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Discuss spare fuseboard in the Electrical Forum area at ElectriciansForums.net

pc1966

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I was taught never to earth a board from another board and to split the earths in a Lucy block or other suitable accessory.

Never questioned it but now I am. Is it fine to take an earth from an existing board?
I don't see any reason why not so long as there are enough free terminals able to take the (probably) 16mm conductors. After all if you took a sub-main then it comes from there.

However, I also think it is good practice to have the MET separate from the CU so it is clear for inspection and test where the DNO earth and extraneous bonding goes, and in that case you would simply take each board's earth from the MET block.

Which is what you already do and, I believe, the best way.
 
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pc1966

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(It was once the case to say "If in doubt, bond it". Some still say this. But I don't think this is a good answer as by following this mantra things can become live in fault conditions that otherwise wouldn't.)
I would still suggest that for anything that:
  • Could introduce a potential by means of it carrying cables, or being somehow in contact with the Earth (below 20k ohm) so "extraneous"
  • Can be touched when also in contact with anything else on the CPC circuit
For example, I would not bond radiators as the pipe work should already be bonded and then they can't introduce anything else, but I would bond cable tray carrying any sort of power cable.
 

pc1966

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Are you bonding cable tray as it's an exposed conductive part and it can become live under fault conditions? In this case the fault would have to be a damaged cable I'm presuming?
Yes. It is quite conceivable for a cable to get damaged on the edge of tray and make contact.
 
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Ive watched a video on the eFixx YouTube about this before and his opinion was that if the cable could introduce a fault which made the cable tray live, this would suggest the cable or containment is unfit for purpose.

Cant see the logic in this personally as surely that would mean only SWA could be installed on tray so the armouring became live rather than the tray if there was a fault?
 

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