Is there an error in 312.2.1.1?

Note 4(b): "Regulation 8(4) of the Electricity Safety, Quality and Continuity Regulations (ESQCR) prohibits the use of a public distribution network neutral as a protective conductor in consumers' installations." 

I noticed that too - and with some unease. We're always being told that JPEL/64 members can't offer interpretations of BS 7671 but rather such matters sit ultimately with the courts, so it feels rather odd for them to be offering an interpretation on some regulations with higher legal status - especially when that interpretation differs perhaps significantly from common understanding of the printed words.

   - Andy.

AJJewsbury said:

I noticed that too - and with some unease. We're always being told that JPEL/64 members can't offer interpretations of BS 7671 but rather such matters sit ultimately with the courts, so it feels rather odd for them to be offering an interpretation on some regulations with higher legal status - especially when that interpretation differs perhaps significantly from common understanding of the printed words.

The notes of the standard are not normative, so there's no need to conform to them to conform to the standard.

The court is at liberty to take into account the notes of the standard (or not) when deciding to interpret the standard, but the legislation says what it says.

The issue is, that by considering PNB, island mode configurations, backup generators, multiple parallel supplies,for example the considerations posted in this thread: TN-C-S (PNB) versus TN-C-S (PME)., we are, unfortunately, where we are ...

It still seems a bit of a leap to suggest that "A consumer shall not combine the neutral and protective functions in a single conductor in his consumer’s installation." applies only to the distributor's N .. I can see that the general context is that a consumer is someone who receives a supply from a supplier/distributor, but it doesn't take much imagination to think the ESQCR's prohibition applies to all of the consumer's installation, even if it's fed through a local transformer or similar. The physics, and therefore the dangers, are surely the same regardless of ownership.

To me it seems the whole problem arises from the mistake of calling the connection between the earthing point and the star point a PEN conductor (which isn't justified by any of the definitions I can find) - get that right and the ESQCR doesn't look like a problem any more.

   - Andy.

More importantly, that new paragraph in '7671 is not actually what the ESCQR says, or anything like it actually ! 
If the law  did say that, all PME would be illegal as we very much rely on the public neutral to be a conductor  for the protective earth to work in those  customer installations... What the law actually says is far simpler and might as well have been quoted verbatim.

Mike

PS
And if it did not rely on the public neutral, then all the worries about open circuit neutrals on the street network, from 'the killing ground' onwards would be moot.

(side note as far as I know the hazard of the interrupted neutral on TNC-x was first seriously brought to public attention in the article The Killing Ground by Peter Chadwick, G3RZP in 1987   part 2  there was  also similar article in Electronics World.  Some of the advice in that article is no longer applicable. 
The reason being that long before EV cars, amateur radio people have been 'exporting' mains earth to their antennas outside, in many cases simple wires, but some have masts and towers to rival the professionals - indeed some actually are the professionals, just on their days off - and problems with diverted earth current are well known to many in those circles. Hams tend to do odd things and may serve as the canaries in the coal mine by having problems no one else does. Fortunately there are not enough of us to trouble the accident stats or require special electrical legislation.)

AJJewsbury said:

it feels rather odd for them to be offering an interpretation on some regulations with higher legal status

gkenyon said:

The court is at liberty to take into account the notes of the standard (or not) when deciding to interpret the standard, but the legislation says what it says.

BS 0 4.3.2 "Interpretation Responsibility for interpreting a standard rests with its user, informed where necessary by appropriate expert advice. Ultimately, the only body with the power to give a definitive interpretation is a court of law."

Leaving aside the criminal courts and other courts with special powers, in general, courts exist to determine disputes when it has not been possible for the parties to reach agreement.

312.2.1.1 is concerned with single-source systems. It seems to me that if a consumer combined the neutral and protective functions in a single conductor in his installation, that would be so clearly unlawful that if a loss arose because of it, the consumer would be advised to admit liability. If any standard could be interpreted differently, it would be no defence in law.

So, Note 4(b) is redundant.

The same note as in 411.4.3 appears in 543.4.1.  543.4.2 to 543.4.8 then outline the circumstances when a PEN conductor may be used, which seems a little odd, but presumably applies where there is a second source of power.

As an aside, as far as R.21 and R.22 of ESQCR are concerned (switched alternative and parallel supplies), the installation must comply with "British Standard Requirements", which are 17th Edition (2008).

ETA: if the dwelling is in England, and let, the installation must also comply with 18th Edition (2018).

well this DTI guidance document to the ESCQR is interesting.  I realize the DTI has since been subsumed, but the guidance has not as far as I know been replaced or updated.

For each major section of the then fairly new ESCQR, it sets out the intention.
Page 19 has the relevant note

Consumers may not combine the functions of neutral and protective
conductors in their installations,
i.e. consumers must not operate TN-C systems or use CNE cables within their installations. Distributors operating such systems must comply with additional requirements (see regulation 9 Protective multiple earthing).

So at the time of drafting, the concern was TNC, not really diverted neutral current.
It is therefore entirely possible that the guidance, or the legislation, should now be revised for the new world order. 

It does not however explicitly say 'cannot ever have a customer side NE link' or indeed mention the abbreviation  PEN. Which is good, as private LV generators still require an NE link somewhere, even if it is a switched one for when the mains fails. The problems arise of course when normal neutral currents and fault-only earth currents get confused about where they should be flowing, and some part of that split path is inadequate. 

Mike.

mapj1 said:

It does not however explicitly say 'cannot ever have a customer side NE link'

Indeed not. However, all the systems in 312.2.1 have a N-PE link somewhere (even TN-S at the star point). If you add another one in the consumer's installation, do you not then have two conductors in parallel between the two links? So now, which is which?

two conductors in parallel between the two links? So now, which is which?

Well indeed, labelling is a problem, though of course we all know that the electrons neither know nor care about the colour of the insulation being blue or green & yellow, so the current splits between the paths in inverse proportion to their resistance, and so, to be safe, both conductors must be sized accordingly much like any other conductors in parallel. The problem is one of naming - rather like the PNB - TNS  thing. 

Actually I understand it is not an uncommon situation on campus type installations with multiple parallel transformers with both HV and LV mains connected between buildings  to allow any one transformer to be bypassed and taken out of service if required during maintenance or building works. Such systems may not quite meet the strictest interpretation of the ESCQR, although if the two rings are called "distribution", rather than "consumer" wiring, it is probably OK, and maybe the bulk of in-service designs that are like that pre-date 2002 anyway. Given the sites tend to be managed and all the maximum current levels are known the risk is better controlled than the random house on a street situation.

Mike

If you add another one in the consumer's installation, do you not then have two conductors in parallel between the two links?

But the usual trick is not to have them both in circuit at the same time - e.g. local generation would either have the generator's N-PE link switched (usually the case if the generator can also operate in parallel with the mains) or be behind a all-pole change-over switch.

If you had another link in-circuit at the same time as the DNO's then you do indeed create a combined N and PE conductor (or even two of them in parallel) - which is exactly what the ESQCR is trying to prohibit.

   - Andy.