ANSI vs. IEC Comparison Table
Introduction
If you have ever looked at a substation single-line diagram (SLD) or a relay control panel, you know that electrical protection is a language of its own. But depending on where the equipment was manufactured or who designed the system, you might find yourself reading two completely different dialects: ANSI/IEEE or IEC.
In North America, the ANSI (American National Standards Institute) system uses standard device numbers (like 50, 51, or 87) to identify relay functions. However, the international community relies on the IEC 60617 standard, which uses graphical symbols and mathematical functions (like I>, I>>, or ΔI>) to describe the exact same operation.
Whether you are an active field engineer commissioning a new switchgear, or a fresh graduate preparing for your upcoming engineering job recruitment exams, jumping between these two standards can be incredibly confusing.
To make your life easier, we have put together this ultimate conversion cheat sheet. Bookmark this page so you have a quick reference the next time you are analyzing a schematic!
1. IEC 60617 Standard Series Symbols
Before comparing the two standards, it helps to understand the basic mathematical parameters used in the IEC system to define relay operations.
| Symbol | Description | Symbol | Description |
|---|---|---|---|
| I | Current | Z | Impedance |
| I (Reverse) | Reverse current | f | Frequency |
| Id | Differential current | n | Rotational speed |
| Id/I | Percentage differential current (restraint) | F | Magnetic flux |
| Inf | Current of nth harmonic | j | Phase angle |
| I1, (Ip) | Positive sequence current component | SYNC | Synchronizing (check) |
| I2, (In) | Negative sequence current component | BLOCK | Element is blocked from operating |
| I0, (Ih) | Zero sequence current component | LO | Lock-out |
| Irsd | Residual current | TCS | Trip circuit supervision |
| I⏚ | Earth fault current | START | Protection element is engaging (ANSI Alarm) |
| Iframe | Current to frame | TRIP | Protection element settings have been met |
| IN | Current in the neutral conductor | X/Y | Translation of signal |
| IN-N | Current between neutrals of two polyphase systems | A/D or /# | Analog to digital conversion |
| Iub | Current unbalance | > | Operation above a set value (e.g., overcurrent) |
| U | Voltage | < | Operation below a set value (e.g., undervoltage) |
| Q | Reactive power | >> | Operation well above a high set stage |
| R | Resistance | << | Operation well below a low set stage |
| X | Reactance | >>> | Operation above a very high set stage |
2. ANSI / IEEE vs. IEC Equivalent Cheat Sheet
Here is a direct comparison of the most common North American ANSI device numbers and their European IEC symbol equivalents.
| ANSI Code | IEC 60617 Symbol | Description |
|---|---|---|
| 12 | ω > | Over speed relay |
| 14 | ω < | Under speed relay |
| 21FL | FLOC | Fault locator |
| 21G | Z < | Under impedance |
| 24 | U/f > | Over excitation |
| 25 | SYNC | Synchronization check |
| 27 | U < | Undervoltage |
| 32 | P < / P > | Directional under power / over power relay |
| 32P | P | Active power |
| 32Q | Q | Reactive power |
| 37 | I < | Non-directional undercurrent |
| 40 | X < | Under excitation |
| 46 | I2 > | Negative-phase sequence (UNBALANCE) |
| 47 | I2 >> / U2 > | Phase Sequence Protection / Voltage protection |
| 48 | Ist | Start-up supervision for motors (STALL) |
| 49F | T > or Ist > | Thermal protection for cables |
| 49M / 49G / 49T | T > | Three-phase thermal protection for machines (M: Motor, G: Generator, T: Transformer) |
| 50 | I >, I >>, I >>> | Instantaneous non-directional overcurrent |
| 50ARC | Arc fault protection | |
| 50BF | Circuit Breaker Failure Protection | |
| 50N/51N/51G | I0 >, I0 >> | Non-directional definite time earth-fault / Inverse time overcurrent |
| 51 | I >, I >>, I >>> | Non-directional inverse time overcurrent |
| 51C | I >, I >>, I >>> | Shunt capacitors overcurrent |
| 51LR | Ilr > | Non-directional locked rotor overcurrent |
| 51V | I(U) > | Voltage restrained/controlled overcurrent |
| 59 | U >, U >>, U >>> | Overvoltage |
| 59N | U0 >, U0 >> | Neutral point (residual) overvoltage |
| 66 | N > | Excessive Start Protection |
| 67 | Iφ > | Directional overcurrent |
| 67N | I0φ > | Directional earth-fault overcurrent |
| 68 | I2 > | Transformer/motor inrush current |
| 68F2 | If2 > | Magnetizing in-rush, 2nd harmonic |
| 68F5 | If5 > | Transformer over excitation, 5th harmonic |
| 79 | AR | Auto-reclose |
| 81 | f | Frequency relay |
| 81L/81U | f < | Under frequency |
| 81O | f > | Over frequency |
| 86 | Protection Lockout | |
| 87 | ΔI > | Differential protection (87G: Generator, 87M: Motor, 87T: Transformer, 87N: Restricted earth fault) |
Conclusion
Mastering both the ANSI numerical codes and the IEC symbols is a massive advantage in the electrical engineering field. It allows you to confidently read schematics from around the world, making troubleshooting faster and more reliable.
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