The modern distribution system has high short-circuit current available and
therefore requires special consideration so that equipment may be applied
within its rating. Furthermore, the switchgear should be protected against
all types of faults, from low-level arcing faults to bolted faults. The protection
system should be selective; that is, the fault at a remote location in the
system should be localized without unnecessary tripping of either the main
breaker system or any intermediate breakers. The distribution system should
be planned to provide continuity and reliability of service. This can be
achieved by using two or more separate distribution systems instead of one
large system. The continuous current rating of the main protective device
should be adequate for the load to be served. Protective devices should not
be paralleled to obtain a higher rating