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bonding of steel trunking


andyman 72

Question

hi guys, just a quick question about bonding if you dont mind. if steel trunking is part of the installation then it should be bonded at every section ( is this correct?)

if the trunking is part of the installation should it have a reading of no greater than 0.05 ohms at any point of the installation to the met ?

thankyou for any advice you can give on this matter :Yheadbang

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10 answers to this question

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hi guys thanks for all your replys. i have got the books back out and i thought i would let you know the findings. here goes

gn3 page 30

conduit rigid metal

2 connected to the main earth terminal (411.4.2)

gn3 page 31

metal trunking

3 earthed (411.4.2)

4 joints mechanicaly sound and of adequate continuity (543.2.4)

hope this will help anyone with the same sort of question

thanks again Guiness Drink

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would taking an earth tag off a socket or swa gland not be substantial as it is connected to the main earth via the circuit.

why i ask is, say you wire a few commando sockets in singles with and swa feed, that are sat ontop of a metal trunking. The trunking would be earthed using the swa? Therefore no need for its own bonding?

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your swa would be connected to the met so therefore you have connected your trunking to the met. with it been part of the installation at any point it should have a maximum reading of 0.05 ohms when tested back to the met.

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Andy when you ask if the trunking should be bonded at every section .do you mean its Earth continuity should be reinforced by earth straps at every section cos bonding is a different thing than earthing.

I think it will be classed as an exposed conductive part rather than an extraneous conductive part if ,as im sure,it is connected to the MET. ?:|

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thanks for your reply a1

yes its for the earth continuity. i would agree that it is a exposed conductive part with it been part of the installation. would you agree to attach it to the met? it is running both single phase and three phase( not high ampage) but both are insulated to 1000v.

as i asked before will it need to be less than 0.05 ohms to comply to the regs?

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That 0.05 ohms figure would indeed prove that the trunking was effectively connected to the MET. If it is to be used as cpc for any of the circuits it would have to satisfy the relevant cpc csa criteria for the largest of the circuit conductors.

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Hi, Andyman, steel trunking should be earthed anyway. Is it not bolted to a dist. bd. or is it isolated , in which case it needs an earth cable connecting it to the earth bar.

Deke

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does the earth have to come from the met? or can it come from the cu or a local earthed point.

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thanks guys. i have moved from domestic to industrial and am trying to find my feet. this is just an observation i have seen and it doesnt seem right so i am questioning it.

it is not connected to the earth bar, nor have they fitted any kind of earth straps for continuity. the cables inside are run in 4mm singles and the trunking is not used as any cpc. they have used metal clad spurs from this( with no flying earth as i know they should ). as i say i am new to this field but when things like this are, to me, wrong i thought i would check with you guys to see if there were any reason why this wasnt done or if it is just me being over keen?

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the trunking will need to be bonded to earth possibly at its sorce ,earth links at all joints ?personally i can,t see the point in this if the screws are tight .Unless you want to go back to Power Centre trunking which was painted then you needed earth links for continuity

yours benji

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