ECN Forum Forums General Topics of the Trade General Discussion Area Unbalanced 480 volt lighting ckt

If the service is 277/480 volts then the neutral must be run and connected to the MDP.
You have no return path for a fault.
When you say "there is a ground fault on the circuit" do you mean a GFI breaker? ARe the lts connected 277 volts or 480? If its 277 volts that may be why the breaker is tripping.