regarding cable tray layout

[Rajan Shakti]

can anyone help me with earthing and grounding of cable tray with separate instrument and power

 

[malcolmsanford]

You do not need to earth a cable try in most circumstances.

A cable tray only needs to be earthed if is considered to be an exposed conductive part, which normally they would not be. Because of the type of cable that you would normally fit. A cable tray should only carry cables like Steel Wired Armoured (SWA), double sheathed cable such as Hi-Tuf or heaven forbid Twin & Earth, or single core cables that are normally enclosed in a flexible conduit such as Kopex.

The second part of your question I assume you mean Band 1 cable (instrument) and band ii (power) cable. Again a tray carrying both of this type of cable would be as above. You would normally find that an instrument cable which for argument sake be a CAT cable, is rated at 600/1000 volts and therefore can run next to a power cable. If this instrument wasn't rated as high, then you would need to either separate them, ie power one side, instrument another, or if that was not possible divide them and insulate them apart.

 

[johnboy6083]

i often bond tray, as 1) its in the client spec, and 2) it will help to reduce Zs at the load end. I do this by bending a banjo on the outside of an enclosure, and linking to the tray with 6mm 6491x.

As Malc has said instrument and control cables are required to be seperated, although to be honest, if using SWA, as most systems do nowadays, then i dont see the benefit, apart from aesthetics, as the SWA acts as an effectove screen anyway, and the insulation is rated to band 2.

 

[malcolmsanford]

John would you consider it an extraneous conductive part to bond, or an exposed conductive part to earth?

 

[Rajan Shakti]

can you see my one latest post and help me for the same and comment on that

 

[malcolmsanford]

can you see my one latest post and help me for the same and comment on that

There are so many posts and threads not sure what is your latest, on what subject and where

 

[Rajan Shakti]

http://www.electriciansforums.net/i...g-protectice-instrument-earth.html#post618834

it would be great help if you go to the link

 

[Rajan Shakti]

regarding instrument and protective earthing on source and destination side

 

[Brightspark2]

How would you like your help?...

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[Rajan Shakti]

i need to know where i should terminate the earth wire which is from my instrument like damper gas detector etc which have metal body and where should i terminate earth wire of my jb and db.do i need a separate bar for both or i can use same earth bar for both.

 

[Rajan Shakti]

whether there will be continuity between instrument earth and P.E if i have two separate bar for both and whether both bars can be connected to earth boss??

 

[johnboy6083]

It depends on where it comes from Malc. If it introduces a potential into the installation, then it must be bonded as it is extraneous, but of not then it is an exposed conductive part, and doesn't have to be bonded.
The 23kOhm test can be used to confirm if it requires bonding. In an industrial situation I think it is good practice to bond all metallic containment, as further work by other trades may change metalwork from exposed conductive parts to extraneous. This isn't as likely in a domestic or small commercial situation.
Im aware of the argument that 90% of the time there will be no risk of the tray becoming live during a fault, however once installed any type of cable can be installed on the tray. I think that a bit of bonding isn't much of a job and I do it as standard

 

[Brightspark2]

It depends on where it comes from Malc. If it introduces a potential into the installation, then it must be bonded as it is extraneous, but of not then it is an exposed conductive part, and doesn't have to be bonded.
The 23kOhm test can be used to confirm if it requires bonding. In an industrial situation I think it is good practice to bond all metallic containment, as further work by other trades may change metalwork from exposed conductive parts to extraneous. This isn't as likely in a domestic or small commercial situation.

I agree most metallic containment, tray in particular in this case is now bonded with straps or bars across the joints also...


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