I was called to do an evaluation of a SB / SI AC-coupled system installed by others. One of the 4 SB's(9000watt TL) had a hard arc fault error which could not be reset. Apparently a fault since commissioning (sic).After checking all visible connections, I isolated each one of three sub-arrays feeding this inverter's combiner. With only sub-array 1 connected (fuse holders closed) the inverter powered up normally. So I opened up 1 (and 3) and closed circuit 2 fuses. Open circuit voltage OK. I powered up the inverter and immediately heard a loud pop. One of the interconnects in that sub-array literally blew apart and opened up. So I isolated arrays 1 and 2 and tried 3 alone. Same thing, vaporization of an interconnect. FYI - no fuses were blown on either defective circuit, but I guess that's not surprising in this scenario.
So the inverter operates fine and only "good" sub-array is #1. I'm curious as to why when all three sub-arrays were combined, there was not a meltdown of 2 & 3 connections before the AFCI error shut the inverter down, but individually the faulty circuits were not caught by the AFCI circuit before the damage occurred. Thoughts anyone? Thanks. At least I know where the loose connections are / were.. Kirk Herander VT Solar, LLC Proven PV provider since 1991 www.vermontsolarnow.com dba Vermont Solar Engineering NABCEPTM Inaugural Certificant VT RE Incentive Program Partner 802.863.1202
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