Work on TN installations come "the 18th"

[EFLImpudence]

Yes, I just meant that's what people will call it -

but then when the neutral fails that's what it will be - like the water bond, not the gas bond because that's not allowed.

 

[ericmark]

I still worry about how much current can flow through any cable connecting the DNO earth to the users earth. I know at point of ayr gas terminal there is a massive resistor connecting the DNO earth to the site earth, however only know physical size of resistor, around size of car derived van. No idea of ohms or why, was it to stop lighting strikes going to DNO or if DNO lost earth not to become the DNO earth?

With a street of houses all with gas and water pipes bonded to the DNO earth any fault current will be shared between all the connections, so no real problem. Where the problem lies if where just one house has it's own earth, so in the case of a fault, all the street tries to use this one earth.

Seen it once in a radio hams house, the 4 mm² earth wire was a load of copper balls on the path. OK the earth was rather good, 4 rods with underground bare copper tape between them.

So if 4 mm² can take 32A and likely would not melt with 60A then as long as the earth is 4Ω or more unlikely to be a problem, but how can one be sure the earth electrode resistance is over 4Ω?

 

[JohnW2]

I must have saved the draft, but can't find it. ....

542.1.201 The main earthing terminal shall be connected with Earth by one of the methods described in Regulations 542.1.2.1 to 3, as appropriate to the type of system of which the installation is to form a part and in compliance with Regulations 542.1.3.1 and 542.1.3.2. Additionally, there shall be an earth electrode, supplementing any earthing facility provided by the distributor, in accordance with one of the requirements of Regulation 542.2.3, to prevent the appearance ofa dangerous touch voltage in the event of the loss of the main connection to Earth.

Does the Draft say this new requirement is for TN-C-S or just PME - and if it does, does anyone think that is what they mean? That is if it says PME does it mean TN-C-S as well? If it says TN-C-S does it really mean that or just PME?

As you can see, the answers to your first question is "Neither" - the reg seemingly applies to all installations. That renders the rest of your questions "not applicable" ....

A seemingly particularly daft aspect is that, as written, it seemingly even applies to TT (as well as TN-S and TN-C-S) - by virtue of 542.1.2.3 (as cited in the draft reg) - hence theoretically requiring that one should "Additionally" have an earth electrode with a TT installation. One has to wonder about the people who wrote, discussed and proof-read that.

Of course, if Risteard is right (only just over a week until we know), this discussion is rather moot, at least for the time being.

Kind Regards, John

 

[JohnW2]

The flat's incoming "Earth" comes to the flat on the Neutral of the supply cable. That is not extraneous. The "Earth" from the ground rod is an extraneous..... ? Yes exactly what is it classed as ?. It is the same as a metallic water supply pipe and as such has to be bonded to the "Earth" that comes to the flat on the Neutral.

If and when the reg that appeared in the DPC becomes reality, there is going to have to be some thinking about terminology, in particular what we are going to call the cable between the 'additional' earth rod and the MET. However, whatever one calls it, I still find your original suggestion confusing. To remind you, you wrote ...

One opton would be a ground rod ( at ground level ) and a substantial conductorm a raising earth, ran up to the top of the building. Each flat then connects it's MET to the rising earth.
Provided the rising earth does not penetrate the equipotential zone of a flat then that is OK. If however the rising earth does penetrate the equipotential zone of a flat then is has to be considered as an extraneous conductor and would therefore need to be bonded to the MET.

I don't understand the "Provided..." clause, and what follows. If one 'connects' the 'rising earth' to a flat's MET, that path to earth (which we agree qualifies as what would currently be called an extraneous-c-p) would inevitably have penetrated the flat's equipotential zone, so I do not understand under what circumstances the rising earth would not penetrate that equipotential zone. You therefore seem to be saying that the rising main would always need to be both 'connected' and 'bonded' to the flat's MET and I don't understand what you mean by that - you're surely not suggesting two G/Y cables in parallel, just to satisfy the semantics, are you?

Kind Regards, John

 

[EFLImpudence]

A seemingly particularly daft aspect is that, as written, it seemingly even applies to TT

I suppose TT would not be "provided by the distributor", so maybe not.

 

[ban-all-sheds]

You therefore seem to be saying that the rising main would always need to be both 'connected' and 'bonded' to the flat's MET and I don't understand what you mean by that - you're surely not suggesting two G/Y cables in parallel, just to satisfy the semantics, are you?

That is exactly what he said would be needed.

He may not have thought it through properly.

 

[JohnW2]

I suppose TT would not be "provided by the distributor", so maybe not.

It says "...supplementing any earthing facility provided by the distributor..." - so seemingly would still apply even if the distributor did not supply any earth, wouldn't it?

Kind Regards, John

 

[EFLImpudence]

"...supplementing any earthing facility provided by the distributor..." - so seemingly would still apply even if the distributor did not provide any earth, wouldn't it?

Would it?

 

[ban-all-sheds]

Can you not supplement a lack of something by adding it?

 

[EFLImpudence]

You might be able to - but if the Distributor does not provide it then the regulation does not require that you do.

 

[ban-all-sheds]

I meant in general.

If something is not there can you not supplement the something by adding the something?

 

[bernardgreen]

"Provided..." clause, and what follows.

The rising ground conductor could be

(1) routed vertically on the outside of the building. It does not penetrate the equipotential zones of the flats.

Hence a single connection to the rising ground may be acceptable to bring the "multiple" "Earth" from the ground rod onto the MET

(2) routed through the interiors of the flats. It does penetrate the equipotential zones of the flats.

Hence there should be a bond where it enters the flat. Would this have to be within a set maximum distance from the entry point as with a bond to a water or gas pipe. Of ot enters and leaves the equipotential zone at two different locations would there need to be a bond between these two locations. The rising ground may fail ( go open circuit ) inside the equipotential zone which then has two extraneous conductive items through its perimeter. For that reason it should be bonded at both entry and exit points.

Then additionally somewhere between entry and exit the "multiple earth" connection from MET to ground rod has to be connected to the rising ground

 

[EFLImpudence]

I meant in general.

If something is not there can you not supplement the something nothing by adding the something?

I said, you might.

John is arguing that the regulation calls for him to supplement his TT earth which he provided with a second rod.

 

[JohnW2]

"...supplementing any earthing facility provided by the distributor..." - so seemingly would still apply even if the distributor did not provide any earth, wouldn't it? Would it?

I would say so.

Quite apart from the semantic argument as to whether can one 'supplement nothing' [see ** below], I don't think that 'explanatory clause' alters the first part of the sentence, which says "Additionally, there shall be an earth electrode". You appear to be suggesting that the sentence as a whole can be interpreted as meaning "Additionally, there shall be an earth electrode, if and only if there is an earthing facility provided by the distributor" - and I really don't think it means that. Apart from anything else, if the authors of the draft reg had intended that, they could surely have said so.

Also note that the draft reg refers to "Regulations 542.1.2.1 to 3". 542.1.2.1 and 542.1.2.2 are fair enough (TN) but 542.1.2.3 relates only to TT and IT, so it appears that the draft reg intends to include them, even though (as well as being silly!) distributors rarely, if ever, provide such earthing facilities these days.

[** Vegans, and those with even more extreme eating habits, often take 'dietary supplements' to supplement those nutrients which are available from their diet. In some cases there will be some essential nutrients which are totally absent from their diet, and I don't think that stops the preparation from 'supplementing' their diet]

Kind Regards, John

 

[JohnW2]

The rising ground conductor could be ... (1) routed vertically on the outside of the building. It does not penetrate the equipotential zones of the flats. Hence a single connection to the rising ground may be acceptable to bring the "multiple" "Earth" from the ground rod onto the MET.

I think that goes without saying. The 'rising ground conductor' and the 'single connection' from it to a flat simply constitute a path from the flat's MET yo the (perhaps soon to be required) 'additional earth electrode'

(2) routed through the interiors of the flats. It does penetrate the equipotential zones of the flats.

I really don't understand why you are trying to distinguish between the 'rising ground conductor' and another conductor which is connected to it and enters a flat. Such a distinction really makes little sense to me.

Hence there should be a bond where it enters the flat. Would this have to be within a set maximum distance from the entry point as with a bond to a water or gas pipe. Of ot enters and leaves the equipotential zone at two different locations would there need to be a bond between these two locations. The rising ground may fail ( go open circuit ) inside the equipotential zone which then has two extraneous conductive items through its perimeter. For that reason it should be bonded at both entry and exit points.

I think we have moved to the 'vanishingly improbable' (sorry, EFLI!), certainly as far as hazards are concerned. If there is structural metal passing through a flat in a block of flats, do you really believe that it must be bonded everywhere it 'enters' or 'leaves. the flat in question? Do you perhaps have shares in a supplier of G/Y cable?

Kind Regards, John