Some PV questions

[SolarPro]

[See previous comment.] While some installation mistakes were made at this site, it's not like this was installed by a fly-by-night outfit or was running blind. The system was fully monitored. The system had to be operational in order for system integrator to get paid. The system was operational up until the second fault. And the system is part of a portfolio that belongs to one of the leading US solar companies.

Point being, the mistakes made at this site could happen just about anywhere, regardless of whether your company uses in-house of subcontracted labor. Maybe someone took a mental vacation. Maybe the right parts weren't on site. Whatever the cause, these aren't mistakes that should be able to initiate a rooftop fire without any advanced warning.

 

[ggunn]

That's not the first fault; that's the second fault. We know that the second fault occurred in the PV output circuit, because that fault would have shut the inverter down. The first fault occurred in a grounded PV source circuit conductor.

Since first fault was in USE-2 run in free air, the insulation could have been pinched by the racking, or worn raw over time. If it was a pinched conductor, that is a classic ground fault that should have been detected during commissioning. If the fault had occurred in an ungrounded source circuit conductor, it would have been detected.

Ah. I had heard that the fault in the conduit was the negative conductor, but I hadn't known it was a positively grounded system so I thought it was the first one. That said, grounded conductor ground fault detection is not a 100% fail-safe; the only thing that will stop a fire when positive and negative conductors short to each other is fault-triggered rapid shutdown, and that's assuming at least one of the faults (assuming both positive and negative faults to ground) is outside the 10' perimeter in the current regs. I have heard rumors of module level shutdown regs coming.