My latest c*ck-up: Having dug 15M trench, put SWA cable in and re-filled, I've now discovered it's a 3 core rather than 2 core cable. Doh! (It did seem a little thick, but I hadn't used any SWA for a while...) I could just go ahead and use it anyway I suppose, but since the core colours are brown, black and grey as for 3-phase system, I can't use the correct single phase colour scheme - there's no blue.
Is there a way round this without digging the whole bloody thing up again?
SR
SR said the following on 11/01/2006 21:48:
No problem
Brown - Live Black - Neutral - with blue insulating tape over the black Grey/Sheath - Earth - with green/yellow insulating tape over the grey
Tape should be used at both ends.
Alternatively, you can put a white label on the brown saying "L" and a white label on the black saying "N", etc.
Don't worry - that's normal. I've not seen any 2 core myself, most if the sheds sell 3 core anyway.
The consensus of opinion on the IEE forums suggest this (old and new 3 phase SWA colours used in single phase installations) (with some differences of opinion):
RED OR BROWN - LIVE YELLOW OR BLACK - EARTH (SLEEVED GREEN/YELLOW) BLUE OR GREY - NEUTRAL (SLEEVED BLUE)
The whole thread is here, so best check it out yourself:
I'm not an expert though I have laid SWA before. Although in many cases the armour should make a sufficiently good earth connection, you should in theory prove it. The easy way around is to, as is commonly done, use one of the cores as an earth as shown above. But you must also connect the armour to this earth CPC via the solder ring that comes as part of the gland kit. I suspect you knew that, sorry, just being careful.
This assumes that you are exporting the supply end earth to the destination, rather than using a local rod.
HTH
Tim
Just use it, but ensure that the cores are properly marked with tape or sleeving at their terminations.
The third core can be connected to earth, either at one end or both ends if not supplying a TT installation.
Don;t forget, if this is making your installation mixed old and harmonised colours, there's a sticker you are required by the IEE regs to put on the CU.
Tim
Sometime before I bought this house in the early '70s, the (then) LEB moved the meter from the cellar. The cable used by them was SWA three phase...
Are you mad? Who is going to see it unless you put a big poster on the house. No one will know unless YOU tell them, so I don't see the problem. A bit of common sense is required. Or you could just dig the trench up, pay out loads more money, throw the perfectly good cable in the bin and buy new cable. Do you really need someone to give you the answer?
There's no problem, he's already done it correctly even though he thought he hadn't :)
This is wrong. Theblack should be in ne colour 3 core cable used as the earth and marked as such.
Not a c*ck up. 2 core would have been that.
You probably have used the right cable. It is bad idea to rely on the cable armour for earthing (obviously it should be earthed, but just not used as the main earthing conductor). It is much better to have a proper copper conductor for the earth. I used 3 core for my shed.
You should sleeve the ends of the cable with the appropriate colours where they are terminated.
Sleeve the black as blue and use as a neutral. Use the brown as live directly. Sleeve the grey as yellow/green and use as earth.
Connect the armour to earth at the house end or both ends according to preference and ease.
If you are TT earthing the other end, then you don't need an earth conductor. Just sleeve the black as blue and don't connect the grey conductor to anythying.
Christian.
It would be better to connect to grey to the armoured at both ends in this case rather than just leaving a floating cable. The house end of couse being connected to the house earth.
The accepted colours for such wiring is grey (sleeved with blue) used as neutral and black (sleeved with green/yellow) used as earth.
Adam
On Fri, 13 Jan 2006 13:07:46 -0000 someone who may be "Christian McArdle" wrote this:-
The electrical installations in many buildings rely on the cable armour for earthing.
Indeed they do, but the point to be made is that using the armour as earth (CPC) will always require design calculations to verify earth fault loop impedance (for disconnection time compliance) and that the armour will not overheat before a fault clears (adiabatic compliance).
OTOH if a copper cable core is used as the CPC you have a CPC which is equal in size to the live circuit conductors and calculations aren't required (provided the feeding fuse/MCB rating doesn't exceed the current rating of the cable). The maximum circuit length (to meet both voltage drop and disconnection time requirements can simply be looked up in Table 7.1 of the OSG.
Also copper doesn't rust in the same way as steel armour, so it will continue to be safe for decades to come.
Christian.
On Tue, 17 Jan 2006 10:03:15 -0000 someone who may be "Christian McArdle" wrote this:-
So, are all those buildings with steel armour as the only earth unsafe after decades?
prevents me
Potentially. It is one of the many reasons for the move towards TN-C-S earthing, where the earth is carried by the neutral conductor.
Christian.
Uh, that's TN-C and isn't allowed in consumers' installations.
Rusting/corrosion of steel armour wires is not a problem, galvanizing protects well.
I was talking about the incoming supply. I certainly wasn't proposing TN-C.
It's more of a problem with the termination, where rusting can lead to high earth loop impedence at the connection point. The armour itself shouldn't be a problem.
Christian.
Thanks Adam and others. I wasn't aware it was permissable to sleve the tails to different colours. Makes life far easier. My previous involvements with SWA cable had all used 2 core and the armour for earth
- hence my initial concern. Happy now though :-)
SR
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