ANSI IEEE Standard Device Numbers
In North America protective relays are generally referred to by standard device numbers. Letters are sometimes added to specify the application (IEEE Standard C37.2-2008). ANSI IEEE Standard Device Numbers are below: (the more commonly used ones are in bold)
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
13 – Synchronous-speed Device
14 – Underspeed Device
15 – Speed or Frequency-Matching Device
25 – Synchronizing or Synchronism-Check Device
26 – Apparatus Thermal Device
27 – Undervoltage Relay
30 – Annunciator Relay
32 – Directional Power Relay
37 – Undercurrent or Underpower Relay
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
13 – Synchronous-speed Device
14 – Underspeed Device
15 – Speed or Frequency-Matching Device
25 – Synchronizing or Synchronism-Check Device
26 – Apparatus Thermal Device
27 – Undervoltage Relay
30 – Annunciator Relay
32 – Directional Power Relay
37 – Undercurrent or Underpower Relay
36 – Polarity or Polarizing Voltage Devices
38 – Bearing Protective Device
39 – Mechanical Conduction Monitor
40 –Field (over/under excitation) Relay
41 – Field Circuit Breaker
42 – Running Circuit Breaker
43 – Manual Transfer or Selector Device
46 – Rev. phase or Phase-Bal. Current Relay
47 – Phase-Seq. or Phase-Bal. Voltage Relay
48 – Incomplete-Sequence Relay
49 – Machine or Transformer Thermal Relay
50 – Instantaneous Overcurrent
51 – AC Time Overcurrent Relay
52 – AC Circuit Breaker
53 – Field Excitation Relay
55 – Power Factor Relay
56 – Field Application Relay
59 – Overvoltage Relay
60 – Voltage or Current Balance Relay
62 – Time-Delay Stopping or Opening Relay
63 – Pressure Switch
64 – Ground Detector Relay
38 – Bearing Protective Device
39 – Mechanical Conduction Monitor
40 –Field (over/under excitation) Relay
41 – Field Circuit Breaker
42 – Running Circuit Breaker
43 – Manual Transfer or Selector Device
46 – Rev. phase or Phase-Bal. Current Relay
47 – Phase-Seq. or Phase-Bal. Voltage Relay
48 – Incomplete-Sequence Relay
49 – Machine or Transformer Thermal Relay
50 – Instantaneous Overcurrent
51 – AC Time Overcurrent Relay
52 – AC Circuit Breaker
53 – Field Excitation Relay
55 – Power Factor Relay
56 – Field Application Relay
59 – Overvoltage Relay
60 – Voltage or Current Balance Relay
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
74 – Alarm Relay
75 – Position Changing Mechanism
76 – DC Overcurrent Relay
78 – Phase-Angle Measuring Relay
79 – AC-Reclosing Relay
81 – Frequency Relay
83 – Automatic Selective Control or Transfer Relay
84 – Operating Mechanism
85 – Pilot Communications, Carrier or Pilot-Wire Relay
86 – Lockout Relay
87 – Differential Protective Relay
89 – Line Switch
90 – Regulating Device
91 – Voltage Directional Relay
92 – Voltage and Power Directional Relay
94 – Tripping or Trip-Free Relay
66 – Notching or jogging device
67 – AC Directional Overcurrent Relay
68 – Blocking or “out of step” Relay
69 – Permissive Control Device
74 – Alarm Relay
75 – Position Changing Mechanism
76 – DC Overcurrent Relay
78 – Phase-Angle Measuring Relay
79 – AC-Reclosing Relay
81 – Frequency Relay
83 – Automatic Selective Control or Transfer Relay
84 – Operating Mechanism
85 – Pilot Communications, Carrier or Pilot-Wire Relay
86 – Lockout Relay
87 – Differential Protective Relay
89 – Line Switch
90 – Regulating Device
91 – Voltage Directional Relay
92 – Voltage and Power Directional Relay
94 – Tripping or Trip-Free Relay
Device Number Suffix:
B – Bus
F – Field
G – Ground or generator
N – Neutral
T – Transformer
86T is a Lockout Relay for a Transformer.
59B is a Bus Overvoltage Relay.
50N is an Instantaneous Overcurrent Relay.