A sectionalizer is a protective device that automatically isolates a faulted section of line from the rest of the distribution system. A sectionalizer should not be confused with a recloser; it does not interrupt fault current. It only counts the number of operations of an interrupting device that feeds the circuit, such as a recloser or relay-controlled breaker back at the substation. After a pre-selected number of current interrupting operations have been "seen", the sectionalizer opens and the feeder or line on the load side of the sectionalizer is not re-energized.
Sectionalizers simplify the job of restoring service after a fault has been removed since they do not require replaceable elements - such as fuse links - and they may be reclosed with a simple hook stick.
The length of primary line that each sectionalizer can protect depends upon the importance of the loads, tree conditions, lightning probabilities, etc. Normally, sectionalizers can effectively control up to two or three miles of line. In addition to sectionalizers, reclosers may be used along distribution feeders as well as the substation. Line reclosers and sectionalizers work together on distribution circuits to insure greater reliability. Although they look almost identical, their functions are quite different!