Under NEC, the generator frame and motor frame must be bonded to the equipment grounding conductor unless they are effectively insulated from ground and the motor driving it.

Under NEC, the generator frame and motor frame must be bonded to the equipment grounding conductor unless they are effectively insulated from ground and the motor driving it.

• A. They are effectively insulated from ground
• B. They are effectively insulated from ground and from each other
• C. They are effectively insulated from ground and the motor driving it
• D. They have double insulation

Answer: (C)

Bonding frames to the equipment grounding conductor provides a low-impedance path to earth so fault current can quickly trip the protective device and keep exposed metal at ground potential. The NEC allows an exception to this bonding when the generator frame and the motor frame are effectively insulated from ground and from the motor that drives it. If there is no conductive path from either frame to earth and no path through the motor or between the frames, there isn’t a fault current path that would require bonding to the grounding conductor. In that isolated setup, bonding is not required. If there were any conductive connection to ground or to the driving motor, bonding would be necessary to ensure a safe fault path.

Bonding frames to the equipment grounding conductor provides a low-impedance path to earth so fault current can quickly trip the protective device and keep exposed metal at ground potential. The NEC allows an exception to this bonding when the generator frame and the motor frame are effectively insulated from ground and from the motor that drives it. If there is no conductive path from either frame to earth and no path through the motor or between the frames, there isn’t a fault current path that would require bonding to the grounding conductor. In that isolated setup, bonding is not required. If there were any conductive connection to ground or to the driving motor, bonding would be necessary to ensure a safe fault path.