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New separate ceramic hob and oven

Discussion in 'Electrics UK' started by ANGLER, 1 May 2017.

  1. ANGLER

    ANGLER

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    Replacing our faulty Rangemaster 110 with a separate ceramic hob and oven.

    The Rangemaster was previously hard wired with 6mm cable for the supply & feed.

    Is it still ok to use the same hard wired outlet for the new appliances?
    Ceramic hob 7.9kw
    Oven
     
  2. EFLImpudence

    EFLImpudence

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    Yes. Does it have 30A fuse or 32A MCB protecting the circuit?

    You can get dual outlet connectors.
     
  3. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    is 7.9kW total output of both appliances?
    Whether the same cable can be used, would be dictated by any deratings that apply to the routing of the cable, possible volt drop, demand of load and condition of cable. So all that would need to be established first.
     
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  4. ANGLER

    ANGLER

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    His has a 32amp MCB. The 6mm cable from the consumer unit to the switch has previously been fed down inside the brick cavity wall.
    The new oven will be approx 2.5 meters further from the original cooker position. The manual for the oven stated a 2.5mm TE and 0.93kw general consumption
     
  5. EFLImpudence

    EFLImpudence

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    0.93kWh is not its rating, That's the usage per hour when on guide.

    It will be alright to connect both.
     
  6. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    Cable routed through/within cavity walls is bad practice, is the cavity insulated?
    The 2.5mm2 will be the flex for the appliance and I doubt the MI would recommend T&E, but heat resistant flex. Voltage drop would be calculated from the origin of the circuit to where the outlet is. Again it would be advised that the condition of the circuit is established. If the oven is going to be 2.5m from the existing postion, does this mean that the circuit is to be extended? I so newly buried cable will require to be routed in prescribed safe zones and RCD protection required, if not present. Unless the cable can be protected mechanically.

    Do you have a link to the MI or appliance
     
  7. ban-all-sheds

    ban-all-sheds

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    Have you ever worked out what the maximum appliance size is for a cooker circuit using 6mm² cable with different installation methods?
     
  8. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    Yes I have, if we take the OPs situation and make some assumptions on specification of cable at 47A and that the cable is routed in a thermally insulated cavity, without derating for any voltage drop. It would be about 5.4kW.
     
  9. ban-all-sheds

    ban-all-sheds

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    Or, more relevantly, about 23.5A.

    Which before diversity is 55A, i.e. 12.65kW cooker.
     
  10. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    That is a fair when applying diversity, which I don't have any problem with.
    We must consider protecting the cable, as the maximum current allowed is on it would 23.5A, it would be wise to down fuse the circuit from 32A to 20A. It would be at this point that I would calculate diversity.

    We have a hob at what seems to be 7.9kW and unknown demand for the oven, so it would be also wise to have this output confirmed.
     
  11. ban-all-sheds

    ban-all-sheds

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    Why do you say that?

    It's on a 32A breaker - do you have a reason for saying that that has always been wrong?


    Unless you are going to assume that Iz isn't 32A, the oven would have to be over 11kW for there to be a problem.
     
  12. EFLImpudence

    EFLImpudence

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    I don't understand. Diversity is the same whenever you calculate it.
    If the appliances' design current is 23.5A then that's what it is.

    Or are you saying you would reverse calculate from 20A?
    10/0.3+10 = 43A = @ 240V 10.4kW
     
  13. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    What I am saying is that if the cable is within a cavity wall. As the OP has stated, and if that wall is insulated. Then we may have a derating to 23.5A.
    The design current is unknown, as we are unaware of the actual load. Just that we are restricted to 23.5A.
    As we are unable to establish the demand at this time assumption are being made. So it may well be that the demand is greater than the capacity of the cable. So we need to protect the cable, the most suitable device would be 20A.

    If we then work out the load that can be applied with diversity making assumption of hob at 7.9kW. The OP has mentioned 2.5mm cable for oven, which I would think would be heat resistance flex, this can carry 25A. So if we consider this, we could be looking at a further 5.75kW.
    My calculation then exceed the 20A rating of the device.

    Am I talking nonsense?
     
    Last edited: 1 May 2017
  14. PrenticeBoyofDerry

    PrenticeBoyofDerry

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    The OP has stated the cable is routed within a cavity wall, if that wall is insulated? Then quite possible, yes installed wrongly and unsafely.

     
  15. EFLImpudence

    EFLImpudence

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    No, not nonsense but I think you are looking at too many things.

    If the design current IS 23.5A, or less, then, with cooking appliances which cannot overload, the OPD rating is not critical, is it?


    Just seen your latest post.
    It is possible the wall was insulated after the installation of the cable - with no regard for the electrics as is the way of these things - but I would say the above still applies.
     
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