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Tackling AFDD Tripping

sparkiemike

How are people tacking AFDD tripping?

In the past if I had a call out for a tripping RCD/RCBO or MCB there are well established procedures and tools to track down the fault.

These range from the visual inspection, insulation resistance testing, earth leakage measurement, RCD ramp testing and RCD time testing. It would not take too long to track down the fault whether it was faulty appliance, water ingress, damaged cable or even a duff protective device. The repair might have taken a bit longer but at least you knew where the fault was.

I had a call out this weekend for a AFDD that was tripping on a ring circuit. The new consumer unit (with 3- AFDDs, RCBOS and surge protection) has been in service the end of November and no issues reported. The customer did his own diagnosing and suspected the fridge/freezer as the circuit stopped tripping when he removed the appliance from the circuit. However, when he plugged the fridge/freezer in to another ring circuit with AFDD protection via a extension lead on a reel it did not trip. At this point I did not know what type of fault it was as the customer did not make a note of LED status on the AFDD.

The fridge has no damage and continuity and insulation resting testing all OK

Ring circuit was intact and insulation testing OK (greater than 500Mohm). The instrument readings were exactly the same as they were at the end of November. Plugged it back in and no tripping. I also ran a 1.8kW load on the same socket for a few minutes to see if I could get it to trip -  all OK.

Ten minutes after leaving the circuit tripped, I returned and from the flashing light sequence on the AFDD it was definitely an ARC fault. Reset the breaker and is was tripping regularly every few minutes.

I plugged in the fridge into another circuit, but this time with my much shorter extension lead. Then proceeded to inspect all sockets and checking tightness of terminals - no issues. Although there are some terminations not accessible for inspection.

Then I noticed the other circuit tripped (with fridge connected via extension lead) - so the conclusion that it is definitely the fridge. As the fridge/freezer is still under warrantee I advised the customer to contact the manufacturer. He plugged it into the original circuit in the hope to keep it running. It did not and I told him again to not run the fridge.

Later that night I get a message that now the other circuit is tripping every time they use the microwave -  not the circuit with the fridge and apparently fridge not plugged in.

At the moment I am not 100% sure it is the fridge and can't rule out a faulty AFDD or has the faulty fridge caused the  microprocessor in the AFDD to go faulty.

As a last resort I told them to switch off all circuits and main-switch and then switch-on one by one. Thinking that these devices have microprocessors maybe they need a restart every now and again - bit like my router at home.

Any suggestions on diagnosing ARC faults?

  • 0 in reply to whjohnson

    firmware update every time one is issued?

    Depends on the nature of the change - it it's just adding yet another few waveforms to the list of "acceptable - don't trip" ones, then you could take the attitude that unless the customer is complaining of unwanted tripping (and has the kind of equipment that generates that particular waveform) then there's no need to upgrade.

    If you wanted to take a precautionary approach (e.g. to cover customers buying in some new equipment and plugging it in themselves in the future) I guess a firmware check/upgrade could be done as part of an EICR.

       - Andy.

  • 0 in reply to AJJewsbury

    What if the firmware was not for the AFDD waveform/signature  but for the Bluetooth itself.  Lets say to address a security vurability in the Bluetooth itself. 

  • 0 in reply to Sergio Fernandez

    well that alone is a good reasoin not to use such a brand - it is a massive exposure of a potential vulnerability.

    Mike.

  • 0 in reply to Sergio Fernandez
    Sergio Fernandez said:
    Personally speaking if I was to fit a CU in my house today I would go for a full RCBO board DP (Daul Pole or Single Pole with switched neutral) with type 2&3 SPD I would also force the DNO/DSO/MO to provide and install mains isolation switch for the safety of the installer. 

    Agreed, although I think that my RCBOs are SPN as opposed to SPSN. My problem was preventing the supplier from putting in an isolator - I had already fitted an Eaton Glasgow and if that says "off", it's off.

    However, it isn't cheap - I shall not see much change from £1k for the house DB (with its Type 2 SPD).

    If you look at the cost of AFDD/RCD/MCB combos from the same manufacturer, you would faint; so the cost-(significant) benefit (very small) ratio is decidedly wonky.

    P.S. In phase 1 of the installation, I put in MCBs for the lights because I could, but only just. :-)

  • 0 in reply to Chris Pearson

    SPN as opposed to SPSN.

    Just be aware that I've seen "SPSN" to mean both "single-pole switched neutral", and "single-pole solid neutral" in different literature Disappointed

       - Andy.

  • 0 in reply to AJJewsbury

    I bet that will catch a lot of people out.  switched neutral   and   solid neutral

  • 0 in reply to mapj1

    Mr Savoury has posted a update video on his previous AFDD episode.

    www.youtube.com/watch

  • 0 in reply to whjohnson

    I have watched it and the others he has done on AFDD and I find it quite interesting.  Several AFDD tested in what seems to be real world potential fault situations.  Several things come to mind

    1)  No real way to test and verify that the AFDD is functioning correctly.  Test button is for the RCBO side of the unit.  POST (Power on SELF Test) may or may not work as intended

    2)  Different propriatory software and hardware across different manufacturers.  Fault or status indicators of differing colours and sequence could lead to confusion for the electrician or the person operating the CU eg Home owner

    3)  Differing trip characterists on the AFDD tripping side, some are more sensative than others.  However they all to claim they conform to the same standard. 

  • 0 in reply to Sergio Fernandez

    I'm sure they all do meet the standard - but as said many times, and also demonstrated with a bit of theatre by DES and others, the acceptance tests as written in the standard are not especially realistic of faults as they occur in the real world.

    Very few of us when tracking down a fault find pairs of carbon rods, spacing adjustable by a micrometer, to be the cause of the problem - people just do not fit that sort of thing to a UK installation ! To be fair even if someone wanted to, I've never even seen it as a standard part in the catalogues.

    Nor do folk go around applying many KV to twin flex to trigger partial decomposition between cores.

    And yet those are the series and parallel arc tests that an AFDD  has to identify to earn its badge of compliance.


    In that sense Dave's rat bite or abrsaion plus some saline to represent rat wee is perhaps more realistic of the sort of damage that might start a fire in a real property - and by not connecting the CPC it overlooks that in the UK at least, an RCD trips for that sort of fault anyway.

    Mike.

  • 0 in reply to mapj1
    mapj1 said:
    the acceptance tests as written in the standard are not especially realistic of faults as they occur in the real world.

    Maybe the people who write the UK standard need to revisit the standard?

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