SWA Cores

Discussion in 'Electricians' Talk' started by Philde, Nov 14, 2017.

  1. Philde

    Philde Member

    An easy question to answer I hope. For single phase domestic SWA circuit, say to shed, should there be a separate conductor for the earth, i.e. use 3 core cable, or is it the norm to use 2 core and use wire armour for the earth conductor? Or is it an 'it depends' situation?


    Cheers.
     
  2. Dr Bodgit

    Dr Bodgit Well-Known Member

    I used 3 core. There's an issue with using the armour as it's cross section area might not be enough especially if equiporential bonding comes into it. I'd suggest just use 3 core.
     
  3. JP.

    JP. Screwfix Select

    Aye Doc in some cases the adiabatic equation will show that the armour is not suitable to use as earth - myself would use 3 core..however saying that I think it would be pertinent to ask the following question to the op..

    What is the supply type at intake 1 (house) Phil?
     
  4. KIAB

    KIAB Well-Known Member

    When I did my C&G electrics some 35 years ago, my lecturer, a spark of many,many years, drummed into us,always use a third core for earth & never relie on the armour for a earth conductor.
     
  5. JP.

    JP. Screwfix Select

    Concur 100% Mr K..however lets hope people are not misconstrued with respect to that - aye tt for instance at shed position etc, when the use of 2c SWA would of course be necessitated in 99% of dom cases (single phase)
     
    Last edited: Nov 14, 2017
  6. Risteard

    Risteard Well-Known Member

    Few and far between. You presumably mean selection from the table will not prove suitability in some instances without resorting to adiabatic calculation, which may well prove it to be adequate.
     
  7. Risteard

    Risteard Well-Known Member

    So did he advocate the use of 5-core for a three-phase four-wire supply?
     
  8. JP.

    JP. Screwfix Select

    Aye exactly Mr R
     
  9. spinlondon

    spinlondon Well-Known Member

    I doubt in domestic installation that you will find the armour is inadequate for use as a CPC, unless it’s a very long run.
    If supplying a building with extraneous conductive-parts then a 10mm2 core is one option, the other being to TT the building.
     
  10. Philde

    Philde Member

    Supply is TN-C-S, distance would be around 4 metres.

    Phil...
     
  11. spinlondon

    spinlondon Well-Known Member

    If there’s nothing that requires bonding in the building, 2 core will be fine.
     
  12. KIAB

    KIAB Well-Known Member

    Can't remember after all these years with three phase, but with 240v he was a stickler for it,but I would always still earth the armour as well.
     
  13. JP.

    JP. Screwfix Select

    I always remember on an electrical course at my company a few years back and I asked the main geezer a question which is below.

    ''Are you allowed to export pme?''- no you cannot the lecturer said.

    Never said owt else on the subject tbqh.
     
  14. spinlondon

    spinlondon Well-Known Member

    Perhaps someone should of asked him to explain how it’s done with street furniture and lighting?
     
  15. Philde

    Philde Member

    Entirely wooden and slate construction, no metalwork (except screws and nails :) ), no other services.


    Thanks

    Phil...
     
  16. JP.

    JP. Screwfix Select

    That was some time back Spin, but I have noticed that some people say that if the intake is tn-c-s then the outbuilding you are supplying must be treated as tt (never exported pme so cant really say what way I would do it tbqh) myself maybe export the pme but also rod it down which I think is logical, thanks Sine) or just go tt full stop..or just export the pme with no faffing? I dont really know on that one. What do you do Spin?
     
  17. spinlondon

    spinlondon Well-Known Member

    Generally I export the PME.
    Long runs, I might consider TT, but not been an issue.
     
    Bazza likes this.
  18. Coloumb

    Coloumb Well-Known Member

    This is worth a read

    https://gadsolutions.biz/regulations/swa-as-the-cpc

    I believe there are certain situations involving a PME supply where it can't be done as copper must be used. I think it only applies if you need to bond for extraneous parts.

    I've used 2 core/swa myself but only of TNS supplies and would have no issues doing it again. Would have to gen-up if it was a PME.

    The ONLY factor I would concern myself with would be cost, ie 3 core swa per m is more than 2 core, but it's not likely to be a factor on a short run with a small CSA.

    Using the swa as the earth is 100% fine providing the terminations are properly glanded off and the correct size gland used. I've seen some done with a bs951 clamp which is totally unacceptable imo.
     
  19. retiredsparks

    retiredsparks Well-Known Member

    Col...just about to post that info...lol
    RS
     
  20. Dr Bodgit

    Dr Bodgit Well-Known Member

    Who's that smartypants youtuber guy, he's got a video on this.
     

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