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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
  • 0

    geoffsd:




    The soap or plate rack is never going to be bonded, they could however be fixed to a metal stud within a wall giving a conductive path.




    The biggest danger is that a fixing screw has nicked the line conductor leaving the rack at mains potential resulting in the death of a lady taking plates out of the dishwasher when she touched the electrically live plate  rack and the earthed dishwasher at the same time, as has happened.


     

    So, in that example, it would have been better if the plate were earthed and the dishwasher not earthed but no one is going to propose that as a satisfactory method -


    UNLESS of course, it were not a dishwasher but a metal bucket - or perhaps a bath - on the floor.

    Lol... agreed, it was however, stated by others previously that they were getting tingles (insulated floor or low enough to allow small amounts of current to pass) from the plate rack but nobody realized that it was likely to turn into a lethal shock hazard.


    A call to an electrician who would have checked the voltage on the extraneous part would have found the problem before it did the damage.

    Legh
     

  • 0

    The soap or plate rack is never going to be bonded, they could however be fixed to a metal stud within a wall giving a conductive path.




    The biggest danger is that a fixing screw has nicked the line conductor leaving the rack at mains potential resulting in the death of a lady taking plates out of the dishwasher when she touched the electrically live plate  rack and the earthed dishwasher at the same time, as has happened.


     

    So, in that example, it would have been better if the plate were earthed and the dishwasher not earthed but no one is going to propose that as a satisfactory method -


    UNLESS of course, it were not a dishwasher but a metal bucket - or perhaps a bath - on the floor.
  • 0

    Legh Richardson:




    geoffsd:




    "Sparks seemed to get carried away with bonding"

    I know, hundreds of thousands of sparks, wiring millions of properties, what ever we're they thinking of?

     

    Oh yes, wiring to the "IEE regulations"!!! 



    Please could you quote or provide a link to these regulations that required isolated metal items to be bonded?

    How do you equalise potential on an item that has none? Introduce one and then equalise it?


    What about a metal soap dish screwed to the wall above the bath?


    What about the cutlery drawer?

    What about a metal plate rack above what might have been a dishwasher in a kitchen?

    Always a good idea to take mearuements if there is some doubt to the quality of bonding and earthing don't you think?


    legh

     




     

    The soap or plate rack is never going to be bonded, they could however be fixed to a metal stud within a wall giving a conductive path.


    The biggest danger is that a fixing screw has nicked the line conductor leaving the rack at mains potential resulting in the death of a lady taking plates out of the dishwasher when she touched the electrically live plate  rack and the earthed dishwasher at the same time, as has happened.


    Andy Betteridge
  • 0

    Please could you quote or provide a link to these regulations that required isolated metal items to be bonded?

     





    I would indeed like to reproduce information/solutions on the forum, perhaps you could take me through the method.



    The easiest way is if what you want to refer to is already on the web - e.g. most (reasonably modern) legislation can be found on this site http://www.legislation.gov.uk/ - e.g. the The Electricity Safety, Quality and Continuity Regulations 2002 can be found here: http://www.legislation.gov.uk/uksi/2002/2665/contents/made (most have a PDF version too, which can be handy).


    Or UKPN's Customer LV Installation Earthing Design document: http://library.ukpowernetworks.co.uk/library/asset/f6acd931-9c79-411f-a98f-f801bce6e63L/EDS+06-0017+Customer+LV+Installation+Earthing+Design.pdf


    Having found what you want you can simply paste the URL into your reply.


    If you only have it on paper then you can either just type it in (if it's not too much) or probably better, take a photo (or scan) of it, and upload the image to this site (using the odd 'two mountains and a moon in a box' Image button) and then include that image in your post.


       - Andy.
  • 0

    geoffsd:




    "Sparks seemed to get carried away with bonding"

    I know, hundreds of thousands of sparks, wiring millions of properties, what ever we're they thinking of?

     

    Oh yes, wiring to the "IEE regulations"!!! 



    Please could you quote or provide a link to these regulations that required isolated metal items to be bonded?

    How do you equalise potential on an item that has none? Introduce one and then equalise it?


    What about a metal soap dish screwed to the wall above the bath?


    What about the cutlery drawer?

    What about a metal plate rack above what might have been a dishwasher in a kitchen?

    Always a good idea to take mearuements if there is some doubt to the quality of bonding and earthing don't you think?


    legh
  • 0
    Lol I thought I was bad at spelling!!! I blame it on spell chequer and not going to school much. Another big surprise UKPN seems to have a sense of humour after all or is it just bitching. I get an awful feeling il get in trouble for this post so il say now SORRY LISA and others if it's too OTT
  • 0

    Slip of the pen there, or a big bathroom?



    Er, um, yes, definitely.... I'm sure I typed "circuits", not "sockets". At least my brain was certainly thinking about circuits, seemingly I have no idea what my fingers were doing. I don't think I can even blame a spehl chequer. Sorry for any confusion.


      - Andy.
  • 0
    Would consider this Shower as a length of metal water pipe?


    Would you bond it even if it is connected with plastic pipes?


    Andy Betteridge
  • 0
    Wiring regulations? you can picture the situation in a few years time, say the 20th/21st edition of the guide book. Thousands of customers have been getting shocks from unearthed metal fuse boxes on TT systems. Various IET posters will be saying it was all a mistake, the IET didn't mean it like that, they were misread!

    Regards, UKPN
  • 0

    UKPN:

    Yes indeed, the method is widely used, not on gas pipes of course they are steel and bonded as a matter of course. The plastic water service, after the stop cock, normally grey throughout the property has a clip and 10mm green yellow at the point of entry so that in the future if the service is changed to copper the bond/clip will be there ready. I am surprised you haven't seen it done. 

    Regards, UKPN. 




     

    Metallic pipes entering the building having an insulating section at their point of entry need not be connected to the protective equipotential bonding (Regulation 411.3.1.2).

    https://electrical.theiet.org/bs-7671/18th-edition-changes/


    So so long as there is a reasonable length of plastic pipe between any metal water pipe inside the property and a buried metal water pipe at the point of entry into the building there isn’t any need to install a main protective bond.


    So if someone did decide to replace sections of plastic pipe with shiny chrome plated pipe for aesthetic reasons, so long as a insulating plastic pipe remains in place it doesn’t matter whether the buried service pipe is plastic or metal, either way it doesn’t need a main protective bond.


    Therefore the idea that a main protective bond should be installed to plastic pipework just in case it is changed to copper is really a non-starter even if the buried service pipe is metal.


    Andy Betteridge 


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