power to outbuilding

[EFLImpudence]

I think "pile of strands" is misleading; are you doing it right?
It is more a neat ring of strands with interior support enabling equal pressure all round which must be equivalent to at least half of a complete tube.

As for protection - apart from that against rodents, what advantage does it give against impact from spades and similar, not to mention mechanical diggers?
The cable will still be virtually ruined.

 

[securespark]

What about tightening a brass bush onto a steel tube?

I'd like a tight bush on my tube.

 

[JohnW2]

I think "pile of strands" is misleading; are you doing it right? ... It is more a neat ring of strands with interior support enabling equal pressure all round which must be equivalent to at least half of a complete tube.

That's the theory. However, even when the strands are arranged neatly, the act of tightening the nut can mess up that 'neatness', possibly with some of the strands coming to overlap. If that happens, only a small proportion of strands will be under appreciable pressure. It is the fact that one can't see what's happening to the strands when one tightens the fitting which makes use of these 'plumbing fittings' different from almost any other method of terminating a stranded conductor.

As for protection - apart from that against rodents, what advantage does it give against impact from spades and similar, not to mention mechanical diggers?The cable will still be virtually ruined.

There's obviously a lot in what you say, but, as I keep saying/asking, if it were perceived that steel armour did not afford a worthwhile degree of mechanical protection, why do we use it and why was it even developed? I feel sure that a similar cable, but with a thin (probably copper) foil sheath would be cheaper to produce.

Kind Regards, John

 

[ban-all-sheds]

It is worthwhile.

My point was that there are situations where the level of mechanical protection provided by the MICC sheath is adequate, therefore the same would hold for copper plumbing pipe.

 

[JohnW2]

It is worthwhile. My point was that there are situations where the level of mechanical protection provided by the MICC sheath is adequate, therefore the same would hold for copper plumbing pipe.

I agree with all that. It is EFLI who seems to have been suggesting that SWA probably does not afford a worthwhile degree of mechanical protection. As I've said to him, if everyone believed that, why would we use it?

Kind Regards, John

 

[securespark]

Don't the regs ask for a cable with such protection in buried situations?

 

[JohnW2]

Don't the regs ask for a cable with such protection in buried situations?

Not specifically. When not enclosed in conduit etc. which provided "equivalent protection against mechanical damage", buried cables are required to have "... an earthed armour or metal sheath or both..." (522.8.10) - so a cable with a copper foil sheath would presumably be acceptable as far as the regs are concerned.

Kind Regards, John

 

[securespark]

But that means the outer covering would have to be copper surely, thus prone to damage?

 

[JohnW2]

But that means the outer covering would have to be copper surely, thus prone to damage?

Well, not necessarily (per regs) copper - but my point was that it would appear that a thin outer copper foil layer (presumably enclosed within PVC or whatever) would satisfy the regs.

In other words, although mechanical protection is one way to go, it seems as if the regs are happy so long as there is an earthed outer covering (which may afford minimal mechanical protection) which will hopefully mean that a protective device would operate if the cable were penetrated, for example by a metal spade.

Kind Regards, John

 

[securespark]

As long as the regs don't demand that the "sheath" is the external covering, like T&E, "insulated and sheathed".

 

[JohnW2]

As long as the regs don't demand that the "sheath" is the external covering, like T&E, "insulated and sheathed".

I'm sure they don't! Mind you, I don't think that there is necessarily any real need for an outer plastic (or whatever) sheathing - since it would not afford any appreciable protection to an underlying copper layer. The "insulated and sheathed" (or, colloquially, 'double insulated') requirement for such things as T+E is to do with protecting people from contact with live conductors.

I suppose that, if you wanted to, you could consider the difference between "insulated and (plastic) sheathed" ('DI') cable and cable with an earthed outer metal layer as being analogous to the difference between Class II and Class I equipment.

Kind Regards, John

 

[ericmark]

I have seen many SWA glands. The Hawk gland was very good with the ability to part open the gland and check the clamping of the steel armouring had a seal on the inner cable and could be used with both SY and SYA cables. But some of the other glands were rather hit and miss and I have seen many where the armouring has come out of the gland.

 

[JohnW2]

I have seen many SWA glands. The Hawk gland was very good with the ability to part open the gland and check the clamping of the steel armouring had a seal on the inner cable and could be used with both SY and SYA cables. But some of the other glands were rather hit and miss and I have seen many where the armouring has come out of the gland.

I can't recall having seen one in which the armour had actually 'come out', but I've certainly seen ones that had become sufficiently loose that the quality of the electrical connection was uncertain and such that it would have taken very little to pull the armour out.

Kind Regards, John

 

[ban-all-sheds]

As for protection - apart from that against rodents, what advantage does it give against impact from spades and similar, not to mention mechanical diggers?

There's little you can do about diggers, but I think the average garden spade wouldn't slice through SWA anywhere near as easily as PVC or rubber sheathed cable.

 

[ban-all-sheds]

I'd like a tight bush on my tube.

What about a piranha on your gland?