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 +), and what it is (product, prefix -). A designation such as =H10+UCB01-CF001 names one object seen through those three lenses.
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. +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.
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 |
| + | Location | Where is the object installed? | +UCB01 |
| - | Product | What component is it (class + serial)? | -CF001 |
| # | Signal / other | Project-defined aspects beyond the core three | #W1 |
Frequently asked.
Is ISO 81346 the same as IEC 81346?
Yes. It is one jointly published standard, so ISO 81346 and IEC 81346 are the same document. People searching either name are after the same structuring and reference-designation rules.
What is the difference between IEC 81346-1 and 81346-2?
81346-1 sets the structuring principles and the aspect prefix signs (=, +, -). 81346-2 classifies objects and assigns the single-letter object codes used in the product aspect. One gives the grammar, the other gives the vocabulary.
Is IEC 81346 the same as KKS?
No. KKS is a power-plant-specific coding system. RDS-PP, the VGB system that succeeds KKS, is built on IEC 81346 principles, so the two are related but not interchangeable. KKS codes do not use the 81346 aspect prefix signs.
How does IEC 81346 differ from ISA 5.1?
ISA 5.1 tags an instrument by its measured variable and loop (FT-101). IEC 81346 tags any object by three independent aspects (function, location, product) and encodes hierarchy. ISA 5.1 is dominant in North America; IEC 81346 is common in European and power projects.
What replaced IEC 61346?
IEC 81346 superseded IEC 61346 in 2009, carrying forward the aspect-based reference designation model while aligning the ISO and IEC editions into a single standard.