[ SINGLE LINE DIAGRAM SYMBOLS · REFERENCE ]
ANSI device numbers
ANSI device numbers name the functions of protective relays and switchgear on single line diagrams, relay settings and schematics: 52 is a circuit breaker, 51 an overcurrent relay, 87 a differential relay. They are defined in IEEE C37.2. The list below gives the common numbers with the IEC 60617 qualifier and the IEC 61850 logical node used for the same function.
- Standard
- IEEE C37.2-2022, IEEE Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations
- Content
- 95 device function numbers and 22 acronyms, with prefixes, suffixes and contact designations
- Newer acronyms
- Cover functions such as arc flash detection, phasor measurement units, digital fault recorders and remedial action schemes
ANSI device number list
| No. | Function | IEC 60617 | IEC 61850 |
|---|---|---|---|
| 1 | Master element | ||
| 2 | Time-delay starting or closing relay | ||
| 3 | Checking or interlocking relay | ||
| 12 | Overspeed device | ||
| 14 | Underspeed device | ||
| 21 | Distance relay | Z< | PDIS |
| 24 | Volts per hertz relay | U/f> | |
| 25 | Synchronizing or synchronism-check device | RSYN | |
| 26 | Apparatus thermal device | ||
| 27 | Undervoltage relay | U< | PTUV |
| 30 | Annunciator relay | ||
| 32 | Directional power relay (reverse power) | PDOP, PDUP | |
| 37 | Undercurrent or underpower relay | I< | PTUC |
| 38 | Bearing protective device | ||
| 40 | Field (loss of excitation) relay | ||
| 46 | Reverse-phase or phase-balance current relay (negative sequence) | I2> | |
| 47 | Phase-sequence or phase-balance voltage relay | U2> | |
| 48 | Incomplete sequence relay | ||
| 49 | Machine or transformer thermal relay | θ> | PTTR |
| 50 | Instantaneous overcurrent relay | I>> | PIOC |
| 51 | AC inverse time overcurrent relay | I> | PTOC |
| 52 | AC circuit breaker | XCBR | |
| 55 | Power factor relay | ||
| 57 | Short-circuiting or grounding device | ||
| 59 | Overvoltage relay | U> | PTOV |
| 60 | Voltage or current balance relay | ||
| 62 | Time-delay stopping or opening relay | ||
| 63 | Pressure switch (sudden pressure relay on transformers) | ||
| 64 | Ground detector relay | ||
| 66 | Notching or jogging device (starts per hour) | ||
| 67 | AC directional overcurrent relay | I> with direction arrow | |
| 68 | Blocking or out-of-step relay | ||
| 69 | Permissive control device | ||
| 71 | Liquid level switch | ||
| 72 | DC circuit breaker | ||
| 74 | Alarm relay | ||
| 76 | DC overcurrent relay | ||
| 78 | Phase-angle measuring or out-of-step protective relay | ||
| 79 | Reclosing relay | RREC | |
| 81 | Frequency relay | f<, f> | PTUF, PTOF |
| 83 | Automatic selective control or transfer relay | ||
| 85 | Pilot communications, carrier or pilot-wire relay | ||
| 86 | Lockout relay | ||
| 87 | Differential protective relay | Id> | PDIF |
| 89 | Line switch (disconnect) | XSWI | |
| 90 | Regulating device | ||
| 94 | Tripping or trip-free relay |
The IEC columns give the qualifier and logical node most often used for the same function. Not every ANSI number has a direct IEC equivalent.
Suffixes
Letters after the number narrow the function down. They show what is measured or protected:
| Suffix | Meaning |
|---|---|
| N | Neutral, for example 51N, residual overcurrent |
| G | Ground, measured with a ground CT, as in 51G, or generator, as in 87G |
| T | Transformer, as in 87T |
| B | Bus, as in 87B |
| L | Line, as in 87L |
| M | Motor, as in 87M |
| V | Voltage controlled or restrained, as in 51V |
| BF | Breaker failure, as in 50BF |
Combinations you will see on one-lines
- 50/51: instantaneous and time overcurrent in one relay, the most common feeder protection.
- 50N/51N or 50G/51G: earth fault overcurrent, residual or from a ground CT.
- 87T, 87G, 87B, 87M: differential protection of a transformer, generator, busbar or motor.
- 27/59: under and overvoltage, often with 81O/81U for over and under frequency.
- 86: the lockout relay that trips the breakers and must be reset by hand.
- 52a and 52b: the auxiliary contacts of a breaker. 52a is closed when the breaker is closed, 52b is the opposite.
Frequently asked questions
What are ANSI device numbers?
Numbers defined in IEEE C37.2 that identify the function of a device in electrical power systems, such as 52 for an AC circuit breaker or 87 for a differential relay. They are used on single line diagrams, schematics and relay settings.
What is 50/51 protection?
50 is instantaneous overcurrent and 51 is AC inverse time overcurrent. A 50/51 relay provides both, and is the standard protection on feeders.
What is device 86?
A lockout relay. It trips the breakers and holds them open until it is reset by hand, so equipment is not re-energised onto a fault.
What is device 87?
A differential protective relay. It compares the current going into and out of a zone, such as a transformer (87T) or busbar (87B), and trips if they differ.
What is the IEC equivalent of ANSI 51?
An overcurrent relay marked I> (IEC 60617), PTOC in IEC 61850.
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The symbols on this page were drawn by Deskely and are free to use. Standards are revised and every project issues its own legend sheets, which take precedence.