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8.5 kw shower cable size

Discussion in 'Electrics UK' started by scottg, 15 Nov 2008.

  1. scottg

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    can i fitt 8.5 kw shower using 6 mm2 cable 3m from mains board
    only thing is its going through loft insulation more than 100mm
    would it be ok to use trunking with insulation on top would this effect cable calculations
     
  2. TopTrumper

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    A whole 3 metres?
    yes 6mm will be fine
     
  3. GaryMo

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    6mm through loft insulation greater than 100mm is rated at 27A (method 101#).
    Your 8.5kW shower is rated at (8500/230) 36.96A.

    The current carrying capacity of the cable in its installed conditions must be at least the rating of the device it's supplying.

    Can you reroute the cable away from the insulation? Clipped direct (method C) with no insulation is rated at 47A.
     
  4. GaryMo

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    How did you come to that conclusion?
     
  5. TopTrumper

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    EASY

    PS, im sure the OP understood every word you just said.
    Are you seriously trying to say 6mm cable for a 3 metre run is not suitable?
     
  6. GaryMo

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    Maybe it's you who didn't understand anything I said?

    Easy as in you guessed without looking at table 4D5?

    Are you seriously trying to tell me that a 6mm cable with a rating of 27A, given its installation method is good for a design current of 36.96A?

    I sincerely hope not!
     
  7. TopTrumper

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  8. GaryMo

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    I would advise 10mm and keep the cable away from thermal insulation.

    Another example of why electric cables and thermal insulation don't mix.
     
  9. TopTrumper

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    Never mind what you would advise him to do,he has already stated
    "It is going through loft insulation"
    So what cable would you say in your expert opinion, does the OP need for this 3 metre run?
     
  10. TopTrumper

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    GaryMo, to help you along a little, here is the instruction manual for the said shower.

    http://www.mira-showers.co.uk/onlinecatalog/pdf/p1088848_w2.pdf

    I would like you to take particular notice to page 9, to help, I will quote you a paragraph,

    The terminal block will not accept cable larger than 10 mm2.

    So as we are looking at tables, what do you say?
     
  11. GaryMo

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    Well, if the terminals won't accept a conductor larger than 10mm then 10mm is the maximum cable size for that given shower.
    So, either change the shower, remove the insulation or re-route the cable.

    It's not rocket science is it?
     
  12. TopTrumper

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    OK.
    Lets assume that the insulation cannot be moved, and there is no other route whatsoever, would you install the 10mm cable?
     
  13. GaryMo

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    I wouldn't install a 10.8kW shower, that's for sure!
    10mm in those conditions is rated for a maximum of 36A.
    A shower would need to be purchased rated at less than 36A, 8kw maximum.
     
  14. TopTrumper

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    So lets get this right,
    if you turned up at a clients house, and they presented you with this shower and there preferred cable route, and the fusebox was 3 metres away, you would tell them your not installing it?
     
  15. GaryMo

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    They would need to take my professional advice.
    I would recommend an alternative route thus avoiding insulation. If that's not possible then I would inform them that I could install a 10mm cable but it's only rated at 36A and can only supply a shower rated at a maximum of 8kW.

    I would NOT install a shower with a rating higher than the current carrying capacity of a cable.

    Why is this so difficult to understand? It's like asking me to put a square peg in a round hole - something has to give.
     

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