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Topic Title: Bonding
Topic Summary: Assume PME
Created On: 26 May 2017 08:10 AM
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 07 June 2017 09:41 PM
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spinlondon

Posts: 5494
Joined: 10 December 2004

No there was not a condition that the Neutral to be multiply earthed, before it was allowed for the Neutral to be multiply earthed.
The conditions that had to be met before the Neutral was allowed to be multiply earthed, were that the Neutral was at least half the CSA of the phase conductor, and that the resistance of the Neutral to Earth was no greater than 20 ohms.

There may be various versions of TN-C-S.
However in the U.K. TN-C-S is only allowed which PME.

Oh ok PME conditions which require a minimum CSA of 10mm2 for main Earthing and bonding conductors can only exist if the earthing and bonding conductors are 10mm2.

Sorry Andy, but it seems you have no idea at all.
According to you, PME is only allowed where PME already exists and the requirement to install larger CSA Earthing and bonding conductors only applies where those larger CSA Earthing and bonding conductors are already installed.
 08 June 2017 01:50 AM
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mapj1

Posts: 9676
Joined: 22 July 2004

However in the U.K. TN-C-S is only allowed which PME.


I'm sure you meant " However in the U.K. TN-C-S is only allowed which is either PME or PNB "

Even that's not what actually happens as there are odd cases where neutral and earth separate, then meet up again and then seperate.- the DNO often side steps this by talking about SNE (separated neutral/earth)
and CNE (combined neutral/earth) rather than "PME", in those cases where it is not quite pure.

-------------------------
regards Mike
 08 June 2017 05:47 PM
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weirdbeard

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Originally posted by: spinlondon

No there was not a condition that the Neutral to be multiply earthed, before it was allowed for the Neutral to be multiply earthed.

The conditions that had to be met before the Neutral was allowed to be multiply earthed, were that the Neutral was at least half the CSA of the phase conductor, and that the resistance of the Neutral to Earth was no greater than 20 ohms.



There may be various versions of TN-C-S.

However in the U.K. TN-C-S is only allowed which PME.



Oh ok PME conditions which require a minimum CSA of 10mm2 for main Earthing and bonding conductors can only exist if the earthing and bonding conductors are 10mm2.



Sorry Andy, but it seems you have no idea at all.

According to you, PME is only allowed where PME already exists and the requirement to install larger CSA Earthing and bonding conductors only applies where those larger CSA Earthing and bonding conductors are already installed.


Spin, just contact the DNO, they can tell you if there is currently Pme available, I believe the average charge to upgrade a non Pme installation upon request to Pme starts from £150+

-------------------------
:beer)
 08 June 2017 09:19 PM
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spinlondon

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Joined: 10 December 2004

Originally posted by: mapj1
However in the U.K. TN-C-S is only allowed which PME.

I'm sure you meant " However in the U.K. TN-C-S is only allowed which is either PME or PNB "
Even that's not what actually happens as there are odd cases where neutral and earth separate, then meet up again and then seperate.- the DNO often side steps this by talking about SNE (separated neutral/earth)
and CNE (combined neutral/earth) rather than "PME", in those cases where it is not quite pure.


Protective multiple earthing
9. - (1) This regulation applies to distributors' low voltage networks in which the neutral
and protective functions are combined.
(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor shall ensure that the supply neutral conductor is connected with earth at -
(a) a point no closer to the distributor's source of voltage (as measured along the distributing main) than the junction between that distributing main and the service line which is most remote from the source; and
(b) such other points as may be necessary to prevent, so far as is reasonably practicable, the risk of danger arising from the supply neutral conductor becoming open circuit.
(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line referred to in paragraph (2)(a) is connected to the protective conductor of a consumer's installation.
(4) The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat.
 10 June 2017 04:20 PM
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AJJewsbury

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Protective multiple earthing
9. - (1) This regulation applies to distributors' low voltage networks in which the neutral
and protective functions are combined.
(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor shall ensure that the supply neutral conductor is connected with earth at -
(a) a point no closer to the distributor's source of voltage (as measured along the distributing main) than the junction between that distributing main and the service line which is most remote from the source; and
(b) such other points as may be necessary to prevent, so far as is reasonably practicable, the risk of danger arising from the supply neutral conductor becoming open circuit.
(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line referred to in paragraph (2)(a) is connected to the protective conductor of a consumer's installation.
(4) The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat.


You'd have to ask the DNOs for a definitive answer to that one - but it seems to me that for PNB systems the additional requirement of 9(2)(a) is satisfied by the one electrode they've already installed under 8(3)(b) - which is permitted to be remote from the source where there's only a single point where consumers are connected - and as long as no further points are necessary (for (b)) then all the requirements of that regulation are satisfied without actually needing multiple earthing as such (notwithstanding the title of the reg course).

It does seem pretty certain that PNB does exist (it would explain G/Y I've seen in N blocks in one or two rural buildings with no apparent LV earthing at the transformer, as well as various current documentation published by various DNOs).

- Andy.
 11 June 2017 10:46 PM
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mapj1

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It does seem pretty certain that PNB does exist


Too damn right, the nearest one to me that I know about is the Ferny Crofts Scout Activity Centre in the new Forest, and I have see a few others in similar remote cases.
That one is very obvious example of a PNB system, all open and visible, with a pole pig style TX on the end of an 11kV line that has the pole a few metres from the building with the metering. The HV transformer metalwork is earthed at pole,and the LV earth is nearer the metering and some way off, and a big red sign saying 'Caution, Earthing by Protective Neutral Bond" both at the TX and the LV ends. NO second LV electrode, and no other customers, so not PME, and no scope for diverted currents.
No idea when the electrodes were last tested,rusty looking enough to be the 1970s. Bits of it are in that genre that Zs affectionately refers to as 'state of the Ark'

-------------------------
regards Mike
 11 June 2017 10:54 PM
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spinlondon

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Joined: 10 December 2004

Sorry Andy but 9(2) states in addition to the requirement of 8(3)(b).
Here's the definition of addition with an explanation of the term addition to:
Addition" is the noun form of "add", as in 2+2=4, or in a non-mathematical sense, to combine two or more things in some way. So "in addition to" means to add one thing to another, that is, to have or use both.

No one (as far as I am aware) is saying PNB does not exist.
Only that it is no longer allowed (by U.K. law) to be used on a public distribution network.
 11 June 2017 11:29 PM
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mapj1

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Well there are several examples in use on the UK networks - what makes you say it is no longer allowed ?
Para 9 does not apply to PNB, as there is no multiple earthing of the PEN.

-------------------------
regards Mike
 11 June 2017 11:42 PM
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spinlondon

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Oh dear.
Do any of you guys actually read anything?
You could at least read what you are posting.
Section 9 (it's not a paragraph) applies where the neutral and protective functions are combined, i.e. as in a PEN conductor.
The requirement is for the PEN conductor to have multiple earthing.
As such PNB is no longer allowed, because as you so rightly state, the PEN does not have multiple earthing.

Edited: 11 June 2017 at 11:52 PM by spinlondon
 12 June 2017 09:08 AM
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AJJewsbury

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As such PNB is no longer allowed

But the DNOs clearly disagree - it's clearly in their published earthing LV policies (as well as being physically visible) - so they must have a different interpretation to you somehow. Either al the DNOs have it wrong, or spin does.

I suspect the better answer is that PNB should be classed as TN-S rather than TN-C-S - but the BS code of practice for earthing has scuppered that. Personally I think it could be classed as either TN-S or TN-C-S depending on the exact arrangement of the earth connection and N-PE link.

Here's the definition of addition with an explanation of the term addition to:
Addition" is the noun form of "add", as in 2+2=4, or in a non-mathematical sense, to combine two or more things in some way. So "in addition to" means to add one thing to another, that is, to have or use both

Yes, but the possibility I was suggesting (a bit subtle I know) was that requirement was additional, rather than the means of satisfying the requirement had to be additional. In the case of PNB (i.e. a single point for consumer connections) the two requirements both require an electrode at the one and same point, so as single physical electrode functions identically to two in the same position. It's just a theory to try and match the observed facts...

- Andy.
 12 June 2017 11:53 PM
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spinlondon

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Joined: 10 December 2004

Not sure if the DNO's agree or disagree.
There was a time where PNB was allowed, usually where the DNO supplied HV to a customer's own transformer.
There was some talk back in 2014 to allow in some circumstances, for up to 4 installations to be supplied PNB.
From what I recall, the proposals included earthing and bonding arrangements to be as per PME, to allow for changing to PME when practicable.
Not aware that the proposals were taken on, there's nothing in the legislation to indicate they were.
As far as I am aware the last amendment to ESQCR was in 2006 and related to Harmonised colours, renewable energy and supplies for railways.
In any event rare cases of PNB aside, the statutory requirements are such that TN-C-S now has to be PME.
If part of a network between the source of voltage and the consumer's installation has combined neutral and protective functions PME conditions apply.
IET » Wiring and the regulations » Bonding

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