bonding cable tray?

[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.

 

[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)

 

[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.

 

[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!

 

[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.

 

[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.

 

[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.

 

[wozz]

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

 

[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.

 

[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?

 

[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.

 

[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.

 

[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.

 

[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

 

[park1]

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

 

[adammid]

That will be good if you could canoe.

 

[Steve3948]

Last 900mm tray job I did 2 months back we bonded in 50sq mmIll post a pic if I can find it

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

 

[steptoe]

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

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 !

 

[Steve3948]

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

 

[Sidewinder]

About 90m long?