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adammid

bonding cable tray?

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adammid

This may seem like an obvious topic to many but for it always leaves me with a feeling of confusion.

Does cable tray used to support SWA require bonding? If so what conductor size should it be?

Also are there any courses available for the earthing and bonding?

Many thanks in advance.

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Technician

I think you will find that tray is an exposed conductive

part, therefore needs to be bonded.

Assessment should therefore be under reg 543.1.1.

Sizes are given in the reg along with other methods

of assessment (sizing).

I think IIRC the minimum size is 4mm (squared)

Edited by Technician

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Revved Up Sparky

The question I often ask myself when I look at metal is this; "could this metalwork realistically become live under fault conditions ?" ... if I think yes, I bond it. With cable tray I think you probably have to assess the possibility of it getting struck by something resulting in insulation damage and thus a live conductor coming into contact with the tray. If the tray is'nt earthed then it becomes live. With SWA it's less likely to ever happen as you have the protective steel armouring.... but if someone messed up and the sheath was'nt earthed..... hmm...... . I would always earth cable tray and I would probably use 6mm CSA for many installations.

Edited by Revved Up Sparky

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adammid

Cheers guys. Good bit of advice. The bit that I was stuck with was what size conductor. I thought it should be min 4mm then I started thinking that it the phase conductor came into contact with the tray then it must be capable of taking the fault current, therefore it must be min of half the size of the phase conductor. I know that this is not correct nor practical but not sure why or how to explain why.??? Help!

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hxsarge

Most people don't bother from what I've seen, I mean do people put them links on every joint too? Only ever did that at tech If you think it needs it just throw some 4mm at it.

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Technician

Assessments on the suitability of conductor

management systems are given the full treatment

in Guidance note 8.

Again IIRC the conductor sizes for tray can be

found in there.

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kelvfoozinda

I always use 6mm to bond trunking/tray and earth tag's on joins in trunking. With tray I can't see the point in bonding links as lengths are bolted together anyway.

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wozz

I'm sure it's in the snags and solutions book, saying doesn't require bonding.

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Revved Up Sparky

Any decent electrician who understands how electricity works will automatically assess the risk of electric shock when installing tray. I think any decision on whether to earth cable tray should take into account what sort of cables the tray is carrying, for example, if the tray is just carrying data or telephone cables and is not near any other metalwork then you might consider omitting an earth, however, I think any electrician who does'nt bother earthing a cable tray that is carrying 240V unarmoured cables is foolish and living on borrowed time. It could only take one nick in the insulation to make the whole tray live and kill yourself or someone else.

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wozz
Any decent electrician who understands how electricity works will automatically assess the risk of electric shock when installing tray. I think any decision on whether to earth cable tray should take into account what sort of cables the tray is carrying, for example, if the tray is just carrying data or telephone cables and is not near any other metalwork then you might consider omitting an earth, however, I think any electrician who does'nt bother earthing a cable tray that is carrying 240V unarmoured cables is foolish and living on borrowed time. It could only take one nick in the insulation to make the whole tray live and kill yourself or someone else.

Thought we was talking about armoured here?

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adammid

Thanks for the post revved up but we are talking about armoured cable, but still there is a possibility if the armouring hadn't been correctly earthed and the cable has been nicked then it may become live like you say.

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Steve3948
Any decent electrician who understands how electricity works will automatically assess the risk of electric shock when installing tray. I think any decision on whether to earth cable tray should take into account what sort of cables the tray is carrying, for example, if the tray is just carrying data or telephone cables and is not near any other metalwork then you might consider omitting an earth, however, I think any electrician who does'nt bother earthing a cable tray that is carrying 240V unarmoured cables is foolish and living on borrowed time. It could only take one nick in the insulation to make the whole tray live and kill yourself or someone else.

OP does state SWA, so if you nick sheath you have steel wire armour on show, don't see that as a problem.

The key is " Is it likely to become Live" the installer needs to judge this for himself, it may already be bolted to the structure of the building which is already bonded at various locations, we always used to take earths off the MCC panel to each tray or ladder run.

Edited by Steve3948

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adammid

The tray that I had in mind when writing the OP was a piece approx 600mm long, bolted onto uni strut on the concrete floor, supporting one SWA. Not much chance of it becoming live but was still wondering.

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Revved Up Sparky
Thought we was talking about armoured here?

Sorry, my mistake. I'll let you hit me with the wet fish.

Wet Fish

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park1

Depends upon the cable types, but normally there is no requirement.

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Canoeboy

Last 900mm tray job I did 2 months back we bonded in 50sq mm

Ill post a pic if I can find it

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adammid

That will be good if you could canoe.

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Steve3948
Last 900mm tray job I did 2 months back we bonded in 50sq mm

Ill post a pic if I can find it

But he said it was only 600mm Looooooong, are you saying yours was only 900mm long :o

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steptoe
But he said it was only 600mm Looooooong, are you saying yours was only 900mm long :o

that reminds me of Paddy's 1st day as a pilot, coming in to land he says to Mick

be-jaysus, thats a short runway,!

Mick replies, Aye, but wid ye luk at the width o it !

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Steve3948
that reminds me of Paddy's 1st day as a pilot, coming in to land he says to Mick

be-jaysus, thats a short runway,!

Mick replies, Aye, but wid ye luk at the width o it !

Well maybe they don't know their width from their length, although I think Amlec's tray was a short length on the floor and a massive 600mm long, with 1 SWA on it :D

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Canoeboy
Well maybe they don't know their width from their length, although I think Amlec's tray was a short length on the floor and a massive 600mm long, with 1 SWA on it :D

Mine was 900mm wide heavy duty rolled deep edge, 3 meters long lengths

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Sidewinder

About 90m long?

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Steve3948
Mine was 900mm wide heavy duty rolled deep edge, 3 meters long lengths

I know, but Amlec's is only 600mm long he does not say how wide it is, :innocent

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Canoeboy

Well mines bigger and wider Guinness:worship

And longer - which according to Hercules (from Steps) is always better :slap

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steptoe
Well mines bigger and wider Guinness:worship

And longer - which according to Hercules (from Steps) is always better :slap

what have you been doing to my poor horse? :o

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