Another multi oven query

Discussion in 'Electricians' Talk' started by Stangat, Aug 11, 2018 at 8:22 PM.

  1. Stangat

    Stangat New Member

    Hi all

    I am fitting a new kitchen and the wife has decided on the new cooking appliances.

    We will have a single oven of 3.45kW, combination oven/microwave of 3.6kW and an induction hob of 7.35kW.
    The existing wiring is a 6mm/32A from the CU which used to be for a 3.5kW double oven and the ignitor for a gas hob.

    It will be nigh on impossible to put in a new cable so I would like to spur off the radial to the hob and then use a two way split to the other two appliances. I'm not sure on the maths of that so would like some help please. Another idea is to use the 6mm after the cooker socket into a mini CU and feeding all three off there, thoughts?

    Thanks

    Ian
     
  2. seneca

    seneca Screwfix Select

    6mm cable with a 32amp mcb is a standard cooker circuit and is ok for load of 15kW which means you're just about ok, subject to wiring installation method, ie, cable not buried in insulation etc.
     
  3. Lectrician

    Lectrician Screwfix Select

    That diversity recommendation is so outdated with modern kitchens though. It is a guide.
     
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  4. Bob Rathbone

    Bob Rathbone Well-Known Member

    The regs only recognise the connection of a separate hob and oven on one final circuit provided that neither is more than 2 mts distant from the cooker switch (isolator). You are proposing 3 items are connected, this is not a recommended method in the regs. I suggest that you install a sub consumer unit in the end of the cooker cable, after the cooker isolator, under the worksurface. Fit breakers for each separate piece of equipment and the job is done. I have not gone into fine detail as it is outside the scope of most DIY. Loading after diversity is about 31A but this may be exceeded on Christmas and other feast days.
     
  5. peter palmer

    peter palmer Well-Known Member

    Aren't most oven ratings a total load of all the elements on together, obviously you cant have the grill and the oven on at the same time though, Most fan oven elements are 2KW or so. A lot of the single ovens I connect up now have such a thin lead supplied with them, some look like a bit of 1mm flex.

    Personally I would put a small consumer unit on the end of the 6mm and run 3 circuits from there, 1x32 and 2x16/20
     
  6. unphased

    unphased Screwfix Select

    There is really no need to be concerned about adding all the appliances to one circuit. The circuit cable is adequately protected from short circuit and overload (32A mcb). What is the worst that can happen? The mcb trips from overload, and that is very very unlikely to happen. It is pointless adding a CU to the circuit and dividing the circuits up like that, totally pointless.
     
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  7. peter palmer

    peter palmer Well-Known Member

    I'm sure its would be fine either way but a JB with a 6mm in, a 6mm out and a couple of pieces of 1mm or 1.5 for the two ovens coming out as well will look dog rough.

    Maybe the ovens are at the other side of the kitchen to the hob as well, if you put a CU in one of the kitchen cupboards you can feed a couple of 2.5 cables in the fabric of the building to the ovens and then use a DP switch.
     
  8. Bazza

    Bazza Well-Known Member

    No they do not. I cannot find a regulation in BS7671 that says this. Please can you provide the reference?
    Thank you.
     
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  9. unphased

    unphased Screwfix Select

    Hi Bazza, its an interesting one this. There is a reference to the 2m rule in the On-Site Guide. I just grabbed a brown copy (which is 16th edition but it also says similar in 17th) under a paragraph titled 'Cooker circuits in household or similar premises'. I too cannot find how this has been decided as there appears to be no definitive reference to it in the Regs. I wonder if its something which has been interpreted to be introduced as a requirement in the On-Site guide? I would like to know where it came from, too.
     
  10. Bazza

    Bazza Well-Known Member

    Yes its in the GUIDE. The GUIDE provides a regs reference where there is one, but there isn'tin this and several other items in the OSG.

    The 2 metre thing is probably just folk law, or it might be a hang over from old regs, or perhaps the crusty erks that write the On Site Comic who think "that's they way its always been done".
     
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  11. collectors

    collectors Member

    Personally i would find a way around the impossible & get another couple of 2.5 Twe cables over their.
    Don't forget to make sure the gas hob is plugged into a 13amp socket with a three amp fuse as you don't want this backed up by a 32amp fuse.
     
  12. Bob Rathbone

    Bob Rathbone Well-Known Member

    I see your point but my suggestion is allowing for the appliances having fitted flexes of current rating less than 32A. You would do it the way you suggest and it is possible that I may also choose that route, but we must offer a solution that a DIY person can use and that will be certain to comply in most cases.
     
  13. Bob Rathbone

    Bob Rathbone Well-Known Member

    Bazza, all through my time as an Electrician the cooker circuit arrangement mentioned was recognised, from the 13th to the 16th. I taught it in College and so did my colleagues. It may have changed in later variations of the regs of which I am un aware.
     
  14. Bazza

    Bazza Well-Known Member

    Yes, as I said, it’s the old
    I've had a look, and its not in the 16th either.
    It is mentioned in the On Site Guide in the Appendix 8 - which gives advice on general standard arrangements for some circuits but, again, the OSG is just something to help the hard of thinking from getting confused with what the regs actually say.

    I hope that your college students havent sprayed too many unneeded switches all over the kitchen walls of the UK!:D
     
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  15. Bob Rathbone

    Bob Rathbone Well-Known Member

    My Shropshire students would fit isolators above the work top for appliances below, that came from their employers, they also fitted cooker control units as required by their employers. So you see that it is not just one 'Out of touch' lecturer that thinks cooker control units are necessary, it is trade practice throughout the Midlands of the UK.
     

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