Hi all as per the subject - I am (re)making the connections to an isolator swit ch for an electric shower. The cable is 10mm and due to the construction of the switch I have to twist incoming and outgoing earths together. I can't seem to find 10mm Green/Yellow Earth sleeving online, 6mm seems the largest . Am I forced to use tape (ugh), or is there a source for the sleeving, or a different approach, that I need appraising of?
Thanks J^n
jkn laid this down on his screen :
6mm sleeving should fit the earth conductor of 10mm T&E.
Sleeves are generally measure in outer diameter, so allowance of wall thickness has to be considered.
suggests the CPC for 10mm conductors is 4sqmm suggesting a diameter of
2.25mm.Even 10sqmm only has a diameter of 3.5mm
Well ... I have currently got the incoming and outgoing earths twisted together for a length (2--3 inches), and I doubt it will fit that. I was hoping not to have to separate them and have them joined in the screw terminal. But if that is what people do, fair enough...
Cheers J^n
jkn used his keyboard to write :
Better when carrying out tests, for them not to be twisted together sharing one sleeve.
I think you need a proper mechanical connection, like a decent crimp.
You are only sleeving the earth line not the whole cable. Plenty of sleeving available for that.
You also need RCD protection.
Twisting together then fitting sleeving over both doesn't insulate the earth properly, as it will still be exposed at the sheath end.
Do you insulate the metal boxes they connect to?
The idea of the sleeving is to minimise the possibility of a short. And the end of the outer sheath is often nicely positioned to catch a terminal. Twisting earths together all their length also makes it more difficult to 'page' the runs neatly. But carry on doing this if you are too mean to pay for more lengths of sleeving.
Fair point. The old isolator had two separate (connected, obviously) earth terminals, but I seemed to have used tape for insulator. The new (MK, supposedly better, hmmph) isolator only has one earth terminal and I am anticipating some awkwardness if I have to sleeve each earth separately and then twist them together for the last couple of CMs.
But it seems like that is the way... thanks to all for the advice.
FWIW I guess I was thinking that '6mm earth sleeving' was 'sleeving for the earth wire in a 6mm T+E cable', whereas I see now that that is not the case... an eBay order for a few metres has just gone in.
Cheers J^n
At the CU on a ring, definitely (you need to do end-end and figure-8 tests that require accessing all 6 conductors individually.
In devices, I am less convinced it's a problem rather than just a mantra.
Adam may shed some light on this, but the only time I can think you'd want to separate conductors in a device is for locating a suspected fault. There's no routine testing I can think of that would need that,
*except* if you needed to isolate a branch because it had a sensitive device on the end. If the device *is* the sensitive part, you might take it off and stick a terminal block on the end of the wires.Never heard of cross-connection testing?
Correct and the reg that applies I would say is somewhere in the regs:-)
It's the sort of thing that you spot and wonder "What else is wrong?"
TBH earth sleeving and the PVC coverings of the L&N cores are not going to do much against a short caused by a socket screw. The live cores should in most cases be semi enclosed inside a terminal to prevent a fault (ie no bare copper sticking out on the live terminals).
However I think dennis is asking if the earth sleeving protects against a earth/earth fault between socket and metal back box should you put the socket screw through the green/yellow insulation and catch the cpc (earth) cable with the screw.
Now I seem to recall that you always fit an earth flylead between sockets and backboxes.
Yes it's unlikely. But if impossible, no point in using sleeving at all. I doubt even dennis needs to know which one is the earth wire with TW&E by its colour.
You don't twist the bare line or neutral together along their length inside a box, so why do it with the earth?
I wouldn't either, but I might twist the ends if the screw was being unreliable holding onto 1 of 2 or 3 conductors (I've had that happen).
I was primarily challenging the notion that "twisting makes it difficult to test" when, at least with my limited knowledge of testing, you'd generally not unwire the backs of devices, only the final cable(s) into the CU.
If you did do a lot of unwiring, it would compromise the testing anyway, as you'd be disturbing stuff needlessly in the name of making it better, when that would generally have the opposite effect.
The best testing would undo nothing, but the rise of electronic elements and the fact you have to isolate the circuit means a small amount is unavoidable.
Interestingly the Americans don't use CPC sleeving in any video I've ever seen. And their line terminals are often extremely exposed as a pan head screw you turn the conductor under. That's one case where I think it would have a provable benefit.
I'm a bit surprised insulated CPCs haven't been mandated here. Ireland has done so (and with the CPC the same size as the phases). And IIRC the French have had insulated CPCs for years. Safety and harmonisation...
it's one of those things. If the cables are correctly paged when fixing the fitting to the box, the earth sleeve is redundant. After all at one time it wasn't sleeved here either. But given a hank of sleeving is so cheap, no reason not to use it anyway.
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