I've decided to make both my sheds TT installations, via buried SWA from the house PME. The SWA shield will be connected to earth at the head end so needs to be isolated at the remote end - question is how to do this to avoid having the risk of two earths at different potentials - is there an isolating SWA gland? If not, how do I do it? (Google hasn't helped, yet)
Could you use a plastic enclosure for the termination instead of a metal one?
Just take the gland into a plastic box / enclosure[1], and don't add an earth tag. That way the SWA is correctly terminated mechanically, but the armour is isolated electrically.
[1] That can be anything you like, such as a plastic clad CU, and adaptable box, or sometimes for outbuildings an external socket is a handy place. E.g:(a cable then runs through the back of the socket into the building)
These little waterproof adaptable boxes are quite nice also:
(TLC Direct have them)
I was just wondering how you could actually end up with different earths, if by definition, earth is earth. I'd certainly not expect huge differences in soil between a house and the other end of the wire. could somebody explain why it is not acceptable to have earths at both ends, or is this the classic floating neutral syndrome again. Brian
I'm terminating into a plastic adaptable box, but it's still going to be possible to touch the outside of the gland if the plastic sheath moves (which it will). I thought I'd seen glands somewhere that have the outside metalwork isolated in some way - maybe I dreamt it.
That is about as good as you are going to get. There is actually a slight failing in the wiring regs as they currently stand in that you can pull the sheath off the SWA gland without the need for a tool and gain access to the earthed metalwork. Its a fairly minor risk though since your would have to do it at the same time as having an fault on the incoming combined PME earth and neutral.
With a PME earth you have the danger that should the suppliers combined neutral and earth be disconnected, then your local neutral and earth will be coupled to line voltage, and typically try to rise toward it.
Not a danger if you are within the equipotential zone of the supply, but could be one if you have access to a "real" and independent earth at the same time.
How about putting the whole of termination inside another, bigger box (with the SWA entering through a simple hole (if plastic) or grommet (if metal))? Then the sheath is not accessible without use of a tool. Adds that bit more security; and a bit more profit for the meticulous professional ;)
SWA (PG16) and IP68 rated so will use these for the entry to the adaptable box and make sure the cable is well clipped to the wall before entering the gland.
Smart arse:-)
I have a vague idea that I have seen heat shrinkable shrouds for SWA glands, but it would have been many years ago.
SteveW
In non critical applications that would be ok as well. Note that the nylon glands don't have anything like the clamping strength you get from a proper SWA gland though.
Perhaps a heavy wrap of self amalgamating tape in place of the normal shroud on a standard SWA gland. If applied tightly and thickly that would require tools (a knife) to remove.
Andrew
That's what I did when I terminated the SWA in my shed (at the last house).
In my case the cable will be mechanically secured to the wall so I think a stuffing gland will solve the problem, but a self-amalgamating wrap sounds like a good idea if not.
An easy way is to fit the normal shroud, and then fit another P clip tightly over the narrow end of the shroud and cable, in effect fixing it in position.
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