We have three 1500 cfm compressors. Two were installed together and have identical Siemens circuit breakers (800Amp) sharing a common panelboard. The third was installed later and is wired and fed separate. Of the two sharing the common panelboard one has extremely high currents (170 Amps) on the motor ground wires in the starter enclosure. All motors are started by Siemens Sikostart starters "in line" without bypass contactors.
All conductors have been thoroughly megged showing high resistance to ground.
Here is the name plate data off the problem motor; MFR:Baldor, ENCL:TEFC, Frame:449T, HP:300, PH:3, Volts:460, Des:B Amps:328, Code:H Hz:60, Rating:40C amb cont, NEMA Nom Eff:95.8%, PF:88% SF:1.15