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Diverted neutral current / broken PEN?

Jamie Bate

Hello all,

Diverted Neutral Currents (DNC) seem to be a big area for debate especially with the push for EV's and the implications that they can cause.

Are there any official figures regarding contacting the DNO regarding these DNC's or recording of it other than on testing documentation (EIC/EICR etc.) ?

This still seems to be an area that needs more information, as variations including the location of the fault, the time of day, year etc. when the test was completed.

If testing a standard PME 100A single phase domestic supply and getting around 8mA on the earthing conductor during the installation being switched on and then reduces 0.01mA when the installation is isolated will probably be more to do with the instrument and 0.01mA = 0.00001A and would indicate that there is no issue. If this stayed at 8mA (0.008A) this is potentially an issue with a broken/deteriorating PEN conductor, however this could change due to variations across neighbouring installations.

When completing this test prior to any other work on the installation and getting readings when not expecting them this is going to impact on any electrical work being carried out, what is deemed as notifiable to the DNO? 

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.

Would it be more appropriate to have anything above 1A reportable to the DNO so they can make their checks and note this on the job/ testing documentation, and where does it become a safety issue regarding work in/on the installation with a broken/deteriorating PEN conductor, as a job could be completed and several weeks later an incident could occur due to further loading and changes to an installation?

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.

  • in reply to Chris Pearson
    Chris Pearson said:
    Another possibility is that the current is going via various supplementary bonding conductors to the CH boilers and pipes and getting into the gas main that way.

    Absolutely, other fortuitous earth paths are a possibility also. What we don't know is the direction of 3A in the earthing conductor and the 9 A in the neutral conductor, and/or (although I'm sure you've discounted for this particular installation) whether there's an N-E fault in the installation?

  • in reply to Jamie Bate

    Looks like we watch the same things.

  • in reply to Chris Pearson

    All is well: Ze = 0.29 Ω.

    The N-E junction is under the side lawn.

    Just now my clamp meter read 0.40 A around L, N, and E together, so quite a few electrons were going the long way round.

    I do wonder whether the N junction in the street is getting a little ropey.

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