1

Master Element

2

Time Delay Starting or Closing Relay

3

Checking or Interlocking Relay

4

Master Contactor

5

Stopping Device

6

Starting Circuit Breaker

7

Rate of Change Relay

8

Control Power Disconnecting Device

9

Reversing Device

10

Unit Sequence Switch

11

Multifunction Device

12

Overspeed Device/Protection

13

Synchronous-Speed Device

14

Underspeed Device

15

Speed or Frequency Matching Device

16

Communication Networking Device

17

Shunting or Discharge Switch

18

Accelerating or Decelerating Device

19

Motor Starter / Starting-to-Running Transition Contactor

20

Electrically-Operated Valve

21

Distance Relay

21G

Ground Distance

21P

Phase Distance

22

Equalizer Circuit Breaker

23

Temperature Control Device

24

Volts-per-Hertz Relay / Overfluxing

25

Synchronizing or Synchronism-Check Device

26

Apparatus Thermal Device

27

Undervoltage Relay

27P

Phase Undervoltage

27TN

Third Harmonic Neutral Undervoltage

27X

Auxiliary Undervoltage

27 AUX

Undervoltage Auxiliary Input

27/27X

Bus/Line Undervoltage

28

Flame Detector

29

Isolating Contactor

30

Annunciator Relay

31

Separate Excitation Device

32

Directional Power Relay

32L

Low Forward Power

32N

Wattmetric Zero-Sequence Directional

32P

Directional Power

32R

Reverse Power

33

Position Switch

34

Master Sequence Device

35

Brush-Operating or Slip-ring Short Circuiting Device

36

Polarity or Polarizing Voltage Device

37

Undercurrent or Underpower Relay

37P

Underpower

38

Bearing Protective Device / Bearing RTD

39

Mechanical Condition Monitor

40

Field Relay / Loss of Excitation

41

Field Circuit Breaker

42

Running Circuit Breaker

43

Manual Transfer or Selector Device

44

Unit Sequence Starting Relay

45

Atmospheric Condition Monitor

46

Reverse-Phase or Phase Balance Current Relay or Stator Current Unbalance

47

Phase-Sequence or Phase Balance Voltage Relay

48

Incomplete Sequence Relay / Blocked Rotor

49

Machine or Transformer Thermal Relay / Thermal Overload

49RTD

RTD Biased Thermal Overload

50

Instantaneous Overcurrent Relay

50BF

Breaker Failure

50DD

Current Disturbance Detector

50G

Ground Instantaneous Overcurrent

50N

Neutral Instantaneous Overcurrent

50P

Phase Instantaneous Overcurrent

50_2

Negative Sequence Instantaneous Overcurrent

50/27

Accidental Energization

50/74

CT Trouble

50/87

Instantaneous Differential

50EF

End Fault Protection

50IG

Isolated Ground Instantaneous Overcurrent

50LR

Acceleration Time

50NBF

Neutral Instantaneous Breaker Failure

50SG

Sensitive Ground Instantaneous Overcurrent

50SP

Split Phase Instantaneous Current

51

AC Time Overcurrent Relay

51

Overload

51G

Ground Time Overcurrent

51N

Neutral Time Overcurrent

51P

Phase Time Overcurrent

51V

Voltage Restrained Time Overcurrent

51R

Locked / Stalled Rotor

51_2

Negative Sequence Time Overcurrent

52

AC Circuit Breaker

53

Exciter or DC Generator Relay

54

Turning Gear Engaging Device

55

Power Factor Relay

56

Field Application Relay

57

Short-Circuiting or Grounding Device

58

Rectification Failure Relay

59

Overvoltage Relay

59B

Bank Phase Overvoltage

59P

Phase Overvoltage

59N

Neutral Overvoltage

59NU

Neutral Voltage Unbalance

59P

Phase Overvoltage

59X

Auxiliary Overvoltage

59_2

Negative Sequence Overvoltage

60

Voltage or Current Balance Relay

60N

Neutral Current Unbalance

60P

Phase Current Unbalance

61

Density Switch or Sensor

62

Time-Delay Stopping or Opening Relay

63

Pressure Switch Detector

64

Ground Protective Relay

64F

Field Ground Protection

64S

Sub-harmonic Stator Ground Protection

64TN

100% Stator Ground

65

Governor

66

Notching or Jogging Device/Maximum Starting Rate/Starts Per Hour/Time Between Starts

67

AC Directional Overcurrent Relay

67G

Ground Directional Overcurrent

67N

Neutral Directional Overcurrent

67P

Phase Directional Overcurrent

67SG

Sensitive Ground Directional Overcurrent

67_2

Negative Sequence Directional Overcurrent

68

Blocking Relay / Power Swing Blocking

69

Permissive Control Device

70

Rheostat

71

Liquid Switch

72

DC Circuit Breaker

73

Load-Resistor Contactor

74

Alarm Relay

75

Position Changing Mechanism

76

DC Overcurrent Relay

77

Telemetering Device

78

Phase Angle Measuring or Out-of-Step Protective Relay

78V

Loss of Mains

79

AC Reclosing Relay / Auto Reclose

80

Liquid or Gas Flow Relay

81

Frequency Relay

81O

Over Frequency

81R

Rate-of-Change Frequency

81U

Under Frequency

82

DC Reclosing Relay

83

Automatic Selective Control or Transfer Relay

84

Operating Mechanism

85

Carrier or Pilot-Wire Receiver Relay

86

Locking-Out Relay

87

Differential Protective Relay

87B

Bus Differential

87G

Generator Differential

87GT

Generator/Transformer Differential

87LG

Ground Line Current Differential

87S

Stator Differential

87S

Percent Differential

87L

Segregated Line Current Differential

87M

Motor Differential

87O

Overall Differential

87PC

Phase Comparison

87RGF

Restricted Ground Fault

87T

Transformer Differential

87V

Voltage Differential

88

Auxiliary Motor or Motor Generator

89

Line Switch

90

Regulating Device

91

Voltage Directional Relay

92

Voltage And Power Directional Relay

93

Field-Changing Contactor

94

Tripping or Trip-Free Relay

50/74

CT Supervision

27/50

Accidental Generator Energization

27TN/59N

100% Stator Earth Fault