ANSI Device Numbers

In the design of electrical power systems, the ANSI (American National Standards Institute) Standard Device Numbers (ANSI /IEEE Standard C37.2) denote what features a protective device supports (such as a relay or circuit breaker). These types of devices protect electrical systems and components from damage when an unwanted event occurs, such as an electrical fault. Device numbers are used to identify the functions of devices shown on a schematic diagram. Function descriptions are given in the standard.

List of device numbers and acronyms

1 – Master Element



Any initiating Device will be term as master element. Control Switches, voltage relays, Current Sensors etc. This device serves may be directly or it will operate some other protective device and will place equipment in or out of protection.

Ex: TNC switch ( Trip Neutral Close) to act as breaker control switch. So TNC is master element for Breaker.

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 – Multi-function Device

12 – Overspeed Device

13 – Synchronous-speed Device

14 – Underspeed Device

15 – Speed – or Frequency, Matching Device

16 – Data Communications Device

17 – Shunting or Discharge Switch

18 – Accelerating or Decelerating Device

19 – Starting to Running Transition Contactor

20 – Electrically Operated Valve

21 – Distance Relay

22 – Equalizer Circuit Breaker

23 – Temperature Control Device

24 – Volts Per Hertz Relay

25 – Synchronizing or Synchronism-Check Device

26 – Apparatus Thermal Device

27 – Undervoltage Relay

28 – Flame detector

29 – Isolating Contactor or Switch

30 – Annunciator Relay

31 – Separate Excitation Device

32 – Directional Power Relay

33 – Position Switch

34 – Master Sequence Device

35 – Brush-Operating or Slip-Ring Short-Circuiting Device

36 – Polarity or Polarizing Voltage Devices

37 – Undercurrent or Underpower Relay

38 – Bearing Protective Device

39 – Mechanical Condition Monitor

40 – Field (over/under excitation) Relay

41 – Field Circuit Breaker

42 – Running Circuit Breaker

43 – Manual Transfer or Selector Device

44 – Unit Sequence Starting Relay

45 – Abnormal Atmospheric Condition Monitor

46 – Reverse-phase or Phase-Balance Current Relay

47 – Phase-Sequence or Phase-Balance Voltage Relay

48 – Incomplete Sequence Relay

49 – Machine or Transformer, Thermal Relay

50 – Instantaneous Overcurrent Relay

51 – AC Inverse Time Overcurrent Relay

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

60 – Voltage or Current Balance Relay

61 – Density Switch or Sensor

62 – Time-Delay Stopping or Opening Relay

63 – Pressure Switch

64 – Ground Detector Relay

65 – Governor

66 – Notching or Jogging Device

67 – AC Directional Overcurrent Relay

68 – Blocking or "Out-of-Step" Relay

69 – Permissive Control Device

70 – Rheostat

71 – Liquid Level 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 Relay

79 – AC Reclosing Relay

80 – Flow Switch

81 – Frequency Relay

82 – DC Reclosing Relay

83 – Automatic Selective Control or Transfer Relay

84 – Operating Mechanism

85 – Communications,Carrier or Pilot-Wire Relay

86 – Lockout Relay

87 – Differential Protective Relay

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

95 – For specific applications where other numbers are not suitable

96 – For specific applications where other numbers are not suitable

97 – For specific applications where other numbers are not suitable

98 – For specific applications where other numbers are not suitable

99 – For specific applications where other numbers are not suitable

AFD – Arc Flash Detector

CLK – Clock or Timing Source

DDR – Dynamic Disturbance Recorder

DFR – Digital Fault Recorder

ENV – Environmental Data

HIZ – High Impedance Fault Detector

HMI – Human Machine Interface

HST – Historian

LGC – Scheme Logic

MET – Substation Metering

PDC – Phasor Data Concentrator

PMU – Phasor Measurement Unit

PQM – Power Quality Monitor

RIO – Remote Input/Output Device

RTU – Remote Terminal Unit/Data Concentrator

SER – Sequence of Events Recorder

TCM – Trip Circuit Monitor

SOTF – Switch On To Fault

A suffix letter or number may be used with the device number. for example, suffix N is used if the device is connected to a Neutral wire (example: 59N in a relay is used for protection against Neutral Displacement) and suffixes X,Y,Z are used for auxiliary devices. Similarly, the "G" suffix denotes a "ground", hence a "51G" is a time over current ground relay. Suffix numbers are used to distinguish multiple "same" devices in the same equipment such as 51-1, 51–2.

Device numbers may be combined if the device provides multiple functions, such as the instantaneous/time-delay AC over current relay denoted as 50/51.

For device 16, the suffix letters further define the device: the first suffix letter is 'S' for serial or 'E' for Ethernet. The subsequent letters are: 'C' security processing function (e.g. VPN, encryption), 'F' firewall or message filter, 'M' network managed function, 'R' router, 'S' switch and 'T' telephone component. Thus a managed Ethernet switch would be 16ESM.