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Topic Title: SWA
Topic Summary: Regulation to state it should be earthed ( armour )
Created On: 17 June 2013 09:35 PM
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 17 June 2013 09:35 PM
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Ampman

Posts: 1041
Joined: 06 February 2006

Been to a call out today ,

Lorry ripped a swa cable out of a joint box through the metal gland

RCD did not trip

Cable live when i arrived dangling near metal work outside ,

Looking at the outside light installation none of the swa has been earthed & glands made off into plastic ip boxes .

My question as above if the armour glands had been earthed then the rcd would of operated ?

Cheers

Ps ive earthed my swa but rest of swa not earthed im to make the client aware .
 17 June 2013 10:19 PM
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John Peckham

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Ampman

PM me your email address and I will send you all you need to know about SWA.

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 17 June 2013 10:37 PM
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dickllewellyn

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Is that offer open to other John? I'm sure you know lots of things I don't!

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Richard (Dick)

"Insert words of wisdom and/or witty pun here"
 18 June 2013 10:30 AM
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AJJewsbury

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Cable live when i arrived dangling near metal work outside ,

My question as above if the armour glands had been earthed then the rcd would of operated ?

Sounds like the load end of the cable was pulled out of the JB - in which case it would be more likely, but not guaranteed - I can see a possibility where the armour/gland connection parts company first, leaving the gland unearthed and then the live conductors are pulled through a now unearthed gland - possibly the ends coming through one at a time if the tails were different lengths, so don't even short to each other.
- Andy.
 18 June 2013 10:48 PM
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sparkiemike

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IMO in this case the armour and glands are exposed conductive parts and should be earthed.
 19 June 2013 07:51 AM
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John Peckham

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Dick


And anyone else who wants a copy of my paper on SWA cables just PM me your email address.

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John Peckham

http://www.astutetechnicalservices.co.uk/
 20 June 2013 02:02 PM
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rougediablo

Posts: 112
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John thanks again for the SWA notes.

Having read through them several times I still have a query regarding whether a banjo is required at the glands in a particular circumstance.

I have recently looked at a domestic installation where a 3 core SWA has been used to supply a 1 phase supply from a metal clad CU to a suitably IP rated insulated twin 13A external socket outlet as follows:

Metal Clad CU located in Garage.

Protective device is an RCBO.

4.0mm/3 core SWA run underground in a plastic duct from CU to external socket outlet.

1 core of the SWA is used as the cpc not the armour.

The SWA is terminated at the CU with a Bite Gland without a banjo. The measured resistance at the CU gland between the armour & the MET is 0.03 ohms.

The SWA is terminated at the socket outlet with a weatherproof brass gland but no banjo inside the enclosure.

It all looks ok to me but what's the general opinion on the absence of the banjos at insulated enclosure end?

I didn't install it, have just been asked for my opinion.
 20 June 2013 02:11 PM
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AJJewsbury

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It all looks ok to me but what's the general opinion on the absence of the banjos at insulated enclosure end?

Provided Zs is adequate (individually) at both the end of the armour and at of the earth core (which with an RCBO would be hard to fail), I don't see a problem.

If you do have a banjo in an insulated enclosure, it's recommended to clamp it between two locknuts, rather than one locknut & the plastic wall of the box - that way the connection doesn't loosen when the plastic deforms under pressure. (Or use a Piranhna nut of course).

- Andy.
 20 June 2013 02:17 PM
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sparkingchip

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Am I right in thinking at the consumer unit there is a plastic gland rather than a brass SWA gland, so the armour of the SWA passes through the gland and the bite gland is attached to the SWA armour inside the consumer unit?

Andy
 20 June 2013 02:50 PM
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rougediablo

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Originally posted by: sparkingchip

Am I right in thinking at the consumer unit there is a plastic gland rather than a brass SWA gland, so the armour of the SWA passes through the gland and the bite gland is attached to the SWA armour inside the consumer unit?



Andy


No the Bite Gland works in the same way as a conventional brass gland & traps the armour between 2 metal parts within an insulated body rather than using a shroud.

Edited: 20 June 2013 at 02:57 PM by rougediablo
 20 June 2013 02:56 PM
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rougediablo

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Originally posted by: AJJewsbury

It all looks ok to me but what's the general opinion on the absence of the banjos at insulated enclosure end?


Provided Zs is adequate (individually) at both the end of the armour and at of the earth core (which with an RCBO would be hard to fail), I don't see a problem.

Zs is fine

If you do have a banjo in an insulated enclosure, it's recommended to clamp it between two locknuts, rather than one locknut & the plastic wall of the box - that way the connection doesn't loosen when the plastic deforms under pressure. (Or use a Piranhna nut of course).

Would be the way I have always done it with an isulated enclosure tbh

- Andy.
IET » Wiring and the regulations » SWA

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