I wonder, if we vote, for or against AFDD, what kind of result might we get?

ebee said:

I wonder, if we vote, for or against AFDD, what kind of result might we get?

Isn't that sort of what already happened with cross-industry representation in the BSI committees responsible for BS 7671, who came to the consensus of what we have?

ebee said:

I wonder, if we vote, for or against AFDD, what kind of result might we get?

Isn't that sort of what already happened with cross-industry representation in the BSI committees responsible for BS 7671, who came to the consensus of what we have?

I don`t know Graham, some things seem to get a big thumbs down in to what I consider the popular vote but seem to make it in sometimes. Well it appears to me but I may well have a totally slanted view of such things and that is why I commented. I`ve seen more suggestions they have very limited safety effect, not much safety versus cost effectiveness but plenty of the "well I wouldn`t have them" sort of attitude. Mind you RCDs probably had a not very good press a few years ago but I am a fan of them.

It depends what you mean by cross-industry. The standards writing circuit is quite cliquey, and a quick look at the list shows it is dominated by larger outfits, presumably  as most small organizations, despite being the majority of the businesses, cannot afford to send someone along being too busy with the day job. I'm not convinced either that the likes of NICIEC actually know what all its 25 thousand odd members actually think/want, and as a result it also probably over represents those who are larger more vocal  perhaps benefiting those wanting bigger contacts and lots of new work, over those who have to maintain it later and in effect have to pay for the design decision.

I'm not sure how one would fix that, it is certainly not a uniquely '7671 thing, but I'd be wary of assuming it is truly a representative cross-section of informed opinions. (The DPC might be better but the commenting process is quite convoluted, not especially well publicized and the window for making comments is quite short.)

Mike

ebee said:

Well it appears to me but I may well have a totally slanted view of such things and that is why I commented.

I can completely understand that. I also understand the situation we've all found ourselves in, moaning that absolutely everything is sub-standard or doesn't work, because of the sheer number of problems we've had to fix.

More importantly, though, I also value the points of view put forward.

Not that I haven't (regularly) done it myself, but Engineers are a cynical bunch (at least about their own profession), and do moan about things "never being right". - there are, as I said, reasons for that. And I also understand that changes in BS 7671 provide yet another set of problems to fix one way or another.


But to make decisions on what ought, or ought not, to be included in a standard, and to what degree, requires a number of different perspectives on an issue to be taken into account ... and also a little thinking outside the box.

For example, with cable sizing, let-through energies etc., there's a huge difference in the perspective of someone working mainly on up-to-100 A domestic installations, vs different range of prospective fault currents, wider variety of circuit configurations, and larger premises, as well as larger loads, in some other installations. Hence, the contents on circuits in BS 7671 itself is far larger than the "here's your answer" (OK, "industry rules of thumb") in the tables in Section 7 of the OSG.

ebee said:

I`ve seen more suggestions they have very limited safety effect, not much safety versus cost effectiveness but plenty of the "well I wouldn`t have them" sort of attitude. Mind you RCDs probably had a not very good press a few years ago but I am a fan of them.

Again, I fully appreciate that, and the point about RCDs is exactly that (and only that) which I was making.

mapj1 said:

and as a result it also probably over represents those who are larger more vocal  perhaps benefiting those wanting bigger contacts and lots of new work, over those who have to maintain it later and in effect have to pay for the design decision.

I'm not sure it's that simple, but I understand the point you're making.

For example, an automotive technician may have a very different view of newer technologies (including safety features) on vehicles, because they see the problems, and have to deal with customers having heart failure when they find out how much it will cost to fix. There are lots of automotive technicians out there.

All of us who've been driving since shortly after Noah parked his boat know cars worked perfectly well without the "gadgets" - but is it wrong some of those features are required on new models? There are lots of drivers out there too.

And with those debates, people are very happy to ask whether a vehicle tech (or driver) is the best person to advise. Could also be said they too have their "vested interest", but in a different way (too hard and costly to fix, more cost and interferes with what I want to do with the vehicle - especially case in point EU automatic speed limiting).

Yes, there would be far greater numbers of drivers and automotive technicians who would have a contrary view to the conclusions drawn by the regulators and standards makers - but does that swell of numbers make the regulations and standards wrong?

It's not an easy thing at all!

A customer of mine had two adapter type Powerbreaker R.C.D.s I went to replace a faulty socket and as a matter of course I tested both Powerbreakers. Both failed to trip off. Fortunately the R.C.D. in the consumer unit worked perfectly.

Lack of regular testing is often the main cause of failure to trip off when needed.

Z.

Agreed Graham, I realise that.  HRC (HBC) fuses, MCBs, RCDs all had their opponents for being considered unessacary back in the day too. In fact a six inch nail instead of a fuse and twist two bits of wire together to get electric to work was not that uncommon either. I just wonder how many feel the need for AFDDs nowadays now we`ve discussed them a few times with some very learned folk on this forum . In fact if we took a poll, then again in 2 years time, then 5 then 10, what would that graph look like? You could say similar votes for SPD (I think they have a lot more respect than they did say 18 months ago) and RCDs (same again with bells on) . How many of us were brave enough to fit consumer units with BS 3036 fuses nowt else (No RCDs)  and thought nothing of it would feel as happy with that situation today.

But, but, but. How do we know that they have actually worked? Apparently the test button only testes the mechanical aspects of the device.

Arc Fault Detection Devices (AFDD) (theiet.org)

Z.

Zoomup said:

But, but, but. How do we know that they have actually worked? Apparently the test button only testes the mechanical aspects of the device.

Arc Fault Detection Devices (AFDD) (theiet.org)

Z.

Same question asked about RCDs. That's the only reason we ever had RCD testing.

Good question to ask ... but there are, now, some people who would say all we ought to be doing with RCDs is pressing the Test button to check they work.

Again, this is something there is no right answer for.

I will just use the example of a fuse. All it takes is for tolerances on the machine to be out for some reason, and it can make a huge difference to the performance of the fuse. Yes, there's an "operating range", and we assume "worst-case" for ADS in BS 7671 ... BUT there's no actual way of knowing the real performance characteristic of the fuse in a circuit without testing it (to destruction).

So, over the years, manufacturers have developed quality control processes to help keep things in tolerance, ways of quality-checking the product (metal thicknesses etc.).

But all of those processes are hidden from us. We have full faith they are being employed in the manufacture of each and every fuse, and the fuse will protect us when we need it.

We also never question circuit-breakers, which perhaps have more issues with tolerances because of manufactured moving parts etc. - exactly the things which "gum up" in RCDs. There's also the accuracy of manufacturing a bi-metal strip, winding the trip coils (and properties of the magnetic materials). Yet we are happy to trust the manufacturer with all of that.

We never had faith in RCDs in that way, and it seems that pattern will be followed with AFDDs.

"Same question asked about RCDs. That's the only reason we ever had RCD testing."

But with R.C.Ds the test button tests the whole gadget, the electrical and mechanical aspects of the device. No test gear needed.

Z.

Zoomup said:

But with R.C.Ds the test button tests the whole gadget, the electrical and mechanical aspects of the device. No test gear needed.

People still didn't believe they worked, so that's why the RCD testing on initial and periodic verification was introduced.

The software in AFDDs could have self-check routines, but it would also be valid to say "how do we know?", "my laptop crashes sometimes" etc.