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Consumer unit feed / main tails more than 3m

Hi, what are the requirements when a consumer unit is to be located where the mains tails are more than 3m from the cut-out? Quickly searching online it seems that a switched fuse unit (60A, 80A, 100A as applicable) is required after the meter? Does anyone know the regulation number in BS7671? Some have mentioned taking high voltage drop and Ze into consideration for a long run. Is SWA usually used? It is safer and could be buried in a wall if needed couldn't it? Mains tails are a bit dodgy anyway as contacting the line you could get the full PFC so I prefer the idea of the earthed armouring. 25mm 3-core SWA at CEF is about £13 per meter. I guess that's what happens in blocks of flats?

In this installation, the current position of the intake and CU is in the kitchen. They would like it moving under the stairs if possible which would mean a 5 or 6 meter run from the kitchen, up above ceiling, across and down into the under-stairs cupboard. I could potentially take an alternative route behind the kitchen units. Thanks.

Parents
  • Could someone please explain the reasoning behind this requirement (never seen one - just do it) when it is perfectly acceptable to install an additional fuse of exactly the same rating as the DNO fuse.

    In other words, how is a fault within the premises 'trained' to selectively blow the addition fuse but not the DNO one?

    Despite it being said to be a DNO requirement, I have always thought it to be a misreading of 434, in particular 434.2.1, even though it does not apply in such an arrangement.

  • Evening all

    You need to have a quick squint at BS 7671 Regulation 433.3.1 and 434.3 to see what those regulations say about meter tails.

    JP

  • Are you saying that the distributor disagrees "that their fuse affords protection to the part of the installation between the origin and the main distribution point of the installation" so an identical one must be fitted?

     

Reply
  • Are you saying that the distributor disagrees "that their fuse affords protection to the part of the installation between the origin and the main distribution point of the installation" so an identical one must be fitted?

     

Children
  • Essentially the DNO are saying that they'll only guarantee their fuse affords protection for the tails if they are less than 2.5m or 3m or whatever, and/or their route between meter and CU is visible, or whatever rules the DNO decides. Bear in mind that the DNO is (in principle) allowed to upgrade the head and/or the fuse rating.

    There's no requirement for selectivity.

  • Essentially the DNO are saying that they'll only guarantee their fuse affords protection for the tails if they are less than 2.5m or 3m or whatever, and/or their route between meter and CU is visible, or whatever rules the DNO decides.

    I had no idea the DNOs were so powerful that they only have to say something to make it so.

    I think that is my point. How do they manage to do that; i.e. limit the protection of their fuse to a short distance when the identical second fuse protects the whole length?