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practical need for supp bonding in bathroom

wallywombat
Can anyone suggest a realistic scenario where supplementary bonding would be required in a bathroom or other 701 location? I'm failing to think of one, although I may be overlooking something blindingly obvious.


It can be omitted as long all three of these are satisfied: ADS in time; RCD present; any extr-c-p connected to main bonding.


If ADS can't be done in time by either MCB/RCD then its not legal anyway.

RCD has to be present anyway.

Water and gas pipes etc should already be main bonded if they introduce a potential.
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    Water and gas pipes etc should already be main bonded if they introduce a potential.



    Ah, but what are extraneous-conductive-parts as far as the installation is concerned aren't necessarily the same as what are extraneous-conductive-parts as far as the bathroom is concerned. Take the classic plumbing setup for hot water - copper cylinder in a cupboard somewhere (possibly in the 2nd bedroom), fed from a plastic cistern in the loft, and an immersion heater fed from an old 15A rewireable fuse with anything up to 5s disconnection time. The hot water pipes aren't effectively connected to the main bonding because of the plastic cistern in the loft - which is of itself fine as the hot water pipework can't introduce a potential into the installation -  but because it's effectively an extension of the immersion heater's c.p.c. it the can introduce a potential into the bathroom. A fault on the immersion heater side-steps all the RCD protection for the bathroom circuits and puts a possibly lethal potential between the hot tap and the (main bonded) cold tap for possibly a lethal duration. You choices then are either to main bond the hot water pipework or supplementary bond everything within the bathroom. (Adding 30mA RCD protection to the immersion circuit might also work, but isn't recognised by the regs as a solution - possibly because of the risk of picking up similar potentials due to faults elsewhere in the installation.)


      - Andy.
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    Water and gas pipes etc should already be main bonded if they introduce a potential.



    Ah, but what are extraneous-conductive-parts as far as the installation is concerned aren't necessarily the same as what are extraneous-conductive-parts as far as the bathroom is concerned. Take the classic plumbing setup for hot water - copper cylinder in a cupboard somewhere (possibly in the 2nd bedroom), fed from a plastic cistern in the loft, and an immersion heater fed from an old 15A rewireable fuse with anything up to 5s disconnection time. The hot water pipes aren't effectively connected to the main bonding because of the plastic cistern in the loft - which is of itself fine as the hot water pipework can't introduce a potential into the installation -  but because it's effectively an extension of the immersion heater's c.p.c. it the can introduce a potential into the bathroom. A fault on the immersion heater side-steps all the RCD protection for the bathroom circuits and puts a possibly lethal potential between the hot tap and the (main bonded) cold tap for possibly a lethal duration. You choices then are either to main bond the hot water pipework or supplementary bond everything within the bathroom. (Adding 30mA RCD protection to the immersion circuit might also work, but isn't recognised by the regs as a solution - possibly because of the risk of picking up similar potentials due to faults elsewhere in the installation.)


      - Andy.
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