The application of circuit breakers and fuses must be considered to determine
which offers the most appropriate protection. Consideration should be given
to anti-single-phase devices when three-pole interrupter swit ches with fuses
are used, because fuses are single-pole interrupter switches. An arcing fault
may not be stopped by a single-pole interruption. It can be backfed from the
other energized phases. Because of this condition, severe equipment burndowns
may occur. Ferroresonance is the result of interaction between the reactance
of a saturable magnetic device, such as a transformer, and system
The low-voltage switchgear discussed in this section involves power circuit
breakers and enclosures of indoor or outdoor type. The frequency of inspection
and maintenance should be 3–6 months when new equipment is installed and
1–2 years for existing equipment. However, if problems with switchgear are
encountered, the frequency can be shortened. Similarly to medium- voltage
switchgear, the conditions that call for frequent inspection and maintenance are
high humidity and temperature, corrosive atmosphere, excessive dirt or dust,
frequent fault interruption, and age of the equipment. The following guide is
provided for the general maintenance of low-voltage equipment; where necessary
it should be supplemented by the manufacturer’s detailed instructions.