The plant hired a new mechanical maintenance manager a few months ago. Yesterday, he spoke to you about the ultrasonic analysis program he started a few weeks after he hired on and said, “I’m actually getting in trouble with this program. They are finding a lot of damaged bearings with this method and now the plant manager and the controller are questioning its validity. They are concerned it is finding false positives and driving up costs. The fox needs to stop chasing its tail. Could something electrical be contributing to the bearing damage? If so, how would I find it?”
How do you answer his questions?
Something electrical certainly could be wrong. The usual culprit in bearing damage situations is undesired current flowing through the bearings to get back to its source. The cure for that is to give undesired current a low-impedance path back to the source. This won’t stop all current from flowing through the bearings, but it will reduce it dramatically and likely to an amount that is negligible.
Walk with your counterpart to several motors that had been tagged by the ultrasonic testing as having bearing problems. Do you see ground rods? Those serve no electrical purpose, and their presence indicates a lack of proper bonding. Each of these motor installations will need to be examined for proper bonding to the equipment grounding conductor (EGC) system. See Article 250, Part V. Also check the EGC system itself to ensure it provides a low-impedance path back to the source.
