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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

    So let's take stock.

    Is anybody persuaded that AFDD would have saved Grenfell?

    Is nuisance tripping a significant phenomenon?

    It would be lovely to have a show of hands. Has anybody in here installed that at home? (I made further progress with my own installation today, but AFDDs are nowhere to be seen.)

  • 0 in reply to Chris Pearson

    Not me. Although I am intrigued as to exactly where this 'crimp' was actually situated. Was it a manufacturer's joint inside the fridge? Or was it in the appliance flex to enable the lead to reach a socket outlet? The report seems to be at odds with itself in places as to whether or the the crimp was the root cause.

    As for AFDDs saving the day? How could it be proved either way? Hager are going down the same route as many motor vehicle makers - 'Sell the service and not the product', is the new mantra. No money to be made in selling the vehicle, rather, why not sell a monthly paid app to enable certain features instead? It is a akin to buying a loaf of bread, yet having got it home you have to pay an app firstly to open the package, then pay another on a slice by slice basis as you consume it.

    Personally, I dislike the introduction of smart and other electronics into mains kit just to enable data gathering. Although not mains, the fact that a otherwise mechanically sound motor vehicle can be rendered useless because some sensor or other decides that the levels of certain gases emitted from the exhaust pipe are out of range, or that the thing itself simply fails, is reason enough to simplify and get rid of the weak links in the chain.

  • 0 in reply to whjohnson

    My understanding is that the crimp with the voids in the CT scans was a crimp as part of a spade terminal connector to what he refers to as the starter relay - which is actually a thermal thing that releases the start capacitor once up to speed. In any case one of the fridge freezer makers factory crimps.

    But as I have said before, given that amount of damage it would be a brave soul who spoke with more than 'perhaps' or 'probably' . This caution leads to the slightly contradictory statements that more than one thing might be true.

    I'm with you on the AFDD being useless in this case, and indeed a great many cases.   It may even make things worse if folk decide an AFDD means you can be more careless.

    As for Dave Savery's results, while the language is a bit unprofessional, I'd agree the fact the thing does not trip under the conditions shown is scarcely confidence inspiring, and suggests the euronorm to which the things are tested is inadequate as I'm sure it passes that.

    Mike

  • 0 in reply to Chris Pearson

    I dodn't think that AFDDs would have averted the tragedy of Grenfell.  A better smoke/fire/heat detection system may have helped saved more people.  So could of regular fire drills and evacuation drills prepare people.  Unfortunately there are many things that I think were done wrong.  I am no expert but asking people to stay put rather than evacuate the builder I think was wrong.  However saying that I have seen a horizontal evacuation work perfectly well in other places.  I also think that wrapping a fire proof building made of rocks and brick and cement in a PetroChemical flammable insulating material was criminal negligence.  

    Back to AFDDs.  I have not fitted any but my understanding is that MOST AFDDs but not ALL are dual function.  They are a RCBO module and an AFDD module in one package.  Thus ever could trip on their respective fault. 

    However the cost and the fact that they are possibly not able to function for their intended task is worrying.  Maybe the BS EN for AFDDs needs to be looked at with respect to the following.

    How are they tested by the manufacturer

    How can they be tested by the installer/Electrican

    How can they be tested by the end user

    Colours of the flags or LED used.  On some Green means good and functional on other Red is used. 

    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. 

  • 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.

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