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The Arc Fault Detection Device… again.

whjohnson
Some humourous but valid observations on AFDDs, the state of the industry, the wiring regs and future amendment requirements.

He also attempts to build a AFFD tester which electrically tests rather than relying upon the mechanical action of the test button on the device itself.

https://www.youtube.com/watch?v=e0ElFaKc_e8

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    That is another very interesting article, and the observation  that XPLE does not char like PVC is new to me. The suggestion that the PVC decomposition products are essential to the 'right sort of arc' ties in with the observed experimental difficulty of establishing a continuous arc and lack of tripping with copper- copper arcs that are in free space (hence graphite electrodes and use of brass-brass arcs in informal testing.).


    I presume that like some others the author will be commenting on AMD2.


    I have some issues with the last part of his conclusions which suggests the solution to the problem of fires may be the rolling out mandatory PAT for domestic appliances in private dwellings, I suspect that is neither practical nor necessary. Looking at the grief that the recent regulations on EICR of rented property are going to cause,  and the lack of folk able to do it well, to extend the reach of PAT would be an unwise suggestion at this time.
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    Chris, the wobbly choc block has been done, by John Ward.

    Try about 5 to 6 mins into  this video for an idea of how well it works with a light load  for that sort of fault, or about 23 mins into this one, for a higher fault current.. I found it underwhelming in the extreme in both cases.
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    mapj1:

    Chris, the wobbly choc block has been done, by John Ward.

    Try about 5 to 6 mins into  this video for an idea of how well it works with a light load  for that sort of fault, or about 23 mins into this one, for a higher fault current.. I found it underwhelming in the extreme in both cases.


    Mike, thank you. That is exactly what I was thinking of except that perhaps he could have tried a larger load (though I take his point about most of them being small ones in homes) or perhaps he could have "tuned" the choc-block.


    I found it got a bit boring!


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    The presenter in this video claims that in the US, AFDDs have reduced numbers of domestic fires by nearly 20% - good enough reason to install them, is it not?
    https://youtu.be/_j3MzFm0_bs
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    Strangely I cannot find that data anywhere!
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    davezawadi (David Stone):

    Strangely I cannot find that data anywhere!




    have you asked the US Fire Administration - presumably such stats will be a matter of public record? Surely Electrium wouldn't just blag such figures, in the hopes that nobody will check.


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    The presenter in this video claims that in the US, AFDDs have reduced numbers of domestic fires by nearly 20% - good enough reason to install them, is it not?

    Even if they prevented 100% of domestic fires they'd still be horrendously expensive for the benefits - at say 6 or 7 final circuits to protect per household at around £150 a throw that'd be around £1000 per home, or £20 BILLION for the country's 20 million households. If society had that sort of money to spare there'd be plenty of other safety improvements we could spend it on that would be far more effective. Of if you want to be clinical about it, see how many lives you'd need to save at UK's usual "value of a prevented fatality" (VPF) of about £1.8m.


    Then add in that they can't detect arcs on distribution circuits, or the higher power final circuits that account for probably the majority of burned out connections (showers etc) and may not work at all with arcs on small contact areas or between copper conductors or faults that are purely resistive heating, they don't look like a good economic case to me.


       - Andy.
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    Farmboy:



    The presenter in this video claims that in the US, AFDDs have reduced numbers of domestic fires by nearly 20% - good enough reason to install them, is it not?


    There were 3,862 fires due to faulty appliances and leads in 2019/20 (Government fire statistics). It isn't clear by any means how many were started by an arc, let alone a detectable one, but let's assume for the moment that all of them were.


    The average area of damage was 16.5 m² i.e. the size of a fairly ordinary sitting room. I haven't found official statistics, but Plumis who make sprinkler systems say the average cost is £25k, which seems reasonable. For comparison, new build costs are around £2,000/m².


    There is no indication whether fires caused by faulty appliances and leads are bigger or smaller than average. So 3,862 fires @ £25k = just under £100M per year.


    There are 24.4 million dwellings in England (Government dwelling stock statistics) so the cost near as makes no difference is £4 per dwelling.


    If an average AFDD lasts 20 years, then a whole CU-full needs to cost less than £80.


    I conclude that at the moment, AFDDs are not cost-effective.


    Now then, would nobody care to discuss the cost-benefit ratio of fire alarm systems? ?


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    Some very interesting points raised, but for me, when it comes to AFDDs the stench of snake oil is still too overpowering. To me, a AFDD is about as useful as a 60% accurate covid test kit.

    It ranks up there alongside a requirement from a previous amendment (subsequently dropped thank goodness) whereby we were going to have to fit earth spikes to every installation regardless of supply characteristics. It really is tie for a review of the the way the IET derives these requirements, because a cynic might be forgiven for thinking that the principle motive is that of manufacturers profits rather than enhanced safety for the consumer/end user. The science seems to have gone out of the window right now.
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    Incidentally, how many people in here have witnessed a significant fire in a dwelling? My local pub caught fire about 40 years ago. The landlord's bedroom was seriously ablaze. I learned then that a fire extinguisher is 3/8 of ******-all use under those circumstances; and even that assumes that you can see where you are going.


    The cause was said to have been rodent damage to the wiring.


    The only time when I actually called the fire brigade was when the neighbour opposite set light to his fence.

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