Post Brexit - Why are we still permitting CENELEC etc to influence how we govern our own engineering affairs?

Interesting that arc fault breakers should be at all controversial. 

In the aftermath of the in-flight fire and breakup of TWA 800 off Long Island in 1996, there was a serious investigation of wiring in (then-)older aircraft. There is a huge amount of wiring in a typical commercial transport, and almost all of it is inaccessible. Lots of it was found to be at risk. And an in-flight fire is one of the worst scenarios imaginable. A couple of years after TWA 800, and before the report was finished, Swissair 111 suffered an in-flight fire and came down near Halifax, Nova Scotia. Swissair wasn't necessarily an "old-wiring" problem; there had been a post-manufacture installation of an entertainment system, and there is fairly good evidence a fault with that was involved. Because of the physical constraints, it can be hard to see induced damage or  inappropriate kinks in wires you are newly installing.

The only reasonable solution to such wiring problems was to post-install AFCI. But at the time they cost real money. Militaries were also interested, in particularly naval aviation, because salty water and sea mist is a harsh environment for aircraft wiring. I remember talking to people at Schneider Electric about the prospects. 

Since then, of course, the price of AFCI has come down enormously. 

It is not just in-wall wiring installation. Even if you have open wiring, mice and martens like to chew insulation. My house is constructed with bricks and concrete on a wooden frame, and the floors in the older part are pure wooden construction with plasterboard ceilings (in the newer part they are concrete) and of course that's where the wires go and the critturs like to live. Type A RCDs were routinely installed on all circuits when I partially rewired in 2006 (they became German law in 2007) but with the occasional four-footed residents I have been thinking I should really put in Type B.

The state of domicile wiring is not good anywhere in Europe. Installations are supposed to be good for 35 years, in a place such as Germany some 70% are older (data from 2010). Some are of the order of 80-90 years old. About a third of building fires are of electric-fault origin; some 600 people die per annum in building fires, 75% of them in their domicile (also 2010 data). We don't have any idea of course how many of those are down to arc faults; AFCI are not a panacea. But some of them are. I should really put in those Type B.

At the risk of deviating somewhat, have you tried testing an AFCI for anything other than it's RCD function ?  The real bone of contention is that they are not demonstrated to do any good. The fact that they are used by Americans who use aluminium wiring and lower voltages and higher currents and seem unable to coordinate flex sizes with the breaker that protects them, is not a guarantee that the same device performs any useful function on a 240V circuit wired in copper. 

In fact if you take your arc welder and put a length of copper wire in the welding grip, and try and strike and sustain an arc with it, you will find it is all but impossible, the stuff either sticks, or burns back to self-extinction almost instantly. Not surprising as for years we made fuse wire from the stuff precisely because it does blow open circuit  gracefully.  There is a reason no-one makes aluminium or magnesium alloy fuse elements. But for the instant, the copper flash in the welder is a very pretty colour. (for the opposite of the no-effect try a wire "sparkler" from a kit of fireworks but be ready for it!! )

If you look at the official EN test for an AFDD you will see that it involves something that might as well be voodoo in terms of "preconditioning" the wire with a few kV to induce the deposition of high temperature PVC char before demonstrating detection of what is really a carbon-carbon arc.

Now you may get charring I suppose, in something like a low current flexible extension lead fitted with the wrong fuse that is burnt and then pulled tight to snap a core so that a series arc forms, but really the best place to fix that is with a thermal cut our in the drum of the extension lead.

Certainly here that has been no solid body of evidence presented to suggest that on UK house wiring (mostly solid copper cores and power in rings of  2.5mm)  they will do anything other than provide a false sense of security from spending some more money than a basic RCBO would have been. The reason for the absence of the substantial body of relevant evidence, I suggest, is that there isn't any.

Mike.

but with the occasional four-footed residents I have been thinking I should really put in Type B.

But why? B-type RCDs generally only differ from A types in their reaction to d.c. currents (or very high frequencies, like F-types) - so can be useful where large d.c. power sources can get into the a.c. loop in fault conditions - unless you've got robot battery powered electronic mice, I'm not sure of the advantage.

   - Andy.

Mike, I'm not being drawn on my own opinion of AFDDs, but I fear we are disappearing down a pseudo-science hole (again).

I am happy to repeat the fact that I have experience of, on more than one occasion, sustained flames from cables, caused by, parallel arcs, but granted in some specified circumstances which are, I openly admit, not often found in domestic fixed wiring, but might be found in appliances.

I would also add what should be obvious in all of this.

It is entirely possible to comment on the product standards in exactly the same was as BS 7671. BS 7671 is not concerned with the specification of products (cue discussion on 722.411.4.1), and, further, if there is a deficiency in a product standard, surely there is a duty to bring it to the attention of the relevant BSI Committee?

They recognise some waveforms typical of arcing and broader than the truncated sinuses which Type A recognises.

You may be thinking of F types that are designed to look for HF, B types have a detection for static DC, normally a hall effect device but sometimes it is done with a core is swept with an AC and asymmetry in the saturation is detected. (that is a surprisingly good technique, and I have used it as the basis of an electronic compass in the past.)

However a rodent will be substantially resistive, and even the semi-obsolescent AC only types will pick that up.

Be aware that by installing more complex devices than you need for circuit protection you are both inviting earlier failure and increasing the standby losses of your installation - all that electronics does not run for free - it may only be a few watts, but up and down the land, a careless attitude to wasted energy  adds up.

Your best bet is perhaps to employ a cat - if you did so in the UK cat food for working cats attracts a lower rate of tax than that for pets, though I suspect Germany is not so silly. ( the sale of 'animal feeding stuffs', unless biscuit or meal, can be zero rated with the exception of 'pet foods'.)

However I fear a truly 'working' cat is an oxymoron. The two states seem to be sleeping and playing.

Mike.

Graham I suspect you are correct. The problem is that the real evidence-based science is getting thinner and thinner with every revision of BS7671. It used to be the case that a scientific innovator put up his work for peer assessment and critique and to be prepared to have his work shot down with solid scientific counter-evidence.

Now, it is as if there are none who are prepared to tell the Emperor the real truth about his new clothes.

Every time we try to question and examine the scientific rationale behind the mandating of of the likes of afdds for example, the shutters come down. We ask 'Why?' and are informed "we've had a meeting of the committee and we think it's a good idea', When we push further for the evidence and proof of concept we are stonewalled, and that's about the sum of it, or at least that is how it seems to me.

I think Mike pretty much has hit the bullseye with his previous comments.

Peter, would I be correct if I said that aircraft wiring is constructed from very fine  flexible multi stranded cable and is constructed from aluminum to save weight?

Mike - (tongue in cheek) Would the cat in question have to be one approved by a committee such as CENELEC prior to use perchance?

Peter Bernard Ladkin said:

And an in-flight fire is one of the worst scenarios imaginable.

Possibly worse than a fire in a submarine!