UFC 3 -520-01
June 10, 2002
Definition and Function
Temperature Control Device functions to raise or to lower the temperature
of a machine or other apparatus, or of any medium, when its temperature
falls below, or rises above, a predetermined value.
Undervoltage Relay is a device that functions on a given value of
Isolating Contactor is used expressly for disconnecting one circuit from
another for the purposes of emergency operation, maintenance, or test.
Annunciator Relay is a nonautomatically reset device that gives a number
of separate visual indications upon the functioning of protective devices,
and that may also be arranged to perform a lockout function.
Directional Power Relay is one that functions on a desired value of power
flow in a given direction, or upon reverse power resulting from arc back in
the anode or cathode circuits of a power rectifier.
Position Switch makes or breaks contact when the main device or piece of
apparatus, which has no device function number, reaches a given position.
Reverse-Phase, or Phase -Balance, Current Relay is a device that
functions when the polyphase currents are of reverse -phase sequence, or
when the polyphase currents are unbalanced or contain negative phase -
sequence components above a given amount.
Phase-Sequence Voltage Relay is a device that functions upon a
predetermined value of polyphase voltage in the desired phase sequence.
Incomplete Sequence Relay is a device that returns the equipment to the
normal, or off, position and locks it out if the normal starting, operating, or
stopping sequence is not properly completed within a predetermined time.
Machine, or Transformer, Thermal Relay is a device that functions when
the temperature of an ac machine armature, or of the armature or other
load carrying winding or element of a dc machine, or converter or power
rectifier or power transformer (including a power rectifier transformer)
exceeds a predetermined value.
Instantaneous Overcurrent, or Rate -o f-Rise Relay is a device that functions
instantaneously on an excessive value of current, or on an excessive rate
of current rise, thus indicating a fault in the apparatus or circuit being
AC Time Overcurrent Relay is a device with either a definite or inverse time
characteristic that functions when the current in an ac circuit exceeds a