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Was the photovoltaics responsible for this meltdown?

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    Was the photovoltaics responsible for this meltdown?

    Got called to help a customer who was experiencing power outages. First I checked the outdoor 200 amp meter/main disconnect and found a melted mess. This one does not have a main breaker, rather it has 2 double pole 100 amp service disconnect breakers, each serving a sub panel on the interior. The house is about 8 yrs old. Recently the owner had pv installed and they put 40 240watt panels up on the roof, with a rated output of 8500 avg watts total. They put the proper disconnects and a properly sized circuit breaker between the roof panels and the meter /main where they connected the grid tie in on the load side of one of the two pole 100 amp service disconnects using insul eater connector taps. I told the homeowner the pv installing company should have changed out the meter/main to a unit featuring a 200 amp main breaker and then separately provide overcorrect disconnecting means for each panel and the pv system separate from each other.
    My feeling is the output load of 40 240 watt panels tied onto the load side of a single 100 amp service disconnect exceeds the twenty per cent allowable for a pv grid tie in system. The 100 amp service disconnect breaker that the pv company coupled to was the one that burned up and melted the busbars it was connected to . The pv installing company is of course denying any involvement and stated that it was due to simply a bad 100 amp breaker. I am not up enough on my pv knowledge as regards the nec to be absolutely sure of my stand. Looking for input. Did the pv company violate any code with the way they tied all those panels to a 100 amp breaker?
    85deg. an Sunny today.

    #2
    They may not have torqued the connections properly. But that could be difficult to establish forensically. I am surprised that the heat did not trip the thermal in the breaker before a total meltdown, so the breaker might indeed have been defective.
    A line (supply) side disconnect is not subject to any 120% rule. But this is s load side disconnect and would seem to grossly violate the 120% rule on the feeder (output side of 100A breaker), but not on the bus which would be line side. The notion of a MLO panel bus being a service conductor has come up before.
    The PV backfeed number simply has to be less than or equal to the service rating for a line side connection, but that is not what the OP is facing.
    Last edited by GoldDigger; 10-07-15, 01:46 PM.

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      #3
      Originally posted by macmikeman View Post
      They put the proper disconnects and a properly sized circuit breaker between the roof panels and the meter /main where they connected the grid tie in on the load side of one of the two pole 100 amp service disconnects using insul eater connector taps. ...
      Did the pv company violate any code with the way they tied all those panels to a 100 amp breaker?
      What code version are you on?

      I think really your question is - "Is this their fault?"
      I'd look closely at the taps - if there was extra resistance there, that would cause heating. And since that is near the 100A breaker that failed, IMO it's likely the heat could propagate to that breaker through the wires.
      Another possibility IMO is the connection on the 100A was loosened by their working in the box.

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        #4
        You can't pin this on the PV design directly, notwithstanding possible code violations. If the problem were that the design did not protect the conductor correctly, that problem should have manifested itself downstream, not upstream at the service breaker as described.

        The max output of the inverter is presumably around 32A, which is not enough to overload a 100A feeder. Unless the homeowner also added a large load to the feeder after the solar was installed (car charger?), it's unlikely the feeder ever saw more than 100A. Think about it: if the occupants ever tried to consume over 100A prior to the solar being installed, the breaker should have tripped. It should have tripped if they did this at night or on a very cloudy day even after the solar was installed.

        Under the 2014 code, there is no violation in tapping more than 20A to a 100A feeder as long as you have an overcurrent device downstream on the feeder. If they didn't do that (it doesn't sound like they did) then it's a violation of the 2014 code. Assuming the feeder isn't oversize, it's a violation of the 120% rule in previous codes, which in one interpretation allow the conductor to be loaded up to 120%. But due to the logic stated above, it seems unlikely these potential violations can be blamed for what happened.

        I agree with Tommy O that the solar installer could have compromised the terminations to the breaker and caused a thermal problem that way. One would think though, that with too much heat around the breaker, the thermal function of the breaker should cause it to trip in such a situation. A breaker that melts or burns up without tripping is a breaker that malfunctioned, in my opinion, regardless of other circumstances. Whatever might have caused the problem, that is why you have a melted mess rather than nuisance tripping.

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