The Misuse of IEEE Device 52- Medium Voltage Contactors and Breakers Are Not the Same!

Many standards and specifications, related to medium voltage (MV) motor and feeder circuits, continue to center around the generic use of the IEEE Device 52 as a circuit identifier for the switching device used within those power systems. IEEE Device 52 is defined as a device that is used to close and interrupt an ac power circuit under normal conditions or to interrupt this circuit under fault or emergency conditions. Many of the current standards include detailed protection and coordination recommendations that are centered on circuit breaker protective settings. Some of these recommended protective settings can be detrimental when MV vacuum contactors are used instead of ac circuit breakers to interrupt the circuit under fault conditions such as in motor and feeder applications. This paper will outline MV contactor and breaker rating differences, compare the appropriate protection variations and requirements between the two, and highlight the dangers to personnel and equipment when assuming that a MV vacuum contactor can provide the same performance and require the same protective settings as a MV circuit breaker.