I have an existing 120/208v, 3ph, 4 wire panel with a 150amp main circuit breaker. When the owner opens the store and truns on all the lights the main breaker will trip within 30 minutes. He will then turn the main breaker back on and will remain on without incident the renainder of the day. Amp probe readings are as follows: A=50amps B=70amps C=42amps Neut=16amps. Any suggestion on what to look for?