Relay Symbol Reference Chart: IEC vs IEEE Schematic Standards

Identifying the correct symbol for relay components is the first step in reading or drafting control schematics. Below is the complete reference mapping IEC 60617 and IEEE/ANSI C37.2 standards, followed by physical pinout translations and faded-marking troubleshooting.

Standard Relay Symbols: IEC vs IEEE/ANSI Reference

Global schematics generally follow one of two visual languages. The IEC 60617 standard (dominant in Europe, Asia, and modern global OEM equipment) uses rectangular boxes for coils and separates the coil from its contacts across the schematic. The IEEE/ANSI C37.2 standard (common in North American power distribution and older US industrial panels) uses circles for coils and often groups contacts directly adjacent to the coil symbol.

What these mean in practice: The directional arrows on time-delay relays are the most critical visual cue. An arrow pointing into the rectangle (IEC) indicates an on-delay: the physical contacts change state only after the timer expires while the coil is energized. An arrow pointing out of the rectangle indicates an off-delay: the contacts change state only after the timer expires once the coil is de-energized. Mixing these up during panel troubleshooting will lead to chasing phantom logic faults.

Contact Configurations and Pinout Mapping

While the coil symbol tells you what triggers the relay, the contact symbols dictate the logic flow. North American electricians typically use NEMA "Form" letters, while IEC schematics use terminal numbering (11/12/14) to define the contact state.

Rows People Get Wrong: The IEC vs. Physical Pin Trap

The most common mistake when wiring a replacement relay—like swapping a failed Omron MY2N 8-pin DPDT relay—is confusing IEC schematic terminal numbers with the physical pin numbers stamped on the relay socket.

• The Trap: A schematic calls for IEC terminals 13 and 14 (Form A / Normally Open). The technician looks at the physical 8-pin relay base and wires the load to physical pins 13 and 14. But an 8-pin base only has pins 1 through 8.
• The Fix: IEC numbers (13/14) are logical identifiers for the schematic, not physical pin locations. On a standard 8-pin octal base, the physical pins for the first NO contact are 5 and 3. The physical pins for the coil are 2 and 7. Always map the IEC logical number to the physical pinout printed on the side of the relay casing before terminating wires.
• Form C vs. Form X: Form C is a standard break-before-make SPDT contact. If a schematic specifies a "make-before-break" transition (where the NO contact closes before the NC contact opens to prevent an open circuit during switching), this is technically a Form X or specialized overlapping contact. Standard Form C relays will cause a momentary dropout; do not substitute them in continuous-power holding circuits.

Regional Variants and Faded Marking Protocols

Schematic standards are not universal, and field conditions rarely match textbook examples. Understanding which standard applies to your region—and how to verify a relay when the silkscreen has burned off—is critical for safe troubleshooting.

Which Standard Applies to Your Region?

• IEC 60617 (Europe, Asia, Global OEMs): Uses rectangular coils, logical terminal numbering (11/12/14), and separates the coil from the contacts on the drawing. If you are working on modern CNC machines, European-packaged HVAC systems, or IEC-standard motor control centers (MCCs), expect this format.
• IEEE/ANSI C37.2 & NEMA (North America): Uses circular coils, device function numbers (e.g., '21' for distance relay, '86' for lockout relay), and NEMA Form letters (A, B, C). Dominant in US utility substations, older North American manufacturing plants, and standard relay switching circuits built before the 2000s.
• Old UK (BS 3939): Largely superseded by IEC, but still found in legacy British infrastructure. It used a hybrid approach with circular coils but different contact cross-referencing. If you encounter a schematic with circular coils but non-NEMA pinouts in a UK facility, assume BS 3939 and trace every contact manually.

Safe Interpretation When Markings are Faded or Missing

Industrial relays in high-heat or high-vibration environments (like extruders or stamping presses) often lose their printed pinout diagrams and part numbers. Do not guess the pinout based on the physical shape of the pins. Use this bench-verification protocol:

1. Identify the Coil: Set your multimeter to resistance (Ohms). Probe pairs of pins until you find a reading between 50Ω and 15,000Ω. A 24VDC coil (like a Schneider RXM2AB1BD) will typically read around 650Ω. A 120VAC coil will read between 2,000Ω and 4,000Ω. If you read 0.0Ω (short) or OL (open), the coil is burned out; discard the relay.
2. Map the Commons (COM): Switch the meter to continuity/diode mode. With the relay unpowered, find the pins that show continuity to the Normally Closed (NC) contacts. The shared pin in a multi-pole relay is the Common. On an 11-pin base, pins 1, 4, and 7 are almost always the Commons.
3. Verify the Throw: Apply the rated DC voltage directly to the identified coil pins using a bench power supply (never use mains AC for bench testing unless the relay is strictly rated for it and you have isolated test leads). Listen for the mechanical click. Re-probe the contacts. The pins that transition from open to closed are your NO (Form A / 13-14) contacts. The pins that transition from closed to open are your NC (Form B / 11-12) contacts.
4. Label Immediately: Use a silver paint pen or industrial label maker to rewrite the pinout on the relay casing before installing it back into the socket.

By cross-referencing the logical IEC/IEEE symbols on the schematic with the physical electrical characteristics of the component, you eliminate the guesswork that leads to short circuits and blown control fuses.