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Arc Fault Current Interrupters - Operating Principles?

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,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat \'57 EE)

"Truth exists; only falsehood has to be invented."
Reply to
Jeff Wisnia
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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.

Reply to
Charles Schuler

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.

Reply to
Fred Bloggs

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