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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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  • 0
    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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  • 0
    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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