It is illegal, and dangerous for both you and the motor. The ground current may "bake" the soil around the ground rods (Both the rod at the motor and the rod at the service and possibly at the transformer also.) As the soil dries the resistance rises and a voltage drop called a touch potential develops. A person standing on the ground and touching the ground rod may receive a shock. The shock may be lethal. As the ground resistance is increasing, the voltage available for the motor is dropping. Low voltage often results in motor damage.
Some of this information is based on a real event, where a circulating current through a safety ground system for a transmission line "Baked" the surrounding earth. A worker was lifted by a crane, in a work basket. The crane was grounded to a different ground rod. When the worker touched the grounded power line, the difference in voltages between the two ground systems knocked him unconscious. You are attempting to generate a similar situation.
Please don'tIt is a condition that gets worse over time. No telling how much time, minutes, hours or days. It may work at first, but you may come back later to find yourself dead.
Bill
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"Why not the best?"
Jimmy Carter
