UFC 3 -520-01
June 10, 2002
Definition and Function
Permissive Control Device is generally a two -position manually operated
switch that in one position permits the closing of a circuit breaker, or the
placing of an equipment into operation, and in the other position prevents
the circuit breaker or the equipment from being operated.
DC Circuit Breaker is used to close and interrupt a dc power circuit under
normal conditions or to interrupt this circuit under fault or emergency
Load-Resistor Contactor is used to shunt or insert a ste p of load limiting,
shifting, or indicating resistance in a power circuit, or to switch a space
heater in circuit, or to switch a light, or regenerative, load resistor of a
power rectifier or other machine in and out of circuit.
DC Overcurrent Relay is a device that functions when the current in a dc
circuit exceeds a given value.
AC Reclosing Relay is a device that controls the automatic reclosing and
locking out of an ac circuit interrupter.
Lockout Relay is a hand or electrically reset auxili ary relay that is operated
upon the occurrence of abnormal conditions to maintain associated
equipment or devices inoperative until it is reset.
Differential Protective Relay is a protective device that functions on a
percentage or phase angle or other quantitative difference of two currents
or of some other electrical quantities.
Tripping, or Trip-Free, Relay is a device that functions to trip a circuit
breaker, contactor, or equipment, or to permit immediate tripping by other
devices; or to prevent immediate reclosure of a circuit interrupter, in case it
should open automatically even though its closing circuit is maintained
A similar series of numbers, prefixed by the letters RE (for "remote") are
normally used for interposing rela ys performing functions that are controlled directly
from a supervisory system. For example, a remote stopping device controlled by the
remote supervisory system would be designated RE5.
A device function number can include a letter suffix. A suffix provides
additional information about auxiliary equipment associated with the device,
distinguishing features or characteristics of the device, or conditions that describe the
use of the device. Because a suffix letter can have more than one meaning, care
should be used when interpreting device function numbers that contain a suffix. If
ambiguity exists regarding the meaning of a suffix, refer to ANSI/IEEE C37.2 to help
with an interpretation. Table 9 -3 lists common suffixes used in conjunction with
protective relay device function numbers.