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Extraneous conductive parts

Former Community Member
Former Community Member
Hello,


Thinking about a domestic dwelling with main bonding to incoming water and gas pipes (even though most are plastic nowadays); all the electrical circuits within the dwelling are protected by RCDs; the only extraneous conductive parts to the bathroom being copper water pipes and copper central heating pipes... Why would the copper pipes need to be main bonded one to another close to the bathroom (in an accessible place for testing, like in an airing cupboard)?


Designing an installation which uses the cold water pipe in place of a main bonding cable (having a cross-sectional area which is greater, after all), why would any of the other three pipes need to be main bonded to that cold water pipe, when all of the pipes connect at the boiler any how?! Yes, if you were to cut all of the pipes and to replace them with plastic pipes then you risk introducing an electrical potential into the bathroom should a fault occur, but wouldn’t anyone doing that plumbing be obliged to consider this risk at that time? 


Otherwise, there is no point considering the use of copper pipes to replace main bonding cables. In which case, it would be necessary to bond the pipes one to another just outside the bathroom and run the cable all of the way back to the consumer unit.


I must excuse myself for being indolent and not referring directly to the wiring regulations, which is from where these ideas stem.
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    but wouldn’t anyone doing that plumbing be obliged to consider this risk at that time?

    Unfortunately not - UK plumbers traditonally haven't been trained to know much about electricity - even the 'safety electrical connection - do not remove' label appears to confuse them on ocasions. In certain circumstances where there are strict procedures (like some particularly stringent work places) you might be able to get it written into site procedures that metallic plumbing shouldn't be replaced by plastic without consideration of the bonding requirements, but as a general rule - certainly for ordinary domestics - we can't rely on plumbing maintaining its continuity.

    Why would the copper pipes need to be main bonded one to another close to the bathroom (in an accessible place for testing, like in an airing cupboard)?

    Normally you wouldn't - main bonding would usually only be applied around the perimeter of an installation to deal with anything that might introduce a potential into the installation. Bonding for a bathroom would normally be supplementary bonding (again bonding everything that would introduce a potential into the bathroom). The only situation I can think of where you'd need to main bond internal pipework for a bathroom is where you're trying to omit supplementary bonding but the condition for any extraneous-conductive-parts entering the bathroom being main bonded hasn't been satisfied. That condition is there to stop faults from elsewhere in the installation entering the bathroom via the metallic pipework - say from an immersion heater in an adjacent bedroom cupboard (as was the fashion a few decades ago). Often (but perhaps not always) it would be easier and cheaper just to supplementary bond within the bathroom rather than a run main bonding conductors up to the bathroom from the MET.


       - Andy.
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  • 0
    but wouldn’t anyone doing that plumbing be obliged to consider this risk at that time?

    Unfortunately not - UK plumbers traditonally haven't been trained to know much about electricity - even the 'safety electrical connection - do not remove' label appears to confuse them on ocasions. In certain circumstances where there are strict procedures (like some particularly stringent work places) you might be able to get it written into site procedures that metallic plumbing shouldn't be replaced by plastic without consideration of the bonding requirements, but as a general rule - certainly for ordinary domestics - we can't rely on plumbing maintaining its continuity.

    Why would the copper pipes need to be main bonded one to another close to the bathroom (in an accessible place for testing, like in an airing cupboard)?

    Normally you wouldn't - main bonding would usually only be applied around the perimeter of an installation to deal with anything that might introduce a potential into the installation. Bonding for a bathroom would normally be supplementary bonding (again bonding everything that would introduce a potential into the bathroom). The only situation I can think of where you'd need to main bond internal pipework for a bathroom is where you're trying to omit supplementary bonding but the condition for any extraneous-conductive-parts entering the bathroom being main bonded hasn't been satisfied. That condition is there to stop faults from elsewhere in the installation entering the bathroom via the metallic pipework - say from an immersion heater in an adjacent bedroom cupboard (as was the fashion a few decades ago). Often (but perhaps not always) it would be easier and cheaper just to supplementary bond within the bathroom rather than a run main bonding conductors up to the bathroom from the MET.


       - Andy.
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