who downrates 32a mcb to 20a for ring mains when cables under more than 100mm of loft insulation ?

Discussion in 'Electricians' Talk' started by ram, Dec 4, 2017.

  1. unphased

    unphased Screwfix Select

    Rise above it, Lee. You and I had these daft exchanges it doesn't do you any good. :)
     
    leesparkykent likes this.
  2. Bazza-spark

    Bazza-spark Screwfix Select

    When you look over his posts he can't even aim his sarcasm at the right people.

    Let him have his moment. We all have the experience to see he knows jack sh i t.

    Kind regards
     
    leesparkykent likes this.
  3. spinlondon

    spinlondon Screwfix Select

    What was the question?
     
  4. JP.

    JP. Screwfix Select

    Aye BS7671 is amazing..everybody should have a copy upon themselves, and that includes people who reside on 't' other side of planet earth, and also of course Moomins..:)
     
  5. Bob Rathbone

    Bob Rathbone Screwfix Select

    If the installer of the insulation buries cables under insulation, it only becomes an issue for us when inspections are due. Yes the slack on the cable will be an issue if the cable is needed to be run on top.
     
  6. Bob Rathbone

    Bob Rathbone Screwfix Select

    A small diameter pipe would be insufficient separation from the thermal insulation and would not allow sufficient air circulation, the pipe needs to be a piece of 75mm rainwater pipe about 300mm long or if more cables are in the bunch, a piece of 100mm did soil pipe.
    It is important to allow air circulation around the cables where they pass through the thermal insulation Cut the pipe along it's length to allow it to be opened and fitted over the cables. Yes it is messing about and their may be alternative methods, this is only one suggestion.
     
  7. JP.

    JP. Screwfix Select

    How many people actually run power power cables in the loft to drop down to so's in the room below? Appreciate its necessary in some situations but its not common surely? The only thing I have done in lofts way back before going over to loop in box is lighting circuits, and maybe a double so pulled from loop under floorboards in room below.
     
    Last edited: Dec 9, 2017
  8. Bob Rathbone

    Bob Rathbone Screwfix Select

    Might be necessary in a bungalow with solid concrete floors, but I do agree that to avoid the insulation would be the better solution.
     
  9. JP.

    JP. Screwfix Select

    Agree Bob. If I did have to run power cables ring final style (dont like radial finals generally) in the loft and drop down and there was insulation going to be put over them to requisite depth which is more then 100mm - then there would be no get out clause with ref to derating - if the regs and calculations show that derating is required then so be it - a 20 amp breaker is not so bad at the end of the day considering loadings etc, and of course at design stage you can always break things up if need be (an extra circuit or two instead of one)

    In other words what has to be done has to be done at the end of the day, otherwise you will not be able to accrue (or write if qualified to do so) a valid cert if things are not done properly with ref to derating when indicated.
     
  10. bright_Spark

    bright_Spark Screwfix Select

    On East riding and Hull city council jobs, you can only bury lighting cables in insulation in lofts, where shower cables or ring mains pass through the insulation, then that cable has to be protected by either conduit or trunking to be kept out of the insulation.
     
  11. Pollowick

    Pollowick Screwfix Select

    And would 75mm pipe be suitable ?

    There was a heated discussion a few months back where one person was adamant that you could not use a piece of 22mm plastic water pipe or 22mm overflow (or similar) to provide protection to a cable passing through bricks and a cavity. He insisted that it MUST be conduit. Would he say the same here?
     
  12. bright_Spark

    bright_Spark Screwfix Select

    We usually clip all mains cables up along the roof trusses neatly above the insulation and use 2" trunking on single circuits but up to 4" trunking on bunched cables. It is utter ******** to be honest in my opinion, as the cables pass through the insulation for such a short length it really doesn't affect them unless the entire circuit length is laid under the stuff.
     
    Sparkielev likes this.

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