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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

    My understanding (which may well be incomplete or wrong) is that the standard's tests for AFDDs work on the assumption that once there is a break in a cable which causes intermittent arcing, the arcing chars some of the insulation over time, and the carbon makes future arcing easier. So the tests are with carbon rods. A lot of the youtube tests try to create arcs with small copper to copper gaps, which tend not to last more than a second or two, and may be seen by the AFDD as a motor-type spark and not trigger a disconnect.

    So when a youtuber shows an AFDD failing to disconnect, it may be that the AFDD is actually working correctly. Or it may be being completely useless. Or the standard isn't up to scratch. We can't tell from the video.

  • 0 in reply to whjohnson

    Well put!

  • 0 in reply to Chris Pearson

    It is a bit of a conundrum. Refuse to fit and the worst may be a C3 on any future EICR. Fit one and it doesn't work, and a life or property is lost and it's a trip to the High court,hopefully with deeper pockets than those of the manufacturer, who will swear blind that the thing worked 'But you didn't set it up properly, or you didn't install the latest firmware update' There's no means of testing for satisfactory operation either way, so why put yourself at risk in the first place?

    Nope, a C3 will do me..

  • 0 in reply to whjohnson

    My understanding is that AFDDs have been used in Germany for several years now.  I wonder if they are the same type as that used in the UK?  It would be interesting to know how the Germany Electrcian/Technician see this product?  Are the UK issues we see due to the AFDD being used on a ring final circuit rather than a radial?  Is th cable used a factor, T&E with exposed Earth/CPC?

    Maybe some imput from AFDD manufacturers could help to further the debate. 

  • 0 in reply to Sergio Fernandez

    If you want the German electricians' discussions on this topic, search for Fehlerlichtbogen-Schutzeinrichtung, (AccidentalArcSafetyDevice)

    or in or in more informal debate/documents Brandschutzschalter (FireSafetySwitch). Naturally you will need to speak German, or make much use of google translate to make sense of the search results.

    This is a typical rant....

    https://www.handwerksblatt.de/themen-specials/hitzige-debatte-um-brandschutzschalter/afdd-norm-brandschutzschalter-notwendig-oder-ueberfluessig

    regds/mfg

    Mike

  • 0 in reply to mapj1

    It is interesting to read that our German colleagues are unhappy about AFDDs as well.  The cost and the way it was forced onto them by industry rather than sound technical engineering. It would good if anyone can reach out to any German Electrcians/Technicians that speak/write English to join the debate.  Are German AFDDs suffering from the same hit and miss scenario as the UK AFDDs?  Do the Germans have a way to test the AFDD in the feild for trip/no trip verification?  Are some of the AFDD used in Germany over sensitive?

  • 0 in reply to Sergio Fernandez

    You may find the more recent German changes informative also.

    https://www.handwerksblatt.de/themen-specials/hitzige-debatte-um-brandschutzschalter/neue-regelung-fur-brandschutzschalter

    To save you some translation effort. I attach the google translation below.

    Also on other fora the general fermentation is that it is a victory for common sense, as now German electricians are free to do an RA to see if they need AFDD in a particular situation or not.  Reading between the lines, I think that many will now be deciding 'not' unless it is wiring for a  fuel dump or an art gallery..

    regards Mike.

    "

    Fire protection switch dispute is finally over

    Heated debate about fire protection switches - topic specials

    Arc fault protection devices, also known as fire protection switches, are no longer mandatory in the new DIN standard VDE 0100-420. This puts an end to a long dispute.

    This article is part of the topic special Heated debate about fire protection switches

    Since October 2019, the revised DIN VDE 0100-420 has only recommended the installation of fire protection switches, so-called arc fault protection devices (AFDD) , instead of making them mandatory . The draft that was first presented included an obligation to install it and caused heated discussions. Now the standard requires that a risk and safety assessment be carried out instead .

    Following protests from the construction industry and trade, the German Commission for Electrical Engineering Electronics Information Technology (DKE) took up their suggestions and changed the standard. This brings to an end a long and heated argument."

  • 0 in reply to mapj1

    Well, judging by that, it seems that good old engineering common sense has prevailed over the marketing hype for once, and about time too.

    Since JPLE64 or whatever they call themselves, seem to have cross border involvement, I wonder why back in Jan 2020, if they were aware of this debacle and subsequent DIN reform at the time, they didn't take it into consideration before mandating AFDDs into BS7671?

  • 0 in reply to whjohnson

    Maybe Grenfell, to say "We are doing something?"

    Even though it seems to be an appliance that caused the initial fire. Anyone who takes an appliance apart knows they are made to a (low) price point. Their moulded plugs are rubbish, the connections inside are tiny and loose. Yet they get away with it.

    Same with the plastic consumer units that were catching fire, but, we know,they couldnt catch fire, as the BS stated it should be made of self extinguishing or non-flammable plastic.But some did not meet the Standard, some Makers were making flammable plastic CUs.

    But the Electricians got the blame for loose connections (yes, there were some), and the CU makers didnt get taken to Court for supplying Goods that didnt meet the British Standard they were supposedly tested and certified for. And of course, the Makers then got more income, as metal CUs were called for in high risk places, so , what should have been a perfectly good plastic CU was changed due to the Manufacturers bypassing the Rules, and then they made more money because of that. Cynical, me?

  • 0 in reply to whjohnson

    Do JPEL64 publish the minutes to their meetings or could we request the minutes to the meeting where AFDD were discussed and then mandated into BS7671.  If JPEL64, BSI and IET  were aware of what was going on in Germany they could have used the word recommend rather than the world shall.  After all the BS7671 has a definitions section that state what they mean when using the word shall.

  • 0 in reply to Sergio Fernandez

    We've been there before in another thread.

    engx.theiet.org/.../afdds---when-do-they-work

    I would urge you to have a look at who sits on the wiring regs committee to find your answers.

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