why current flow through ground wires of submersible 3 phase motor?
If a 3-phase motor is powered through a variable frequency drive (VFD), there can be some ground-fault current due to capacitive coupling between the stator winding and the motor core. However, I would expect that to be a much lower current, and you have not mentioned a VFD. If this is a new installation, I would suspect a wiring error. The ground wires should be connected only to the motor frame at the motor and only to an earth ground or grounded bus at the source.