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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?

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  • 0

    This is why I am only using Hager due to the protools diagnostic app. Firmware updates available to improve the reliability of the devices. 

  • 0 in reply to Sparky Chris

    I wouldn't be in too much of a rush to go down the Hagar route, at least not until you have watched this

    Hager's Arc Fault Dud Device?

    www.youtube.com/watch

  • 0 in reply to whjohnson

    I saw that video the other day.  David.S of DSES reallly does know his stuff.  If he highlights something to you, you are well advised to look into it further. 

  • 0 in reply to whjohnson

    I’ve seen that. Bit of a rant I think. The Hager sales guy got his back up at Elex and it was downhill from there.

  • 0 in reply to sparkiemike

    David.S does have his own unique style of presenting videos.  That may not be to everyone's taste but his content is sounds and his knowledge is good.   Many people have learnt a lot from his videos.  For example 4 or 5 years ago he was discussing should dual RCD CU be used in the domestic areana.  He heighlights points like troubleshooting, Nuisance tripping,  Diversity, Earth fault leakage from LED and such other electronics.  He has started many a discussion in the electrical community.  Now a days most people fit a minimum full RCBO cu but back then people fitted Dual split load RCD.   Unfortunately some electricians are still fitting dual split load RCD as they have to follow the design from the main contractor.  I went to a Taylor Wimpey flat recently,  finished only 6 months ago and it has a Dual RCD board.  Personally I think dual Split load RCD CU were never compliant.  That can gone back to probably the 16th Edition of BS7671

  • 0 in reply to sparkiemike

    I wouldn't be so quick to judge. He raises some valid points. I would also take some time to read through the comments posted below the video, there some well-informed minds commenting there amongst the usual dross.

    Interesting to note the type testing requirements from the AFDD Standard. What this appears to mean is that it is not possible to construct a MFT type AFDD test function due to the amount of energy dissipated during the test.

    Also, for those who think that an appliance arc fault would be picked up, for example the grenfell fridge - a AFDD would not have detected it.

  • 0 in reply to whjohnson

    What this appears to mean is that it is not possible to construct a MFT type AFDD test function due to the amount of energy dissipated during the test.

    I read that comment too, and found it a very unlikely excuse, or the quoted energies are off by miles..

    It is quite practical to dissipate one or two  kJ into a few cubic inches of metal box and then let it out slowly. There may need to be be quite a long interval between re-tests of course, but that is a reasonably limitation. ( e.g. you permit a 1kJ  strike every minute, that  is a mean dissipation of just under 17 watts continuous equivalent - a level like that can be quite easily hand held.)

    A common approach is to allow material phase changes, such as melting and re-solidifying wax, within your metal block, as then you can even absorb heat with negligable rise in temperature above some limit near the melting point, in much the same way as water stays cool until all the ice has melted or boiling water does not get much above 100C until all the liquid has become gas.

    Mike

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  • 0 in reply to whjohnson

    What this appears to mean is that it is not possible to construct a MFT type AFDD test function due to the amount of energy dissipated during the test.

    I read that comment too, and found it a very unlikely excuse, or the quoted energies are off by miles..

    It is quite practical to dissipate one or two  kJ into a few cubic inches of metal box and then let it out slowly. There may need to be be quite a long interval between re-tests of course, but that is a reasonably limitation. ( e.g. you permit a 1kJ  strike every minute, that  is a mean dissipation of just under 17 watts continuous equivalent - a level like that can be quite easily hand held.)

    A common approach is to allow material phase changes, such as melting and re-solidifying wax, within your metal block, as then you can even absorb heat with negligable rise in temperature above some limit near the melting point, in much the same way as water stays cool until all the ice has melted or boiling water does not get much above 100C until all the liquid has become gas.

    Mike

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