Cable Tray cross bonding?

[Crosswire]

I am running a load of cable tray at the minute. I said it required cross bonding with 4mm cable, but my boss said it wasn't required as we are using metal joiners...........


Who is right?

 

[Deleted member 9648]

'Cross bonding' ????........you may need to link joints in the tray with a copper link to ensure earth continuity if the joints are not electrically continuous ,but 'cross bonding' ?..is this the same as the ancient-mythical practice of wasting ones time linking boiler pipes together etc.?

 

[Crosswire]

'Cross bonding' ????........you may need to link joints in the tray with a copper link to ensure earth continuity if the joints are not electrically continuous ,but 'cross bonding' ?..is this the same as the ancient-mythical practice of wasting ones time linking boiler pipes together etc.?

Errr......not sure.

What I mean is to link from one length of tray to the next length of tray with a bit of 4mm green and yellow single core cable with a crimped lug at each end, bolted to both lengths of tray with a 4mm pan head brass bolt, and secured to the tray with a 4mm nut, with the bolt passing through the hole of the lug.

I am considering this in the event that the metal cable tray joiner is not sufficient to maintain electrical continuity between the two abutting lengths of tray.

My question is, is the steel cable tray joiner sufficient to maintain electrical continuity, or will I need to use another method E.G. the copper link you suggest, or the method described above?

Cheers!

 

[bonnie lad]

i have put miles of tray in on jobs, only ever used tray joints for continuity, bond final ends of tray onto DB,s or panels with 4/6mm earth bond with lugs. no need to cross bond to other services.

 

[Crosswire]

i have put miles of tray in on jobs, only ever used tray joints for continuity, bond final ends of tray onto DB,s or panels with 4/6mm earth bond with lugs. no need to cross bond to other services.

No, not to other services, just from one tray to another............

Although they will be connected to other services at the MET, of course...



Anyhow, thanks for the reply, will stick to tray joints unless I hear otherwise

 

[ian.settle1]

Can also depend upon what is specified by the client.

Place where I work for a FM company the client specify's that every joint on trunking and tray has a earth link across every joint, they also all specify that where different runs of tray cross or are next to each other they are also bonded together as well as bonded to the Distribution Board and the earth tape that runs around the building.

 

[lamb]

Cable tray (or other steel containment) containing only sheathed cables, even if bare MICC, is not an exposed conductive part of an electrical installation. Therefore it is not required to be connected to the MET by a cpc.
If it is earthed this would be down to the job spec or working practices.

However, if likely to introduce earth potential from one building or installation to another, main equipotential bonding would be required at point of entry.

This is a specific topic covered in IEE Guidance Note 8 : Earthing and Bonding.

 

[Sparky Ninja]

Can also depend on the location. I had installed tray on a rooftop and it was necessary to bond to the existing lightning protection, as it was at a different potential, even though it was bonded at the origin.

 

[Crosswire]

Cable tray (or other steel containment) containing only sheathed cables, even if bare MICC, is not an exposed conductive part of an electrical installation. Therefore it is not required to be connected to the MET by a cpc.
If it is earthed this would be down to the job spec or working practices.

However, if likely to introduce earth potential from one building or installation to another, main equipotential bonding would be required at point of entry.

This is a specific topic covered in IEE Guidance Note 8 : Earthing and Bonding.

Well definitely gonna earth it because , although not an exposed conductive part, I certainly consider it an extraneous conductive part.

I know it doesn't fall under the bonding requirements of 411.3.1.2, but this and the ceiling grid will be earthed, in the event that they may become live under fault conditions.

Not got guidance notes 8 (got 1 and 3), so can't look it up

 

[caddy]

Well definitely gonna earth it because , although not an exposed conductive part, I certainly consider it an extraneous conductive part.

I know it doesn't fall under the bonding requirements of 411.3.1.2, but this and the ceiling grid will be earthed, in the event that they may become live under fault conditions.

Not got guidance notes 8 (got 1 and 3), so can't look it up

Unless the cable tray comes out of the ground how could you define it as an Extraneous conductive part if it cant introduce an earth potential. Of course if the cable tray can introduce an earth potential then it would need to be bonded accordingly. there is also no requirement to earth a ceiling grid, since ceiling grids are push fit you would have to link every length of grid together to ensure contiuity, just as you suggest doing with the cable tray.

Sometimes bonding everything metal you can get your hands on can lead to an increased risk of a shock.

 

[mogga]

just another bit to the Argument who is going to pay for this cross bonding If your boss has said NOT to do it and you go and do it will he pay both your time and material for doing it??

 

[Crosswire]

Unless the cable tray comes out of the ground how could you define it as an Extraneous conductive part if it cant introduce an earth potential. Of course if the cable tray can introduce an earth potential then it would need to be bonded accordingly. there is also no requirement to earth a ceiling grid, since ceiling grids are push fit you would have to link every length of grid together to ensure contiuity, just as you suggest doing with the cable tray.

Sometimes bonding everything metal you can get your hands on can lead to an increased risk of a shock.

Ok you are right, it is not an extraeneous conductive part, but surely it IS an exposed conductive part:

"Conductive part of equipment which can be touched and which is not normally live but which can become live when basic insulation fails"

Also I remember once on a job another sparks had stripped out lights simply by cutting the flex off at the light and leaving it dangling still plugged into the klik rose. When the circuit was turned back on one of the flexes was touching the ceiling grid which resulted in the whole ceiling grid becoming live!

We found this out when owner of the building touched the grid.

Had the ceiling grid been earthed this would not have happened. If it managed to become live via the push fit connections , then there is continuity, and by the same logic it can become earthed without copper links.

Every bone in my body is telling me to earth it - I can't see how this could be wrong

 

[Crosswire]

just another bit to the Argument who is going to pay for this cross bonding If your boss has said NOT to do it and you go and do it will he pay both your time and material for doing it??

He has said not to make the links, but to earth the tray at the end. If I can make a convincing argument he will change his mind.

Also I can just tell the apprentice to do it when he is not there

 

[chris gray]

why would you consider bonding every link? thats going to take you for ever and for what? youll gain continuity by your roofers/links or what ever means of connection you make between the tray.
each to their own but a supplementary bond at the start would suffice.

 

[Crosswire]

why would you consider bonding every link? thats going to take you for ever and for what? youll gain continuity by your roofers/links or what ever means of connection you make between the tray.
each to their own but a supplementary bond at the start would suffice.

Ok fair 'nuff. That was what my boss said. Just that I've seen lengths of tray linked with supplementary bonding in the past, and copper links do exist. Just wondered if they were required.