Earthing Spike

[PBC_1966]

You are connecting it to earth. How is that not earthing?

The purpose is to equalise potential. That is bonding.

I wasn't disputing that you might be bonding two things together to equalize potential. But if one of those things is already connected to earth, then you bond the second item to the first, then that second item ends up earthed just as the first one was.

All I was trying to say is that if you connect something to earth, then it is earthed.

 

[EFLImpudence]

What potential did the second item have?

 

[PBC_1966]

The reality underlying the confusion which many see between bonding and earthing is that one cannot bond (previously unearthed) item A to earthed item B without also earthing A, and that one cannot earth both A and B without them being, to at least a reasonable extent, 'bonded' to one another.

Exactly. You can bond A to B without any earthing being involved, but if A or B is earthed to begin with then the other must end up earthed as well after you've connected them together. Whether your reason for so connecting/bonding them is to equalize potential between them or to operate a protective device in the event of a fault is immaterial to the fact that both items are connected to earth, and can thus quite properly be described as earthed.

 

[JohnW2]

It wouldn't need to be in every house in order to provide protection in one particular house.

Whilst the sensing would not have to be in every house, the 'disconnection' (of whatever) surely would have to be? In any event, as you go on to say ...

Of course, it would either have to open the incoming neutral ahead of the N-E link, or be provided with a separate switching pole for the earth connection to the neutral, either of which would introduce another potential failure point.

... neither of which are allowed by current regs, presumably largely because of the reason you mention.

Kind Regards, John

 

[PBC_1966]

Earthing is installed to clear faults..

Earthing can also be to provide shielding or functionality.

I think I'm seeing the problem here: We have a lot of people looking at this purely from the point of view of the delivery of electrical power around the house, and then from the very BS7671-centric view in terms of how it might now explicitly define earthing and bonding for that purpose.

I'm looking at it from the basic electrical point of view which applies to communication circuits, radio-frequency devices and all manner of other things in which earthing simply means the connection of something to earth.

Perhaps this is where we're at crossed purposes.

 

[PBC_1966]

What potential did the second item have?

Before being connected to the first, already earthed item? If not directly connected to anything else or being influenced by capacitive or inductive coupling from anything else, zero.

 

[PBC_1966]

Whilst the sensing would not have to be in every house, the 'disconnection' (of whatever) surely would have to be?

Not in order to protect that one house and its occupants from the dangers of a substantial potential on the incoming neutral. If it detected the incoming neutral going above a certain potential relative to true, local earth, it would completely isolate the house from the incoming supply - including the PME earthing lead.

 

[JohnW2]

In practical terms, what matters is whether there is any credible scope for doubt about meaning.

No, it isn't. It's no different than calling you Dave. ... It [clarification] should be sought first, just in case. The person calling you Dave while obviously not talking to anyone else should not be corrected, then. OK.

There are a few people who, for decades, have (for inexplicable reasons!) always called called me, and referred to me, by a name which is not correct, and which no-one else ever uses to refer to me (call them unilaterally-declared 'nicknames' if you like). They know, I know, and everyone else around knows who they are talking about. If we all tried to constantly 'correct' these people, it would become incredibly tedious, and would achieve nothing!

We therefore all knew exactly what was being talked about, and that it was something that had never been notifiable.

We did but he didn't. He was looking at out of date references and saw Earthing conductors were notifiable and thought that meant what he was doing. Only people who don't know the difference would use the wrong term so they should be taught.

I'm not sure that I understand what you're talking about here. He never used the term 'earthing conductor' and even if he'd looked in the pre-April 2013 notification rules, I don't think that he would have found it there (but, as you have implied, he would have discovered that " installing or upgrading main or supplementary equipotential bonding" was not notifiable then, any more than it is now). AFAICS, no-one but you has used the term "earthing conductor" anywhere in this discussion.

Kind Regards, John

 

[JohnW2]

Whilst the sensing would not have to be in every house, the 'disconnection' (of whatever) surely would have to be?

Not in order to protect that one house and its occupants from the dangers of a substantial potential on the incoming neutral. If it detected the incoming neutral going above a certain potential relative to true, local earth, it would completely isolate the house from the incoming supply - including the PME earthing lead.

Yes, but, as I said, that would involve disconnecting something that one isn't allowed to disconnect. I may be wrong, but I think what eric had in mind is that if all houses which had an elevated neutral disconnected their L's (and N's, but after the PME earth branch-off, the switching of which is not allowed) from their incoming supply that would probably do away with the problem/hazard without doing anything which is 'not allowed'

Kind Regards, John

 

[PBC_1966]

Yes, but, as I said, that would involve disconnecting something that one isn't allowed to disconnect.

Ah, I thought we were hypothesizing about a new system being introduced to guard against such things, and that thus it would become the accepted norm.

I may be wrong, but I think what eric had in mind is that if all houses which had an elevated neutral disconnected their L's (and N's, but after the PME earth branch-off, the switching of which is not allowed) from their incoming supply that would probably do away with the problem/hazard without doing anything which is 'not allowed'

Yes, that would make sense.

 

[JohnW2]

Ah, I thought we were hypothesizing about a new system being introduced to guard against such things, and that thus it would become the accepted norm.

Yes, I realise that's what you thought but I was really continuing to talk about what eric had suggested (and you had challenged)....

I may be wrong, but I think what eric had in mind is that if all houses which had an elevated neutral disconnected their L's (and N's, but after the PME earth branch-off, the switching of which is not allowed) from their incoming supply that would probably do away with the problem/hazard without doing anything which is 'not allowed'

Yes, that would make sense.

Indeed it would. However, that's even more less likely to happen than the "new system" that you were hypothesising about, since a protective system which only works if all one's neighbours also implemented it (simultaneously) is, I suspect, unlikely to be particularly viable! ... and if you were thinking about a nationwide DNO implementation, their record in getting cutouts up-to-date suggests that we might be talking of a timescale of a century or more

Kind Regards, John

 

[bernardgreen]

I'm looking at it from the basic electrical point of view which applies to communication circuits, radio-frequency devices and all manner of other things in which earthing simply means the connection of something to earth.

Perhaps this is where we're at crossed purposes.

I agree with that.

A question,

A domestic kitchen has two large stainless steel work tops. One is L shaped along two walls and the second is on the island unit. It is possible to and maybe likely that a person could be touching both at the same time. There are fixed electrical items under both work tops and portable electrical items can be used on both work tops. There are power sockets, hot and cold water taps on both work tops. It is likely that more than one person will be working in the kitchen. On the third wall there is a large stainless steel fridge and freeezer.

The work surfaces have "earth" terminals welded to them. Do you use these terminals and if so for what purpose.

 

[bernardgreen]

True bonding ( not earthing ) of items non of which have any path to the safety earth ( CPC ) should be identified as such. Labeled as a "Non Earthed Bond" and connected by a conductor whose colour will not mislead people into thinking it is an earth wire. Some equipment racks are bonded together by bare copper cable / bus bars and clearly labelled " DO NOT EARTH " The electrical safety earth goes only as far as the inter winding screens and cores in the power supply transformers. Special measures come into play if the potential of the rack framing reaches a certain level above ( not sure ) ground or electrical safety earth.

 

[JohnW2]

A domestic kitchen has two large stainless steel work tops. One is L shaped along two walls and the second is on the island unit. It is possible to and maybe likely that a person could be touching both at the same time. There are fixed electrical items under both work tops and portable electrical items can be used on both work tops. There are power sockets, hot and cold water taps on both work tops. It is likely that more than one person will be working in the kitchen. On the third wall there is a large stainless steel fridge and freeezer. ..... The work surfaces have "earth" terminals welded to them. Do you use these terminals and if so for what purpose.

As with the bath, I would say that the answer is dependent upon a relative risk-assessment of of the pros and cons of connecting the worktops to earth (or together) in the actual situation.

In the situation you describe, I think a lot of my assessment would depend upon whether or not the taps (or anything else nearby) was already connected to earth (mainly depend on type of pipework) and, if earthed, whether they were in electrical continuity with the worktops (if they were, then the whole question would become rather moot).

My first thoughts are that if the taps (and other nearby things) were not connected to earth, I would personally probably not earth (or bond) the worktops - feeling that the risk posed by all that touchable earthed metal (given all the fixed and portable electrical equipment around) would probably outweigh the risk of the worktop becoming 'live' (particularly given no apparent second point of contact with earth to hand). However, it would depend on an on-site assessment of the individual situation.

Kind Regards, John

 

[bernardgreen]

However, it would depend on an on-site assessment of the individual situation.

as well as consideration of the way the kitchen would or could be used and a sensible interpretation of the book(s) of rules.

if earthed, whether they [ the taps ] were in electrical continuity with the worktops

maybe the taps linked by copper pipe connect the work tops but then the supply to the kitchen is in plastic pipe. ( hence the water pipes are bonding the work tops together but not earthing them ).

What if the taps are bonded via pipe work to the MET and not in contact with the work tops. Potential difference between taps and un-bonded / earthed work top could be enough to tingle due to a class two appliance capacitively coupling 115 volts to the work top.

And placing an earthed metal appliance on one work top would "earth" that work top but only when the appliance was plugged in to a socket.

So many variables that are changing from minute to minute while the kitchen is being used.