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Bonding a metal bath

David-Adams
Good evening


I am having one of those moments where I can’t sleep because I am worrying about something I probably don’t need to. That’s the rational part of me talking, unfortunately the anxiety monster won’t b***** off. 


We have just had our old cast iron bath replaced with a nice new shiny steel one. The old bath was bonded back to the terminal block by main consumer unit over 6mm earth cable via the airing cupboard. We also have an electric shower. 


The new bath has no taps on it (they are wall-mounted and fed by copper pipes). The waste is all plastic. The electric shower has been replaced with a new electric shower. The copper pipes in the airing cupboard have been connected via a new 4mm earth cable. My electrician says that according to the 18th edition, there is no requirement for the metal bath to be bonded. 


I have no reason to doubt him, except for the anxiety monster eating away at my brain I mentioned earlier. What limited literature I have found seems to suggest this is correct, but in some circles it is a hotly debated topic with contradicting views. I was just wondering if someone could confirm this for me please. I would also be interested in understanding why this is the case to satisfy my own natural curiosity of all things!


Many thanks in advance
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    Sparkingchip:

    In some instances the regs accept 70 volts rather than 50 volts as the upper limit for touch voltage, so that isn’t set in stone.

    However, when naked, barefoot and wet, you also have to consider the “phantom voltage” that there may be on metal pipework and taps due to the ten or so volts that there may be due to the earth being taken from the DNO neutral which is after all a live conductor.


    One of the people most likely to notice a tingling feeling due to phantom voltage is the window cleaner in soggy training shoes washing the window panes in the steel Crittal window frames that the electrician has carefully connected supplementary equipotential potential bonding conductors to, with the window cleaner being outside of the equipotential zone standing in the garden.


    Andy Betteridge 




    Tying the PME earth to all extraneous and exposed metalwork will reduce the floating neutral voltage caused by out of balance DNO three phase supplies.

    As I remember, metal windows were regarded as an anomaly (non-extraneous) and it was only necessary to supplementary bond the metal studdied supported windows. However, 'you don't have to bond that' is not an answer I would have thought was acceptable in a court of law if by some chance a peradventure were to happen 


    Legh

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  • 0

    Sparkingchip:

    In some instances the regs accept 70 volts rather than 50 volts as the upper limit for touch voltage, so that isn’t set in stone.

    However, when naked, barefoot and wet, you also have to consider the “phantom voltage” that there may be on metal pipework and taps due to the ten or so volts that there may be due to the earth being taken from the DNO neutral which is after all a live conductor.


    One of the people most likely to notice a tingling feeling due to phantom voltage is the window cleaner in soggy training shoes washing the window panes in the steel Crittal window frames that the electrician has carefully connected supplementary equipotential potential bonding conductors to, with the window cleaner being outside of the equipotential zone standing in the garden.


    Andy Betteridge 




    Tying the PME earth to all extraneous and exposed metalwork will reduce the floating neutral voltage caused by out of balance DNO three phase supplies.

    As I remember, metal windows were regarded as an anomaly (non-extraneous) and it was only necessary to supplementary bond the metal studdied supported windows. However, 'you don't have to bond that' is not an answer I would have thought was acceptable in a court of law if by some chance a peradventure were to happen 


    Legh

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