Is the UK the only country that continues to permit and deploy TN-C-S earthing systems?

Philip Oakley said:

an contributor (Australia I think) suggested that the problem was that it (DNC) is unique to UK

PME, or more broadly TN-C-S (i.e. TN-C distribution network, separated out at the consumer service head) is NOT unique to the UK, although in some countries other acronyms are used. Examples include (but may not be limited to, and in no real order):

• Australia (where it is called MEN - multiple earthed neutral)
• New Zealand (also called MEN)
• Republic of Ireland (termed TN-C-S)
• South Africa
• Germany
• Austria
• Netherlands
• Norway (just starting to use the arrangement)
• USA (called MGN - multiple grounded neutral)
• Canada

I would be really surprised if someone in Australia believes diverted neutral currents (and open-circuit or high resistance neutrals) in TN-C-S systems are unique to the UK, because I understand there have been a number of cases in Australia, among the most serious being a very sad and widely publicised case of severe electric shock received by a child in 2018 as a result of a broken MEN neutral: www.wa.gov.au/.../Investigator-releases-report-into-electric-shock-of-Denishar-Woods-20190927

In the USA, diverted neutral currents are known to be problematic, and there have been reported cases of diverted neutral currents in and around marinas etc. that might have been responsible for cases of electric shock that resulted in drowning.

Thank you Graham.

Reading between the lines of the correspondents replies, it sounds like the supplies they work on have the MET supplied by their electric supplier, so a slight shift across the interface responsibilities between arrangements.

I'm also guessing that there is a lot of well distributed (distance between) supplies in their Au context, while many of our DNCs are either cluttered or old supplies. Experiences vary.

Thanks again for the clarifications.

I am confused. Is the discussion about diverted neutral currents or lost neutral?

If all the countries listed have PME like arrangements why is it that from what I have experienced only UK regulations and UK EV charge point manufacturers worry about open pen detection., maybe with a few exceptions where companies highly value the UK market. As far as I know it's never included in granny chargers. Is it because the other countries all have a supplementary earth connection to some sort of very good TT earth. 

Chris Pearson said:

I am confused. Is the discussion about diverted neutral currents or lost neutral?

Well ... aren't "high resistance neutral" and "lost neutral" quite simply the extreme cases of diverted neutral current (the resistance of the neutral is so high that the alternative path is now preferred by the current, or is the current's only option)?

Any case of diverted neutral current might cause local rises in earth potential, or rises in potential of conductors connected to the TN-C-S neutral with respect to local Earth.

Alan B said:

If all the countries listed have PME like arrangements why is it that from what I have experienced only UK regulations and UK EV charge point manufacturers worry about open pen detection

Good question.

The reason we consider PME as potentially problematic in the UK is because of the DTI guidance on ESQCR: see the bottom of page 20, where it states:

Special consideration should be given to the earthing and protection arrangements for certain installations where reliance on the connection of the consumer’s protective conductor with the distributor’s combined neutral and protective conductor could result in more significant risks.

Previous legislation and industry practices with PME also highlight the risk. Basically, the Government told us to be careful!

PEN fault protection is being actively considered in the Republic of Ireland.

Some other countries, like Germany, have other measures in place, such as foundation earth electrodes, and they don't see it as an issue.

Australia, I understand, are putting the onus on distributors to monitor for PEN faults with the smart meter system.

New Zealand believe the risks are low and have advised anyone receiving tingles or minor shocks to report this to the distributor.

And yet other countries have different views in their legal system (at the moment) and are not taking action.

So, it's actually a "luck of the draw" that we are in the UK and the UK legislative framework and hazard perception have led to this point. Let's be quite clear ... there are far greater risks of injury from driving the EV than charging it (even from unprotected PME) !

Alan B said:

Is it because the other countries all have a supplementary earth connection to some sort of very good TT earth. 

No, as above Germany does, but not everywhere else. Whilst BS 7671 now recommends installations with TN earthing arrangements have an additional earth electrode connected to  the MET, it can be easily demonstrated that for it to guarantee to provide protection, the earth electrode resistance that needs to be achieved is very low - single figures in fact ... but would depend on the three-phase unbalance of the distribution network downstream of the break. Worst-case is that all properties downstream of the break are on the same phase, or that phase is the only loaded phase downstream of the break, and you would need earth electrode resistance of less than 1 ohm.

But there's no saying other countries won't get on board if tragic incidents like the one in Australia happen elsewhere.

Unfortunately the report itself appears to have gone awol.

Another page https://www.wa.gov.au/government/announcements/release-of-beldon-electrical-accident-report shows the WA method of connection being discussed, with the MET being on the DNO side, and no DNO side CPC (i.e. only a 2-wire supply).

Yes, the original video was about 'lost neutral', however it has a lot of similarity with diverted neutrals, especially in fault conditions and depending on where the potential path to earth was located. This then created the comment that TN-C-S was somehow 'wrong', and my seeking of clarification.

seconded, as one who travels and tries to use the local supplies I have taken loads of  photos of the electrics in strange places. The risks are the same, perhaps greater, in very many places, the difference is mainly that the locals don't worry about them as they are small beer compared to other dangers, especially in the developing world.

TN-'x' == don't really care if its earthed or not, really is the only common standard ;-)

In Russia and much of the former communist bloc that followed their wiring rules, 2 wire supplies even within the building were common and when a 3 pin socket was needed, the 'earth' for it was generated by a short link to neutral behind the sockets -  totally defeating the point of a CPC in my view,  -  though in the former East Germany that was already changing in the mid 2000s, and has probably improved further, though personally I've not been further East recently.

Mike

Philip Oakley said:

shows the WA method of connection being discussed, with the MET being on the DNO side, and no DNO side CPC (i.e. only a 2-wire supply).

In the UK, the distributor provides the TN-C-S earthing terminal.

In other countries, it is not always the case, and the consumer takes the neutral and separates the supply.

At the end of the day, it's all TN-C-S, and the same risks apply, regardless of where the legal fault might be, and where the "-S split" occurs.