A sectionalizer is an automatic circuit-opening device. After a circuit has been de-energized by a backup protective device-such as a recloser or reclosing breaker-a sectionalizer isolates the faulted section of a distribution line. After the fault has been isolated, the rest of the circuit is returned to service upon reclosing of the backup.
The sectionalizer counts the overcurrent interruptions of the backup device and can be set to open after one or two counts have been registered within a pre-determined time span.
A sectionalizer opens during the open interval of the backup. Although it cannot interrupt faults, it can be closed into them. Sectionalizers can be used in place of fuses or between a reclosing device and a fuse. They only detect current interruptions above a pre-determined level and have no time-current characteristics, permitting easy coordination with other protective devices on the system.