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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.

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    stuff:
    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.

     


    It may also depend upon what Voltage is present within the S.W.A. cable.


    Z.


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    I am not typing it all out. 

    b9893d8b7cc91d518de8106284b102a5-original-20210530_200900.jpg
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    125 The regulation applies to any conductor (other than circuit conductors), including the conductive parts of equipment, such as outer metallic casings, which can be touched and, though not live, may become live under fault conditions.


    EAWR
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    Back to the OP ...


    If the armour is serving as the CPC, which is normal, it is self-evident that it must be continuous with the earthing arrangements at both ends.


    If the cable is surface mounted, AND a core is being used as the CPC, AND the cable is neatly terminated into enclosures with insulating glands, then I agree that there are no ECPs, so the armour does not have to be earthed.


    If the cable is terminated into normal SWA glands, then they are ECPs. End of story!
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    Chris Pearson:

    If the cable is surface mounted, AND a core is being used as the CPC, AND the cable is neatly terminated into enclosures with insulating glands, then I agree that there are no ECPs, so the armour does not have to be earthed.

     


    So you completely disagree with the extract from the IET Guidance Note 8 which I posted?


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    I think they both say the same thing.  Unless this cable is installed very oddly, the armour is an ECP and should be earthed.


    If they really do not want to they would have to  totally insulate it ,but that would be silly.

    Show them that quote....

    Mike.
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    So you completely disagree with the extract from the IET Guidance Note 8 which I posted?

    It all depends on the assumptions the authors of the GN had in mind. In perhaps 99% of situations SWA is selected because something with lesser performance (e.g. T&E) wouldn't have been suitable for the conditions - thus some demand is being placed on the armour and therefore it needs to be earthed. If you want to write one statement that covers 100% of situations from a design point of view, then always earth it seems a logical approach.


    In the perhaps 1% of situations where SWA has been installed where T&E would have been perfectly adquate, I agree it's still not clear cut. For me it boils down to whether the insulation, armour and sheath of an SWA cable meet the demands of 412.2.4.1(ii)(a) - or whether the presence of the armour detracts from the protection offered by the plastic sheath. It's not clear to me that it doesn't.


      - Andy.
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    Presumably SWA has been chosen because the protection afforded by the armour is required, but then the armour only provides limited protection because of inadequate installation methods.


    It seems fair to say either install the SWA correctly and earth it or use something else.
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    Sparkingchip:
    Chris Pearson:

    If the cable is surface mounted, AND a core is being used as the CPC, AND the cable is neatly terminated into enclosures with insulating glands, then I agree that there are no ECPs, so the armour does not have to be earthed.

     


    So you completely disagree with the extract from the IET Guidance Note 8 which I posted?




    Yes, because exposed-conductive-part = conductive part of equipment which can be touched ... .


    I cannot think of any circumstances when you would specify SWA, but not use it as intended, but that wasn't the issue in the OP.


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    In principle you could mis-use SWA and put it in plastic conduit or something and terminate the ends in plastic boxes- it might be perfectly safe but is a senseless waste of cable. GN8 is very sensibly not considering that case, and I do not think that is what is happening here either.


    To the OP, you could do worse than to print out that scan of guidance note 8 and wave it at the person trying to kid you it is OK...


    Mike.

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