Does copper h/w cylinder need bonding?

[ban-all-sheds]

But how, then, do people get shocks from unearthed statically charged items if they are not earthed?

 

[JohnW2]

Yes, but that bonding, in your LPG example, is between the lorry, which may be staticallly charged, and an earthed tank to prevent a spark when the nozzle approaches. Bonding the tank to anything else would not help.

Indeed so - and I don't think anyone has suggested otherwise.

No matter what the context, or what 'type' of electricity one is talking about, or whether or not one is talking about anything to do with electrical installations (which, as I've tried to illustrate, do not have a monopoly on 'equipotential bonding') the (one and only) point of equipotential bonding is to minimise a risk/hazard which would/could arise if the parts in question acquired significantly different potentials.

I would suspect (but obviously do not know) that if, for example, I had metal fence posts in the vicinity of my gas tank which the tanker's 'nozzle' could possibly approach ('accidentally'/unintentionally), their operating procedures might also require those objects to be bonded to the tanker. Indeed, in gas/oil refineries etc., it would not surprise me if almost everything was bonded to everything else 'just in case'.

As with a person receiving a shock when touching a car, it is the person that needs earthing.

I'm not sure that I get that one - improving the earthing the person would appear to exacerbate the situation!

Kind Regards, John

 

[EFLImpudence]

You have done what you frequently do and introduced a situation nothing to do with the original subject and then expand on that.

 

[JohnW2]

You have done what you frequently do and introduced a situation nothing to do with the original subject and then expand on that.

Hmmm.

It was really JohnD who started all this, by talking about the bonding of conductive parts entering a building which had no electrical installation - a theoretical issue which has absolutely nothing to do the subject of this forum! As for my more recent posts, as I said, it was you who introduced the "metal fence posts".

Kind Regards, John

 

[John D v2.0]

Well I've found it yet interesting anyway, thanks!
Actually my original post was to try to distinguish bonding and earthing for the benefit of the op.
Turned out I wasn't completely clear!

 

[JohnW2]

Well I've found it yet interesting anyway, thanks! Actually my original post was to try to distinguish bonding and earthing for the benefit of the op. Turned out I wasn't completely clear!

Yes, I understood what point you were trying to make.

I think the main problem is that (in the context of an electrical installation), although one's reasons for doing it differ, both 'earthing' and 'bonding' involve connecting two things with a bit of cable, one of which things will be 'earthed' (to the installation's 'earth'). In that sense, they do not differ - one cannot bond something without 'earthing' it (to the installation's 'earth'), and one cannot 'earth' something (to the installation's 'earth') without 'bonding' the two things which have been connected.

Although I have been accused of going 'off-topic', it is really only when one moves away from electrical installations (usually to situations in which static electricity presents the hazard) that one can really see the difference - since in those situations there can be a very real need for 'bonding' ('equipotential bonding'), but in a context where there is no question of it being done to facilitate the operation of a protective device in an electrical installation (which is the reason for earthing things within an electrical installation). I think you were probably trying to make the same point when you started this discussion by talking about the possible need for bonding in the absence of an electrical installation.

Just for any readers who are not totally clear ....

Earthing (in an electrical installation) is done so as to facilitate the operation of a protective device (fuse, MCB, RCBO, RCD) in the event of a fault in an electrical installation, thereby hopefully disconnecting the electricity before anyone (or anything) becomes harmed as a result of the fault.

Bonding (electrically joining two metal objects) is done so as to hopefully eliminate the possibility of there being (as the result of a fault) a dangerous voltage ('potential difference') between two metal things that could be touched simultaneously, thereby hopefully preventing electric shocks as a result of the fault.

However, as above, since both involve connecting something to the installation's earth, one can't really do one without the other, no matter what was one's reason for doing it.

Kind Regards, John

 

[John D v2.0]

Thanks John.
My only comment is bonding in terms of bs7671 does include earthing to the suppliers earth as it has to be connected to the met.

However the concept of bonding itself doesn't necessarily involve earth. In fact the main "earth"could be not the same as local earth, so by bonding and thereby "earth"ing your water pipe, you might be taking it further away from earth and closer to "line" voltage.

However since bonding is designed to create an equipotential zone, the fact that you've taken it further from earth in the process of bonding via the supplier "earth" isn't a big problem.

 

[JohnW2]

Thanks John. My only comment is bonding in terms of bs7671 does include earthing to the suppliers earth as it has to be connected to the met.

Indeed - or the local earth rod in the case of a TT installation. That's why I added the qualification "(in the context of an electrical installation)" to my statement that "one cannot bond something without 'earthing' it".

However the concept of bonding itself doesn't necessarily involve earth. In fact the main "earth"could be not the same as local earth, so by bonding and thereby "earth"ing your water pipe, you might be taking it further away from earth and closer to "line" voltage.

Again, indeed - and, again, that why I put all my references to 'earth' and 'earthing' in quotes. In the context of an electrical installation, 'earthing' means providing a path to the installation's MET, and is why the implicit bonding it creates is to the installation's MET, even if that MET is at a potential very different from true earth (without any quotation marks).

However since bonding is designed to create an equipotential zone, the fact that you've taken it further from earth in the process of bonding via the supplier "earth" isn't a big problem.

Indeed so (yet again!) - as above.

An interesting point/complication we haven't really discussed, is that, whilst bonding within an installation achieves what it is meant to achieve (an equipotential zone) regardless of the potential of that equipotential zone (relative to true earth), for 'earthing' (to the MET) within an installation to achieve what it is meant to achieve (facilitating the operation of a protective device) relies on this 'earthing' (via the MET) providing an effective return path to the supplier's transformer. This will not necessarily be the case if a fault (or faults) result(s) in the MET rising to, or near to, line potential - and I suppose may be at least part of the thinking behind the proposed upcoming requirement that all electrical installations should have a local TT electrode.

Kind Regards, John

 

[John D v2.0]

relies on this 'earthing' (via the MET) providing an effective return path to the supplier's transformer. This will not necessarily be the case if a fault (or faults) result(s) in the MET rising to, or near to, line potential

True, basically doing away with ads and only having the equipotential zone. So an earth free location. That's a valid means of protection, assuming the correct clearances between the earth free zone and any true earth!

 

[JohnW2]

True, basically doing away with ads and only having the equipotential zone. So an earth free location. That's a valid means of protection, assuming the correct clearances between the earth free zone and any true earth!

Yes, but it wouldn't be an "earth free location" in the absence of fault(s), so the protection would not be 'valid' in the absence of fault(s) unless everything that should be 'earthed' (to the MET) was ('earthed' to the MET).

Kind Regards, John

 

[John D v2.0]

Yes, but it wouldn't be an "earth free location" in the absence of fault(s), so the protection would not be 'valid' in the absence of fault(s) unless everything that should be 'earthed' (to the MET) was ('earthed' to the MET).

Kind Regards, John

It would, if the met didn't provide an effective path to the transformer, which was your original point. In that case it would be earth free.
Unless the problem with the path to the transformer was at the dno end, in which case the transformer would be isolated so earthing wouldn't matter at the consumer end

 

[JohnW2]

It would, if the met didn't provide an effective path to the transformer, which was your original point. In that case it would be earth free.

I was thinking/talking about a situation in which the MET normally did provide an effective return path back to the transformer, but might not in the case of a supply-side fault.

Kind Regards, John

 

[John D v2.0]

I was thinking/talking about a situation in which the MET normally did provide an effective return path back to the transformer, but might not in the case of a supply-side fault.

Kind Regards, John

Ok well in that case it's normal ads.
It's either ads and everything is fine, or it's a earth free situation! Assuming all other things are in place for an earth free location eg clearances

 

[JohnW2]

Ok well in that case it's normal ads. It's either ads and everything is fine, or it's a earth free situation! Assuming all other things are in place for an earth free location eg clearances

All true.

However, I fear I probably didn't express myself clearly enough. Talking about a normal (not normally 'earth-free') location/installation, I was making the point that, if the return path from MET to tranny were lost, although the 'earthing' (to the MET) would no longer facilitate ADS, the fact that by 'earthing' things one had also bonded them to the MET (and hence to everything else 'earthed' or bonded to the MET) ought to make the location fairly safe ('equipotential'), even if the MET were at a high voltage above true earth.

In other words, I was really reinforcing my previous statement that one cannot 'earth' something (to the installation's MET) without also bonding it (hopefully to all exposed-c-ps and any bonded extraneous-c-ps).

Kind Regards, John