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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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    Hello Chris.

    It's something I picked up several years back when I was reading the specs and experience of AFDDS in the USA vs UK, but I must admit I can't find that first-hand now.

    AFDDs for sale in the UK must comply with BS EN 62606.  I haven't got access to that, but Schneider have a technical description of their AFDDs with respect to BS EN 62606 and this refers to the requirement that an AFDD must trip in 1 second at 2.5 amps.  It doesn't say what it does below that value; I think it does not respond to avoid nuisance trips, but am open to correction.  If I can find something more definite I will post it here.

    I've attached Schneider's technical description here - it's Table 1 on page 6.  So it looks as though the tripping threshold is actually 2.5 amps.
    Schneider EDCED117020EN.pdf

    Regards,

               Colin.
  • 0
    Hello Farmboy.

    Good one!  I was rather engrossed in my own situation of low current, personally monitored and/or off!  A series fault in a BS 6004 cable running above 2 amps could be a candidate for an AFDD.  I wouldn't fit one left to my own devices because, after a lifetime in the industry I haven't met such an incident that resulted in a fire.  However, it looks like we'll soon all be made to.  Mainly good for the manufacturers' and their shareholders I think.

    Regards,

             Colin.

  • 0
    Colin Jenkins:

    Hello Farmboy.

    Good one!  I was rather engrossed in my own situation of low current, personally monitored and/or off!  A series fault in a BS 6004 cable running above 2 amps could be a candidate for an AFDD.  I wouldn't fit one left to my own devices because, after a lifetime in the industry I haven't met such an incident that resulted in a fire.  However, it looks like we'll soon all be made to.  Mainly good for the manufacturers' and their shareholders I think.

    Regards,

             Colin.

     




    Hi Colin,


    I was interested in your perspective because other more learned members than I on the forum seem to have been focussing on the technicalities and motivation(s) regarding AFDD installation, whereas yours seemed more from an interested users viewpoint (the other side of the coin, so to speak). 


    Personally, I think they're just one big con, and to alter a borrowed phrase: they're designed by computer, built by robot, installed by reluctant doubtors and used by the clueless - all pushed by alleged financial greed in the apparent face of no credible evidence of efficacy at all. We'd be forgiven for thinking this is politics.


    Regards


    F 


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    Chris Pearson:
    mapj1:

    Funny I often end up going to bed with my dishwasher etc, but then we are married.?


    Careful what you "go to bed" with!




    That Britsh medical journal link should have come with a health warning for folk about to eat their lunch.. injured by the fan blades 15cm from the vacuum cleaner  inlet, dear oh dear. And its not quite the activity I meant, as I suspect you know very well !


  • 0
    Colin Jenkins:

    Hello Chris.

    It's something I picked up several years back when I was reading the specs and experience of AFDDS in the USA vs UK, but I must admit I can't find that first-hand now.

    AFDDs for sale in the UK must comply with BS EN 62606.  I haven't got access to that, but Schneider have a technical description of their AFDDs with respect to BS EN 62606 and this refers to the requirement that an AFDD must trip in 1 second at 2.5 amps.


    I asked because I think that the generation of myths should be avoided. BS EN 62606:2013+1 does not, as far as I can see, specify a threshold.


    Here is table 1 from the BS - maximum break time against test arc current


    2,5 A     5 A    10 A     16 A     32 A    63 A

     1,0 s  0,5 s  0,25 s  0,15 s  0,12 s  0.12 s


    That they must trip within 1.0 s at 2.5 A does not mean that do not at lower currents, but I think that one could infer that they need not do so. Certainly, I don't think that one could rely on them tripping significantly lower than 2.5 A.


    Interestingly Schneider say: "a series arc is dangerous as soon as its value equals or exceeds 2.5 Amps".


    It may be that a lighting circuit feeds only fixed luminaires whose total consumption is < 2.5 A in which case AFDD would be pointless; but as soon as you have lamp-holders, it would be difficult to be sure.


  • 0
    Hello Chris.

    Thank you for your comments.  I think this was John Ward's puzzle when he was trying to get an Eaton AFDD to trip with a 100 watt lamp on a loose connection and it wouldn't trip.  He subsequently succeeded with a bigger load connected; it's one of several he did on Youtube.  The guys in the Youtube link at the top of this thread seemed to run into the same issue.

    Regards,

              Colin.
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    I have just added a comment in the DPC - there were already 31 of them, the vast majority of which are against on the grounds of cost. I have said (1) not cost effective (average cost of potentially preventable fires is £4 per household per year) and (2) if we must have them, add circuits whose total load is < 2.5 A to the list of exceptions. Fire alarms, etc. would already fall into this category.
  • 0
    Hello Chris.

    With my apologies, it looks like the no-trip threshold is 1.5 amps.  It's on page 6 of Wylex's AFDD/RCBO leaflet attached here.

    Regards,

                  Colin.         20200113123032_0_Wylex Single Module AFDD Cat Nov 19.pdf
  • 0
    For those of an electronics persuasion, and an interest in what is in the box, the 'Siarc' algorithms mentioned in the Wylex data are a Siemens patent - I presume this one  that patent expires 2031 and links to a few earlier ones,  so I guess they want to recover their R and D money before the other breaker manufacturers jump on the same wagon. Which would be fine if it wasn't being foisted upon us by force.
  • 0
    Colin Jenkins:

    Hello Chris.

    With my apologies, it looks like the no-trip threshold is 1.5 amps.  It's on page 6 of Wylex's AFDD/RCBO leaflet attached here.

    Regards,

                  Colin.         20200113123032_0_Wylex Single Module AFDD Cat Nov 19.pdf


    Colin, no need to apologise at all. At, say 2 A that Wylex device could spend many seconds, minutes or even hours thinking about whether to trip or not and still be in spec. To be honest, I hadn't realised that there is a threshold current for these devices.


    I am so tempted to do some experimentation JW-style, but I am far too mean to buy an AFDD. ?


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