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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
    Chris Pearson said:
    What about arc "faults" as thermostats close?

    Probably made worse on frost-free fridge/freezer when the timer kicks in and defrost heater is on. Might explain the  intermittent nature of the tripping.

    How are AFDD manufacturers going to add unrecognised arc signatures that are part of the normal operation of the appliance.

    HAGER seem to have realised the problem and have brought out "ProTools" on their AFDDs which apparently gives better diagnostics on your smartphone and the ability to update the AFDD. I think this is the only realistic way forward if I am going to recommend AFDDs to clients.

  • 0

    Given the tendency of fridges to catch fire, is there a possibility that they aren't nuisance trips, but arcing across a failing thermostat contacts?

  • 0 in reply to Simon Barker

    It’s possible, but how do you know?

  • 0 in reply to sparkiemike

    Because it keeps tripping the AFDD!

  • 0 in reply to Simon Barker

    Or is just a arc signature that the AFDD does not recognise? How do you determine which device is at fault; the AFDD or the appliance? 

  • +1 in reply to sparkiemike

    Really the problem is that these devices have been brought  in with no sensible supporting test gear, to either identify arc faults or to put the AFDDs through their paces in terms of trip/no trip verification.

    For situations as described this is essential, or you may as well go around changing things hopefully, and perhaps when every appliance has been replaced and the building fully rewired you can conclude it was the AFDD after all. 

    You can bet the AFDD vendor won't pay for that, but it is a problem of their creation.

    Personally I see the things as immature, and unhelpful, and far worse, in the regs, without supporting evidence of any great benefit to the users of electricity.

    Mike

  • 0

    I was never comfortable with fridges designed so that the water from inside is channeled into a sump situated on top of the pump, so that it evaporates. Not the best idea to my mind. 

  • 0 in reply to OlympusMons

    The physics is perfectly sound. The only problem that I have experienced is when the drain gets blocked - then the fridge gets wet inside.

  • 0 in reply to OlympusMons

    well, the water was extracted from the air when it was cooled, this is just putting it back, The pump is a sealed unit after all, just happens to be both hot, and full of propane, pentane or hexane, in these post CFC 'ozone friendly' but perhaps more explosive days..

    The nastiest failure of one of the self defrosting machines I have had to handle was one where some mince or something had been pushed to the back of the fridge, and the little tank accumulated this bloodied mess that then took on a mouldy and furry life of its own with the heat of the compressor. We were able to rescue the fridge, but it was a serious cleaning job, both the evaporator dish and the plastic tubes that dripped into it ended up needing a thorough going over.

    Mike

  • 0

    Plot thickens. Tenant has called to say that the AFDD has tripped the past 3 Thursday's at teatime. She is using the same appliances at the same time every other night of the week but it has went the past 3 Thursdays at same time. It is a 14 storey tower block and this flat is on the 8th floor. 

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