jiw
Guest
For a number of years, bearing failure in ac motors has been documented as a result of current flow through the bearings. As the rotor spins in the field windings, a voltage can be induced in it. If the motor shaft is connected by belt or lovejoy type coupling so that it is not well grounded the voltage will cause a current to flow through the bearing races and balls to ground. From a high potential to a low potential. This was not a very great problem until the increased use of variable frequency drives. Because of the nature of their operation they can greatly increase the problem, especially if they use a high carrier frequency which makes the motor operate quieter. When you break apart these failed bearings, it looks like a nice little bead in the race. The cheap fix is to lay a heavy grounded bare wire across the shaft, the more expensive is a grounding brush holder drilled and tapped to the shaft end bell, some even recommended a conducting grease, but very impractical on sealed bearings. Now to the static electricity issue, Static and induced voltages are very different, but they both always flow from a high potential to a low potential. Therefore if it was a hazard to bearings, the chain would do more harm than good. 'Course, if you get the combine insulated real well, it will be real interesting when you get off the ladder as you will be at the same potential as the combine until that first foot hits the ground!