Reference designation according to IEC 81346
How to name each device in an electrical schematic so that anyone can tell, just by reading its name, what it is, which part of the installation it belongs to and where it is.
What a reference designation is
It is the unique name that identifies each device throughout the documentation of an installation: in the schematic, on the panel label, in the bill of materials and in the terminal plan. The IEC 81346 standard (EN IEC 81346 in Europe) sets how that name is built, so that it is the same in every document and every discipline: electrical, mechanical or process.
The series has two main parts. Part 1 gives the rules for structuring the installation and writing designations. Part 2 defines the letters that indicate each device's class. IEC 81346 replaced the former IEC 61346, and its letter table replaced those of earlier standards such as IEC 60750, which is where still very common names like K1 for a contactor come from.
The three aspects: =, + and -
The same device can be seen from three points of view, which the standard calls aspects. Each one is written with its own prefix sign:
| Sign | Aspect | Answers | Example |
|---|---|---|---|
| = | Function | What is it for? Which part of the installation does it belong to? | =A1 production line 1 |
| + | Location | Where is it physically? | +CP1 panel 1 |
| - | Product | Which device is it? | -Q1 switch 1 |
How they combine
The aspects are written one after another. A full designation reads like this:
Each aspect can have several levels by repeating the sign: -A1-K2 is relay K2, which is part of device A1.
You do not always need to write the full designation. In a schematic that already belongs to =A1 and +CP1, -Q1 is enough; the full designation is used in reports, labels and wiring between panels.
Class letters according to IEC 81346-2
The letter after the - sign indicates the device's class according to its inherent function, that is, what the device does by itself, regardless of what it is used for in your installation. These are the entry classes of IEC 81346-2:2019:
| Letter | Inherent function | Examples |
|---|---|---|
| B | Picking up information and providing a representation | Sensors, instrument transformers, limit switches |
| C | Storing for subsequent retrieval | Capacitors, batteries, tanks |
| E | Emitting light, heat or other radiation | Lighting lamps, heaters |
| F | Protecting against dangerous or undesirable conditions | Fuses, surge protective devices |
| G | Providing a controllable flow | Generators, pumps, fans |
| H | Treating matter | Filters, mixers |
| K | Treating input signals and providing an appropriate output | PLCs, auxiliary relays, controllers |
| M | Providing mechanical movement or force | Motors, cylinders, actuators |
| N | Enclosing another object partly or fully | Covers, housings, lids |
| P | Providing perceptible information | Indicator lights, displays, gauges, buzzers |
| Q | Controlling access or flow | Contactors, circuit breakers, motor protection switches, valves |
| R | Restricting or stabilising | Resistors, diodes, non-return valves |
| S | Detecting a human action and providing an appropriate response | Push buttons, selector switches, keypads |
| T | Transforming | Transformers, frequency converters, power supplies |
| U | Locating and holding other objects | Brackets, DIN rails, fixings |
| W | Leading from one place to another | Cables, conductors, busbars |
| X | Interfacing objects | Terminals, terminal strips, connectors, sockets |
The letters A, I and O are not used as classes, and D, J, L, V, Y and Z are reserved for the future. The standard adds two- and three-letter subclasses for more detail: for example BT for temperature sensors, BG for position detectors or CA for capacitors.
From classic notation to IEC 81346-2
Many panels are still drawn with the classic notation, and FaseCAD's example templates use it because it is the one most often found in real drawings. These are the same devices with the current letters:
| Device | Classic notation | IEC 81346-2 |
|---|---|---|
| Motor protection switch | Q1 | -Q1 |
| Contactor | KM1 | -Q2 |
| Three-phase motor | M1 | -M1 |
| Push button | S1 | -S1 |
| Indicator light | H1 | -P1 |
| Auxiliary relay | K1 | -K1 |
| Inductive sensor | B1 | -B1 |
| Terminal strip | X1 | -X1 |
The two most visible changes: contactors move from K to Q, because they control a flow of energy, and indicator lights move from H to P, because they provide information.
Designation in FaseCAD
In FaseCAD every symbol carries its designation and can be numbered automatically. The full structure by function, location and product according to IEC 81346, with navigators to find any device, terminal or cable, is planned.
See the example schematics FAQ
Common questions
Is IEC 81346 mandatory?
In general it is not required by law, but it is the international reference for designating devices, and many customers and engineering firms require it in their specifications.
What is the difference between = and +?
The = sign says which function or part of the installation the device belongs to; the + sign says where it physically is. One panel (+CP1) can house devices from several functions (=A1, =A2).
Do I have to use the two-letter subclasses?
No. The standard lets you use just the entry-class letter or refine it with two or three letters. What matters is that the whole project follows the same rule.
Links
- IEC 81346-1:2022 · Basic rules: structuring and reference designations (official IEC page)
- IEC 81346-2:2019 · Classification of objects and codes for classes (official IEC page)
- IEC 81346 on Wikipedia
- Electrical symbols according to IEC 60617 · FaseCAD guide
- Electropedia · IEC's International Electrotechnical Vocabulary