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Electricals in cathedral ceiling

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  1. #1
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    Default Electricals in cathedral ceiling

    I'm renovating a room with a cathedral ceiling. This includes removing the plasterboard ceiling, packing the 200mm deep cavity between the ceiling rafters with R4.1 insulation, and replastering. The roof is tiled and sarked.
    Is the wiring currently in there better located on top of the insulation (i.e. against the underside of the sarking, and I'd have thought where it would get pretty hot), or under the insulation (i.e. lying on top of the plaster). Or doesn't it matter either way?

  2. #2
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    I assume it is lighting cable then it doesn't matter.

  3. #3
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    The R value of your insulation is only achieved if installed as intended. You'll probably get better thermal performance from R3.5 insulation that has a bit of air space, than R4.1 that is compressed to fit into a cavity.
    Before you speak, ask yourself: Is it necessary, it is true, does it improve on the silence? - Baba

  4. #4
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    Bros, are you saying that if lighting wiring it doesn't matter ..... therefore if power it does? Of course in this case the sparky achieved the impossible by thinking it logical to connect 3 floor level power points via the ceiling .....

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    Yes I said that about lighting as the cable would be carrying light loads and while there is a derating factor if the insulation is on it it would be unlikely to make any difference. Power on the other hand is different as you could plug both low current device and high current devices in and derating could make a difference.
    If you lay the insulation on the cable the lighting would be derated from 20A to 16A hardly much for lighting but for power it would be 25A to 20A

  6. #6
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    Quote Originally Posted by Bros View Post
    Yes I said that about lighting as the cable would be carrying light loads and while there is a derating factor if the insulation is on it it would be unlikely to make any difference. Power on the other hand is different as you could plug both low current device and high current devices in and derating could make a difference.
    If you lay the insulation on the cable the lighting would be derated from 20A to 16A hardly much for lighting but for power it would be 25A to 20A
    Thanks Bros, I think you told me a sparky is going to move this for me. I don't do no electrics.

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