So to summarise, BS7671 mandated the fitting of AFDDs without evidence of any positive effect they might have, and are now waiting for the evidence to build up over time to prove that they work, so that in the end the story will fit the narrative.

And of course, someone makes a lot of money in the meantime.

Do I have that correct?

whjohnson said:

So to summarise, BS7671 mandated the fitting of AFDDs without evidence of any positive effect they might have, and are now waiting for the evidence to build up over time to prove that they work, so that in the end the story will fit the narrative.

And of course, someone makes a lot of money in the meantime.

Do I have that correct?

Not really, but if you want to be a journalist, go ahead.

David Stone said:

. There is immediately a serious problem with the data, and that is that fixed wiring and appliances are not differentiated.

Well, there you go.

You asked me to provide something (and in return said you'd do something).

I did, and before you've provided anything, are criticising what I provided. I thought we had a deal?

I guess I've been reeled in

Overall trends in the leading fire causes for the 10-year period of 2009 to 2018 show the following: ĵ Cooking as the leading cause of residential building fires for the 10-year period. ĵ An 18% increase in residential cooking fires. (This is likely due to an NFIRS coding edit implemented in 2012.) ĵ A 30% decrease in residential heating fires. ĵ A 17% increase in residential other unintentionally or carelessly set fires. ĵ A 2% decrease in residential electrical malfunction fires

So cooking can be very dangerous.

Z.

No Graham, you have missed what I intended. The data you have provided proves nothing and I gave some hints as to what is required. Strangely getting this data is very difficult, and may not exist. Are you suggesting that your data PROVE that AFDDs make a significant difference to fire statistics as implied by the manufacturers? If so I cannot really see it in your data. The problem with this data is that there is so much variation on a relatively small number that extracting anything much is impossible using statistical techniques. Analysis of variance (ANOVA) is unlikely to give significance, and that is why we need much more, much more specific data. Then a multiple regression analysis will tend to sort out the variation sources and give a useful statistical significance. This is always the problem with statistics, almost no one collects enough data, and yet they expect useful results.

See the document referenced by Graham. Page 9.

Lets look at the number of electrical fires in America. Overall the number is falling very slightly on the trend line but is so small that this is probably insignificant. It may be due to many things, but a slight improvement in the appliance stock is likely, as appliances now tend to take less power than earlier. Even if all of this were due to AFDDs, the cost/benefit is well over to the "not worthwhile" side, because at least 500 million AFDDs were sold over the period at $50 each, and this exceeds the total cost of all electrical fires by 2 times! ($2.5 billion /  $1.3billion). I suppose there might be a small gain per year, but the down trend is only about $10 million per year which is nothing.

I think that any numerate person can see that, even with this simplified statistical data, that AFDDs are not cost effective in the USA.

The present devices need an arc for a period of several cycles at a current of 3A or so, sparks do not cause trips and only a small number of fires are caused by arcs, most are due to overheating from other causes. That is my case.

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?

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.