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ANSI device numbers table (IEEE C37.2)

The device function numbers 1 to 94 assigned by IEEE C37.2, the combinations that appear most often on protection drawings, and the matching IEC 61850 logical node where the mapping is well established.

IEEE C37.2device function numbersIEC 61850-7-4logical nodes

Search the table

By number, name or logical node. A number on its own (“87”) finds that number and its combinations.

Common combinations and suffixes

As they appear on protection one-line and three-line diagrams for substations and industry.

Number	Name	Description	Logical node	Guide
21N	Ground distance	Distance elements that measure the phase-to-ground loops with residual current compensation.	PDIS	See guide
27/59	Undervoltage and overvoltage	Pair of voltage functions in the same relay or bay.	PTUV / PTOV	See guide
50BF	Breaker failure	If the breaker does not clear the fault within the set time, trips the adjacent breakers.	RBRF
50/51	Phase instantaneous and time overcurrent	Combination of 50 and 51 in the same relay.	PIOC / PTOC	See guide
50N/51N	Ground (residual) overcurrent	50 and 51 applied to the residual current 3I0; also written 50/51N.	PIOC / PTOC	See guide
50G/51G	Measured ground overcurrent	Overcurrent fed by a neutral CT or a core-balance CT, not by the sum of the phases.	PIOC / PTOC
51V	Voltage-restrained or voltage-controlled overcurrent	The inverse-time characteristic changes with voltage; used on generators (industry practice).	PVOC	See guide
52a / 52b	Breaker auxiliary contacts	The «a» contact is closed when the breaker is closed; the «b» contact, when it is open.
59N	Neutral or residual overvoltage	Measures the residual voltage 3V0 (broken delta or neutral) to detect ground faults.	PTOV	See guide
67N	Directional ground overcurrent	Residual overcurrent that operates only in the set direction.	PTOC + RDIR	See guide
74TC	Trip circuit supervision	Alarm on loss of continuity of the trip coil or trip circuit (industry practice).
81O / 81U	Overfrequency and underfrequency	81 with suffix O (over) or U (under) according to the operating direction.	PTOF / PTUF	See guide
81R	Rate of change of frequency (ROCOF)	Operates on df/dt; used in load shedding and, in inverter-based generation, as one more input of a hybrid anti-islanding logic; many utilities do not accept it as the only method, and the main method is usually direct transfer trip.	PFRC	See guide
87B	Bus differential	Differential with CTs in every bay connected to the bus.	PDIF
87G	Generator differential	Compares the currents on the neutral side and at the terminals of the stator.	PDIF	See guide
87L	Line differential	Compares the currents at the line ends over a communications channel.	PDIF
87M	Motor differential	Stator differential of a medium-voltage motor.	PDIF	See guide
87N	Restricted earth fault (REF)	Zero-sequence differential of a grounded-wye winding; also called 64REF.	PDIF	See guide
87T	Transformer differential	Differential with ratio and vector group compensation and harmonic restraint.	PDIF

Device function numbers 1 to 94

Numbers 95 to 99 are reserved by the standard for specific applications where no other number fits; each project defines their meaning.

Number	Name	Description	Logical node	Guide
1	Master Element	Device that initiates operation, such as a control switch or a voltage relay.
2	Time-Delay Starting or Closing Relay	Introduces a time delay before a starting or closing sequence.
3	Checking or Interlocking Relay	Permits an operation only when the required position or status conditions are met.
4	Master Contactor	Makes and breaks the necessary control circuits, governed by the master element and the permissives.
5	Stopping Device	Shuts the equipment down and holds it out of operation, for example an emergency stop pushbutton.
6	Starting Circuit Breaker	Connects a machine to its source of starting voltage.
7	Rate of Change Relay	Operates when the rate of change of a quantity exceeds a set value (2008 edition).
8	Control Power Disconnecting Device	Switch or fuse that connects and disconnects the control power supply.
9	Reversing Device	Reverses the field or the phase sequence of a machine, for example the direction of rotation of a motor.
10	Unit Sequence Switch	Changes the order in which units are placed in or taken out of service.
11	Multifunction Device	Device that performs three or more functions, such as a multifunction numerical relay (2008 edition).
12	Overspeed Device	Operates when the machine exceeds its set speed.
13	Synchronous-Speed Device	Operates at or near synchronous speed.
14	Underspeed Device	Operates when the speed falls below the set value.
15	Speed or Frequency Matching Device	Matches the speed or frequency of a machine to that of another machine or the grid.
16	Data Communications Device	Switch, router, modem or network device that is part of the protection and control system (2008 edition).
17	Shunting or Discharge Switch	Opens or closes a shunting circuit, for example to discharge a capacitor.
18	Accelerating or Decelerating Device	Closes, or causes the closing of, the circuits that accelerate or brake a machine.
19	Starting-to-Running Transition Contactor	Transfers the machine from the starting connection to the running connection.
20	Electrically Operated Valve	Solenoid- or motor-operated valve in water, air, oil or gas circuits.
21	Distance Relay	Measures the impedance seen from the relay location and operates when the fault is inside its zone.	PDIS
22	Equalizer Circuit Breaker	Controls the current-equalizing connections of machines in parallel.
23	Temperature Control Device	Maintains the temperature of an apparatus or enclosure, for example with a space heater.
24	Volts per Hertz Relay	Operates when the V/Hz ratio exceeds the set value; protects transformers and generators against overexcitation.	PVPH	See guide
25	Synchronizing or Synchronism-Check Device	Permits closing only when the voltage, angle and frequency on both sides are within limits.	RSYN
26	Apparatus Thermal Device	Operates on the temperature of the protected apparatus, for example the oil or winding of a transformer.		See guide
27	Undervoltage Relay	Operates when the voltage falls below the set value.	PTUV
28	Flame Detector	Monitors the presence of the pilot or main flame, for example in a gas turbine or a boiler.
29	Isolating Contactor or Switch	Disconnects one circuit from another for emergency operation, maintenance or testing.
30	Annunciator Relay	Gives a visual indication that a protective or alarm device has operated.
31	Separate Excitation Device	Connects a circuit, such as the field of a machine, to a separate excitation source during starting.
32	Directional Power Relay	Operates when power flows in the set direction; on generators it detects motoring (reverse power).	PDOP / PDUP
33	Position Switch	Opens or closes a contact when an apparatus or mechanism reaches a given position.
34	Master Sequence Device	Establishes or sets the operating sequence of the devices during starting, stopping or other switching operations.
35	Brush-Operating or Slip-Ring Short-Circuiting Device	Raises, lowers or shifts the brushes, or short-circuits the slip rings of a machine.
36	Polarity or Polarizing Voltage Device	Operates, or permits another device to operate, on a given polarity, or verifies the polarizing voltage.
37	Undercurrent or Underpower Relay	Operates when the current or power falls below the set value, for example on a pump running dry.	PTUC
38	Bearing Protective Device	Operates on excessive bearing temperature or another associated mechanical condition.
39	Mechanical Condition Monitor	Operates on an abnormal mechanical condition other than the bearings, such as excessive vibration.
40	Field (Over/Under Excitation) Relay	Operates on an abnormally low value or loss of field current; protects the generator against loss of excitation.	PDIS (usual implementation)	See guide
41	Field Circuit Breaker	Applies or removes the field excitation of a machine.
42	Running Circuit Breaker	Connects a machine to its source of running voltage.
43	Manual Transfer or Selector Device	Manual selector that changes control circuits or operating modes, for example local or remote.
44	Unit Sequence Starting Relay	Starts the next available unit of a group when the preceding unit fails or is unavailable.
45	Abnormal Atmospheric Condition Monitor	Operates on an abnormal ambient condition, such as dangerous fumes, explosive gases or fire.
46	Reverse-Phase or Phase-Balance Current Relay	Operates on unbalanced or reverse-sequence phase currents; protects machines against negative sequence.	PTOC
47	Phase-Sequence or Phase-Balance Voltage Relay	Operates when the voltage phase sequence is not the expected one or the voltages are unbalanced.		See guide
48	Incomplete Sequence Relay	Returns the equipment to its normal position if a starting or operating sequence is not completed in time.		See guide
49	Machine or Transformer Thermal Relay	Operates when the temperature (or its calculated thermal image) of a machine or transformer exceeds the limit.	PTTR
50	Instantaneous Overcurrent Relay	Operates with no intentional time delay when the current exceeds the set value.	PIOC	See guide
51	AC Inverse Time Overcurrent Relay	Operates with a definite or inverse time characteristic with respect to the current.	PTOC
52	AC Circuit Breaker	Power circuit breaker that closes and interrupts an AC circuit under normal and fault conditions.	XCBR
53	Exciter or DC Generator Relay	Forces the build-up of the field of a DC machine during starting.
54	Turning Gear Engaging Device	Engages or disengages the turning gear (slow-roll mechanism) of a turbine shaft (2008 edition).
55	Power Factor Relay	Operates when the power factor leaves the set range.
56	Field Application Relay	Automatically controls the application of field excitation to a synchronous motor.
57	Short-Circuiting or Grounding Device	Short-circuits or grounds a circuit, manually or automatically.
58	Rectification Failure Relay	Operates on the failure of one or more elements of a power rectifier.
59	Overvoltage Relay	Operates when the voltage exceeds the set value.	PTOV
60	Voltage or Current Balance Relay	Operates on a voltage or current difference between two circuits; used, for example, to detect a blown VT fuse.
61	Density Switch or Sensor	Operates on a gas density value, for example the SF6 of a circuit breaker (2008 edition).
62	Time-Delay Stopping or Opening Relay	Introduces a time delay in a stopping or opening sequence.
63	Pressure Switch	Operates at a given pressure or rate of change of pressure; includes the transformer sudden pressure relay.
64	Ground Detector Relay	Operates on failure of the insulation to ground of a machine, transformer or other apparatus.	PHIZ	See guide
65	Governor	Regulates the mechanical power of the prime mover, for example the opening of valves or wicket gates.
66	Notching or Jogging Device	Limits the number or frequency of successive starts of a machine.
67	AC Directional Overcurrent Relay	Operates on overcurrent flowing in a given direction.	PTOC + RDIR	See guide
68	Blocking or Out-of-Step Relay	Blocks a trip or a reclose under a given condition; the most common use is power swing blocking.	RPSB	See guide
69	Permissive Control Device	Permits or prevents a closing or operating action depending on its position.
70	Rheostat	Variable resistance in an electric circuit, manually or motor operated.
71	Liquid Level Switch	Operates at a given liquid level, for example the oil level in a transformer conservator.
72	DC Circuit Breaker	Closes and interrupts a DC power circuit under normal and fault conditions.
73	Load-Resistor Contactor	Connects or shorts a limiting, shunting or indicating resistor in a power circuit.
74	Alarm Relay	Operates a visual or audible alarm; with the TC suffix it is used for trip circuit supervision.
75	Position Changing Mechanism	Moves a main device from one position to another, for example the withdrawable truck of a switchgear cubicle.
76	DC Overcurrent Relay	Operates when the current in a DC circuit exceeds the set value.
77	Telemetering Device	Transmitter or receiver of remotely measured values.
78	Phase-Angle Measuring or Out-of-Step Protective Relay	Operates at a given phase angle between two quantities; used to trip on loss of synchronism.	PPAM	See guide
79	AC Reclosing Relay	Controls the automatic reclosing and lockout of an AC circuit breaker.	RREC
80	Flow Switch	Operates at a given flow of a liquid or gas, or at a given rate of change of flow.
81	Frequency Relay	Operates when the frequency, or its rate of change, leaves the set values.	PTUF / PTOF
82	DC Reclosing Relay	Controls the closing and automatic reclosing of a DC circuit breaker, generally in response to load.
83	Automatic Selective Control or Transfer Relay	Automatically selects between sources or conditions, or transfers the load between them.
84	Operating Mechanism	Complete electrical mechanism of a tap changer, regulator or similar apparatus.
85	Pilot Communications, Carrier or Pilot-Wire Relay	Teleprotection relay over power line carrier, pilot wire or another channel; receives or sends the signal to the remote end.	PSCH
86	Lockout Relay	Trips and holds the equipment out of service until it is reset manually or electrically.		See guide
87	Differential Protective Relay	Operates on the difference between the currents entering and leaving its protected zone.	PDIF
88	Auxiliary Motor or Motor Generator	Drives auxiliary equipment such as pumps, fans or compressors.
89	Line Switch	Disconnect or isolating switch in a power circuit.	XSWI
90	Regulating Device	Keeps a quantity, such as voltage, current or power, within limits; for example the tap changer control.
91	Voltage Directional Relay	Operates when the voltage across a breaker exceeds a value in a given direction.
92	Voltage and Power Directional Relay	Permits closing when the voltage difference is suitable and trips when power flows in the reverse direction.
93	Field-Changing Contactor	Changes the level of field excitation of a machine.
94	Tripping or Trip-Free Relay	Trips a circuit breaker, or prevents its immediate reclosing if it is closed onto a fault.	PTRC

Most common suffixes

N	Neutral (residual current or voltage)
G	Ground (direct measurement) or generator
BF	Breaker failure
T	Transformer
B	Bus, battery or blower
L	Line or logic
M	Motor or metering
P	Phase or pump
O / U	Over / under
X, Y, Z	Auxiliary relays
a / b	«a» contact: open with the device in its reference position (breaker open); «b» contact: closed in that position
POTT, PUTT, DCB, DCUB, DUTT	Teleprotection schemes (2008 edition acronyms)
SOTF	Switch onto fault

How to read the table

IEEE C37.2 assigns a number to each device function and lets you qualify it with letter suffixes: 87T is transformer differential, 50BF is breaker failure and 51N is neutral time overcurrent. The names follow the 2008 edition of the standard, still current in its 2022 revision; numbers 7, 11, 16, 54 and 61 changed meaning in 2008, so older drawings may use them differently.

A modern numerical relay combines many functions, so on drawings it is shown with the list of numbers it has enabled or with device number 11 (multifunction device). In IEC 61850 each function is a logical node: PDIS for distance, PDIF for differential, PTOC for time overcurrent, PIOC for instantaneous overcurrent, RREC for reclosing. We show the logical node only when the mapping is the one used by the main manufacturers; each manufacturer adds its own prefixes (for example LEXPDIS for loss of excitation in ABB), and “usual implementation” means that IEC 61850-7-4 has no specific node for that function.

Some combinations, such as 81R, 51V, 21N or 74TC, are industry practice built on the suffixes of the standard, not numbers it assigns. Sources: IEEE C37.2 (official abstract at standards.ieee.org) and manufacturer reproductions and technical references; the full text of the standard is sold by IEEE.

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