So for the past 5 years if so I have been seeing and experienced a phenomena known as diverted neutral current or diverted networks current.
It has a few names. Much like the incredibly slow realisation that type AC RCDs have had their day. Even though type A has been about over twenty years.
I get at least two / three messages a week from electricians who are now using clamp meters to check the earth conductors of LV installations. Low and behold they find anything from 2A up to 169A in a few cases.
I have research this at work for the last few years and some of the work I have ensured is published via the following link.
We have also managed to produce a visual guide for measuring this issue. This work also helped with the Broken PEN IET article.
It appears the aged life expired state of the LV network is a bigger problem and will only continue to grow. The use of CNE cable has been a tad o IMO. Years ago the RECs admitted cost was the key factor, but made the decision based upon a REC. a government owned network. Since privatisation the DNOs have fixed on fail, leaving the LV side unmonitored to a large extent. This is now slowly changing. But we assume a broken PEN conductor or failure of this can cause hazardous over voltages but also large amounts of network currents bypassing the broken PEN and importing and exporting on domestic earthing in some cases.
whilst the number are small in the scheme or things. It’s a growing issue. The network know about it. But the industry appears to not be discussing it. Why do we not get a safety alert for all electricians nationally. If we find this why are the DNOs and yes some are taking horrific decisions. And in some cases charging. I’ve issued a safety alert for the Railway where I work.
be good to gauge folks thoughts as a broken pen gives you CNE consideration in a home, not allowed by BS 7671 and also brings up the whole what is safe isolation with this in mind. We never consider earth as a energised conductor and only ever consider rise of voltage. Maybe with changing and ageing networks, non linear loads etc. We need to change the way we see things.
I live in hope the networks will be more open on this.
But the industry appears to not be discussing it.
Well, discussions are being held. As Mike says, lots of discussion driven by EV charging equipment installation.
The 9th Edition (2022) of IET Guidance Note 3, published last week, includes a safety check for diverted neutral currents, in Appendix D.
the subject has been kicking about since 2014
If you look back in history, it's been going on a lot longer than that.
The DTI guidance on ESQCR 2002 acknowledges the issue, but it's been discussed much earlier. CP 1013:1965 has discussion on PME, There are some interesting snippets, such as recommendations for consumer's earth electrodes, but most telling. Well worth a read. But issues must have been known at the time the Electricity Act 1947 was drafted, otherwise the provisions in the legislation would not have been put in place.
On and off over the years, since at least as long as I have held C&G "wiring regs" qualifications, i.e. > 30 years, there have been various debates regarding "exporting PME" outside what we used to call the "equipotential zone". The discussions on EV and PME are a continuation of this particular issue, to be honest.
"Neutral current diversion" is not new either, although perhaps we are seeing more effects due to the prevalence in plastic pipes, and the age of the network?
Finally, if we think that TN-S would resolve the issue ... there are such things as protective conductor currents. May only be mA from a single dwelling, but in other premises, and parts of distribution networks, we are looking at many amperes, perhaps 10s of A. And of course, these currents have the same capability for wreaking havoc if the protective conductor breaks (just like the CNE conductor in PME systems - at least with PME the lights go dim rather than relying on a person alone to find out by touching an exposed metal part connected to the installation earthing system).
I personally would like to see more transparency on such a important safety matter, even if it is a work in progress.
Agreed, although coming to agreement on the seriousness of the issue is quite difficult - particularly, as I pointed out in the immediate para above, protective conductors are not necessarily "safe to touch", and never were - especially if you disconnect them in a live system.
Now Graham, you know I have read CP 1013 and BS 842, plus every edition of G12 and associated docs.
The term throwing ones rubbish over the fence comes to mind (DSO).
Neutral current diversion" is not new either, although perhaps we are seeing more effects due to the prevalence in plastic pipes, and the age of the network?
Now that I totally agree has possibly exaserbated the issue. I am bemused the ENA have been able to influence the new electrode recommendation as per told by IET a colleague who we both know well. cautions were always supposed to be taken when installing electrodes as to the effects on the network currents, but this seems to have gone out the window.
In the old old days, stuff was debate at the institute with peer feedback, this is the only place we now have to attempt to recreate that transparency.
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