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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?

Parents
  • 0

    Not to sound awkward but this post is turning into a discussion about the merits of AFDDs and that has been done already  AFDDs - when do they work? 

    They are a part of the wiring regulations and have become at least "recommended" and "should" be installed. Whilst ripping a protective device it out is an option, fault finding on circuits with AFDDs is going to become part of our landscape. 

Reply
  • 0

    Not to sound awkward but this post is turning into a discussion about the merits of AFDDs and that has been done already  AFDDs - when do they work? 

    They are a part of the wiring regulations and have become at least "recommended" and "should" be installed. Whilst ripping a protective device it out is an option, fault finding on circuits with AFDDs is going to become part of our landscape. 

Children
  • 0 in reply to sparkiemike

    Not in mine it won't - I can stand as many C3s for my installations arising from future EICRs as you can chuck at them.

  • 0 in reply to sparkiemike

    GN3 says we are not allowed to code no Arc Fault Detection Device afdd if the designer did not specify any

  • 0 in reply to Newfutile
    Newfutile said:
    GN3 says we are not allowed to code no Arc Fault Detection Device afdd if the designer did not specify any

    How many people have access to the original designer's specification when doing an EICR?

  • 0 in reply to Simon Barker

    I think GN3 needs another update very soon. Some example points below

    Should EICR get you to check the firmware of an AFDD? (Hager units have bluetooth to update the signature file)

    Should an EICR check solar PV and Battery storage in a domestic dwelling?

    Should an EICR have a section to be completed about fire/heat/smoke alarms in a domestic dwelling?

    Most importantly GN3 can not advise on how to test an AFDD or a Pen fault device properly.

  • 0 in reply to Sergio Fernandez

    You don't test MCBs, fuses or SPDs.  So what's with the obsession for testing AFDDs?  You press the little button, and if it switches off, it's good.

  • 0 in reply to Simon Barker

    Until it switches off when it should not,

    Now at that point with a fuse or MCB you can do clever things with the meter and even  if the problem is not immediately apparent, you can isolate a problem wire or appliance quite quickly, or alternatively decide that all is well and the MCB is defective - which given their simplicity, is quite rare.

    SPDs you do I hope  inspect the series fuse link or breaker to confirm it has not left the planet. On critical kit you would use a pulse generator to  test it with a 'baby surge' just to verify that it was clipping as expected.

    RCDs and RCBOs do actually go wrong depressingly frequently, so those we do test not only when there is a problem but also at first installation and EICR.

    AFDDs contain the RCD part, which really should be tested, and the AFDD part, which is probably more complex and even more likely to play up, but for now no sensible field test kit exists.

    Mike.

  • 0 in reply to mapj1

    "to confirm it has not left the planet"   -   :-)      are we  still allowed a laugh every now and again.  cheers.

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