This guide is intended for general use in the application of ac high-voltage circuit breakers for shunt reactor current switching. The current to be interrupted is generally less than 300 A rms; however, shunt reactor switching imposes a unique and severe duty on the connected system and the circuit breaker. Successful interruption is the result of a complex interaction between the circuit breaker and the circuit; this interaction can result in significant overvoltages. The purpose of the guide is to describe, principally for the benefit of the user, the shunt reactor switching duty, the overvoltages generated, and the control of those overvoltages. The guide further details the specification of circuit breakers and procedures to predict field performance based on test data. NOTE—Shunt reactors connected to the tertiary windings of transformers have typical currents in the order of some thousand Amperes.