The earliest AFCIs were notorious for false tripping. They worked on the
principal that an arc generates broadband noise throughout the radio
spectrum. They would listen to a slice of radio spectrum, where there
wasn't supposed to be any transmitters, and if they detected noise it was
assumed to be broadband noise from an arc. Turns out that not all
broadband noise is arc generated so noise from appliances and other
electronics would cause them to trip. Not to mention overload from a
strong nearby amateur transmitter. The variations in performance between
brands of AFCI were probably related to what chunk of frequencies they
monitored since each company's breaker seemed to listen to a different
frequency band as dictated by their patents. The next iterations were to
add filtering and make the breakers smarter.
In an arc situation the arc will occur at the voltage peaks and quench
itself each time the AC voltage goes through zero. That means that if you
could monitor the zero cross and correlate that with whether the noise was
disappearing you could differentiate between plain old noise and arc
related noise. The next generation of AFCIs were incorporating the
filtering and smart noise monitoring to determine if the detected arc was
real or not and worthy of tripping the breaker.
Being able to smart detect an arc by monitoring the noise as well as the AC
waveform got rid of a lot of false tripping except in areas of the power
grid that have poor power factor. The poor power factor made it difficult
to determine where the AC waveform crossed zero and arc noise should
disappear. We ended up providing a filter kit for areas where we couldn't
control that and just squelched as much of our products contributing noise
as possible in order to make our customers happy.
The whole issue was exacerbated by Brand A AFCI not fitting in Brand B's
panel. As well as any of the brands not sharing information as to which
date codes had all the latest changes so that we could recommend to our
customers what breakers to get if they had issues. Lots of finger pointing
between breaker manufacturers and the users that plugged their products
into the power coming thru those breakers.
That was a few years ago so I would assume that the breaker/box
manufacturers have made some improvements since then and have some
recommendations on what date codes might have the latest changes and work
best for you.
Earl
N8SS
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