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[fisha]

My problem with the water rig i have built is that, its powered from a 13amp socket, however the rigs water is fed from the mains which would already be earthed elsewhere. My plan was to earth the rig from a nearby earthbar and loop all the extraneous parts of the rig including the copper pipes with an earth. My question is if i do this do i need to connect the earth from the socket to this as well. i.e. to satisify equipotential bonding. I may be going over the top here ericmark. However it would be nice to include something about the earthing in my report. The mains water is connected to a plastic tank however the water inside the tank will be treated with calcium nitrate solution to increase its conductivity. Would you stay away from the earthbar in the nearby panel and just earth the rig from the socket . Thanks again for your reply its been a great help

[ericmark]

Personally I would only earth to one earth and that would be the plug. To link earths to other points could allow large currents to flow through the earth wires. Although one would hope the room has bonding which will mean all earth points are at same potential one can't guarantee this.

Earths are given different names.
main protective bonding conductors would according to earth type need to be 6mm or 10mm where as the circuit protective conductors would be the size of supply cable so may be only 1.5mm. If the two are not at same potential then weakest link is your supply cable. To melt that cable could be dangerous so personally I would not take the chance.

The danger point varies according to conditions with 12v being considered as max for a bathroom but 50v being considered safe limit elsewhere. Even if the water did conduct it is unlikely to exceed 50v between earths so reasonably safe.

Maybe an experiment with one meter of liquid is in order. I will expect one meter in a 15mm pipe will be a high resistance. It is will plain water and although you may add chemicals in the rig the supply will be plain water.

In a college you don't know what goes on in every room. Welding can produce very high earth currents in one place I worked because of this workshop bonding was with 50mm earth cable. You have no idea how the college is wired so I would only connect to earth through the plug.

Using a RCD plug may be a good idea but likely all sockets are RCD protected anyway. So for your report you may want to include an enquiry as to if sockets are RCD protected.

[fisha]

been really busy working on the project. But id like to reply to say thanks very helpful i actaully did exactly what you said anyway as it actually made a liitle more sense when i thought about. You ve compleetely cleared things up for me thansk again