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Discuss Bonding tray in 18th edition in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

edexlab

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I've not yet got a copy or read the 18th ed
But I heard the other day from a young Engineer at work who's doing the course ( his first time doing regs exam) that in the 18th it's compulsory to bond all joins in tray etc

Can anyone elaborate on this?
 

Ian1981

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I've not yet got a copy or read the 18th ed
But I heard the other day from a young Engineer at work who's doing the course ( his first time doing regs exam) that in the 18th it's compulsory to bond all joins in tray etc

Can anyone elaborate on this?
The requirement to earth or bond tray is the same as it’s always been
 

edexlab

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  • #3
Yes I thought it might be ...

When he mentioned it I asked him what had changed in regard to this , he just said it was a new requirement and in future we'd probably have to do it.

To be fair he's never used BS7671 so I did think that maybe he's mistaken.

In the job I do, we run tray fixed to steel box section frames (powdercoated) and generally it's the customers responsibility to ensure bonding is suitable to that particular countries regs


ie in China and India they do nothing, but other countries have varying amounts of bonding to frame and tray

One company insists we link every single join in tray and bond repeated intervals to all steelwork so in view of this it's always agreed in the contracts that all power supplies and bonding are carried out by a local contractor
 
D

Deleted member 26818

Is the tray extraneous or an exposed conductive-part?
 

LeeH

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Esteemed
 
Usually there is no need to either earth or bond traywork. If the cabling is insulated and sheathed, Class 2 equivalent construction, the traywork won't be an exposed conductive part so no earthing required. Traywork doesn't usually introduce an earth potential that isn't already present, so no bonding required.

That being said, inspectors love to snag traywork which isn't earthed or bonded.
 

edexlab

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  • #8
Heard that argument a couple of times!

One firm I worked with had us go round checking all the tray on a big job with a long lead and test to show the Clerk that the tray continuity was ok , potential to earth was no worse than sll the metal work around the place etc and that bonding at couple of points was sufficient

Still ended up having his way and bonding every thing even after a Chartered Engineer agreed that it wasn't needed
 
T

Toneyz

It makes me wonder what the world these clerks of works and electrical consultants live in the other day I was doing some testing with a contracts manager and the consultant asked if the classroom sink needed bonding they still have in some of these specs about bonding window frames and suspended ceilings.
 
I've not yet got a copy or read the 18th ed
But I heard the other day from a young Engineer at work who's doing the course ( his first time doing regs exam) that in the 18th it's compulsory to bond all joins in tray etc

Can anyone elaborate on this?
Yes true ,it has to be continuous any cut in the tray will hinder that hence you put another link to make it continuous.
 
D

Deleted member 26818

Can anyone quote the Reg. No. that requires tray to be bonded?
Would probably help if we knew whether the tray is extraneous or an exposed conductive-part.
 

edexlab

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  • #12
Cables are insulated and sheathed so not an exposed part

Any earth potential is the same as the metal framework and walls that the tray is attached to

So I would say it's neither exposed or extraneous
 

edexlab

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  • #14
In this case the whole structure is one big faraday cage
Even where tray joins are bolted together I think there's enough surface area clamped together or fixed to brackets which are fixed via tapped holes all along the length of runs to make the continuity consistent .
 
Why does it have to be continuous? It's generally just another bit of steelwork, neither extraneous nor exposed conductive part.
I would say it is extraneous.
 

edexlab

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  • #16
I'm going to suggest we test it properly to determine as it's not really black and white whether it does need doing or not
Its all down to how different people decipher the reg
In my post before I said it was neither but it can be argued either way
 

Ian1981

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Well does it introduce a potential to the location it serves?
Is it in good contact to an outside earth at true earth potential?
I doubt it’s going to be extraneous but then I’m not on site.

Is it an exposed conductive part ie does it form part of the electrical installation or is it mearly a support system for the cables ?
 
Well does it introduce a potential to the location it serves?
Is it in good contact to an outside earth at true earth potential?
I doubt it’s going to be extraneous but then I’m not on site.

Is it an exposed conductive part ie does it form part of the electrical installation or is it mearly a support system for the cables ?
It is a safety precation,it might introduce potential depending on wher and how it is istalled.
I thought by bonding it you are establishing contact with the outside earth
 

Ian1981

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It is a safety precation,it might introduce potential depending on wher and how it is istalled.
I thought by bonding it you are establishing contact with the outside earth
Bonding randomly can create its own hazards
Often when installed the tray supports are fixed to say the metallic structure of the building so are connected to earth that way if the structural frame is bonded by being an extraneous conductive part
 
T

Toneyz

Yes true ,it has to be continuous any cut in the tray will hinder that hence you put another link to make it continuous.
Cable tray couplers.
 
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