11

Multifunction Device

-Device that performs three or more comparatively important functions, that could be designated by combining several device numbers.

21

Distance Relay

A relay that functions when the circuit admittance, impedance, or reactance increases or decreases beyond predetermined limits.

23

Temperature Control Device

A device that functions to raise or lower the temperature of a machine or other apparatus, or of any medium, when it's temperature falls below, or rises above a predetermined value.

25

Synchronizing or Synchronism Check Device

A device that operates when two AC circuits are within the desired limits of Frequency, Phase Angle, or Voltage, to permit or to cause the paralleling of these two circuits.

27

AC Undervoltage Relay

A relay that functions on a given value of AC Undervoltage.

30

Annunciator Relay

a non-automatically reset device that gives a number of separate visual indications upon the functioning of protective devices, and which may be arranged to perform a lockout function.

43

Manual Transfer or Selector Device

A manually operated device that transfers the control circuits in order to modify the plan of operation of the switching equipment or some of the devices.

49

Machine or Transformer Thermal Relay

A relay that functions when the temperature of a machine armature or other load-carrying winding or element of a machine or the temperature of a power rectifier or power transformer (including a power rectifier transformer) exceeds a predetermined value.

50

Instantaneous Overcurrent or Rate of Rise Relay

A relay that functions instantaneously on an excessive value of current or on an excessive rate of current rise, thus indicating a fault in the circuit being protected.

51

AC Time Overcurrent Relay

A relay with either a definite or inverse time characteristic that functions when the current in a circuit exceeds a predetermined value.

52

AC Circuit Breaker

A device that is used to close and interrupt an AC power circuit under normal conditions or to interrupt this circuit under fault or emergency conditions.

59

Overvoltage Relay

A relay that functions on a given value of overvoltage.

62

Time-Delay or Stopping Relay

A time-delay relay that serves in conjunction with the device that initiates the shutdown, stopping, or opening operation in an automatic sequence or protective relay system.

63

Pressure Switch

A switch that operates on given values or on given rate of change in pressure.

67

AC Directional Overcurrent Relay

A relay that functions on a desired value of an Overcurrent flowing in a predetermined direction.

69

Permissive Control Device

Is generally a two-position manually-operated switch that, in one position permits the closing of a circuit breaker, or placing of an equipment into operation, and in the other position prevents the circuit breaker or the equipment from being operated.

71

Level Switch

A switch which operates on given values, or on a given rate of change, or level.

72

DC Circuit Breaker

A circuit breaker that is used to close and interrupt a DC power circuit under normal conditions or to interrupt this circuit under fault or emergency conditions.

74

Alarm Relay

A relay other than an annunciator, as covered under device function 30, that is used to operate, or to operate in connection with, a visual or audible alarm.

79

AC Reclosing Relay

A relay that controls the automatic reclosing and locking out of an AC circuit interrupter.

81

Frequency Relay

A relay that functions on a predetermined value of frequency (either under, over, or on normal system frequency) or rate of change of frequency.

86

Lockout Relay

An electrically operated hand, or electrically, reset relay or device that functions to shut down or hold an equipment out of service, or both, upon the occurrence of abnormal conditions.

87

Differential Protective Relay

A protective relay that functions on a percentage or phase angle or other quantitative difference of two currents or of some other electrical quantities.

89

Line Switch

A switch used as a disconnecting, load-interrupter, or isolating switch in an AC or DC power circuit, when this device is electrically operated or has electrical accessories, such as an auxiliary switch. magnetic lock, etc.

90

Regulating Device

A device that functions to regulate a quantity, or quantities, such as voltage, current, power, speed, frequency, temperature, and load at a certain value or between certain (generally close) limits for machines, tie lines, or other apparatus.

94

Tripping or Trip-Free Relay

A relay 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 if it should open automatically even though its closing circuit is maintained closed.

98

Transfer Trip Equipment

Includes receivers, transmitters, and auxiliary operating and alarm relays.