dsPICDEM MCHV-2 Development Board motor connection
The protective ground of the motor should be a connection from the metal frame or housing of the motor to earth. If the motor's ground terminal is not obviously a connection to the frame or housing, check with an ohmmeter to make sure it has no connection to the motor windings. If it is only connected to the motor frame or housing, it should be connected to an earth ground, preferably the protective ground terminal of a power outlet. It could also be connected to a cold water pipe.