In the design of electrical power systems, the ANSI 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. ANSI/IEEE C37.2-2008 is one of a continuing series of revisions of the standard, which originated in 1928.
1. Master Element
is the initiating device, such as a control switch, voltage relay, float switch, etc., which serves either directly or through such permissive devices as protective and time-delay relays to place an equipment in or out of operation.
2. Time Delay Starting or Closing Relay
is a device that functions to give a desired amount of time delay before or after any point of operation in switching sequence or protective relay system, except as specifically provided by service function 48, 62, and 79.
3. Checking or Interlocking Relay
is a relay that operates in response to the position of a number of other devices (or to a number of predetermined conditions) in an equipment, to allow an operating sequence to proceed, or to stop, or to provide a check of the position of these devices or of these conditions for any purpose.
4. Master Contactor
is a device generally controlled by device function 1or the equivalent and the required permissive and protective devices, that serves to make and break the necessary control circuits to place an equipment into operation under the desired conditions and to take it out of operation under other or abnormal conditions.
5. Stopping Device
is a control device used primarily to shut down an equipment and hold it out of operation. (This device may be manually or electrically actuated, but excludes the function of electrical lockout [see device function 86] on abnormal conditions.)
6. Starting Circuit Breaker
is a device whose principal function is to connect a machine to its source of starting voltage.
7. Anode Circuit Breaker
is a device used in the anode circuits of a power rectifier for the primary purpose of interrupting the rectifier circuit if an arc-back should occur.
8. Control Power Disconnecting Device
is a disconnecting device, such as a knife switch, circuit breaker, or pull-out fuse block, used for the purpose of respectively connecting and disconnecting the source of control power to and from the control bus or equipment.
9. Reversing Device
is a device that is used for the purpose of reversing a machine field or for performing any other reversing functions.
10. Unit Sequence Switch
is a switch that is used to change the sequence in which units may be placed in and out of service in multiple-unit equipments.
11. Reserved for Future Application
(USBR assigned – Control Power Transformer).
12. Over-Speed Device
is usually a direct-connected speed switch which functions on machine over-speed.
13. Synchronous-Speed Device
is a device such as a centrifugal switch, a slip-frequency relay, a voltage relay, and undercurrent relay , or any type of device that operates at approximately the synchronous speed of a machine.
14. Under-Speed Device
is a device that functions when the speed of a machine fall below a pre -determined value.
15. Speed or Frequency Matching Device
is a device that functions to match and hold the speed or frequency of a machine or of a system equal to, or approximately equal to, that of another machine, source, or system.
16. Reserved for Future Application
(USBR assigned – Battery Charging Device).
17. Shunting or Discharge Switch
is a switch that serves to open or to close a shunting circuit around any piece of apparatus (except a resistor, such as a machine field, a machine armature, a capacitor, or a reactor).
18. Accelerating or Decelerating Device
is a device that is used to close or to cause the closing of circuits which are used to increase or decrease the speed of a machine.
19. Starting-to-Running Transition Contactor
is a device that operates to initiate or cause the automatic transfer of a machine from the starting to the running power connection.
is one used in a vacuum, air, gas, oil, or similar line, when it is electrically operated or has electrical accessories such as auxiliary switches.
21. Distance Relay
is a relay that functions when the circuit admittance, impedance, or reactance increases or decreases beyond predetermined limits.
22. Equalizer Circuit Breaker
is a breaker that serves to control or to make and break the equalizer or the current-balancing connections for a machine field, or for regulating equipment in a multiple -unit installation.
23. Temperature Control Device
is a device that function to raise or lower the temperature of a machine or other apparatus, or of any medium, when its temperature falls below, or rises above, a predetermined value.
24. Reserved for future Application
(USBR assigned – bus tie circuit breaker, contactor, or switch.)
25. Synchronizing or Synchronism-Check Device
is a device that operates when two a-c circuits are within the desired limits of frequency, phase angle, or voltage, to permit or to cause the paralleling of these two circuits
26. Apparatus Thermal Device
is a device that functions when the temperature of the shunt field or the amortisseur winding of a machine, or that of a load limiting or load shifting resistor or of a liquid or other medium, exceeds a predetermined value: or if the temperature of the protected apparatus, such as a power rectifier, or of any medium decrease below a predetermined value.
27. Undervoltage Relay
is a relay that functions on a given value of under-voltage.
28. Flame Detector
is a device that monitors the presence of the pilot or main flame of such apparatus as a gas turbine or a steam boiler.
29. Isolating Contactor
is a device that is used expressly for disconnecting one circuit from another for the purposes of emergency operation, maintenance, or test.
30. Annunciator Relay
is a non-automatically reset device that gives a number of separate visual indications of the functions of protective devices, and which may also be arranged to perform a lockout function.
31. Separate Excitation Device
is a device that connects a circuit, such as the shunt field of a synchronous converter, to a source of separate excitation during the starting sequence; or one that energizes the excitation and ignition circuits of a power rectifier.
32. Directional Power Relay
is a device that functions on a desired value of power flow in a given direction or upon reverse power resulting from arcback in the anode or cathode circuits of a power rectifier.
33. Position Switch
is a switch that makes or breaks contact when the main device or piece of apparatus which has no device function number reaches a given position.
34. Master Sequence Device
is a device such as a motor-operated multi-contact switch, or the equivalent, or programming device, such as a computer, that establishes or determines the operating sequence of the major devices in a equipment during starting and stopping or during other sequential switch operations.
35. Brush-Operating or Slipping Short-Circuiting Device
is a device for raising, lowering, or shifting the brushes of a machine, or for short-circuiting its slip rings, or for engaging or disengaging the contacts of a mechanical rectifier.
36. Polarity or Polarizing Voltage Device
is a device that operates, or permits the operation of, another device on a predetermined polarity only, or verifies the presence of a polarizing voltage in an equipment.
37. Undercurrent or Underpower Relay
is a relay that function when the current or power flow decreases below a predetermined value.
38. Bearing Protective Device
is a device that functions on excessive bearing temperature, or on another abnormal mechanical conditions associated with the bearing, such as undue wear, which may eventually result in excessive bearing temperature.
39. Mechanical Condition Monitor
is a device that functions upon the occurrence of an abnormal mechanical condition (except that associated with bearing as covered under device function 38), such as excessive vibration, eccentricity, expansion shock, tilting, or seal failure.
40. Field Relay
is a relay that functions on a given or abnormally low value or failure of a machine field current, or on excessive value of the reactive component of armature current in an a-c machine indicating abnormally low field excitation.
41. Field Circuit Breaker
is a device that functions to apply or remove the field excitation of a machine.
42. Running Circuit Breaker
is a device whose principal function is to connect a machine to its source of running or operation voltage. This function may also be used for a device, such as a contactor, that is used in series with a circuit breaker or other field protecting means, primarily for frequent opening and closing of the breaker.
43. Manual Transfer or Selector Device
is a manually operated device that transfers the control circuits in order to modify the plan of operation of the switching equipment or of some of the devices.
44. Unit Sequence Starting Relay
is a relay that function to start the next available unit in a multiple-unitequipment upon the failure or non-availability of the normally preceding unit.
45. Atmospheric Condition Monitor
is a device, that functions upon the occurrence of an abnormal atmospheric condition, such as damaging fumes, explosive mixtures, smoke or fire.
46. Reverse Phase or Phase Balance Current Relay
is a relay 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.
47. Phase-Sequence Voltage Relay
is a relay that function upon a predetermined value of polyphase voltage in the desired phase sequence.
48. Incomplete Sequence Relay
is a relay that generally 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. If the device is used for alarm purposes only, it should preferably be designated as 48A (alarm).
49. Machine or Transformer Thermal Relay
is 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
is 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 apparatus or circuit being protected.
51. A-C Time Overcurrent Relay
is a relay with either a definite or inverse time characteristic that functions when the current in an a-c circuit exceed a predetermined value.
52. A-C Circuit Breaker
is a device that is used to close and interrupt an a-c power circuit under normal conditions or to interrupt this circuit under fault of emergency conditions.
53. Exciter or D-C Generator Relay
is a relay that forces the d-c machine field excitation to build up during starting or which functions when the machine voltage has been built up to a given value.
54. High-Speed D-C Circuit Breaker
is a circuit breaker which starts to reduce the current in the main circuit in 0.01 second or less, after the occurrence of the d-c overcurrent or the excessive rate of current rise.
55. Power Factor Relay
is a relay that operates when the power factor in an a-c circuit rises above or falls below a predetermined value.
56. Field Application Relay
is a relay that automatically controls the application of the field excitation to an a-c motor at some predetermined point in the slip cycle.
57. Short-Circuiting or Grounding Device
is a primary circuit switching device that functions to short-circuit or to ground a circuit in response to automatic or manual means.
58. Rectification Failure Relay
is a device that functions if one or mote anodes of a power rectifier fail to fire, or to detect and arc-back or on failure of a diode to conduct or lock properly.
59. Overvoltage Relay
is a relay that functions on a given value of over-voltage.
60. Voltage or Current Balance Relay
is a relay that operates on a given difference in voltage, or current input or output, or two circuits.
61. Reserved for Future Application.
62. Time-Delay Stopping or Opening Relay
is 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. Liquid or Gas Pressure or Vacuum Relay
is a relay that operates on given values of liquid or gas pressure or on given rates of change of these values.
64. Ground Protective Relay
is a relay that functions on failure of the insulation of a machine, transformer, or of other apparatus to ground, or on flashover of a d-c machine to ground.
is the assembly of fluid, electrical, or mechanical control equipment used for regulating the flow of water, steam, or other medium to the prime mover for such purposes a starting, holding speed or load, or stopping.
66. Notching or Jogging Device
is a device that functions to allow only a specified number of operations of a given device or equipment, or a specified number of successive operations within a given time of each other. It is also a device that functions to energize a circuit periodically or for fractions of specified time intervals, or that is used to permit intermittent acceleration or jogging of a machine at low speeds for mechanical positioning.
67. A-C Directional Overcurrent Relay
is a relay that functions on a desired value of a-c over-current flowing in a predetermined direction.
68. Blocking Relay
is a relay that initiates a pilot signal for blocking of tripping on external faults in a transmission line or in other apparatus under predetermined condition, or cooperates with other devices to block tripping or to block re-closing on an out-of-step condition or on power savings.
69. Permissive Control Device
is generally a two-position, manually-operated switch that, in one position, permits the closing of a circuit breaker, or the placing of an equipment into operation, an in the other position prevents the circuit breaker or the equipment from being operated.
is a variable resistance device used in an electric circuit, which is electrically operated or has other electrical accessories, such a auxiliary , position, or limit switches.
71. Liquid or Gas-Level Relay
is a relay that operates on given values of liquid or gas level or on given rates of change of these values.
72. D-C Circuit Breaker
is a circuit breaker that is used to close and interrupt a d-c power circuit under normal conditions or to interrupt this circuit under fault or emergency conditions.
73. Load-Resistor Contactor
is a contactor that is used to shunt or insert a step of load limiting, shifting, or indicating resistance in a power circuit, or to switch a space heater in circuit, or to switch a light or regenerative load resistor, a power rectifier, or other machine in and out of circuit.
74. Alarm Relay
is 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.
75. Position Changing Mechanism
is a mechanism that is used for moving a main device from one position to another in an equipment: as for example, shifting a removable circuit breaker unit to and from the connected, disconnected, and test positions.
76. D-C Overcurrent Relay
is a relay that function when the current in a d-c circuit exceeds a given value.
77. Pulse Transmitter
is used to generate and transmit pulses over a telemetering or pilot-wire circuit to the remote indicating or receiving device.
78. Phase-Angle Measuring or Out-Of-Step Protective Relay
is a relay that functions at a pre-determined phase angle between two voltages or between two currents or between a voltage and current.
79. A-C Reclosing Relay
is a relay that controls the automatic reclosing and locking out of an a-c circuit interrupter.
80. Liquid or Gas Flow Relay
is a relay that operates on given values of liquid or gas flow or on given rates of change of these values.
81. Frequency Relay
is a relay that functions on a predetermined value of frequency (either under or over or on normal system frequency) or rate of change of frequency.
82. D-C Reclosing Relay
is a relay thast controls the automatic closing and re-closing of a d-c circuit interrupter, generally in response to load circuit conditions.
83. Automatic Selective Control or Transfer Relay
is a relay that operates to select automatically between certain sources or conditions in a equipment, or performs a transfer operation automatically.
84. Operating Mechanism
is the complete electrical mechanism or servomechanism, including the operating motor, solenoids, position switches, etc., for a tap changer, induction regulator, or any similar piece of apparatus which otherwise has no device function number.
85. Carrier or Pilot-Wire Receiver Relay
is a relay that is operated or restrained by a signal used in connection with carrier-current or d-c pilot-wire fault directional relaying.
86. Locking-Out Relay
is 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
is a protective relay that functions on a percentage or phase angle or other quantitative difference of two currents or of some other electrical quantities.
88. Auxiliary Motor or Motor Generator
is one used for operating auxiliary equipment, such as pumps, blowers, exciters, rotating magnetic amplifiers, etc.
89. Line Switch
is a switch used as a disconnecting, load-interrupter, or isolating switch in an a-c or d-c power circuit, when this device is electrically operated or has electrical accessories, such as an auxiliary switch, magnetic lock, etc.
90. Regulating Device
is 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.
91. Voltage Directional Relay
is a device which operates when the voltage across an open circuit breaker or contactor exceeds a given value in a given direction.
92. Voltage and Power Directional Relay
is a relay that permits or causes the connection of two circuits when the voltage difference between them exceed a given value in a predetermined direction and causes these two circuits to be disconnected from each other when the power flowing between them exceeds a given value in the opposite direction.
93. Field-Changing Contactor
is a contactor that functions to increase or decrease, in one step, the value of field excitation on a machine.
94. Tripping or Trip-Free Relay
is a relay that function to trip a circuit breaker, contactor or equipment, or to permit immediate tripping by other devices; or to prevent immediate re -closure of a circuit interrupter if it should open automatically even though its closing circuit is maintained closed.
95.* (USBR assigned – Closing Relay or Contactor)
98.* (USBR assigned – Loss of Excitation Relay)
99.* (USBR assigned – Arc Detector)
from 1 to 94 are suitable.
These letters denote separate auxiliary devices, such as:
- C – Closing Relay or Contactor
- CL – Auxiliary Relay, Closed (energized when main device is in closed position).
- CS – Control Switch
- D – “Down” Position Switch or Relay
- L – Lowering Relay
- 1. – Opening Relay
- OP – Auxiliary Relay, Open (energized when main device is in open position).
- PB – Push Button
- R – Raising Relay
- U – “Up” Position Switch or Relay
- X – Auxiliary Relay
- Y – Auxiliary Relay
- Z – Auxiliary Relay