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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
    Assuming your bath is upstairs and not in the garden.


    The old bath was not bonded - it was earthed ensuring you would get the maximum shock had you touched it at the same time as a live wire or appliance.


    As your new bath is not connected to anything electrical or to any metal which is connected to anything electrical you must not earth it (bond it unnecessarily).

    Think of it as a metal door handle or a metal knife and fork. It cannot become live nor provide a path to earth.


    Nothing to do with the 18th or any other edition.
  • 0
    Ask yourself the question, would bonding the bath to earth  make it safer or more dangerous?


     Andy B.
  • 0
    normally we earth things that might credibly come live during a fault - such as the case of a washing machine, if a wire comes off inside, or perhaps the  metal pipes to an electric shower, in case the element splits and makes the water live .. The idea is that the current to the earth blows the fuse or fires a trip, so you do not have to.

    We bond things we may simultaneously touch, that could credibly have a connection to different voltages. The idea is to reduce the risk of  shock.


    Unless you intend to throw a live appliances into the bath, hair dryer or a fan heater perhaps, you do not need either, unless some how one or other condition above is met.
  • 0
    Even if you do plan on throwing live appliances into the bath, then I would expect it to be safer if it's not earthed (or bonded).  Leaving the bath isolated means there's no path for the current to flow through the water, through the bath, to earth.
  • 0
    but if there is an RCD in the supply to the throwing in appliance it is more likely to trip  and ADS if the water is more or less earthed.
  • 0

    bob-tahoma:

    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.



    It may be that when the bathroom was last refitted, or electrics installed, the current regulations specified a lot of bonding. Since 15th Edn, requirements have reduced. So in all probability, that old "bond" was redundant.
    The copper pipes in the airing cupboard have been connected via a new 4mm earth cable.

    If that means that the hot and cold pipes have been connected to each other, it was probably unnecessary because they are likely to be connected elsewhere. Soldered copper pipes do not need to be bonded more than once.
    My electrician says that according to the 18th edition, there is no requirement for the metal bath to be bonded.

    I agree with your electrician. It is electrically isolated now and best left that way.
  • 0
    The 15th edition regulations on bonding were virtually the same as they are now.


    The laws of physics have not changed either.
  • 0

    geoffsd:

    The 15th edition regulations on bonding were virtually the same as they are now.


    The laws of physics have not changed either.




    I haven't a copy so I cannot be sure, but there is bonding everywhere in my 15th Edn house. I don't know about the baths, but the kitchen sink is included. ?

  • 0
    Yes, people used to do that (including things like window frames) and a myth has come about that the 15th required bonding everything but it is not so because, as I said, the regulations were virtually the same as they are now.


    It was due to misreading and/or misunderstanding the regulations - much like is done now when people read 411.3.1.2 where they look at the list of parts while ignoring "extraneous-conductive-parts including the following" although I will agree that "including" is misleading.



    Is your kitchen sink an extraneous-c-p?



    Also, diagrams which are printed showing bathrooms with everything bonded do not usually point out that it only applies if the parts are extraneous-c-ps and the even more ignored "simultaneously accessible".
  • 0
    Working on the basis that various posters don't know the difference between bonding and earthing, I would go for bonding the bath. Take a 4mm back to the airing cupboard. Then you will sleep at night. If you take any notice of the 18th guide book you won't bond anything. (Although it's been saying bond everything for 50 years)

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