Bonding college water rig project


Postby fisha » Fri Apr 22, 2011 12:14 pm

Hi guys I m a fourth year instrumentation student i have built a water treatment rig from unistrut and it contains copper piping. Connected onto the metal work are electrics including relays and and a 230-24v supply. The rig contains solenoid valves and 230v pumps. There is a panel adjacent to the rig do i need a direct connection from the earth bar to the metal work and is it ok to bond the copper pipes to the earth supplying the pumps. I was thinking the metal work would require a 10mm2 earth directly to ground while the copper pipes(half inch) could be bonded to the incoming earth to the pumps. Can anyone advise further please. Any information would be greatly appreciated. thanks guys
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Postby ericmark » Fri Apr 22, 2011 8:02 pm

You have given a little more information here. I would think 4mm earth wires are large enough. You really need to do a sort of risk assessment. Likely all 230v parts already have a earth and the 24 volt items are likely feed from an isolation transformer.

Having done projects in University I realised the main problem is where will it be demonstrated. Using a PLC to show lecturer we know how to program we used the Alan-Bradley 230v PLC free-standing. However the same project used to show school children what can be done in University and the PLC had to be housed inside a box which required a tool to access the PLC.

It is really down to a risk assessment. How much you need to worry depends on your position. As a student it is up to the lecturer to decide if it is safe. As a lecturer then I would want to pass the responsibility to some one who knows the rules. So I would get it PAT tested.

To me it seems you are going OTT. If the supply is from a 13A socket then clearly the electrical earth needs only the same size cable as supply. However if not part of the same cable as supply then 4mm is minimum size.

I have watched electricians connect an earth wire from one bit of tray work to another when the two bits of tray were bolted together. Rather pointless. In theory it should have an earth cable with tails crimped onto it with C crimps running the length of the tray work. In practice only seen this in Petrol Chemical works. If the theory of earthing is part of project then maybe you need to run earth wires. If not unlikely required.
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