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Earthing or bonding ?

MrJack96

I see it a lot where the SWA isn’t serving as a protective conductor which I know it must still be earthed at one end due to being an exposed conductive part. My question is if multiple SWAs are all earthed at the supply end and meet again at a bit of equipment if we then connect all the SWAs together locally is this still classed as earthing even though they are already earthed at the supply? 

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  • 0

    Ah it is the simplest questions that raise the most problem cases. 

    In reality of course the SWA outer and the paint on the conduit do greatly reduce scope for a large area shock, so even if nicked or scratched still change a possible fatal shock into an unpleasant but survivable, if  vocabulary expanding, experience. But with uncertain performance it is in the same league as an improved floor covering, like using gravel at substations, to drain well and to discourage inadequate footwear choices - does not reduce the shock current to zero, still very much worth doing.

    If we did not use the phrase elsewhere, we could have called it additional  protection...

    It is perfectly possible to terminate SWA, and for that matter other cables with armours or shields, much  in the manner of split con,   combing the armour wires to a terminal and only clamping to the outer for strain and water sealing, and while it may raise an eyebrow from the purists,  it is not electrically dangerous, and can be made mechanically and environmentally superb. (it can also be stuffed up royally, but then so can SWA glands - I have seen a few pull right out at the armour. )  It's not great for EMC as it introduces several tens of nH in the earth loop, but at 50Hz no one cares.

    Back to the original post.
    If those glands are graunched into a metal plate, ideally with a star washer under the nut, then the linking green wires are not needed - all the glands are already connected.
    If the quality control is poor, and there is a risk the panel may be painted, or the nuts only finger tight, then the links may make sense as a redundant path.

    Mike.

  • 0 in reply to mapj1

    Yes Mike, I wish they would supply correctly sized star washers (hardened too) with gland packs, it would cost pennies and be of great help.

  • 0 in reply to David Stone

    meanwhile M20 (BW20 BW20s ) and M24 (BW25) finetooth internal star washers ( https://www.accu.co.uk/711-internal-fine-tooth-locking-washers?page=1 ) are worth the investment, as well as the M4s.

    If they wanted to make life better, they could tighten the rattle fit tolerance on the nuts AF dimensions at the same time and ditch the banjo for something more like the piranha.

    M.

  • 0 in reply to David Stone

    Earthing nuts rule o.k! They are reliable and effective.

    www.ebay.co.uk/.../265151900008

    Z.

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