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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.

Parents

  • 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.

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  • 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.

Children
  • in reply to Alan M Walton
    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.

  • in reply to Alan M Walton

    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. 

  • in reply to Alan M Walton

    Maybe there needs to be a new version of the SMART meter designed (single and 3 phase) so that it can detect PEN faults.  This in time could be rolled out in due course when the DNS/DSO/MO swap out the electrical meter.  In the here and now maybe the initial thing to do is educate people in the industry on how to test for it (DNC/Broken PEN).  Possibly it could be encluded as a feild in the EICR/EIC.  just 2 boxs for the Ampage either side of the MET.  Once electrcians are asked for the infromation they will start to think, well why is it needed. 

  • in reply to Alan M Walton

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

    They sort of do already - a PEN fault will typically result in a change (usually a fall) of L-N voltage (as it's also L-PEN and the open PEN is pulled up by connected loads) - (the same principle as many of the open-PEN detectors used on EVSE).- so the meter may (under certain conditions) see a broken PEN as a supply fail and report it.

       - Andy.

  • in reply to Sergio Fernandez
    Sergio Fernandez said:
    just 2 boxs for the Ampage either side of the MET

    What if there are no extraneous-conductive-parts - under those conditions? Such a measurement won't help, but that doesn't stop a potential existing between exposed-conductive-parts and Earth, i.e. Class 1 equipment outdoors, in an open-PEN event.

    Where is the current path back to Earth? Your neighbour's installation perhaps !

  • in reply to gkenyon
    gkenyon said:
    What if there are no extraneous-conductive-parts

    Very good point

    gkenyon said:
    Where is the current path back to Earth? Your neighbour's installation perhaps !

    Probably

    With more people discussing it (DNC / Pen fault), then more people will become aware of it as a possible issue.  We are all engineers at differing levels and with different diceplins.  An open debate helps to bring ideas to the table to help design and implement a solution for the greater good. 

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