Equipotential bonding for a metal barn

[Dartlec]

Just started PIR on an installation at a local farm/stables/tack room/feed barn today. Looks like it could be a fairly long/fiddly job...

Today was a metal workshop with a fairly simple set up. However, I'm not 100% sure on the position with equipotential bonding to the structure.

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• Dartlec
• 19 Sep 2008
• 1

The entire structure is metal, and therefore clearly an extraneous conductive part. Therefore I would consider it should be bonded and will note such on the PIR, most likely as a code 2. However, I'm not sure how such bonding would be installed in practise.

Since they have an 'electrician' on the staff who will do any of the remedial work they will likely ask what needs doing so any practical advice welcomed.

The structure is simple metal RSJs bolted together and clad, but would it be normal to separately bond every beam, or trust the bolted connections to ensure continuity? The work involved in bonding every individual piece would be substantial, and the testing of their effectiveness likewise.

For a TT system, it had a remarkably good earth (1.92Ohm) considering where the earth rod is:

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• Dartlec
• 19 Sep 2008
• 1

In general the installation is pretty good considering - RCDs are in place, and the wiring in the workshop at least is all SWA. The only 'slight' issues I found were 2.5mm cable run from a 32A MCB and swapped neutrals on the two light circuits

Mind you, this is what I still have to look at next so who knows what joys I shall discover.

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• Dartlec
• 19 Sep 2008
• 1

Gavin

 

[Lectrician]

Main eq bonding to one of the main steels will be fine. They are all bolted together anyway.

As for your TT earth - Did you test purely to the rod? I doubt that rod can offer that low a reading in isolation (as you should be testing it). The low reading is likely due to many parallel paths, the extraneous conductive parts, and could also be influenced by low insulation resistance between N and E - and with those highbays in the pic, you have come big juicy inductors just waiting to give you some **** ins res readings

 

[Dartlec]

Thanks for that Lectrician, I'm sure the client will appreciate only having to run one conductor.

No I haven't tested to the rod yet so I realise there could well be many parallel paths (there are certainly enough earthing conductors about). I'm breaking it down into achievable parts for certification purposes at the moment so treated the board I was testing as a sub board, and have only tested Zs so far.

Gavin