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SWA Cable Above ground and earthing the armour

sparkiemike
When using SWA cable underground I always earth the armour, regardless of whether the armour is used as the cpc or not. The armour does provide some mechanical protection and it is important that the armour is earthed so that if the cable were penetrated (e.g. by a garden fork), the supply would automatically be disconnected by the protective device under this fault condition.
I have a situation on an existing domestic installation where I will be changing the consumer unit.  The 3-core SWA cable to the hot-tub rotary isolator is above ground and clipped to an outside wall.
The cable has not been terminated with brass glands, and at the ends the armour have been taped up, so no exposed conductive parts. The armour is not being used as the cpc.
At the rotary isolator for the hot-tub, stuffing glands have been used. The cable feeding the hot-tub does rest on the ground for about 1m before going into the hot-tub enclosure.
The earthing arrangement is TNCS, however at the hot-tub rotary isolator, the TNCS earth is not exported and there is an earth electrode for  the hot-tub’s cpc
Would you expect the armour to be earthed? Is it acceptable to terminate SWA without brass glands?
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    Apart from the so-called mechanical protection of SWA, isn't the reason for its use usually so that an RCD is not necessary at the source end?


    So, if the cable itself does not require an RCD for the installation method, then the armour is not actually necessary. Therefore I suppose it does not need to be earthed - but why would anyone not earth it at source?


    I do realise that there is likely to be an RCD at source anyway because of the circuit use.
  • 0
    I agree Geoff, and normally I would earth it at source with appropriate gland. But seeing this relatively  new installation made me ask the question. I think it is pretty rough, but can’t come up with any regulations it does not comply with.


    That said, this document from Prysmian https://www.whyprysmian.co.uk/BS5467.pdf makes the following statement on page 2;  “Armour bonded and earthed at both ends -  Yes”. That looks like a manufacturer’s instruction/recommendation to me.

  • 0
    IMO Its standard practice to install the cable correctly, leaving both swa ends 'blowing in the wind' is as you would imagine wrough work and might invalide any liabilty if someone was careless causing a fault. It should be earthed at one end. if not being used as a cpc and mechanically made secure at the other end


    Legh.
  • 0
    My view is that the one metre length of S.W.A running on the ground would persuade me to correctly gland the S.W.A. cable at the supply end with a correctly fitted gland and I would earth the gland at the supply end. This will protect the cable live conductors and ensure correct disconnection in case of cable damage. As the armouring is protecting the live conductors it must be earthed. 131.2.2., 134.1.1., The use of R.C.D.s is not recognised as a sole means of protection and does not obviate the need to apply one of the protective measures specified in Sections 411 to 414. (415.1.2)


    Z.
  • 0
    I assume that there is insufficient armour to be able to attach it to a brass gland at the new CU. It is appropriate to terminate the armouring in a stuffing gland at the downstream end, but I cannot find a regulation which requires a surface-mounted SWA cable to be earthed at the upstream end.


    The only caveat is that if the outer sheath were damaged, the armour would become an exposed conductive part.
  • 0
    Also, if the cable armour is unearthed and the cable damaged on the ground the armour could become live and the R.C.D. would not trip off. Somebody barefoot could come into contact with the faulty part of the cable and form a circuit to earth and thus receive a shock. R.C.D.s are not guaranteed to provide 100 per cent prevention of death, especially if faulty or slow in operation. Hopefully if the armour is earthed the R.C.D. will trip off automatically in case of mechanical damage of the cable, or the M.C.B. will trip off BEFORE a shock risk is present.


    Z.
  • 0

    Chris Pearson:

    I assume that there is insufficient armour to be able to attach it to a brass gland at the new CU. It is appropriate to terminate the armouring in a stuffing gland at the downstream end, but I cannot find a regulation which requires a surface-mounted SWA cable to be earthed at the upstream end.


    The only caveat is that if the outer sheath were damaged, the armour would become an exposed conductive part.




    We are back to the discussion about the fact that SWA has single insulated conductors surrounded by a plastic filler or plastic yarn with wire wrapped around them covered with a plastic sheath.


    Single insulated conductors inside metal containment, so the metal containment needs earthing just as metal trunking or conduit containing single insulated singles does.


    Andy 

  • 0

    Sparkingchip:




    Chris Pearson:

    I assume that there is insufficient armour to be able to attach it to a brass gland at the new CU. It is appropriate to terminate the armouring in a stuffing gland at the downstream end, but I cannot find a regulation which requires a surface-mounted SWA cable to be earthed at the upstream end.


    The only caveat is that if the outer sheath were damaged, the armour would become an exposed conductive part.




    We are back to the discussion about the fact that SWA has single insulated conductors surrounded by a plastic filler or plastic yarn with wire wrapped around them covered with a plastic sheath.


    Single insulated conductors inside metal containment, so the metal containment needs earthing just as metal trunking or conduit containing single insulated singles does.



    So what's the regulation, Andy?


    I don't think that the armour of SWA can be considered to be exposed unless the cable has been damaged.

  • 0

    Chris Pearson:




    Sparkingchip:




    Chris Pearson:

    I assume that there is insufficient armour to be able to attach it to a brass gland at the new CU. It is appropriate to terminate the armouring in a stuffing gland at the downstream end, but I cannot find a regulation which requires a surface-mounted SWA cable to be earthed at the upstream end.


    The only caveat is that if the outer sheath were damaged, the armour would become an exposed conductive part.




    We are back to the discussion about the fact that SWA has single insulated conductors surrounded by a plastic filler or plastic yarn with wire wrapped around them covered with a plastic sheath.


    Single insulated conductors inside metal containment, so the metal containment needs earthing just as metal trunking or conduit containing single insulated singles does.



    So what's the regulation, Andy?


    I don't think that the armour of SWA can be considered to be exposed unless the cable has been damaged.


    So Chris, why use the S.W.A. at all? Would you just run twin and earth down to the load, even for the 1 metre section on the ground?


    Z.




     

  • 0

    Zoomup:




    Chris Pearson:




    Sparkingchip:




    Chris Pearson:

    I assume that there is insufficient armour to be able to attach it to a brass gland at the new CU. It is appropriate to terminate the armouring in a stuffing gland at the downstream end, but I cannot find a regulation which requires a surface-mounted SWA cable to be earthed at the upstream end.


    The only caveat is that if the outer sheath were damaged, the armour would become an exposed conductive part.




    We are back to the discussion about the fact that SWA has single insulated conductors surrounded by a plastic filler or plastic yarn with wire wrapped around them covered with a plastic sheath.


    Single insulated conductors inside metal containment, so the metal containment needs earthing just as metal trunking or conduit containing single insulated singles does.



    So what's the regulation, Andy?


    I don't think that the armour of SWA can be considered to be exposed unless the cable has been damaged.


    So Chris, why use the S.W.A. at all? Would you just run twin and earth down to the load, even for the 1 metre section on the ground?


    Z.





    Zoomy, who said that the cable is on the ground?


    What's the alternative - a bit of T&E. There's a bit of T&E at daughter's house which is dry and crazed. She got a bit upset when I started digging with my thumbnail. ? The plan is to replace it with some T&E, but perhaps I am being misguided - is SWA better, or worse, or the same, when it comes to exposure to sunlight (on a south-facing wall)?

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