Not really, sadly.

The DNO have no way to measure diverted current, as on anywhere that has TNC distribution, earth and neutral currents are indistinguishable from the substation end of things, coming in on the same wire, and on the load side there is no requirement for installers or users to even measure let alone report currents flowing in the earth bonding  of any level, and even if there was,  there is no organization to report it to that would keep a record.

When there is no fault to correct what would you like the DNO do on receiving such a report  that there is 1 amp (or even 50) flowing between their TNCS earth and the water pipe at a house. ? It could just means the water pipes, in parallel with the street PEN conductor, are actually a lower resistance than it  is.

"Proper" faults, like loss of earth, loss of power or out of spec voltages that are associated with a significant fault PEN are recorded, and the faults are then diagnosed and normally addressed pretty sharpish, and there are figures for those, collated by the HSE.

In an ideal world this information  would all be measured and telemetered in and associated with every MPAN but I fear it is not practical.

Mike.

I have heard of anything 5A and above being reportable to the DNO which seems reasonable, however what if you were to get a reading of 4.5A, due to those variations this could be higher taking it beyond the 5A at other points in the day etc.

Diverted N currents can easily be an order of magnitude higher than than in some "healthy" circumstances - it's unavoidable where other metalwork (e.g. water or gas pipes) are in effect connected in parallel with a length of neutral (PEN) conductor. It's less down to whether the installation is connected or not, rather the size of the loads that happen to be running at the time (and their imbalance if polyphase) - the larger the neutral current, the larger the amount that'll flow through parallel paths. That's why for PME installations we end up with such massive main bonding  conductors. In some circumstances, DNO try to mitigate the problem - e.g. in blocks of flats or where there are multiple occupiers in a steel framed building, they'd often these days have a single N-PE link for the entire building and run separate N and PE conductors to each intake - but there are probably still millions of installations out there with parallel paths that offer resistances not significantly higher than the supply N.

There are two sides to this coin though. In normal healthy circumstances, the diverted N current is a bit of a nuisance rather than an immediate danger. A few tens of amps flowing along a low impedance with likely only generate a potential difference of a handful of volts. The much more significant problem comes when the supply PEN conductor goes open-circuit - then that potential few amps (or fractions of an amp) can result in exposed metalwork being held a very hazardous voltages (even when there aren't any parallel paths) - that's really the issue that plagues EV installations.

As for detection of partially failed PEN conductors - measuring the standing current isn't really a direct metric - as the reading can be influences both ways by the size and nature of the loads (in other installations as well as your own) and the presence/absence of parallel paths (e.g. metallic pipework or structural steel)  - a much more direct method would be simply to measure the L-PEN loop impedance - i.e. the normal Ze test. I'm not sure of the nature of the majority of PEN fault - whether it's typically some gradual degradation, or some short event that causes the break - broken overheads and gaping holes being blow in underground cables by short circuits probably fall under the latter, loose connections the former.

   - Andy.

The real issue is you probably do not know you have a PEN fault in parallel with buildings with good service bonding, as noted, the plumbing or what have you will be comparable or lower resistance than an intact supply cable, so the Zs test may well pass, and unless you know what it was before, a bit of degradation would be hard to spot. 

The time you find out, and by then the PEN may have been open circuit for years, is when the plumbing or gas pipes or whatever are changed, and instead of the usual  little sparkle, as the current interrupts and the open circuit voltage barely twitches and if at all, it only rises by single figures, you get something far more unpleasant ., where a significant chunk of the full phase voltage is available to do some damage.

Rare, but also both impressive and dangerous to the unsuspecting plumber.

Mike

The real issue is you probably do not know you have a PEN fault in parallel with buildings with good service bonding, as noted, the plumbing or what have you will be comparable or lower resistance than an intact supply cable, so the Zs test may well pass

Which is why I suggested a Ze test - as that's conventionally done from the end of the Earthing conductor while it's disconnected from the installation (and so disconnected from main bonding etc). Of course that won't necessarily spot a broken/high resistance PEN that's bridged by extraneous-conductive-parts in neighbouring installations, but then clamp tests the installations protective conductors wouldn't necessarily spot that either.

   -  Andy.

As we were reminded yesterday on an EESS training course, electricity doesn’t just take the earth path with the lowest impedance, it takes all earth paths and you are not going to stop it.

So I am not sure what you are going to achieve and how, unless you actually remove all the parallel earth paths by replacing metal pipework with plastic and so on.

Jamie Bate said:

There is lots of information, about how and why etc, but no physical figures, I am aware that Smart metering maybe able to measure volts/current/power etc however this still seems a little vague.

The reason is, that, as others have said, what is acceptable for one installation may not be acceptable for another.

The amount of neutral current in "non-fault" conditions increases with lower soil resistivity, and also with increased amount of extraneous-conductive-parts in contact with the ground ... and obviously with single-phase load current (or in three-phase installations, load current unbalance between phases). But that neutral current may only travel a short distance before it gets back into the DNO's combined neutral and earth (CNE) in the supply, as that is earthed at regular intervals.

What causes problems is where there are either breaks in the distributor's Neutral in places, and/or a much lower resistance path to "go round" the return CNE in the supply cable.  The design criteria that DNOs use help to address the latter for the most part, but there are still, occasionally, problems.

I've just heard that diverted neutral currents was discussed in Parliament this week.  It has just accured to me that smart meters report supply disconnection automatically. So my question is why can't they be adapted to report PEN faults as well. The technology is there to report lost of power if the supply fuse is pulled. So why can't the rise in amps on the 'earth' be reported  as well. Most PV installations have apps to show where power is coming and going from battery,solar panels and supply. So why can't a CT be put around the 'earths' as well.

Alan M Walton said:

So my question is why can't they be adapted to report PEN faults as well.

Single-phase meters (and three-phase ones without a neutral) can't (on their own) actually detect an open-PEN fault. However, I guess there's no reason why data from a number of single-phase meters on a given three-phase main couldn't be used to help the DNO determine that there may be a PEN fault they might want to investigate.

Would require some form of AI algorithm and a knowledge of meters on each main etc.

This is quite timely for me because I was pondering asking a question in a new thread.

So this afternoon, in rough terms, 12 A in the line, 9.0 A in the neutral, and 3.0 A in the earthing conductor. 0.05 A in the gas bonding. (The plastic water pipe is also bonded!)

The problem isnt giing away over night. So i was thinking about the next generation. The technology is their to record any amp on any cable. It's how we use today's knowledge and pair them up/ combine technologies together for the future.