EG4 6000XP Showing 50W Solar input during pitch black

[ChrisG]

Do you mean that you had a pv conductor connected to the box itself - not just to breakers inside it? That would certainly explain part of the picture - especially that you had trouble once you connected the combiner box to ground as well. Maybe I'm misinterpreting what you mean.

I know in the manual for the 6000XP, the only thing it says about grounding the array is "Do not ground negative PV lines, only solar panel frames".

What you found was AC voltage on the PV lines which is what Adam had on the 6500ex which also ties to what @HighTechLab mentioned.

 

[Capn D]

The PV inputs are not fully isolated from the inverter circuit. This is also part of why they can't be grounded.

28 milliamps is enough current to stop your heart.