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Mar 07 2019 08:01

Hi all

Does anybody know how to fault find AFDD devices?

I have a light circuit that trips once every 3-6 months or so.

Reset it and it goes again?

Mar 07 2019 08:39

When does it trip? Whilst on or when being switched on? Does it trip when a particular light or set of lights is being switched on and if so does it do so for all light switches that operate those lights or just one? I assume you have carried out general fault finding tests such as Insulation resistance testing etc with light switches in both on and off states, particularly any two way switching.

Mar 07 2019 08:45

I have a flow chart somewhere; will see if I can find it.
Schneider have special gear that they can hook up to establish the exact wave-form of the arc fault (assuming there is one); but that's only worth doing if the unit is tripping repeatedly.
But at that time-frame if usual testing finds nothing, I'd swap it out to identify whether unit or circuit problem; and send it back to supplier for lab testing.
Some (most?) AFDDs have a RCD function as well, typically 300 mA, so the intermittent fault could be a current imbalance. Or it could be rodent damage - which can be very difficult to pin down 9sometimes only causes a problem when they piss on the bare conductors - then it dries out again.
So not a good idea to assume it's a "nuisance" trip; the thing might be doing exactly what it was intended to do.

Mar 07 2019 10:25

Thanks for the tips guys

Have yet to establish any fault pattern. (its just so infrequent)

Its a Schneider iDPNN Arc C10A

Interesting that its a coarse RCD as well.

I have 4 of them next to each other. Looks like I will need to start taking notes when its trips. (see if its the same one)


Mar 07 2019 16:03

I believe the schneider units have 300 ma RCD. So it takes a fair bit to trip that, EG for a crossed-connection a kettle or heater load would, but a light wouldn't.

That model has overcurrent as well, at 6A could trip with the blowing of an incandescent lamp (just like a normal mcb).