>>Since the topic of AFI's has come up I wonder if anyone has actually tested >>one, even an AC one. >> >> From what I've read from some tests on the Mike Holt site for AC breakers is >> that they couldn't get them to work at anything less than standard ISC for >> the breaker. > >I've not tested them, but I have read every patent on AFCI technology I can >get my hands on. > >They don't sense that the load is arcing, in the sense -- say -- of an >electric motor which arcs because of how the brushes work, or any number of >other loads which arc. What they detect is arcing current well above the >rated ampacity of the circuit breaker. A "series" arc, where the arc is >passing through a load, is limited to the load itself -- a 12 amp rated vacuum >cleaner makes, maybe, a 12 to 15 amp spike when it arcs. A "parallel" arc, >where the arc is passing directly from line to neutral, or line to ground (not >all AFCIs include ground-fault detection), will conduct up to the current >available from the transformer. However, because it is not a constant load, >it doesn't trip the over-current protection of the breaker, the arc just sits >there until either it self-extinguishes or it causes a fire. > >There have been a lot of discussions on Mike's board about how useless AFCIs >are. In the case of RE systems that have significantly less available current >(maybe 50 or 100 amps, rather than hundreds to thousands), it's unlikely that >a standard AFCI would "see" a high enough current to decide that a "parallel" >rather than "series" arc was happening. But if the AHJ wants them, the AHJ >gets them ... >-- >Julie Haugh >Senior Design Engineer >greenHouse Computers, LLC // jfh at greenhousepc.com // greenHousePC on Skype
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