Earthing steel bath

[PompeySparks]

I don't think that's the main issue - after all, if adequate main bonding (and any required sipplementary bonding) is in place, then it should be perfectly OK to 'take a bath on the neutral bar' (or anything connected to it), even in the face of a supply neutral fault! I think the much more important reason for not unnecessarily connecting things (like isolated baths) to earth is that it increases the risk of shock should someone be in contact with something live (the frayed lead of a vacuum cleaner is often cited!) when they touch the 'unnecessarily earthed' bath (or whatever).

Kind FRegards, John

I agree with your main point but was just looking at it from a different perspective. There are many scenarios to consider. A modern house may be piped in entirely plastic (including incomers) and only non extraneous runs of copper inside, therefore having no MPBs (unless pointlessly clamped to MPDE!) and therefore no alternative paths for the neutral current to take.

 

[JohnW2]

I agree with your main point but was just looking at it from a different perspective. There are many scenarios to consider. A modern house may be piped in entirely plastic (including incomers) and only non extraneous runs of copper inside, therefore having no MPBs (unless pointlessly clamped to MPDE!) and therefore no alternative paths for the neutral current to take.

As far as I can make out, no-one has yet found a legal way of getting gas into a house without a metal incomer. However, if they did manage to have no extraneous-conductive parts (e.g. if they had no gas), and hence no main bonding, I still don't think there would be a problem in 'taking a bath on the neutral bar' even in the presence of a 'lost neutral' - because the very reason for the absence of MPB is that the interior of the house is already equipotential without it. You say, rightly, that there would be 'no alternative paths for the neutral current to take' but, provided the house really was equipotential, nor would there be any possible paths for it to take through people - so, again, theoretically 'no problem'.

However, as I said, any earthed metal increases the risk of shock (if people touch it and something live). Some earthing is obviously unavoidable - but, if it's not necessary, one is at less risk by not having it!

Kind Regards, John

 

[PompeySparks]

Some very good points John but contrary to logic and well established electrical principles, I would still not want to touch something sitting at 230v even if not in simultaneous contact with an earthed item or an unbonded extraneous item...

As you have said, the 22kohm rule is not perfect!

 

[JohnW2]

Some very good points John but contrary to logic and well established electrical principles, I would still not want to touch something sitting at 230v even if not in simultaneous contact with an earthed item or an unbonded extraneous item...

Sure, and I suppose that my underlying 'gut feeling' would say the same - but you, I and many other know that such a feeling is ('provided the assumptions are correct') without any scientific/engineering basis. It really does not matter what potential (relative to some external reference) we touch, provided that we can't touch anything at the potential of that 'external reference' at the same time. I guess that 'proviso' above is the reason why many of us might be 'nervous', despite our knowledge, because we might have niggling fears that the 'equipotential zone' might not actually be quite as equipotential as we would have hoped!

As you have said, the 22kohm rule is not perfect!

Indeed - although, as I said, in practice I don't think there really is an issue. If we changed the rule-of-thumb to say "if >1M&#937;, then don't bond, if <10&#937; bond, but if between 10&#937; and 1M&#937; you should 'call a friend' for advice", then I doubt that the friend would ever get called, and I have no real problem with the risk of a <0.25 mA shock!

Kind REgards, John