Gas pipe earth???

[SaladFingers]

The gas pipe doesn't need 'earthing' - it may require 'bonding' if it is deemed to be 'extraneous' where it enters the property.

Bonding is earth.

 

[EFLImpudence]

Bonding is earth.

Wrong.

We bond it because it is already earthed.

 

[SaladFingers]

Bonding is earth.

Wrong.

We bond it because it is already earthed.

Wrong.

Bonding is a cable going to your main earth terminal from extraneous conductive parts, so you are actually earthing it.

That reason is to bring all metalwork that's extraneous to the same potential.

 

[EFLImpudence]

That reason is to bring all metalwork that's extraneous to the same potential.

And why is it at a different potential?

I know you're just stirring it but if you really do not understand please read up on the subject.

 

[JohnW2]

Bonding is earth.

Wrong. We bond it because it is already earthed.

In practice, that is virtually always the case, but the regs have been written in a way that theoretically requires bonding of things that are not 'already earthed'.

As you know, the regs require main bonding of any conductor which is "liable to introduce a potential, generally Earth potential ...". The "liable to" bit is obviously relevant to this thread - measurements you undertook today might demonstrate that the OP's garage door frame is not 'already earthed' but, as we have been discussing, it is possible that it would be 'liable to' become appreciably connected to earth under certain (mainly wet) circumstances. On that basis, someone might decide that it required bonding, because of this 'liability' to introduce earth potential.

Since the authors of the regs chose to add "...generally Earth potential", I guess we have to presume that they had in mind some scenarios in which the introduced potential might be something other than Earth potential. I think that even I would have to scrape the barrel of the 'vaninshingly improbable' to think of any such scenarios - but the fact remains that the IET seem to believe that it might, in some circumstances, be necessary to main bond something which wasn't 'already earthed' and wasn't even 'liable to introduce earth potential'.

Kind Regards, John

 

[SaladFingers]

That reason is to bring all metalwork that's extraneous to the same potential.

And why is it at a different potential?

I know you're just stirring it but if you really do not understand please read up on the subject.

I'm not srirring, but if you need to ask me why it's at different potential, or why it may be, then its you who needs to do some reading up.

 

[EFLImpudence]

Stop being an idiot.

I'm asking to determine if you know.

 

[JohnW2]

I never really understood this concern, since any currents between the two sets of CPCs would be limited to what the shop's TT electrode could sink - i.e. not very much.

As long as it remains a TT supply there is no significant risk of a CPC acting as a fuse.

Exactly my point (the reason why I didn't understand the concern) - and the reason is that "as long as it remains TT", the currents that could flow between the two sets of CPCs would be very limited - usually to less than 5A. To get a 'fusing (melting) current that low would require a (copper) conductor of ~0.02mm². Of course, if it ever ceased to be TT, then everything would change - but the concern was said to be about the fact that one of the properties was TT - which is what I didn't understand.

Even so the idea of a "fuse" several feet long glowing white hot before melting under the floor boards is not one I can allow.

I think you might be hard pressed to find a conductor as small as 0.02mm² even in common comms cables but, if you did have one, I don't think the amount of energy dissipated, over a fraction of a second, would be enough to cause any problems. However, as I've said, it's just not going to happen whilst one of the properties is TT.

A coming together of the two sets of CPCs simultaneously

would be permanent via the common metallic water supply if the isolating plastic section had not been added.

Again, "so long as it remains TT" (and my understanding was that the concern relates to the fact that it is TT), that can't possibly be a concern - you certainly aren't going to melt a water pipe with 5A, and no CPC in the installation is going to have a problem with 5A.

Even that presents a minor concern with possible electrolysis of water into gas.

That sounds like scraping the barrel to an even greater extent than I've been known to do! Where (and how large) is the PD going to be to result in this electrolysis? ... and we are, of course, talking about AC.

If the shop, which is fed from a different street cable did convert to PME then the CPC to CPC link would become a link between two different network neutrals and would then carry some of the network load when the two network neutrals were at different potentials.

Sure, but that would be an totally different situation and discussion. What I didn't (and still don't) understand were the concerns seemingly specifically based on one of the properties being TT. In any event, what you describe is really no different from the situation which exists all over the place, where adjacent properties with TN-C-S supplies are 'connected' via metal water (or gas) supply pipes. As you probably know, I have the opposite of your situation - my TT installation seemingly 'enjoys' the PME 'earth' of an adjacent property (Ze around 0.25&#937, presumably via the water pipe connecting the properties.

Kind Regards, John

 

[SaladFingers]

Stop being an idiot.

I'm asking to determine if you know.

Now now, let's not begin name calling - keep the discussion technical.

I've already said, as it's extraneous. It doesn't go back to the same point.

 

[JohnW2]

Now now, let's not begin name calling - keep the discussion technical. I've already said, as it's extraneous. It doesn't go back to the same point.

I really think you're doing a disservice to this forum, and its members. Many people get confused enough about this topic without you making things worse. If you genuinely didn't understand, I'm sure that many of would be pleased to try to help you understand - but it seems probable that you do understand, and are merely trying to introduce confusion.

Kind Regards, John

 

[SaladFingers]

Now now, let's not begin name calling - keep the discussion technical. I've already said, as it's extraneous. It doesn't go back to the same point.

I really think you're doing a disservice to this forum, and its members. Many people get confused enough about this topic without you making things worse. If you genuinely didn't understand, I'm sure that many of would be pleased to try to help you understand - but it seems probable that you do understand, and are merely trying to introduce confusion.

Kind Regards, John

No problem at all.

Regards.

 

[JohnW2]

No problem at all.

Thanks - but I'm not exactly sure what you mean by that. Hopefully you mean that you are going to stop playing, and therefore reduce the potential problem for other forum members - is that what you meant?

Kind Regards, John

 

[SaladFingers]

No problem at all.

Thanks - but I'm not exactly sure what you mean by that. Hopefully you mean that you are going to stop playing, and therefore reduce the potential problem for other forum members - is that what you meant?

Kind Regards, John

That's right John,

I didn't mean to cause a stir. However it appears, I do respect the knowledgable on here and the people requiring help.

 

[dylanlennon]

This is probably another stupid question but...won't the steel have an earth at it already as the bit that the flex goes into for the electric garage door, sits on top of the steel frames, joined by nuts & bolts?

I think you're probably getting confused by two different 'earths' we are talking about - (1) the 'earth' of your electrical installation (i.e. the 'earth conductors' in the wiring of your house and garage) and (2) 'true earth' - which in this context means the ground/soil on which the garage is built (and which the metal of the garage door frame may be in some degree of electrical continuity with, particularly under wet conditions).

For (1) to be connected to the metal door frame is fine (and doesn't create the need for bonding) - that's no different from any other metal appliance, tool, switch or socket in your house or garage. The potential danger which, if it exists, requires bonding [of (1) to (2)] arises if any of the garage metalwork (like the door frame) is connected to (2).

Is that clearer?

Kind Regards, John

Ahhh yes, a lot clearer. Thanks.

 

[JohnW2]

That's right John, I didn't mean to cause a stir. However it appears, I do respect the knowledgable on here and the people requiring help.

Thanks. That's good to hear.

Kind Regards, John