Quick SWA question

[Bright_Spark]

when running SWA from a metal clad housing to another when the SWA is 10mm and on a TN-S system...would you..

a) Use 3 core and use one as an earth as well as the armouring?

b) don't use the 3rd core and just use the SWA armouring?

something rings a bell from the regs stating that option A is a no go..but not having it to hand right now, i thought id ask.

what does everyone think - appologies if this has been asked before - i dont have time to go through page after page after page of previous topics.

cheers

 

[RF Lighting]

The general way to do it is use the third core as the earth to what ever you are supplying, and then earth the armouring for the sake of cable protection only, rather than relying on this as the supply earth.

There is no reason why you can't just use the armouring and not use the third core* but the first method tends to be the favourite.







*On some cables the armouring does not have a sufficient CSA to comply with the regs, and must have a seperate 'auxilary' earth run in with them (either combined in the cable or a seperate earth cable). But this only applies to the larger sized swa.

 

[securespark]

No offence, but it seems like no-one has time to reply, either!!

 

[Bright_Spark]

No offence, but it seems like no-one has time to reply, either!!

conclusion - many people lead a busy life !

 

[BigJon]

Id be tempted to use the 3rd core as an earth (mark it ofcourse), and the wire armour will also be earthed throught the gland, if you've got the spare core may aswell utilise it, Thats just what I would do in practice, dont have the regs at hand tho.

 

[Adam_151]

You can use a core in parrallel to the armouring to decrease Z's and to re-enforce it (incase someone rips the armouring out of the gland)

...armouring still has to cope with the thermal constraints of a fault though (but unless you have a massive PFC then its not usually an issue) and have Z's low enough that if someone sticks a fork through it...

If there is a spare core there you'd be barmy not to use it along with the armouring, and besides you shouldn't leave it floating

EDIT: clarity

 

[securespark]

Yes, the NIC recommend ALL unused cores of any cable be grounded.

 

[Spark123]

*On some cables the armouring does not have a sufficient CSA to comply with the regs, and must have a seperate 'auxilary' earth run in with them (either combined in the cable or a seperate earth cable). But this only applies to the larger sized swa.

Although some sizes do not comply with table 54G the armour can still be used if it complies with the adibatic equation (which isn't really DIY stuff).

 

[plugwash]

something rings a bell from the regs stating that option A is a no go..but not having it to hand right now, i thought id ask.

while i'm not 100% positive i belive that is a misquoting of the regs, there is a rule against using the armour as the earth but only in marina wiring.

 

[mr walker]

hi in my oppinion ,we have a common precidure in the the trade if it is single phase we use one of the conductors as earth in a 3 core swa normally black/grey if it is a 3 phase installation we run a extra earth as well as the steel wire armoured i.e. a 25mm 4 core swa l1,l2,l3+n will have a 16mm earth wire +swa earth hope this helps!

 

[RF Lighting]

hi in my oppinion ,we have a common precidure in the the trade if it is single phase we use one of the conductors as earth in a 3 core swa normally black/grey

Black OR grey?

It has to be black.

Do you sometimes use black as neutral too? I hope not.

 

[plugwash]

why not theres no reg against it just some dubious advice from the NICEIC

 

[mr walker]

we commonly use grey as neutral going from the old colures however some unscruplius firms mainly shop fitters still use black
many thanks
MR WALKER

 

[ban-all-sheds]

why not theres no reg against it just some dubious advice from the NICEIC

Mmmm - not sure it's dubious - I can see a lot of sense in disassociating black from neutral

 

[plugwash]

i don't see how associating grey (another phase color) with neutral is any better.

the only advantage i can see to the NICEIC method is it keeps the old-new mapping the same for single phase and 3 phase cables (which must make jointers jobs easier and help in change of use scenarios on a jointed cable) but for domestic installations thier advice is just going to encourage far more neutral earth reversals for no gain.