[RE-wrenches] AFCI compatibility with modified waveform inverters

R Ray Walters ray at solarray.com
Sun Mar 28 21:18:53 PDT 2010


Can't say whether the AFCIs will work with the mod sine (I'd guess not) but I do know that even a pair of Outbacks (in parallel) will not supply enough current for an AFCI to actually trip in a fault situation.
AFCIs are designed to stop a 70 amp or higher arc, while the Outbacks only surge to 50amps (230 v). We had an inspector with an AFCI test device flag us once, because the AFCIs wouldn't trip.
I studied up on them, and showed him why they didn't trip, and he let us pass. 
Not sure if this means off-grid systems are safer than grid because of the lower surge currents available, (Yes IMHO) or if it just means AFCIs are a waste of money off grid (Yes , Fact)
I hope some future iteration of the code will provide us an exemption from AFCIs for small off grid systems. 
Or it would be nice if one of the inverter manus could qualify their inverters for AFCI protection, then the whole house would be protected and it would make life simpler for the wiring. (except maybe the stove igniter might trip the AFCI??) Hmmm

So many more safety issues to ponder over some cold brews....

R. Walters
ray at solarray.com
Solar Engineer




On Mar 28, 2010, at 4:11 PM, Kent Osterberg wrote:

> Fellow wrenches,
> 
> Does anyone have any experience with using AFCI breakers with modified waveform inverters?  I've got a customer building a new weekend home that thinks he wants a modified waveform inverter, but I don't know if the required AFCI circuit breakers will work.  A few years ago Xantrex published a list of GFCIs that would work with their modified waveform inverters.  I haven't seen any such info about the AFCI breakers.  Thanks.
> 
> Kent Osterberg
> Blue Mountain Solar, Inc.
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