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surface-mounted SWA – earthing

Former Community Member
Former Community Member
Just trying to find a regulation that states a reason why the armoured metal of surface-mounted SWA needs earthing. Obviously, when buried underground, it does - 522.8.10.  I have read previous posts on this, but the question seems to have remained unanswered.

It would be considered best practice to at least earth the supply end, but best practice is not regulation. And, considering the statement at the end of Chapter 12, could it not be argued that short runs of surface-mounted armoured without earthing are ‘safe’? Where is the risk?

The armour does not meet the definition of an exposed conductive part when neatly terminated so it can not be touched – under what fault conditions could it become live?

SWA conductors are not double insulated, but is the risk any less than conductors in a plastic conduit?

Manufacturer instructions… it could be that they stipulate that the armour needs to be earthed, but where these are not available for review, how can a non-conformity be raised?

I’d appreciate any replies that point to a specific regulation or group of regulations.

Thanks in advance.

  • 0
    There was a long thread in the last week concerning exactly this, and whether the armour should be considered an exposed-c-p.


    But consider something sharp and metallic, like a nail, piercing the armour and making contact with a live conductor. This is easy to do, as the armour doesn't protect (much) against pointy things - its better against flat things like spades. Now all the armour is live, plus the brass BX glands at each end (assuming they're used) and nothing has tripped.
  • 0
    I think that the consensus was that the gland boots do not adequately conceal the glands, which accordingly, remain ECPs.
  • Former Community Member
    0 Former Community Member

    Thanks for the response, Much appreciated.

    The case I have described, the steel wire does not meet the definition of an exposed conductive part – as described in Part 2 -  No part of the steel can be touched.

    The scenario you mention is extremely unlikely; who would take a hammer and nail to a surface-mounted cable? The armour is pretty robust and would take a healthy battering in most situations. This could apply to any surface-mounted cable – a nail penetrates a live conductor without coming in contact with the cpc, and the nail remains live without tripping.

    I'm not advocating that the steel should not be earthed. I'm just after the regulation that says it must? Opinion is great for guidance (sometimes), but if I raise a non-conformity against somebody's work, I need to back it up with a regulation or standard.

  • 0
    You don't have to actively put a nail in it - you could be tie-wrapping an SWA to a tray that has a burr sticking up, or cleating to a wooden post that happens to to have the tip of a nail pointing out, etc. And because it's an SWA, its not just the nail that becomes live, its the entire length of armour - and especially its two ends - which are now live. Are the ends of the armour completely sealed off in a way such that even a skilled person opening an enclosure couldn't make contact with them? (Because who treats a bit of exposed armour as dangerous?).


    But please read the whole of the previous thread - in short, its not obvious whether the armour counts as an exp-c-p
  • Former Community Member
    0 Former Community Member
    Ok, Thanks again. 

    The scenario is SWA clipped along a wall. No metallic parts.

  • 0
    Why install the cable without earthing the metal containment?
  • 0
    stuff:


    The armour does not meet the definition of an exposed conductive part when neatly terminated so it can not be touched – under what fault conditions could it become live?



     




    Single fault, a failure of basic insulation.


  • 0
    Surely as a conductive part in very close proximity to live conductors  its better to earth it just in case  then even if its only capacitive coupled to the live core its totally safe. In my view unless the regs share I definatley SHOULDNT earth it then it will be earthed
  • 0
    If there are metal glands at the ends, and the singly insulated cores pass through them are not sleeved, then the glands must be earthed. It is quite hard to earth the glands and not the armour. Of course there do not have to be glands at all if the end is just splayed out into free cores.

    However if this is an inspection failure and you are looking for the right code, one has to ask why the armoured cable was used at all. There is then the question of if the cable still is suitable for its environment if the armour is not earthed.

    That previous thread.



    Mike.
  • Former Community Member
    0 Former Community Member
    Hi, Thanks for the above replies. It really is appreciated.

    I think all of the above could be argued against – which is what I am trying to avoid. I need a clear-cut regulation which, when I raise a non-conformity against, will put the responsibility on the installer to prove compliance rather than the other way around. I think I found my answer –

    Regulation 134.1.1 – “…The installation of electrical equipment shall take account of manufacturers instructions. “

    I don’t think any SWA manufacturer would approve a termination method that would preclude the earthing of the steel.

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