Geoffrey Davis asks this question, which concerns clarification over the requirements of BS 7671 with regard to earthing central heating systems in domestic properties. It has been answered by the NICEIC (Theme - HVAC):
Question: I'm after some clarification about the requirements of BS 7671 with regard to earthing central heating systems in domestic properties.
After trawling through BS 7671 (and I hope I'm not over simplifying it), if it is considered an extraneous conductive part, but is connected along with metallic water and gas pipework, which is itself earthed then (subject to confirmation by test) would this be considered OK. If I its not judged to be an extraneous part, it does not require earthing anyway - is this correct?
Either way, is there a requirement or benefit from the supplementary bonding often seen beneath boilers?
Is this a reasonable interpretation of the Regulations?
Answer: Your opinion is indeed correct. If there is main protective bonding in place and all circuits are RCD protected, then supplementary is not required.
It is all down to whether the pipework from the boiler is confirmed as being extraneous.
Take a look at the IET Guidance Note 8 'Earthing and Bonding' for more clarification.
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