Robert Peruzzi, Ph.D., P.E., DFE, Electrical Engineering Expert
The shrink-wrap failures had been isolated to a group of several transistors within the electro-mechanical modules within the equipment, but the root cause of those transistors failing had not been determined. The equipment; however, seller had more than 1,000 units in the field with no similar failures. In addition, the electro-mechanical module manufacturer had more than 20,000 units in the field with no similar failures. Electrical contractors hired by the buyer had measured power quality, and reported no faults found in the three-phase power at the equipment terminals. This paper presents circuit analyses of the failing electro-mechanical module, basics of electrostatic discharge damage and protection, and the root cause of these failures — an electrical code-violating extraneous neutral-to-ground bond in a secondary power cabinet.
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Robert Peruzzi, Ph.D., P.E., DFE, Electrical Engineering Expert with DJS Associates, Inc., can be reached via email at experts@forensicDJS.com or via phone at 215-659-2010.
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