ISO/IEC 81346 structures plant documentation around 4 identifying aspects: function, location, component, and terminal, producing one or more reference designations for each object [S2][S7].
The standard series covers basic rules, classification of objects and codes for classes, power supply systems, construction works, and manufacturing and processing systems [S4].
What IEC 81346 governs in plant documentation
ISO/IEC 81346 establishes structuring principles and reference designations for industrial systems, installations, equipment, and industrial products. Its purpose extends beyond drawing labels: every identified object must connect unambiguously to its technical documentation and physical counterpart [S2][S4].
The series uses the “=” function, “+” location, “−” component, and “:” terminal notation. A full reference designation can combine these aspects, while an abbreviated form may be used when the available information supports it [S7]. The core requirement is not visual tidiness but traceable identity across drawings, schedules, databases, procurement records, commissioning systems, and operations records [S2].
Part 1 provides the basic rules, while Part 2 handles classification of objects and class codes. The resulting class code is intended to remain stable over an object's lifecycle and can appear in the reference designation or elsewhere in supporting information [S2][S4].
Select a standard with the correct disciplinary scope
Specification work should identify the applicable part before a tag structure is approved, because the series contains discipline-specific supplements rather than one universal plant template. Part 10 addresses power supply systems, Part 12 addresses construction works, Part 14 addresses manufacturing and processing systems, and Part 50 addresses processes [S3][S4].
For a process plant, Part 10 can be relevant where power supply objects are documented, but it does not replace the basic structuring rules in Part 1 or the object classification framework in Part 2. ISO 81346-10:2022 is a 15-page first-edition international standard specifically titled for power supply systems [S3].
Part 14 covers manufacturing and processing systems [S4]. Part 12 covers construction works [S4].
Compare identification by aspect and by discipline
A functional tag answers what an object does, a location tag answers where it is installed, a component tag identifies the physical item within an assembly, and a terminal tag identifies a connection point. Comparing the four approaches against information depth, lifecycle stability, and documentation scope shows why a complete reference designation is more useful than a single-purpose label. [S2]
The functional approach using “=” is compact and functional, but two similar pumps can carry the same function code. Adding location through “+” distinguishes installations or areas, while the component aspect “−” narrows the result to a particular item. The terminal aspect “:” extends the identifier to a connection point [S7].
For disciplines, the comparison is different. Part 2 covers the classification of objects and codes for classes, while Parts 10, 12, and 14 cover power supply systems, construction works, and manufacturing and processing systems, respectively [S4]. Part 1 is the common rules foundation, not a substitute for the applicable disciplinary supplement.
Who benefits from structured reference designations
The framework is designed for organizations that must correlate documentation with many physical objects across engineering, erection, operation, and maintenance. IEC TC 3 identifies consistent documentation through the complete lifecycle as a core engineering requirement for plants containing multiple technical disciplines [S2].
The approach is suitable for EPC contractors, owners with standardized asset registers, plant designers, procurement teams, commissioning specialists, and maintenance planners. It also supports software environments that structure industrial assets, components, and locations against ISO 81346 principles [S5].
It is not a substitute for a P&ID, equipment list, data sheet, or asset hierarchy. Those records carry technical content that a reference designation cannot express. It is also not a universal sign-off for automation architecture or cybersecurity. Systems carrying process or security requirements still need their applicable engineering standards and project specifications, while the reference designation supplies the common identity layer.
Apply the rules before bulk data migration
The required deliverable is a controlled mapping between every object and its identifier, not a set of aesthetically consistent labels. IEC TC 3 states that unambiguous identifiers are the core of consistent documentation and of the correlation between documentation and physical plant objects [S2].
A practical review should test each proposed designation for uniqueness within its defined scope, confirm that the class code is valid, verify which aspects are present, and record any abbreviation used. The review must also reconcile the designation against P&IDs, equipment lists, database records, procurement documents, and field labels before bulk loading or migration.
Object classification is a separate control problem. IEC 81346-2 was revised because the earlier scheme had disadvantages and was not easy to implement outside electrotechnical and process-related systems; the revised framework was designed to support all disciplines involved in construction while retaining the old system as far as possible [S2]. Legacy-tag conversion therefore needs an explicit mapping and review, not simple text replacement.
Control the common documentation failure modes
Duplicate identifiers prevent an object from being tracked unambiguously, while orphaned or inconsistent tags break the link between design records and field assets. Both conditions affect maintenance, work-pack generation, procurement, and handover [S2]. The identifier must be evaluated as structured data, including its aspect, class code, object record, and scope.
Three additional constraints deserve attention. First, an object may be identified in more than one way depending on the information available, so shorthand must not be interpreted as a second physical object. Second, documentation can exist in both paper and database form, so the database schema must preserve the same reference designation used on engineering deliverables. Third, classification and reference designation serve different functions and should be governed as related but distinct controls [S2].
For imported data, assign the source value, parsed aspects, selected class code, normalized designation, validation result, and approver. The IEC 81346 reference designation builder demonstrates the core parsing model with the four aspects and their letter codes [S7]. A controlled transformation is safer than importing vendor labels unchanged.
Source and verify the governing documents
Engineers should work from the applicable double-logo standard and confirm the edition listed in the project specification. The series includes IEC 81346-1:2022 for basic rules and IEC 81346-2:2019 for object classification and class codes, with ISO 81346-10:2022 addressing power supply systems [S3][S4].
The wording quoted in IEC TC 3’s technical history captures the operational requirement: “Unambiguous identifiers of any objects in the plant/installation are the core to ensure consistency of the documentation and the correlation between the documentation and the physical objects in the plant/installation” [S2]. That is the acceptance criterion for a tagging regime, not whether the tag looks consistent on one drawing.
For audit and handover evidence, retain the governing standard edition, object-class mapping, naming rule set, validation log, and approved exceptions. If a project uses legacy IEC 61346:1996 identifiers, the standard was withdrawn and replaced by the ISO/IEC 81346 series [S4].
The next trackable signal is the proportion of sampled plant objects whose P&ID tag, equipment register entry, procurement record, and field label resolve to the same controlled object identity. A mismatch rate should be reduced before handover.