A.F.D.D. with a combined M.C.B. unit, the tripping may just be due to overcurrent, so we may not know which part of the device has caused the tripping off.

All the ones I looked at had some means of indicating the cause of the trip - usually coloured/flashing LED - different flashes for Arcs, RCD or overcurrent - so probably better than many an RCBO.

  - Andy.

And she can't dry them outside because it's raining and the wind isn't blowing!

Never mind eh, Mrs Gumby is delighted to be doing her bit for the environment despite being charged a hefty premium to put up with regular supply interruptions.

I wonder which of his algorithms told him it was ok to visit his German mistress despite his own advice to the rest of us?

whjohnson said:

AFDDs are a completely different ballgame to the other passive devices I have mentioned.

Circuit-breakers have, for some time, had intelligence in them. Granted, not the "for use by ordinary persons" breakers, but it's nothing new to me to see "computers" in protective devices.

I think you're dead right, that there's way more mileage out of "SMART" devices to be marketed in the future.

Wife phoning husband who is at work.

"George there's an  arc fault on our wiring I'm worried about a possible fire"

George; "Are you sure dear?"

Wife. "Yes George there are flashing lights."

George. "Can you see or smell smoke?"

Wife. "No George, but the lights are still flashing."

George. "I have an important meeting in 30 minutes here."

Wife. "Can't you come home George, I'm very worried."

George rushes home.

George upon inspecting consumer unit.

"Oh, dear, there's nothing wrong. It's just the flashing lights on the smart meter dear."

Wife. "Well they were signalling a fault dear. They were. Honestly."

Z.

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.

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.

whjohnson said:

and now we intend to introduce fragile silicon chips into the mix

They are here already in other protective devices - for HV and very large LV installations ... and have been for over 25 years.

If your installation has multiple arc faults, then you have bigger things to worry about than how long your AFDD is going to last.

Please expand on that comment.

Z.

The threading on this topic has got terribly confused, so my last post doesn't make sense without context.  It was a response to an earlier post by whjohnson:

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?

To which my response was that if you have so many arc faults in your installation that the AFDDs start failing, then the AFDDs failing is the least of your problems.  You need to fix all those faults before the entire installation burns down.

Thankyou all for the replies.

In summary, they meet a product standard, but we do not know how that product standard works in real life situations, or even if it will work at all.

The Manufacturers should be shouting from the rooftops how these devices save lives and properties through their advanced designs, yet we have silence. If they are so good, why aren't they promoting their designs?

It seems there are no peer reviewed papers showing that they save lives/property, but some reports that fire figures may be slightly down, from the USA.

I've got to ask, how did the JPEL committee approve their use without factual evidence?

If they have evidence, maybe it could be published?

If there was some credible evidence that they work, then it would be an easy sell, but how can one recommend, or mandate them with such poor information available to the Installers? 

Maybe it is time for the JPEL Committee to get the Manufacturers to release their testing data to show they work, then we wouldn't be so cynical if it showed they do work, and we could sell them with no doubts as to their life saving capabilites.

In the meantime, I still don't know if, and when, they would work, and have to sell these to Customers, and say they are for their own good, but cannot back up that statement.

"I've got to ask, how did the JPEL committee approve their use without factual evidence?"

Alan,

I have been trying to ask this question so many times in so many ways but all I get is along the lines of 'No need for you to know that. Trust us, we know what we are doing", which makes me even more suspicious about these things than I already was.

All we seem to get is a swerve back to 'It's just like RCDs were back in the day'.

I say, RCDs are pretty simply devices which use easily understood physics and passive components.

AFDDs on the other hand have a computer driven by algorithms for which they rely upon to recognise the fault and operate accordingly.  These algorithms are pretty much beyond the comprehension of the average bear and are pretty much a black art to the humble sparky. This leaves a serious credibility and trust issue when it comes to adoption and acceptance of something new which might work but not in every instance, or even when it should.

My summary is that I shall not be recommending them in any future instance until they have a proven track record for doing what they say they do on the tin, regardless of JPLE/BS7671 et al.