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"it is that pesky SY braided stuff again; so what's wrong with it"

psychicwarrior

More a discussion come question perhaps, but are there any really good reasons why a choice of SY would be made for a fixed wire low voltage power circuit  over something else ?

My understanding of the braiding,  is that it has nothing to do with armouring and is not acceptable as armouring;  but is it still an exposed conductive part to be earthed and if it is not [earthed], how much of a risk  ?

from reading Eland (who have a pdf on the SY stuff) to mention one manufacturer, is that it is a somewhat standards tested cable (https://www.elandcables.com/media/13rlt2rk/ec-statement-on-the-use-of-sy-cy-yy-cables-rina-18th-ed-with-summary.pdf)

In the case observed being a 3phs circuit, it was 5core (one as cpc) from a metal db (through plastic stuffing gland) to a plastic interlock socket, 16a 3pole mcb and it appeared the braiding was unterminated.   it was not on a run likely to be disturbed.   Nothing noted on the EIC about its use either.

regards

Habs

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    In your view, does/could the braid qualify as 'mechanical protection' in the case of BS7671  like SWA would/does (arguably)  e.g. if buried in fabric < 50mm without RCD ?

    In my view, even the armour of SWA cables doesn't count as 'mechanical protection' (i.e. to 522.6.204 (iv)) - as it's too easy for nails/screws to penetrate between the strands (in one experiment I even got the fairly blunt tine of a garden fork to pierce through SWA to a live core without too much effort) - rather SWA would come under option (i) - i.e. 'earthed metallic covering', that should trigger ADS should the cable be pierced by something metallic though to a line conductor.

    Is the braid suitable to act as a protective conductor, as if not then it could only be for just the [increased to some degree] mechanical protection; but is it ever an exposed conductive part  required to be earthed ?

    The distinction between a protective conductor and an exposed-conductive-part always seemed a bit strange to me - if there's a fault then the exposed-conductive-part will have to survive carrying just as much fault current for just as long as a c.p.c. - yet we have all sorts of rules for sizing c.p.c.s but apparently none for exposed-conductive-parts. I suppose there is some difference in that generally we'd expect a c.p.c. to remain serviceable after a fault (so for example it can't be allowed to get so hot it permanently damages surrounding insulation) whereas an exposed-conductive-part might be considered more expendable - but all the same we'd not want an exposed-conductive-part vaporizing or burning back to break the circuit before the protective device opens. Yes, the steel braid can provide some useful mechanical protection (especially where the cable might be abraded or cut into by a wide sharp edge, rather than pierced by something pointy) but generally that can't be relied upon without the earthing/ADS approach as well. As I said, my gut feel is that steel (or copper) braid would likely do as least as well as the aluminium foil of BS 8436 cables - but without the numbers available that's hard to prove.

       - Andy.

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  • 0

    In your view, does/could the braid qualify as 'mechanical protection' in the case of BS7671  like SWA would/does (arguably)  e.g. if buried in fabric < 50mm without RCD ?

    In my view, even the armour of SWA cables doesn't count as 'mechanical protection' (i.e. to 522.6.204 (iv)) - as it's too easy for nails/screws to penetrate between the strands (in one experiment I even got the fairly blunt tine of a garden fork to pierce through SWA to a live core without too much effort) - rather SWA would come under option (i) - i.e. 'earthed metallic covering', that should trigger ADS should the cable be pierced by something metallic though to a line conductor.

    Is the braid suitable to act as a protective conductor, as if not then it could only be for just the [increased to some degree] mechanical protection; but is it ever an exposed conductive part  required to be earthed ?

    The distinction between a protective conductor and an exposed-conductive-part always seemed a bit strange to me - if there's a fault then the exposed-conductive-part will have to survive carrying just as much fault current for just as long as a c.p.c. - yet we have all sorts of rules for sizing c.p.c.s but apparently none for exposed-conductive-parts. I suppose there is some difference in that generally we'd expect a c.p.c. to remain serviceable after a fault (so for example it can't be allowed to get so hot it permanently damages surrounding insulation) whereas an exposed-conductive-part might be considered more expendable - but all the same we'd not want an exposed-conductive-part vaporizing or burning back to break the circuit before the protective device opens. Yes, the steel braid can provide some useful mechanical protection (especially where the cable might be abraded or cut into by a wide sharp edge, rather than pierced by something pointy) but generally that can't be relied upon without the earthing/ADS approach as well. As I said, my gut feel is that steel (or copper) braid would likely do as least as well as the aluminium foil of BS 8436 cables - but without the numbers available that's hard to prove.

       - Andy.

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