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2.9kW Oven on 32A radial - not properly protected?

Discussion in 'Electrics UK' started by AlEightyFour, 10 Jun 2019.

  1. AlEightyFour

    AlEightyFour

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    Hello all

    Just pulled out my oven to get it out of the way for a builder and something looks wonky to me.

    -Hob and Oven on a 32A radial
    -6mm2 T&E in the ceiling/walls feeds to a splitter box behind the oven (fine so far)
    -Hob seems fine - is a 32A device and appears to be on its OEM flex
    -Oven however seems borderline dangerous, to me:
    ---2.5mm2 solid T&E from the splitter, no fuse (confirm: 2.5mm2 on 32A radial, in free-ish air behind the oven)
    ---Oven is 2.9kW (i.e. ~13A) and has weedy little wires inside to suit (photos) - also only protected by the 32A radial

    So it seems to me like I have an oven and local cabling not protected for overload.

    I thought I'd post up just in case I was being too cautious - can anyone can tell me why this might be safe & within current regs? Looks like it was installed in 2013 ish. If nothing convinces me then it will be going back in with a 16A fuse between the 6mm2 and the 2.5mm2! (which AFAIK is the correct way to do this, open too other suggestions.

    Nothing else on the 32A radial. There is a 45A oven isolator above the worktop as required.

    Thanks in advance!

    Al
     

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  2. EFLImpudence

    EFLImpudence

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    As are 99%. Standard circuit.

    Ok. 2.5mm² is good for 27A.

    All is fine.

    Ovens cannot cause an overload. The elements cannot draw more than they need.
    A short circuit (L to N) or earth fault (L to E) will trip the 32A MCB.

    Yes, all perfectly normal.
     
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  3. sparkwright

    sparkwright

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    Not so sure using 2.5 mm2 solid core T+E is a good choice of cable to run from the splitter to the oven though.

    Something more flexible would be a better choice.
     
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  4. ban-all-sheds

    ban-all-sheds

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    Because the oven won't create an overload and its cable is adequately protected from fault currents by the circuit fuse/MCB.
     
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  5. winston1

    winston1

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    Wrong on both counts. Where would you get a 16 amp fuse anyway?

    There is no requirement for an isolator above the worktop, though they are often fitted.
     
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  6. AlEightyFour

    AlEightyFour

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    Thanks for the replies folks. That's good to hear. Will reinstall with some flex on it and stop worrying unduly .

    Will do some searching around appliances that "can't cause an overload". Clearly, this is news to me but it makes sense so thanks for the pointer. I guess an oven has physical separation of all the conductors on its side (as opposed to something like a motor where you could clearly get an overload).

    Al
     
  7. Simon35

    Simon35

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    A motor can be overloaded, and therefore draw more than its rated current by being mechanically overloaded. That's what a thermal overload protects against. Nothing to do with separation of conductors.

    Conductors in contact are short circuiting, which is a different type of fault.
     
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  8. Simon35

    Simon35

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    Double post.
     
  9. EFLImpudence

    EFLImpudence

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    Firstly an 'overload' is an appliance drawing more current than it should for a time; it is not a L to N short-circuit fault nor a L to E earth fault which would cause many amps (hundreds) and trip even the 32A MCB instantly.

    The oven does have two or three separate parts, but that is not the reason.

    The oven has resistive loads, i.e. the elements have a certain resistace which cannot decrease (unless the temperature drops).

    For example: a 24Ω element - when 240V is applied to it, it results in a current of 10A (2400W - ohms law)
    The resistance might increase when hot, thus even reducing the current slightly.

    Some people argue that a fault in the element might short the heating element to the earthed casing but this is highly unlikely to be a problem as it is all but impossible that the element wire would join itself to the casing in a stable manner after initially just touching and arcing to earth at a small contact point.
    Say it did happen half way along the element. This would halve the resistance causing 20A. To be honest, I don't know if a 10A element could sustain 20A in itself. It seems unlikely because, if it could, then it would not get (very) hot at its designed 10A.

    It would be like expecting a fuse to sustain high currents without blowing - although fuses are designed to sustain relatively high currents as they are not wanted to be red hot all the time.
     
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