Usually, there is a suitable alternative for circuits within the scope of BS 7671,

I'm not so sure - these days BS 7671 covers a lot more than just fixed/rigid installations and I can imagine a few situations where both flexibility and metal covering would be useful. The last time I saw SY used was to supply the "crusher skips" at my local recycling centre - as the skips are regularly unplugged and moved about flex is certainly needed and given the environment where Joe public is regularly carrying (& dropping) all sorts of items including sharp ends of scrap metal an earthed metal covering in the flex seems pretty sensible to me.

As far as actual safety is concerned - which I think boils more down to the laws of physics rather than words on paper - what's the difference between a power circuit and a control/auxiliary circuit? OPDs are likely to be similar, PFC ditto, if anything an an industrial control circuit is less likely to have RCD protection than a final power circuit. If it's deemed to be safe on one, how come it's a potential problem on the other?

   - Andy.

AJJewsbury said:

The last time I saw SY used was to supply the "crusher skips" at my local recycling centre - as the skips are regularly unplugged and moved about flex is certainly needed and given the environment where Joe public is regularly carrying (& dropping) all sorts of items including sharp ends of scrap metal an earthed metal covering in the flex seems pretty sensible to me.

Oh dear ... SY cable is not usually suitable for outdoor use AFAIK, so that's also potentially no good either. However, probably outside the scope of BS 7671 because the skip would be Machinery as defined in the Regulations, BS 7671 stopping at a socket-outlet would be my recommendation?

I've seen this type of arrangement with mobile and transportable units before, and it's problematic when the cable sits in a puddle ... and perhaps doesn't need saying that often the braid is left not terminated at either end on occasion! Certainly, not easy to terminate in BS EN IEC 60309 plugs and free outlets.

If not, I think discussed at length above, SY is not usually considered to provide any more mechanical protection than other cable types - the issue being that there is no constructional standard in any case, so not always something you can rely on for mechanical protection?

Yes, this type of application does require something special - perhaps an industrial connecting lead with metal conduit, similar to that used with Electrak tap-offs (but suitable for outdoor use) might be appropriate?

AJJewsbury said:

As far as actual safety is concerned - which I think boils more down to the laws of physics rather than words on paper - what's the difference between a power circuit and a control/auxiliary circuit? OPDs are likely to be similar, PFC ditto, if anything an an industrial control circuit is less likely to have RCD protection than a final power circuit. If it's deemed to be safe on one, how come it's a potential problem on the other?

Good points ... quite likely impulse withstand according to IEC 60664-1 and rigour of testing (depending on the particular constructional standard) is the answer ... but that is a question for product standards and the standards for guidance for use of cables etc. ... and again not specifically BS 7671.

AJJewsbury said:

The last time I saw SY used was to supply the "crusher skips" at my local recycling centre - as the skips are regularly unplugged and moved about flex is certainly needed and given the environment where Joe public is regularly carrying (& dropping) all sorts of items including sharp ends of scrap metal an earthed metal covering in the flex seems pretty sensible to me.

Oh dear ... SY cable is not usually suitable for outdoor use AFAIK, so that's also potentially no good either. However, probably outside the scope of BS 7671 because the skip would be Machinery as defined in the Regulations, BS 7671 stopping at a socket-outlet would be my recommendation?

I've seen this type of arrangement with mobile and transportable units before, and it's problematic when the cable sits in a puddle ... and perhaps doesn't need saying that often the braid is left not terminated at either end on occasion! Certainly, not easy to terminate in BS EN IEC 60309 plugs and free outlets.

If not, I think discussed at length above, SY is not usually considered to provide any more mechanical protection than other cable types - the issue being that there is no constructional standard in any case, so not always something you can rely on for mechanical protection?

Yes, this type of application does require something special - perhaps an industrial connecting lead with metal conduit, similar to that used with Electrak tap-offs (but suitable for outdoor use) might be appropriate?

AJJewsbury said:

As far as actual safety is concerned - which I think boils more down to the laws of physics rather than words on paper - what's the difference between a power circuit and a control/auxiliary circuit? OPDs are likely to be similar, PFC ditto, if anything an an industrial control circuit is less likely to have RCD protection than a final power circuit. If it's deemed to be safe on one, how come it's a potential problem on the other?

Good points ... quite likely impulse withstand according to IEC 60664-1 and rigour of testing (depending on the particular constructional standard) is the answer ... but that is a question for product standards and the standards for guidance for use of cables etc. ... and again not specifically BS 7671.