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surface-mounted SWA – earthing

Former Community Member over 3 years ago

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 Sparkingchip over 3 years ago

Is the armour an unused conductor?

https://d2z8ufzpcqvblm.cloudfront.net/sites/www.voltimum.co.uk/files/fields/attachment_file/gb/others/Z/2007061145227060883572007060863222007060882044162bk1snag22_0.pdf
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0 Former Community Member over 3 years ago

I think the conversation has drifted a little from my OP. We are all in agreement that the steel wire should be earthed.

I don’t know why the installer chose to use SWA, but the SWA installation did not have any exposed conductive parts. The SWA was terminated at both ends using non-metallic boxes and glands, the steel was not brought into the box, the steel was not used as a cpc – a scenario not covered in Guidance Note 8. So if your reason for earthing the Steel is ECP, then that wouldn’t stand up in this situation.

The installation was neat and tidy, and on the whole, the electrician looked as if he knew what he was doing. Now, if that electrician was Ajjewsbury or Chris Pearson, and I told them they had not complied with BS7671 they would come straight back at me with – “prove it!”…. So how do I prove it? My ‘opinion’ is irrelevant; Guidance is helpful but not enough. I would need to offer up a Regulation to demonstrate non-compliance or produce a regulation that reverses the situation where the installer has to demonstrate compliance.

In my view, although technically compliant with BS7671 from a safety perspective, the installation method is not compliant with cable manufacturer instructions – Hence my choice of Regulation 134.1.1 – “…The installation of electrical equipment shall take account of manufacturers instructions. “. If I raise this as a non-conformity, it will put the onus of the installer to demonstrate how their installation is compliant.
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0 AJJewsbury over 3 years ago

But do the cable manufacturer's instructions say anything about Earthing the armour? I don't recall ever seeing such a thing. I've seen things like 'Should not be installed at temperatures below 0OC or above +60°C' or 'should be installed according to national wiring rules'.

I'd suspect the manufacturers would want to avoid such detailed instructions such as the need to Earth things - partly to avoid any liability (better to pass the buck onto JPEL/64) and partly not to want to unnecessarily rule their products out from the more unusual situations (e.g. separated systems, d.c. PV or SELV).

- Andy.
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0 Chris Pearson over 3 years ago

Thank you for the further clarification.

If I came upon this installation as described, I would struggle to go worse than C3 and might not code at all. If the cable had been made off into normal conducting glands then C2 would be justified on the basis that a single fault (e.g. something pierces the cable) would present a danger not only at the point of damage, but also at the ends of the cable. 411.3.1.1

If you are going to invoke manufacturer's instructions, then I think you need to identify them. If they exist for SWA, do they also exist for T&E or singles. I suspect not.

As for compliance, presumably there is an EIC where the installer has certified it.
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0 Former Community Member over 3 years ago

stuff:

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

Hi stuff, what kind of wall is it? Domestic, commercial or industrial?

And what is your involvement? Are you doing an EICR? Is the work in question certificated?
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0 lyledunn over 3 years ago

Prove it is right! Apart from the buried scenario, the argument hinges on whether it is an ECP. I was asked to comment on an EVSE installation last week. Very neat job with 3no 7Kw 3-phase twin outlet units supplied from a new TPN board. The wire armour of the SWAs was not earthed either end. All in 100mmx100mm plastic trunking apart from a short length underground in 110mm Wavin. Wire armour cut back and insulated in the EVSE pillars and in the trunking all with what looked like heat shrink insulation and tape.

At least there is no chance of exporting the PME!
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0 Former Community Member over 3 years ago

Replying to previous posts - This is the point of my OP.

I’ve googled SWA data sheets but not found anything to say the steel ‘must be earthed’, but equally, I’ve not found any literature – anywhere - supporting no earth…

Where SWA is a requirement, you would expect the steel to be earthed, but in this scenario, the steel is surplus to requirements hence the installer's method of termination. Would a manufacturer support this method? I doubt it.

To be honest, I don’t have an issue with it, but I have been tasked with approving the installation after another electrician has already condemned the lack of earth – so the issue needs to be resolved. I feel, on this occasion, that it would not be unreasonable for me to ask the installer to prove compliance rather than me disprove.

I’ll probably word the nc something along the lines of “ It is unlikely that the SWA cable manufacturer would support an installation where the steel armour is not earthed…”

Btw – domestic – through cavity wall to outside.
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0 Chris Pearson over 3 years ago

I think that the presumption here must be that if the installer has certified the work as being compliant, it complies.

I would only accept the second electrician's opinion (it is no more than that) if he can demonstrate exactly how the work does not comply.

Time to move on!
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0 SRI LANKA over 3 years ago

when SWA cable install on the surface in-wall or tray it may be safe and can be visibly anybody but unsafety area as factory /or Roadway area can be damage rather by knocking vehicle or machinery by accidently at the time live cable and armor guard can be connected together, cause of that can shock to people or damage to equipment if armor guard earthed at the sort circuit happening time power can be automatically cut off so that purpose always armor guard should have earthed

Therefore I proposed armored guard must earth separately without connecting cable by metal gland and only use PVC gland to connect a cable to panel board for only neatness purpose
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0 Former Community Member over 3 years ago

Chris Pearson:

I think that the presumption here must be that if the installer has certified the work as being compliant, it complies.

If only that were true ?
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surface-mounted SWA – earthing

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