Taking cables from a house to a garage

[steptoe]

You have read the Regulation, haven't you?It's in section 531.3 RCDs in a TN system.

The actual Reg. starts. "In a TN system."

case closed

you are not permitted to have a TN system in a normal domestic enviroment in the UK

you are now clutching at straws to justify the unjustifiable.

mixed earthing systems are specifically prohibited under BS7671,

not the law,

but EAWR does not permit them either for consumer installations.

it is illegal

my last post in this thread.

 

[spinlondon]

Where. There is only one connected to the MET. Where is this other you refer to? The Accessory you added a rod to maybe? Well the earthing for that accessory is not the same as the rest of the installation in the same way (omg here we go, can of worms opening) as if you don't export your TNCS to a shed and TT the shed instead.

Now it's an accessory.

I read 'that part of the installation'.

Would the shed be classed as part of the same installation, or a separate installation?

 

[spinlondon]

case closedyou are not permitted to have a TN system in a normal domestic enviroment in the UK

you are now clutching at straws to justify the unjustifiable.

mixed earthing systems are specifically prohibited under BS7671,

not the law,

but EAWR does not permit them either for consumer installations.

it is illegal

my last post in this thread.

I don't suppose you could provide a Regulation from either BS7671 or

EAWR89 to support this outlandish claim could you?

Why do they have these Regulations if the sytem is outlawed

411.4.2, 411.4.4, 711.411.4, 740.411.4, 530.3.2 and 537.1.2?

 

[steptoe]

REG 16

obviously you do not comply

end off,

 

[ADS]

case closedyou are not permitted to have a TN system in a normal domestic enviroment in the UK

Now who doesn't know what they're talking about - the two most common domestic systems in the UK are TN systems:

TN-S and TN-C-S

I think your getting confused with TN-C, which is illegal in the UK

 

[PBC_1966]

Three more pages since I left last night, and I still see no actual electrical explanation as to why an extra earth electrode on a TN-C-S system is supposed to be dangerous, nor any attempts at explaining how a purpose-made rod differs electrically from a bonded underground metallic water pipe connected to the same point.

Picking up on this issue from earlier:

No, but at least in the past the supply authorities would not permit TN-C-S to be used unless the network was PME.

I would like to know where you have got that information

I believe it was covered by the Electricity Supply Regulations 1937. You'll find references in the 13th & 14th editions (possibly 15th as well).

I checked through the 14th edition last night and found the relevant references.

D.34 (iii) Where Protective Multiple Earthing (P.M.E.) is provided by the supply undertaking, in accordance with the conditions laid down by the Minister of Power or Secretary of State for Scotland, with the concurrence of the Postmaster General (see Appendix 5), the earthing lead shall be connected to the consumer's earthing terminal and, together with the neutral conductor of the consumer's installation, shall be so arranged that connection to the neutral conductor of the incoming supply can be carried out by the supply undertaking.

So there you have the clear reference in the 14th edition that TN-C-S was to be used only with a PME distribution system.

The relevant references to PME from appendix 5, "Typical form of approval used in particular instances by the Minister of Power when authorizing the use of Protective Multiple Earthing."

NOTE.- The approval conveyed by the form is issued to Area Boards only, when they seek to use multiple earthing under Regulation 4 (viii) of the Electricity Supply Regulations, 1937, for the purpose of applying the system known as Protective Multiple Earthing to all consumers' installations on a particular distribution system. {.....}2. {.....}

(2) Protective multiple earthing shall not be installed in any system unless there is at the supply transformer of the system a connection to a separate earth electrode (as defined in paragraph six) from each of the following points, the said electrodes being so placed that their resistance areas are distinct: {.....}

(B) the neutral point of the transformer, which point shall be bonded to the metal sheathing and any metallic armouring of the distributing mains of the system {.....}

(4) In each distributing main of the system, connections from the neutral conductor to earth electrodes or to the metal pipes of one or more water supply systems shall be made (each being above ground and in such a position that it may be inspected) at points at or near the end remote from the supply transformer of the main and of each branch thereof, and at such other points (so far as practicable at regular intervals) as will ensure that the overall resistance to earth of the neutral conductor -

(a) is such that the fuses or automatic circuit breakers protecting the high voltage side of the supply transformer operate in the event of a breakdown between windings; and

(B) does not anywhere exceed ten ohms.

So there are your references that in the past TN-C-S was not permitted unless the distribution system was PME.

Back to the local electrode issue, I was sure I'd seen other references to this in older books, and a scan through the 13th edition reveals such. Here is the entire applicable regulation so you can read it all in context, just with my emphasis added on one of the notes:

409 Where in accordance with Regulation 406 protection against dangerous earth-leakage currents by means of a fuse or overload circuit-breaker is admissible, the means of earthing shall comply with one of the alternative methods set out in Clauses (A)-© belowA) The earthing-lead shall be connected to a means of earthing provided by the supply undertaking which affords a metallic return path to the earthing-point of the supply, either by -

(i) the metal sheath (and armour) of the incoming supply cable;

or (ii) an additional conductor, e.g. a "fifth wire" of an overhead line.

Or (B) Where Protective multiple earthing is carried out by the supply undertaking in accordance with the conditions laid down by the Minister of Fuel and Power with the concurrence of the Postmaster-General (see Appendix F), the earth-continuity conductor, together with the neutral conductor of the consumer's installation, shall be so arranged that connection to the neutral of the incoming supply can be carried out by the supply undertaking.

NOTE 1. - Where earthed concentric wiring is in use in the consumer's installation, the outer metal conductor fulfills the function both of earth-continuity conductor and of neutral conductor.

NOTE 2. - Where the requirements are met by compliance with Clause (B), compliance with Clause © below is desirable as an added precaution.

Or © The earthing-lead shall be connected, at a position as near as practicable to the consumer's terminals, to an effective earth electrode buried in the ground, for example a metal water-pipe system having metal-to-metal joints (see Appendix E) or to a copper strip or rod. Connection to a water-pipe shall be made as near as practicable to its point of entry into the ground. A gas pipe shall not be used as an earth electrode.

NOTE. - Attention is drawn to the increasing use of non-metallic water-pipes and mains, which cannot be used for earthing.

So there you have it: Over 50 years ago the Regs. recognized the adding of an earth electrode to a TN-C-S system as an extra safeguard.

 

[ianmacd]

So there you have it: Over 50 years ago the Regs. recognized the adding of an earth electrode to a TN-C-S system as an extra safeguard.

I disagree with your interpritation of that and suggest that that 409© is suggesting that the rod/whatever is connected to the PEN (without using the term PEN). Is this not just what is done in other countries that use PME (i.e. rodding at entrace to customers premesis but on PEM)?

This really comes down to a position of responsibility. BS7671:2008 does not support the use of 2 differing but interconnected earthing systems and in fact suggests it should not be done. Even the passages from 50 years ago suggest the same (depending on how you read them).

It is not an electrical argument (as 6 inches of copper will make bu**er all difference), its an argument about segrigation of responcibilities/duty. The MET belongs to a customer and should only have one method of earthing attached to it. If a rod is needed it should be on the PEM (and obviosly done by DNO). If someone installs a rod onto a PEM with TNCS then 7671 can no longer be used as a defence.

 

[Andy™]

i still fail to see how connecting a rod is 'dangerous', but connected metallic pipe (which is effectivly a rod) is safe

 

[ianmacd]

[quote name='Andy

 

[PBC_1966]

I disagree with your interpritation of that and suggest that that 409© is suggesting that the rod/whatever is connected to the PEN (without using the term PEN).

I'm not sure how you're getting that interpretation of it. 409© says "the earthing lead shall be connected ..... to an effective earth electrode."

It doesn't say anything about connecting it directly to the supplier's neutral.

But that's just semantics over the language used. As you acknowledge, electrically there is going to be no difference of any significance whether the electrode is connected to the neutral block at the cutout directly or to the consumer's MET which is linked to that neutral block by a few inches of cable.

Is this not just what is done in other countries that use PME (i.e. rodding at entrace to customers premesis but on PEM)?

I can't speak for other countries, but in the U.S. the requirement is to connect the electrode to the incoming neutral at some point at or before the main supply disconnecting means. Typically the supply neutral will pass through the meter base and directly to the neutral bar in the main distribution panel, that bar being bonded to the casing, and the cable to the electrode run from the neutral/earth bar. Sometimes it's run to the neutral terminal at the meter base.

However, as noted in the recent thread about outbuildings, it's also a requirement to install a separate earth electrode at each such building, so there can still be extra earth electrodes installed beyond the neutral/ground separation point at the main panel.

 

[ADS]

411.4.2 NOTE: The PE and PEN conductors may additionally be connected to Earth, such as at the point of entry into the building.

Doesn't say who can do it - in fact I've never seen a DNO earth rod at the entrance to anyones house - they'd never foot the bill for that, they won't even fit an isolator for nothing.

And before anyone gets picky-

PEN conductor is connected to the MET which is connected to the rod - you're not gonna get closer to the entrance to the building than that - unless you start hacking open the supply cable.

And can you honestly tell me ther's a difference between the above arrangement and connecting it 6 inches lower (eg before the cutout).

Come on!!

 

[ianmacd]

I'm not sure how you're getting that interpretation of it. 409© says "the earthing lead shall be connected ..... to an effective earth electrode." It doesn't say anything about connecting it directly to the supplier's neutral.

See Note 1 for B.

 

[ADS]

For anyone interested, I've spoken to the DNO (Scottish Power) and I've spoken to the IET (the big red book people)

Neither of them can see anything wrong with connecting a rod to the MET as an additinal reference to earth when PME conditions apply.

The DNO said it doesn't affect their setup at all and the IET said if the DNO are alright with it then there's no reason why you can't.

Now, I think, the case is finally closed.

 

[ianmacd]

Got that in writing?

 

[ianmacd]

411.4.2 NOTE: The PE and PEN conductors may additionally be connected to Earth, such as at the point of entry into the building.Doesn't say who can do it - in fact I've never seen a DNO earth rod at the entrance to anyones house - they'd never foot the bill for that, they won't even fit an isolator for nothing.

And before anyone gets picky-

PEN conductor is connected to the MET which is connected to the rod - you're not gonna get closer to the entrance to the building than that - unless you start hacking open the supply cable.

And can you honestly tell me ther's a difference between the above arrangement and connecting it 6 inches lower (eg before the cutout).

Come on!!

I do not disagree with you that electrically this should make naff all difference but this comes down to arse covering. At the end of the day if you install a rod to a MET with a TN Earth too then that is not covered by the BRB so (as I mentioned above) no protection by 7671. If IET want to ammend 7671 to take into account what they said then thats fine but I bet you won't get anything in writing form DNO about that.

 

[ADS]

The IET said that's what PME is - multiple earthing - you're just adding another one.

The DNO didn't care coz it's on the consumer side and it doesn't affect there system in the slightest.

 

[PBC_1966]

See Note 1 for B.

Kind of a red herring I think. There may not be any concentric involved at all, so I don't see how that affects the basic issue at hand.

At the end of the day if you install a rod to a MET with a TN Earth too then that is not covered by the BRB so (as I mentioned above) no protection by 7671.

I don't agree that it's not covered, as I don't see anything which precludes it, but even if that were so, does that mean that you do not think a TN-C-S system should include a bond to an underground water line? Or to structural metalwork buried in the ground? Or to any other metallic objects which will provide a path to earth?

If the water supply is metallic, for example, are you going to insist that an insulating section be inserted just before the bond to prevent to buried section from acting as an electrode? And that the hot-water cylinder will have to be carefully insulated (electrically) from masonry supports to prevent an extra earth path from being formed? And so on, for every other piece of bonded equipment in the building?

The IET said that's what PME is - multiple earthing - you're just adding another one.

Precisely. And they already have earth electrodes on the consumer side of the installation from the aforementioned bonded services and structures anyway.

 

[m4tty]

sorted

 

[ianmacd]

Kind of a red herring I think. There may not be any concentric involved at all, so I don't see how that affects the basic issue at hand. I don't agree that it's not covered, as I don't see anything which precludes it, but even if that were so, does that mean that you do not think a TN-C-S system should include a bond to an underground water line? Or to structural metalwork buried in the ground? Or to any other metallic objects which will provide a path to earth?

If the water supply is metallic, for example, are you going to insist that an insulating section be inserted just before the bond to prevent to buried section from acting as an electrode? And that the hot-water cylinder will have to be carefully insulated (electrically) from masonry supports to prevent an extra earth path from being formed? And so on, for every other piece of bonded equipment in the building?

Precisely. And they already have earth electrodes on the consumer side of the installation from the aforementioned bonded services and structures anyway.

AFAIK TNCS can only be supplied if the network is PME so I do not see how an lead sheath earth can not be a neutral as into the cutout it should still be a combined PEN and seperated there.

I'm sure I said above that I am not debating the electrical benefits BUT the fact that the regulations we should be following to allow ourselves to be protected by 7671 if we install a rod. The regulations say that there should only be one earthing system.

Since we are not involved directly in writing or updating 7671 then your additional points about multipaths, while correct, are not really relivent. Also, doesn't the BRB say that pipes are not earth electrodes (although they do introduce an earth potential)?

 

[Andy™]

For anyone interested, I've spoken to the DNO (Scottish Power) and I've spoken to the IET (the big red book people)Neither of them can see anything wrong with connecting a rod to the MET as an additinal reference to earth when PME conditions apply.

The DNO said it doesn't affect their setup at all and the IET said if the DNO are alright with it then there's no reason why you can't.

Now, I think, the case is finally closed.

id like to see that in writing