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Arc Fault Current Interrupters - Operating Principles?

Discussion in 'Electronic Design' started by Jeff Wisnia, Apr 12, 2006.

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  1. Jeff Wisnia

    Jeff Wisnia Guest

    Would someone who has had a hand in the design or testing of AFCIs
    please clue me in on their operating principles?

    My curious mind wants to learn about the detection parameters used in
    those AFCI "circuit breakers" now required by code for some new
    construction locations.

    Do they measure and count the current spikes (or the "noise") which
    occurs when a "frying" short happens, but when the average current drawn
    probably wouldn't be enough to trip a normal overcurrent breaker?

    I've noticed those breakers have a pigtail lead which connects to the
    ground buss in the panel they're mounted in. Does that mean they also
    provide GFCI in addition to arc fault protection?

    My question was prompted by an aquaintance who has an AFCI breaker in
    his home which frequently pops when he turns off a tungsten lamp load
    with a wall switch. I suspect the switch may be arcing enough when
    opening to trip the AFCI and suggested he try replacing that switch with
    one having more of a "snap action".

    Thanks guys,

    Jeffry Wisnia

    (W1BSV + Brass Rat '57 EE)

    "Truth exists; only falsehood has to be invented."
  2. That leaves me out but I'll post anyway as I have investigated this subject
    and learned very little (proprietary information, I suppose). Seems to me
    that the arcing might be modulated by 60 Hz and the sideband energy would be
    spaced accordingly and the specturm would be somewhat predictable. Perhaps
    several key sideband frequencies are sampled? Do they use DSP? ... possible
    with modern ICs.
    That's the idea ... the arc fault current is below the trip current of an
    ordinary breaker and the detector is looking for the arc signature (see the
    above about spectrum).
    Some do and some don't.
    Yes, switches often arc and old ones get worse in some cases. Also, switch
    design and build quality are issues.
  3. Fred Bloggs

    Fred Bloggs Guest

    The AFCI are the ultimate in fire protection breaker technology-
    designed to look for the telltale arcing between adjacent wires with
    damaged insulation. They are programmed to trip on a broad class of arc
    signatures but if IIRC there is no standardization of the arc profile as
    yet. That switch is not making a clean break of the tungsten lamp
    current- try replacing it with a newer and higher rated switch.
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