The 45A rating of the cooker switch is the maximum current that the switch contacts can handle. There is no fuse in that switch. Its a switch than can safely pass 45Amps through it.

The only current limiting device in a cooker circuit is usually just the MCB in teh consumer unit. That is usually sized to protect the cable that runs from the CU to the cooker switch.

 

[Chri5]

Generally for a socket built in a cooker switch you add 5 amps to the cooker load.

So a 6kw Cooker is 6000w / 230v = 26 amp + 5 amp = 31 amp

The cable is plenty fine subject to various factors. The cable length and the method of installation being the main two, but other factors such as grouping could apply.

Hopefully you have left the route open for inspection, since as a absolute minimum the electrician will want to make sure the route is good (away from heating pipes, sensible routes through joists and walls, not near vast amounts of insulation materials).

32 amp fuse via an rcd or a 32 amp rcbo if your concerned about leakage and possible nuisance trips and thus every circuit on that rcd fails.

I'd go ccu and buy some suitable heat proof flex between ccu and cooker, which may cause a standard lump of TE to be over the operating temp- unlikely, but prudent none the less. Correct flex will terminate better and remain flexible.

 

[c0wb0y]

The 45A rating of the cooker switch is the maximum current that the switch contacts can handle. There is no fuse in that switch. Its a switch than can safely pass 45Amps through it.

The only current limiting device in a cooker circuit is usually just the MCB in teh consumer unit. That is usually sized to protect the cable that runs from the CU to the cooker switch.

Aaa this makes sense: so am I correct in assuming that this 45A socket isn't *REALLY* a local isolation or saftey fuse: its just there to allow max 45A to pass through. The safety bit takes place at the MCB which is where the sparky will do his thing..?

 

[riveralt]

Aaa this makes sense: so am I correct in assuming that this 45A socket isn't *REALLY* a local isolation or saftey fuse: its just there to allow max 45A to pass through. The safety bit takes place at the MCB which is where the sparky will do his thing..?

Well clearly it doesn't make sense to you - since the purpose of the dual pole cooker switch IS to ISOLATE the supply to the cooker.

The safety bit does not just take place at the MCB, especially if you put the wrong MCB in the CU, it takes place at the RCD (which again you haven't mentioned) and every point along the circuit and starts with the circuit design, its installation and eventually its testing and certification.
You should not be having this conversation with us you should be having this conversation with your electrician. S(he) is the one who will determine cooker diversity, the cable size, the cable route and the MCB size.
By the way, domestic electricity is ac and not dc.
Do you actually know what the purpose of the MCB is?

 

[c0wb0y]

Well clearly it doesn't make sense to you...You should not be having this conversation with us

This rant isn't aimed at any particular poster but as a long time lurker on these forums, I've noticed posts go off on a tangent because some still feel they have a monopoly on knowledge due to a City n Guilds qualification they may have. Forums are a means of sharing knowledge and they have transformed many industries: take the IT industry: I now know 10 year olds who are incorporating heat exchangers into their PC cases for cooling having read/learnt everything online. I too have learnt an incredible amount on these forums but always get the vibe that some here find knowledge sharing to be detrimental to their own business and therefore, withhold info. Being self employed, I do all my VAT and TAX returns having learnt everything from reading posts. This hasn't put accountants out of work as they still have their place. With qualifications, laws and regulations keeping sparkys in business, it doesn't mean knowledge can't be discussed. Here (on DIYNOT), you almost have to begin with a disclaimer along the lines of 'I will hire a pro but just wanted to know bla bla'...embrace the world people!

 

[EFLImpudence]

Fiddling with the pc or doing your own accounts is not illegal.

You have been given a lot of answers to your questions.

You have been advised to have these conversations with the electrician who will have to do the work and sign a document to say he did it.

Obviously, you object to the replies with which you disagree but that doesn't make them wrong.

Perhaps, with your username, you are trying to find out what to do at work tomorrow.

DIYnot ??? Think about it.

 

[c0wb0y]

The good folks here have given me great replies and for that, I do thank them. These jobs around the home cost and I find answers here have saved me a lot of cash and troubles over the past few years. My last post was more of a 'I was just saying....'