A explaination of the current regs, the way I interpret them, and the way things seem to have been done and why. (Every quote from 17th edition - yellow. For wiring regs.)
Firstly what is meant by an equipotential zone?
According to On Site Guide
Equipotential bonding. Electrical connection maintaining various exposed-conductive-parts at substantially the same potential. (See also Protective equipotential bonding.)
Me: Sinply states metalwork Forget what any pipe contains or is used for it is metalwork same for the iron metalwork used in the building construction (provided it is exposed which normally it isn't in a domestic property)
What Main Protective Conductors are required:
OSG-2.pdf
Metallic installation pipes
Metallic gas installation pipes
Other installation pipes e.g. oil
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Next bit refers to pipework burried in the screed of a floor at ground level. Common pratice for central heating pipes, hot/cold water pipes and gas pipes. in which case they would need to be in a metallic duct which may well be in electrical contact with the gas pipe it encloses.
If pipes are metallic they would normally be considered as extraneous-conductive-parts. So that includs central heating and hot/cold water supplies.
Me: There seems to be no mention of where these pipes or the 'metalwork', which forms the pipes either originate from or end finally up.
Central heating radiators must be considered exposed-conductive-parts. They are however conneced electrically to the metal pipework and so are in effect bonded.
I think that takes care of why I believe internal pipework needs bonding. Simply says it needs to be. I cannot see any situations included where exclusions to above mean the requirements don't apply neither are any calculations shown.
Forget where those connection need to be applied for the moment.