AI Summary
Key Takeaways
- IEC 60617 and IEC 81346 remain the global reference for PLC schematic symbols and reference designations in 2026.
- IEC 81346 has been harmonized into IEC 62491 since 2024, but the RD reference codes (-S, -K, -Q, -M) remain unchanged.
- ANSI/NEMA symbols differ from IEC mainly on contactor coils and discrete relays; a 2024 annex closes the historical gap.
- EPLAN, AutoCAD Electrical, and Studio 5000 libraries now ship ready-made IEC 60617/2024 symbol packs; outdated blocks are a top field-error source.
- Send your BOM to Moritta@KOEED.COM for a 24h cross-reference.
A 2026-ready PLC schematic uses IEC 60617 graphic symbols plus IEC 62491 reference designations, validated against vendor libraries before any wiring change.
By KOEED Editorial · 2026-06-30 · 8 min read · Engineering Notes
If you wire panels, read P&IDs, or troubleshoot legacy PLC cabinets, two ISO/IEC standards still decide what shows up on your screen: IEC 60617 for the picture, and IEC 81346 (now harmonized into IEC 62491) for the label. This Engineering Notes refresh walks through the 2026 picture, what changed since 2024, and where KOEED's multi-brand PLC catalog fits in.
TL;DR
- IEC 60617 = graphic symbol library; IEC 81346 = reference designation rules.
- Reference prefixes (-S sensor, -K relay, -Q breaker, -M motor) are unchanged in 2026.
- ANSI/NEMA still use square outlines for relays where IEC uses a slashed coil rectangle.
- Send legacy BOMs to Moritta@KOEED.COM for a 24-hour quote.
Why schematic symbols still matter in 2026
Even with tag-based programming in Studio 5000, TIA Portal, and GX Works, the schematic on the cabinet door is still line-drawing geometry: a slashed circle for a sensor contact, a coil for a relay, an arrow for a 4-20 mA loop. Maintenance technicians, panel builders, and CE/UL inspectors all read those shapes by eye. A wrong symbol or a hand-drawn shortcut is one of the fastest ways to trigger rework during a 2026 functional safety audit (ISO 13849-1:2023).
IEC 60617 at a glance
IEC 60617 is the international graphical symbol database for electrical diagrams. The 2024 consolidations, continued in 2026, reorganized the database into function-based sections: power supply, switching, protection, measurement, and so on. For PLC technicians, the most-used subset still includes:
| Symbol |
Function |
Letter class |
IEC 60617 ref. |
| Slashed circle |
Mechanical switch contact (NO/NC) |
-S |
S00265 |
| Coil rectangle |
Relay / contactor coil |
-K |
S00369 |
| Triangle pointing down |
Solid-state output |
-Q |
S00644 |
| Circle with arrow inside |
Lamp / indicator |
-H / -P |
S00965 |
! Warning
Legacy panel drawings often use pre-1996 ANSI/IEEE symbols (a plain circle for contacts instead of a slashed one). When you match a drawing to a 2026 IEC 60617 library, cross-check the issuing year of the drawing before swapping symbols.
IEC 81346 and the move to IEC 62491
IEC 81346 was long the "letter codes" reference designation system: a single uppercase letter signaling the function class of an object, plus a sequential numeric identifier. Since 2024, the IEC consolidations moved the RD rules into IEC 62491, while keeping the letter scheme identical. The classes a PLC technician sees most often:
| Letter |
Class |
Typical PLC example |
| -S |
Sensor / switch |
-S1 = conveyor level prox |
| -K |
Relay / contactor |
-K2 = line contactor |
| -Q |
Breaker / disconnector |
-Q1 = main breaker |
| -M |
Motor / actuator |
-M3 = servo pump |
| -A |
Assembly / module |
-A1 = 1756 chassis |
| -U |
Splitter / converter |
-U2 = remote I/O drop |
What changed since 2024
Three shifts are visible across 2025 and 2026 tooling:
-
Library consolidation. EPLAN 2026, AutoCAD Electrical 2025.1, and SEE Electrical Expert 2025 ship merged IEC 60617 + IEC 62491 databases. Drawing files published before 2024 still reference the old split.
-
Edition of IEC 60617. Sections S00001 to S00999 are now stable; sections above S01200 (renewable / battery storage) were added in the 2024 update and continue to expand in 2026 maintenance releases.
-
ANSI/NEMA bridge annex. NEMA ICS 19-2024 now includes a one-page annex mapping legacy US relay and coil symbols to IEC 60617 entries, closing a long-standing gap for cabinets shipped to both EU and US lines.
> Tip
Before re-issuing an old drawing to a 2026 contract, open it in Studio 5000 or TIA Portal and run a "library upgrade". The tool will surface retired symbols and propose the modern equivalent, but always review, never auto-accept.
Cross-vendor cross-reference
Symbol standards do not pick a vendor, but the modules you mount behind them do. KOEED maintains active stock across nine brands, with three coverage anchors relevant to a schematic walk-through:
When a reference designation on an old drawing (e.g. -A1 / slot 3) cannot be matched to a current vendor part, ask KOEED's AI Diagnostic to scan a panel photo, or send the original BOM to Moritta@KOEED.COM for a 24-hour cross-reference.
Reading a circuit diagram in the field
When you walk up to a 1990s cabinet, three pre-checks collapse the troubleshooting time from hours to minutes:
-
Identify the standard on the drawing's title block. Look for "Per IEC 60617" or "Per ANSI Y32.2".
-
Check the reference designation prefix. -S / -K / -Q / -M locates the device class in seconds.
-
Validate signal conventions. 4-20 mA loops and 0-10 V analog signals can be sanity-checked with the PLC Analog Calculator; Modbus RTU frames with the Modbus CRC Calculator; and Hex/Float conversions with the PLC Hex to Float Converter.
Sourcing modules for a 2026 retrofit?
Send your BOM, old or new, to Moritta@KOEED.COM. Active stock, EOL stock, and cross-references in one quote within 24 hours.
Send My BOM
Related on the KOEED Blog
Frequently asked questions
Is IEC 60617 still maintained in 2026?
Yes. The IEC SC 3C working group releases maintenance updates to the IEC 60617 database. The 2024 consolidation reorganized entries by function, and 2026 maintenance releases continue to expand sections above S01200.
What replaced IEC 81346?
IEC 81346 has been harmonized into IEC 62491 since 2024. The reference designation letter codes (-S, -K, -Q, -M, -A, -U) stay identical, so legacy drawings still parse correctly under the 2026 rules.
How do IEC symbols differ from ANSI/NEMA symbols?
The two systems agree on most passive components. The main differences are contactor coils and discrete relays, where ANSI uses a square outline and IEC uses a slashed coil rectangle. NEMA ICS 19-2024 ships a one-page bridge annex.
Where can I look up an unknown schematic symbol?
Start with the IEC 60617 online database at iec.ch, then cross-check against a PanelView, EPLAN, or AutoCAD Electrical library. For a matching part, send the photo and BOM to Moritta@KOEED.COM.
Does KOEED stock modules for legacy drawings?
Yes. Allen-Bradley 1746 / 1747 / 1756 / 1769, Siemens 6ES7 S7-300 / S7-400, Mitsubishi MELSEC-A / Q, Omron SYSMAC, Schneider Modicon, Yaskawa Servo, and Fanuc CNC modules are listed at koeed.com/collections.
KOEED Editorial
Industrial automation editor at KOEED. Writes about PLC sourcing, cross-reference, and legacy system support. Reach the team at Moritta@KOEED.COM.
