Light circuit trips gfci receptacles on separate circuit

[Rathbk]

I have a new shop that was just wired, with one light circuit and two receptacle circuits fed through a new 200 Amp load center (120/208). All receptacles are gfci, and they all trip the gfci (almost always) when the light switch (on the separate circuit) is turned on, but only if they are plugged into a load. The receptacles that do not have a load plugged in never trip. There is not a cross-connected neutral after the load center. Both receptacle circuits were on the same phase bar in the load center, and the light circuit was on the other phase bar. The wire for the light circuits and the receptacle circiuts lay next to each other for only about 20 feet, so an induced inductance feedback doesn't appear to the the culprit. Everything tested correctly, and we finally solved the immediate issue by moving the light circuit onto the same phase bar in the load center as the two receptacle circuits. So the problem only occurs when the light circuit is on the other phase bar in the load center. What could be causing this, and how can we fix it permanently so we can use the second phase bar in the load center for future circuits? I'm at a loss.

 

[charlie b]

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