The Under/Over Frequency Relay is sensitive to both underfrequency and overfrequency conditions. For instance, in an ac power plant, it can be used to protect a generator against underspeed and/or overspeed, because frequency is proportional to speed. Frequency setpoint and hysteresis adjustments are provided for underfrequency and overfrequency, along with two independent sets of contacts: one for underfrequency and one for overfrequency.