earthing the armour on SWA

[SparkyTris]

Under what circumstances would it be appropriate to NOT earth the armour on SWA cable?

a close relative of mine went to his local electrical factor's (in Scotland) with a shopping list i gave him for some SWA and brass gland kits for running power to an outdoor appliance.

The helpful chap at the wholesaler said that earthing SWA is an "out of date technique and is no longer done"

This came as a bit of a surprise. is this some new legislation?

Apparently the (detached) garage on this relative's house is fed from the CU by SWA, and the SWA on this run is not earthed (although there is an earthed conductor inside the armour)
seems strange.

The supply is PME. (just like everywhere else in the area)

 

[ban-all-sheds]

Under what circumstances would it be appropriate to NOT earth the armour on SWA cable?

When you didn't need to use SWA in the first place.

The helpful chap at the wholesaler said that earthing SWA is an "out of date technique and is no longer done"

He's a ****.

Apparently the (detached) garage on this relative's house is fed from the CU by SWA, and the SWA on this run is not earthed (although there is an earthed conductor inside the armour)
seems strange.

Sure it's not earthed via whatever it's glanded to?

It is strange. Where does the cable run, and why is it armoured?

 

[bernardgreen]

Under what circumstances would it be appropriate to NOT earth the armour on SWA cable?

NONE

The armour must be earthed in such a way that if the cable is damaged so as to expose Live conductors then at least one protective device will operate and remove the supply to the SWA

 

[ban-all-sheds]

I don't think that the armour is an exposed-conductive-part, is it?

 

[bernardgreen]

I don't think that the armour is an exposed-conductive-part

It performs the same protective function as steel conduit. Would you leave steel conduit to become Live if the cables inside were damaged ?

 

[ban-all-sheds]

I don't think that the armour is an exposed-conductive-part, is it?

 

[SparkyTris]

Where does the cable run, and why is it armoured?

the cable goes from the main CU which is at the service/cutout position in the middle of the house, into the concrete raft and out under a concrete path to a detached garage where it terminates in a standard "garage" CU.

you can just about see the garage swa in this shot, with the white cable clip, emerging from the lower RHS of the CU. no gland apparent.

He assures me that there is no gland on either end of the SWA. unfortunately now he is offshore and I am a few hundred miles away.

Untitled

• SparkyTris
• 18 Nov 2014
• 1

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[aesmith]

I don't think that the armour is an exposed-conductive-part, is it?

But you'd still earth it if you were installing, wouldn't you?

 

[ban-all-sheds]

the cable goes from the main CU which is at the service/cutout position in the middle of the house, into the concrete raft and out under a concrete path to a detached garage where it terminates in a standard "garage" CU.

So SWA is required for protection, and therefore the armour must be earthed.

 

[ban-all-sheds]

But you'd still earth it if you were installing, wouldn't you?

The question was "Under what circumstances would it be appropriate to NOT earth the armour on SWA cable?".

So with this SWA I'm installing, why am I using SWA?

 

[JohnW2]

But you'd still earth it if you were installing, wouldn't you?

The question was "Under what circumstances would it be appropriate to NOT earth the armour on SWA cable?". So with this SWA I'm installing, why am I using SWA?

Yes, if I understand your point correctly, then I agree. If one installs SWA when one doesn't actually need SWA (which might be the case, for example, with an outdoor run entirely clipped to a wall), then there is theoretically no need to earth the armour (although I imagine that most people would still earth it.

Kind Regards, John

 

[JohnW2]

The helpful chap at the wholesaler said that earthing SWA is an "out of date technique and is no longer done" ... This came as a bit of a surprise. is this some new legislation?

As has been said, as a generalisation that is nonsense. If the cable needs to be SWA (e.g. if buried underground), the the armour must be earthed. As I've just written to BAS, I agree that if one installs SWA when SWA is not needed, then there would probably be no requirement to earth the armour (although most people probably would).

I wonder if the chap was trying to say that relying on the armour as the only earth/CPC is something which some people don't approve of these days (even though it's fine regs-wise, provided the armour is adequate), instead feeling that there should always be an earth core in the cable (in addition to the armour)?

Kind Regards, John

 

[SparkyTris]

JohW2 - That is an interesting possibility which may have some validity.... of course I wasnt actually there at the wholesaler's so I don't know.

regarding SWA not being strictly necesary when clipped to walls... I installed a run of it last year in exactly this manner when in my view it was entirely necessary. The wall in question formed one side of a field of livestock field in which there are often sheep and goats. I judged that only SWA would be truly goat proof!
I daresay there is a subset of regs regarding electricity & stock with which I may not be intimate. (fnarr fnarr)

 

[bernardgreen]

I judged that only SWA would be truly goat proof!

When a radio transmitter reported itself as having a faulty aerial a site visit found the heavy duty co-axial aerial feeder cable had been munched on by farm animals. Never under-estimate the munching power of animals

 

[JohnW2]

JohW2 - That is an interesting possibility which may have some validity.... of course I wasnt actually there at the wholesaler's so I don't know.

Well, I think it's either that or else the wholesaler didn't have a clue as to what he was talking about - since it nearly always (with very few possible exceptions, as below) necessary for the armour to be earthed.

regarding SWA not being strictly necesary when clipped to walls... I installed a run of it last year in exactly this manner when in my view it was entirely necessary. The wall in question formed one side of a field of livestock field in which there are often sheep and goats. I judged that only SWA would be truly goat proof!

That's the point, and is why I said that a cable clipped to a wall "might" not have to be SWA. The regs are necessarily a bit vague, since they can't possibly consider every possibility (sheep & goats etc!) - so the regs necessarily leave it to the designer to decide what degree of protection of a cable is necessary in the situation concerned. In your case, there is clearly the need for a fair degree of protection - in a standard urban garden, maybe not!

Kind Regards, John