Earthing tray

[brizospark]

Does cable tray have to be earthed / bonded in ALL cases?

 

[yellowvanman]

Nothing in the regs to say it should, but a specific question to an ECA assessor got the reply 'earthing of tray etc - recommended'

 

[telectrix]

but surely, by definition, extraneous means not a part of the wiring system. tray is a part of the wiring system as is trunking and conduit.

 

[topquark]

"Extraneous conductive part" is a conductive part liable to introduce a potential, generally Earth potential and not forming part of the electrical installation.... acording to the BRB.

Now "Electrical Installation" is an assembly of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes.

So cable tray is part of the electrical installation as I'd read it.....leaves it kind of ambiguous .... where's IQ when you need him

 

[Deleted member 26818]

My understanding, is that it is an exposed-conductive-part, and as such requires earthing.
However I can easilly see where it might also be an extraneous-conductive-part, and so will then require bonding.
Of course the real dilema is choosing the size of earthing/bonding conductor.

 

[topquark]

My understanding, is that it is an exposed-conductive-part, and as such requires earthing.
However I can easilly see where it might also be an extraneous-conductive-part, and so will then require bonding.
Of course the real dilema is choosing the size of earthing/bonding conductor.

Yep, that's the dilema

 

[topquark]

Anyone got a copy of GN8? If so any wise words from there?

 

[Big n Daft]

Quit fannying about.
Just bond it with 6mm and have done.
I suppose the debate on cable size has just opened up now...............

 

[Deleted member 26818]

Technically, the earthing conductor should be sized to withstand the maximum possible earth fault current of the circuits carried by the tray.
If bonding is required then it should be sized by either using the adiabatic equation, or tables 54.7 or 54.8.

 

[telectrix]

but you would not realistically get fault currents from all the circuits carried in the tray simultaneously. i would size the earth bond according to the anticipated fault current of the highest rated circuit.