IEC 81346.
IEC 81346 is an international standard for structuring technical systems and assigning reference designations to their parts. Co-published as ISO/IEC 81346, it identifies an object by three independent aspects. What it does, function, prefix, where it sits, location, prefix plus, and what it is, product, prefix -. A designation such as =H10+UCB01-CF001 names one object seen through those three lenses.
What IEC 81346 means.
The standard grew out of IEC 61346 and the older German DIN 40719, and it now underpins sector systems like RDS-PP for power plants and RDS-CO for buildings. It is the European counterpart to the North American habit of area-loop instrument tags.
How an IEC 81346 designation is read
Read =H10+UCB01-CF001 one prefix sign at a time. H10 is the function aspect. The object's role in the process, independent of where it is or what hardware delivers it. Plus UCB01 is the location aspect. The cubicle, room, or area it lives in. -CF001 is the product aspect. The physical component itself. The signs concatenate in any order the project fixes, and a repeated sign builds hierarchy, so H10.H1 is a sub-function of H10. One real object can carry all three aspect blocks or just the one a given document cares about.
Why the three aspects are kept separate
Function, location, and product change on different clocks. A metering pump keeps its function designation when it is moved to another skid, and keeps its location designation when the failed unit is swapped for a different model. A flat tag that fuses all three forces a rename every time any one of them shifts. Splitting them is what lets the same drawing set survive revamps without the tag register drifting out of agreement with the plant.
IEC 81346 vs ISO 81346 vs the part numbers
There is one document carrying two logos. ISO and IEC publish it jointly, so ISO 81346 and IEC 81346 refer to the same text. The parts split the work. 81346-1 gives the structuring principles and the prefix signs. 81346-2 classifies objects and assigns the single-letter object codes. 81346-10 covers power plants and 81346-12 covers construction and building services. Sector schemes sit on top. RDS-PP, the VGB successor to KKS and RDS-CO are both 81346 applications, not separate standards.
Where you meet IEC 81346 on a drawing
European EPC P&IDs, single-line diagrams, and cable schedules use it heavily, as do power generation and large building-services projects. A tag like =H10+UCB01-CF001 on a P&ID is doing the same job an ISA 5.1 tag like FT-3201 does, but it encodes hierarchy and location that the loop tag leaves implicit. Drawings that bridge a North American operator and a European contractor often carry both conventions on the same sheet.
Object class letters in 81346-2
The product aspect leads with a class letter from 81346-2 that says what kind of object it is by purpose, not by trade name. C is for storing energy or information, F for protection, K for processing signals, P for presenting information, Q for switching a power circuit, and so on. The letter plus a serial number, CF001 gives a component a stable identity that survives a vendor change, which is the same reason an instrument index keys on tag rather than model number.
What is a kenletter in NEN-EN-IEC 81346?
In the Dutch adoption of the standard, NEN-EN-IEC 81346, the kenletter is the single object-class letter that opens the product aspect (the block after the minus sign). It classifies an object by what it does, not by its trade name: K is a signal-processing object such as a relay or controller, M is a motor, Q is a switching device such as a circuit breaker, and W is a cable or conductor. Because the kenletter set comes from IEC 81346-2, the same letter means the same class in every national adoption, NEN-EN-IEC 81346 in the Netherlands and DIN EN IEC 81346 in Germany, and RDS-PP for power plants builds its component codes on those same letters.
IEC 81346 aspect prefixes
The three core aspect signs from 81346-1. Each answers a different question about the same object. A full reference designation chains the blocks the project needs.
| Sign | Aspect | Question it answers | Example block |
|---|---|---|---|
| Function | What does the object do in the process. | H10 | |
| plus | Location | Where is the object installed. | plus UCB01 |
| - | Product | What component is it, class plus serial. | -CF001 |
| # | Signal, other | Project-defined aspects beyond the core three | #W1 |
IEC 81346-2 object-class letters (the kenletter)
The object-class letter that opens the product aspect, defined in IEC 81346-2. Common classes shown; the letter names what the object does, not its trade name, and is shared across NEN-EN-IEC 81346 and RDS-PP.
| Kenletter | Object class (what it does) | Typical objects |
|---|---|---|
| B | Converting an input variable into a signal for processing | Sensors, measuring transducers |
| C | Storing energy, information, or material | Batteries, capacitors, tanks |
| E | Providing radiant or thermal energy | Heaters, lamps |
| F | Direct protection against a hazardous condition | Fuses, safety and relief devices |
| G | Initiating a flow of energy or a reference signal | Generators, power supplies |
| K | Processing signals or information | Relays, controllers, PLCs |
| M | Providing mechanical energy for driving | Motors |
| P | Presenting information | Indicators, displays, meters |
| Q | Controlled switching of a flow of energy or signals | Circuit breakers, contactors |
| R | Restricting or stabilizing a flow | Resistors, restrictors |
| S | Converting a manual operation into a signal | Switches, pushbuttons |
| T | Transforming energy while keeping its kind | Transformers |
| U | Holding objects in position | Supports, mountings, enclosures |
| W | Guiding or transporting from place to place | Cables, conductors, busbars |
| X | Connecting objects | Terminals, plugs, sockets |
Common questions
Is ISO 81346 the same as IEC 81346.
What is the difference between IEC 81346-1 and 81346-2.
Is IEC 81346 the same as KKS.
How does IEC 81346 differ from ISA 5.1.
What replaced IEC 61346.
What does the kenletter K mean in IEC 81346.
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