Low-Voltage Release and Low-Voltage Protection

Author: E.E. Kimberly

Any automatic starter of a type described, which uses a shunt coil on the final contact-holding solenoid, will automatically disconnect the motor from the line if the line voltage decreases to an abnormally low value. If such a starter will restart the motor without attention after such a voltage failure, it is said to provide low-voltage release. With such an arrangement it is certain that the starting resistance will be used when the motor restarts after line-voltage recovery provides resumption of service; and this condition is desirable for gome fan and pump applications. Low-voltage release is undesirable and dangerous, however, when used in control of motors in some types of service, because of the hazard involved in the unsupervised starting of some kinds of machinery. Starters that are so designed as to require supervised starting after every stop are said to provide low-voltage protection. Automatic control equipment costs much more than manually operated control for comparable service.