Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning main equipotential bonding and plastic services, and whether bonding is required, is answered by SELECT:
The question was answered 'yes' - it is required, by the ECA, but 'no' by the NICEIC; the latter confirming the original questioner's reasoning that it did not introduce an earth potential and to main bond the internal copper pipe work of a property would actually introduce a hazard.
Which is correct answer?
Answer: Generally, main water services today are of an alkathene type and, where internal plastic type pipework is also installed, there will be no necessity to provide main equipotential bonding to these services, as there would be no conductive parts likely to introduce a potential.
Where internal copper pipework is installed throughout a building, then this pipework may be in touch with earth at some point in the installation and would therefore be considered to be an extraneous conductive part which would therefore require to be main bonded.
This is where differences of opinion may occur - i.e. as to whether metal pipework is considered to be an extraneous conductive part or not. If the designer considers that metal parts are not extraneous conductive parts, then there would be no requirement to main bond. Such an example might be a metal window frame which is not likely to introduce a potential and therefore not present a hazard.
For further information, IEE Guidance Note 8 on earthing and bonding should be consulted.
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