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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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    Just remember that in the smaller sizes of SWA the bedding is an extruded plastic that looks like and gives the impression of being supplementary insulation between the basic insulation on the conductors and the steel armour.


    But, on the larger sizes of SWA, generally 25 mm and above, the bedding is plastic string similar to the plastic garden twine I have just used to tie my tomato plants to support canes in my greenhouse, there is absolutely no way that this plastic string can be considered as supplementary insulation.


    So as far as I am concerned SWA has single insulated conductors within metal containment and that metal containment needs to be earthed, which isn’t difficult.


    On the odd occasion I only earth one end of the armour I use heat shrink or as tape to ensure the end of the armour cannot be touched from within the enclosure on the end that isn’t earthed to avoid there being two accessible earthing systems within the same enclosure.


    To sum up, I’ll stick with guidance from the authors of the IET GN, incidentally I did read the page in the GN that acknowledges some of the authors and contributors ?
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  • 0
    Just remember that in the smaller sizes of SWA the bedding is an extruded plastic that looks like and gives the impression of being supplementary insulation between the basic insulation on the conductors and the steel armour.


    But, on the larger sizes of SWA, generally 25 mm and above, the bedding is plastic string similar to the plastic garden twine I have just used to tie my tomato plants to support canes in my greenhouse, there is absolutely no way that this plastic string can be considered as supplementary insulation.


    So as far as I am concerned SWA has single insulated conductors within metal containment and that metal containment needs to be earthed, which isn’t difficult.


    On the odd occasion I only earth one end of the armour I use heat shrink or as tape to ensure the end of the armour cannot be touched from within the enclosure on the end that isn’t earthed to avoid there being two accessible earthing systems within the same enclosure.


    To sum up, I’ll stick with guidance from the authors of the IET GN, incidentally I did read the page in the GN that acknowledges some of the authors and contributors ?
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