UFC 3 -520-01
June 10, 2002
Asymmetrical Current--A current wave that is not symmetrical about the zero axis.
The current is offset from the zero axis with the magnitude of current above and below
the zero axis unequal.
Automatic Transfer Switch (ATS)--A switch designed to sense the loss of one power
source and automatically transfer the load to another source of power.
--A transformer having
a single continuous winding, portions
which are common for the input and output windings.
Available Short-Circuit Current-- The maximum current that the power system can
deliver through a given circuit point to any negligible impedance short circuit applied at
the given point, or at any other point that will cause the highest current to flow through
the given point.
Backup Protection--A form of protection that operates independently of specified
components in the primary protective system. It may duplicate the primary protection or
may be intended to operate only if the primary protection fails or is temporarily out of
-- The highest magnitude short circuit current for
a particular fault location.
The impedance at the fault location i s usually very low or zero for a bolted fault.
grounding, the permanent joining of metallic parts to form an electrically conductive path
to assure electrical continuity with the capacity to conduct safely any current likely to be
--A conductor used specifically for the purpose
Branch Circuit-- The circuit conductors and components between the final overcurrent
device protecting the circuit and the equipment.
-- In terms
of UPS systems,
a transformer that provides
to the UPS loads when the UPS equipment fails, is temporarily overloaded, or is out of
service for maintenance.
Circuit Breakers Incorporating Ground Fault Protection--Circuit breakers that
perform all normal circuit breaker functions and also trip when a current to ground
exceeds some predetermined value.
Clearing Time-- The total elapsed time between the beginning of an overcurrent and
the final interruption of the circuit at rated voltage. For a fuse, the clearing time is
considered the sum of the melting time and the arcing time. For a breaker, the clearing
time is the elapsed time between the actuation of a release device and the instant of arc
extinction on all poles of the primary arcing contacts.