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Structuring Principles and Reference Designations for Industrial Systems (IEC 81346)
A Comprehensive Guide to IEC 81346-1:2009 and IEC 81346-2:2009
1. Understanding the Structuring Principles
IEC 81346 provides a systematic framework for structuring information about industrial systems, installations, equipment, and products throughout their lifecycle. The standard is organized into two key parts: Part 1 establishes the overarching structuring principles, while Part 2 defines the reference designation system. Together, they form a comprehensive methodology that enables engineers to decompose complex industrial installations into manageable, consistently labeled subsystems and components.
Adopting IEC 81346 from the earliest design phase dramatically reduces cross-disciplinary miscommunication. A unified structuring language means electrical, mechanical, and process engineers refer to the same equipment with the same codes, eliminating the translation errors that plague handover documents.
The cornerstone of IEC 81346 is the concept of “aspects”. The standard recognizes that a single physical object can be viewed from multiple perspectives — what it does (function), what it is (product), and where it is located (location). By separating these aspects, the standard allows engineers to create clean, unambiguous reference designations that remain stable even when the physical implementation changes.
| Aspect | Letter Code | Description | Example |
|---|---|---|---|
| Function | = | What the object does within the system | =F1 (Main Protection Function) |
| Product | – | The specific manufactured item or component | -K1 (Circuit Breaker, Model XYZ) |
| Location | + | Where the object is physically situated | +A101 (Panel A101) |
When designing a new system, start with the functional aspect first. Define what needs to happen before selecting specific products or determining locations. This approach preserves design flexibility during early engineering phases.
2. The Reference Designation System
The reference designation system defined in IEC 81346-2 provides a structured coding scheme for identifying objects across all aspects. The system uses prefix letters to indicate object classes, followed by numeric or alphanumeric identifiers. This creates a hierarchical naming structure that scales from individual components to entire installations.
Reference designations follow a tree-like structure: =F1-K1-A1 means “within the Main Protection Function (F1), the Circuit Breaker (K1), Terminal Block A1.” This prefix notation (= for function, - for product, + for location) immediately tells the reader which aspect is being referenced. The system supports both single-level and multi-level designations depending on the complexity of the installation.
A common pitfall is mixing aspects within a single designation chain. For example,
=F1-K1+A101 is invalid because it jumps from the product aspect to the location aspect without a clean transition. Always maintain aspect consistency within a single designation path unless the standard’s cross-aspect referencing rules are explicitly followed.Part 2 of IEC 81346 defines a comprehensive set of letter codes for different object classes: A for measuring equipment, K for relays and contactors, M for motors, Q for switching devices, and many more. These codes are internationally recognized and map directly to symbols used in circuit diagrams, P&IDs, and 3D plant models.
3. Practical Engineering Applications
IEC 81346 is not merely a theoretical taxonomy; it has profound practical implications across multiple engineering disciplines. In large-scale projects such as chemical plants, power stations, or manufacturing lines, the reference designation system becomes the backbone of all documentation — from schematic diagrams and wiring lists to maintenance manuals and spare parts catalogs.
Engineering teams that implement IEC 81346 consistently report 30–50% reduction in time spent cross-referencing documents during commissioning. The structured naming eliminates ambiguity when multiple contractors are working on different subsystems of the same installation.
Modern engineering tools such as EPLAN, AutoCAD Electrical, and Aveva PDMS support IEC 81346 natively. When configured correctly, these tools automatically propagate reference designations across schematics, 3D models, and terminal plans, ensuring consistency without manual effort. The key is to establish the structuring hierarchy early and enforce it through project standards and template libraries.
| Engineering Domain | Typical Application | Benefits |
|---|---|---|
| Electrical Engineering | Cable schedules, terminal diagrams | Traceable end-to-end wiring |
| Mechanical Engineering | P&ID, equipment layouts | Consistent equipment tagging |
| Process Engineering | Functional descriptions | Clear cause-effect matrices |
| Maintenance | Spare parts management | Faster fault localization |
Never retrofit a reference designation system to a project that is already in detailed engineering. The effort to re-tag existing documentation is enormous and error-prone. IEC 81346 must be adopted at the concept design phase — ideally during the front-end engineering design (FEED) stage — to deliver maximum value.
For engineers designing industrial control systems, the functional aspect (= prefix) is particularly valuable because it maps directly to control logic and safety instrumented functions. A safety function like “Emergency Shutdown of Reactor R-101” receives a functional designation such as =F101, which remains constant even if the specific safety relay or PLC module is later replaced with a different product.
Frequently Asked Questions
Q: What is the difference between IEC 81346 and the older IEC 1346?
A: IEC 81346 superseded the earlier standards IEC 1346-1 and IEC 1346-2, consolidating and harmonizing reference designation practices across multiple industries. Key improvements include clearer guidance on the aspect concept and expanded letter code tables.
A: IEC 81346 superseded the earlier standards IEC 1346-1 and IEC 1346-2, consolidating and harmonizing reference designation practices across multiple industries. Key improvements include clearer guidance on the aspect concept and expanded letter code tables.
Q: Can IEC 81346 be used for existing (brownfield) projects?
A: Yes, but with careful planning. A migration strategy must be defined, typically starting with the functional aspect to create a mapping layer between old and new designations. Full adoption is most practical during major revamps or control system upgrades.
A: Yes, but with careful planning. A migration strategy must be defined, typically starting with the functional aspect to create a mapping layer between old and new designations. Full adoption is most practical during major revamps or control system upgrades.
Q: How does IEC 81346 relate to IFC (Industry Foundation Classes) in BIM?
A: IEC 81346 provides structuring principles that complement IFC classification. While IFC focuses on building information modeling taxonomies, IEC 81346 offers a reference designation system optimized for industrial installations. The two can be used together for integrated plant lifecycle management.
A: IEC 81346 provides structuring principles that complement IFC classification. While IFC focuses on building information modeling taxonomies, IEC 81346 offers a reference designation system optimized for industrial installations. The two can be used together for integrated plant lifecycle management.
