S.W.A. Armour Earthing.

Hmm. some folk clearly worry more than I do, perhaps I'm a bit too gung ho. ?


However,  if the armour is at a dangerous potential relative to the terra-firma earth or the metalwork of the building to which the cable is attached, then surely the whole of the SWA needs over-sleeving or putting into plastic conduit ?

We have just agreed, I think, that the outer plastic is not intended to serve as insulation and should not be relied upon. I'd never propose we use the armour for the 3rd core in a 3 phase system or anything like that, but if we are to treat a CPC as it as if it is live , then perhaps we should pretend  it is the same as if we had.


It is perfectly possible to fit a stuffing gland to an SWA cable in a way that it does not pull out without destroying the gland  and tearing it put  from the box first. Like any gland you do need to select the right sort of gland for the cable, and not some cheap knock off,  and use the right size spanners to the correct torque ( you need a few ft-lbs for the ones that fit a 25mm hole) to do it well.

It is also fair to say that on installations I have seen, there appear to be  plenty of SWA glands fitted in a way that do not fare as well as I'd like in a decent pull test. That may be partly a lack of technique or maybe some makes of glands are better at gripping the cable than others. Certainly some of the SWA designs that only grip the armour and have no rubber gland compression part are pretty poor.


In summary, I agree the GK solution is perfectly fine, if erring on the over engineered, but am not really convinced my approach is especially unsafe.

Mike

Hmm. some folk clearly worry more than I do, perhaps I'm a bit too gung ho. ?


However,  if the armour is at a dangerous potential relative to the terra-firma earth or the metalwork of the building to which the cable is attached, then surely the whole of the SWA needs over-sleeving or putting into plastic conduit ?

We have just agreed, I think, that the outer plastic is not intended to serve as insulation and should not be relied upon. I'd never propose we use the armour for the 3rd core in a 3 phase system or anything like that, but if we are to treat a CPC as it as if it is live , then perhaps we should pretend  it is the same as if we had.


It is perfectly possible to fit a stuffing gland to an SWA cable in a way that it does not pull out without destroying the gland  and tearing it put  from the box first. Like any gland you do need to select the right sort of gland for the cable, and not some cheap knock off,  and use the right size spanners to the correct torque ( you need a few ft-lbs for the ones that fit a 25mm hole) to do it well.

It is also fair to say that on installations I have seen, there appear to be  plenty of SWA glands fitted in a way that do not fare as well as I'd like in a decent pull test. That may be partly a lack of technique or maybe some makes of glands are better at gripping the cable than others. Certainly some of the SWA designs that only grip the armour and have no rubber gland compression part are pretty poor.


In summary, I agree the GK solution is perfectly fine, if erring on the over engineered, but am not really convinced my approach is especially unsafe.

Mike