Hi Chaps.

We have a pain in the ass alarm installed in a grain store, full of mice, dust, dirt and eh, grain. it consists of lots of separate containers and buildings. Four doors were previously wired in one pair because the customer wouldn't pay for us to run new cables. i got fed up trying to find chewed cables and patch them up so i took a day and ran 20mm steel tube round the outside of the building. Its all good now but my manager insists the tubing has to be earthed. is this so? i don't see why, its 12 volts and i never earth ali tubing.

Anyone know for sure?

i would like to disagree and be right this time.

p.s. he is //.B.W.F.// i didn't get plastic 20mm

Yep, should be earthed.

id say no as the voltage is too low, does he earth ali contants, steel sabs etc.

why should it be lurch?

Does everything metal have to be earthed? if i fitted it without 8 core running through it would it still need earthed?

its tricky.

by the way, thanks for the help

id say no as the voltage is too low, does he earth ali contants, steel sabs etc.

why should it be lurch?

But is'nt it classed as an extraneous conductor? I often see structural steel work in buildings with earth clamps etc on them, so I wonder if this is why it should be earthed. It could potentially become live could'nt it?

i dunno i never use the stuff but as he says what about ali.

OK, no one is sure. I aint using it again

Thanks chaps.

If the building is metel clad and the conduit is fixed to it then the conduit will be at the same potential as the building, normally a building would be earthed anyhow.

If not then I would suggest that it should be earthed, I think a "cross bond" to another known electricial earth would be ok here, such as a cold water pipe? Otherwise it's a earth cable back to the dis board to be connected and tested to part p by a sparks.

You could suggest that the cable is double insulated therefore the conduit does not need earthing? Also that at 12v I think this is SELV voltage which again may not need earthing, metel sounders are not earthed are they?As with all safety issues, safer is better, if a mains cable came into contact with the conduit and the conduit is insulated it's a lethal mixture!

Does everything metal have to be earthed? if i fitted it without 8 core running through it would it still need earthed?

Possibly, but once you run the cable through it it needs earthing so it's irrelevant.

I would quote numbers here but I can't actually find any copy of the regs here. Just as well I haven't sent off that application form to the NICEIC just yet then!

Possibly, but once you run the cable through it it needs earthing so it's irrelevant.

I would quote numbers here but I can't actually find any copy of the regs here. Just as well I haven't sent off that application form to the NICEIC just yet then!

Its not the cable that's the problem, without the tubing a bare 8 core carrying 12volts is not a problem to anyone. The walls are all metal and the tubing is screwed to it. i know that the screws may rust and stop conducting though.

My gaffer is usually right when he's wrong if you know what i mean