Dear, dear will you spend some time viewing this please........?

Do I really have to?

AFDD - Arc Fault Detection Device - Part 1 - Bing video

"But Dear, when the device switches off after eventually detecting an arc fault it needs to be turned on, possibly to a faulty circuit, before it reveals its reason for switching off. I though that we should not energise a faulty circuit or faulty appliance. That could be dangerous."

Z.

Zoomup said:

"But Dear, when the device switches off after eventually detecting an arc fault it needs to be turned on, possibly to a faulty circuit, before it reveals its reason for switching off. I though that we should not energise a faulty circuit or faulty appliance. That could be dangerous."

Oh dear.

What the FIRST thing that happens when a domestic RCD trips (or, as I've seen, RCD trip at work, that's intended for operation by ordinary persons)?

A user tries to reset it. Simples. Same with mcb's ... only after it trips again will anyone investigate further.

I don't really see that as a clear argument that AFDDs are dangerous. Sorry Zoomup 

gkenyon said:

A user tries to reset it. Simples. Same with mcb's ... only after it trips again will anyone investigate further.

Father always said not to replace a fuse until the cause of the blow had been found, but I think that one might be permitted one try with an MCB.

At work, not too long ago, we were informed that we could not have tea because there was no power to the water heater. This was a serious matter. I found a CU, opened the door, saw a tripped MCB and reset it. Doubtless I broke many rules (including standing on a chair rather than a ladder) but I fixed the problem.

A similar near existential crisis at our place had a temporary 3 phase extension lead running between two buildings and up a stairwell to the offending coffee room in  under an hour. That is because it was the one used by site services. The cynic in me suspects that anyone else  would have had to put a ticket in and wait..

Mike

Recently a fast food takeaway had a problem with a walk in chiller room cooling system. It kept tripping everything off including chest freezers full of food on the same circuit. The compressor motor had gone short circuit L to E. The owner had tried to run the walk in chiller room via a long extension lead on a good working socket outlet. As the compressor was still faulty it caused an immediate tripping off of a M.C.B. It also damaged the socket outlet switch so that it became faulty. It is not a good idea to liven up a faulty circuit. The first trip tells you that something is faulty. Don't tempt Darwinism.

Z.

So, an A.F.D.D. trips off due to a fault, then is reset by somebody but it won't stay on. Do the flashing lights stay on that identify the type of fault?

AND, what benefit is there in knowing the type of fault anyway by the flashing lights, as an electrician will normally and hopefully locate it by conventional means anyway. 

Z.

Zoomup said:

So, an A.F.D.D. trips off due to a fault, then is reset by somebody but it won't stay on. Do the flashing lights stay on that identify the type of fault?

AND, what benefit is there in knowing the type of fault anyway by the flashing lights, as an electrician will normally and hopefully locate it by conventional means anyway. 

Different manufacturers have different implementations, and you'd need to check specific products out, but why wouldn't the electronics inside the AFDD be able to stay on from the input, whilst the output circuit (containing the supposed fault) is disconnected?

I was wondering about the longevity of these things. How many non-arc faults - over-current/short circuit -  will they tolerate before the electronics gives up the ghost? There's a arc extinguishing chute in there somewhere which needs to snuff out heavy fault current arcs withing the device itself.  I know that certain brands of RCBO tend to die after relatively few operations under service conditions. That'll be one hell of an expensive 'fuse' to replace when it fails.

All protective devices are only specified to operate for a finite number of times (in the case of fuses themselves, 1).

Indeed. But there is a lot of variance in terms of resilience between products from different manufacturers when it comes to electro-mechanical devices, and now we intend to introduce fragile silicon chips into the mix.