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Consumer unit feed / main tails more than 3m

Jimi

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.

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  • 0

    It is just ohms law made incredibly complicated by an unnecessary nomograph.. Basically how far along you can slide line tap with a length of thin cable along a fatter distribution cable and achieve the same PSSC at the ends M,N and B. It is the street main and house radial situation.

    It deserves a prize for being a really, really poor explanation, and I rather wonder if the authors did not grasp the simplicity of the point either.

    Which document is it from ?

    Also of course short circuit faults are something of an ideal fantasy - in reality all faults have some voltage drop, if they did not there would be no energy dissipated at the point of fault, and no flash no heat and no sound.

    Mike.

  • 0 in reply to mapj1

    It’s from Annex43D of IS10101 2020, effectively just an informative to the equivalent of Chapter 43 in BS7671 although the Irish Standard refers to it as Part 43! I vote it as the worst attempt at an informative explanation in either standard. It looks like it was taken from IEC 1246/08, whatever that is. I didn’t get it until AJ explained so perhaps the authors didn’t intend the readership to extend to duffers like me! 

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  • 0 in reply to mapj1

    It’s from Annex43D of IS10101 2020, effectively just an informative to the equivalent of Chapter 43 in BS7671 although the Irish Standard refers to it as Part 43! I vote it as the worst attempt at an informative explanation in either standard. It looks like it was taken from IEC 1246/08, whatever that is. I didn’t get it until AJ explained so perhaps the authors didn’t intend the readership to extend to duffers like me! 

Children
  • 0 in reply to lyledunn

    Flippin ek, everybody does seem to make things very complicated. I have just worked in a 60s bungalow. The meter is in an outside cabinet on the attached garage wall, remote from the consumer unit in the bungalow. In the garage is a 60 Amp fuse contained within a metal clad Wylex switch fuse. The run from garage switch fuse to the bungalow consumer unit is about 6 metres. The run is in 16.00mm2 T&E cable run above the ceiling. It is fully visible in the garage. This installation has had no problems with this arrangement over the years and continues to operated perfectly.

    This is the type of switch fuse used, although it is if an older design.....

    Wylex 108M 60 Amp Metal Switchfuse Isolator Single Phase | eBay

    Z.

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