testing bathroom supplementary equi-potential bonding

[rookie]

Hi

I've done a search of the archives but can't find an answer to the following question:

I totally refitted my bathroom a few months ago, but was unaware at the time of the requirement for supplementary bonding. Now I'm aware of it I'd like to make sure that I have it and it functions correctly.

I suspect that the original bathroom had the bonding as the house was built in the 70s, and as I understand the wiring regs bonding was a requirement at this time. I'd therefore like to make use of this bonding if present (with additions for a new shower pump) to avoid having to do any destructive work. However, if it is present it is largely under the floor boards, under my laid flooring, and thus I can't easily check for it by eye. I'd therefore appreciate any input on how I might go about testing for it using a basic multimeter on the exposed pipework, lights etc.

Thanks in advance

-Neil

[Christian McArdle]

This will be difficult, as it is likely that your main equipotential bonding already provides a low impedence path between copper pipework and electrical fittings. I doubt your 1970s house has plastic pipework.

Christian.

[Andy Wade]

All the bonding connections should be accessible, or reasonably so (in principle...). It should be possible disconnect each in turn and make a resistance measurement to another bonded point. The resistance of 4 mm^2 copper at 20 deg. C will be 4.6 milliohm per metre or less. Excessively high readings should arouse suspicion as they suggest that the path may be a long one, i.e. not bonding "in close vicinity."

You need a good low resistance ohmmeter for this sort of thing (resolution to 0.01 ohm) and a reliable long test lead. An ordinary multimeter's no good, except for detecting open circuits.