Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Design of Graphical Symbols for Technical Documentation (IEC 81714)
Understanding IEC 81714-2:2006 and IEC 81714-3:2004
1. Graphical Symbol Design Requirements
IEC 81714 establishes the rules and guidelines for designing graphical symbols used in technical documentation across all engineering disciplines. Part 2 of the standard specifies the methodology for creating new symbols, including grid systems, line widths, orientation rules, and the relationship between symbol meaning and visual representation. This ensures that symbols created by different standards bodies or engineering organizations maintain a consistent visual language.
When designing a new graphical symbol, always start with the basic grid defined in IEC 81714-2. The grid system uses a module of 12.5 mm (or 10 mm for reduced-size symbols) as the fundamental spacing unit. This ensures proportional consistency when symbols are scaled or reproduced in different media.
The standard defines several categories of graphical symbols based on their application domain and complexity. Basic symbols represent fundamental concepts (e.g., resistance, flow), while composite symbols combine multiple basic elements to represent complex equipment or processes. The design process must follow a systematic approach from conceptual sketch to finalized symbol registered in an internationally recognized database.
| Symbol Category | Description | Example |
|---|---|---|
| Basic Symbol | Represents a fundamental concept or component | Resistor, Valve, Pump |
| Composite Symbol | Combines multiple basic symbols for complex equipment | Motor Starter, Control Valve Assembly |
| Qualifying Symbol | Modifies the meaning of a base symbol | Adjustability, Variability |
| Application-Specific | Designed for a particular engineering domain | P&ID, Electrical, Pneumatic |
A symbol that looks visually clear to the designer may be ambiguous to users from different cultural or technical backgrounds. Always validate new symbols against the IEC 81714-3 classification coding to ensure they do not conflict with existing registered symbols. Duplication of visual forms with different meanings is a common and dangerous source of misinterpretation.
2. Classification and Coding of Symbols
IEC 81714-3 defines a comprehensive classification and coding system for graphical symbols. Each registered symbol receives a unique alphanumeric code that identifies its domain, function, and specific meaning. This coding system enables efficient retrieval from symbol libraries, automated insertion into CAD systems, and unambiguous reference in technical documentation and standards.
The classification code structure follows a hierarchical pattern: the first level identifies the broad technical domain (e.g., electrical, mechanical, fluid power), the second level defines the functional category (e.g., conversion, storage, control), and subsequent levels provide increasing specificity. This system mirrors the approach used in IEC 81346 for reference designations, creating a consistent information framework across related standards.
Engineering organizations that maintain custom symbol libraries should register their symbols through national standards bodies to obtain IEC 81714-compliant classification codes. This investment pays dividends when exchanging documents with partners or clients who use different CAD platforms — the universal coding eliminates ambiguity even when the visual rendering differs slightly.
3. Engineering Implementation and Quality Assurance
Implementing IEC 81714 in an engineering organization requires more than just access to a symbol library. The standard defines quality criteria for symbol design, including minimum legibility requirements, appropriate line-to-background contrast, and suitability for reproduction at various sizes. Symbols must be testable against these criteria before they are approved for use in official documentation.
Modern CAD systems and technical documentation platforms increasingly support automated symbol validation against IEC 81714 rules. These tools check line width ratios, grid alignment, text placement, and classification code validity, significantly reducing the manual effort required for quality assurance. However, the engineer’s judgment remains essential for evaluating semantic clarity — whether the symbol communicates its intended meaning effectively to the target audience.
| Quality Criterion | Requirement | Verification Method |
|---|---|---|
| Minimum Legibility | Symbol must be clear at A4 reproduction size | Print test at 1:1 scale |
| Line Width Ratio | Thick-to-thin line ratio ≥ 2:1 | CAD dimension check |
| Grid Alignment | All vertices on grid intersection points | Grid snap verification |
| Classification Code | Valid code per IEC 81714-3 | Database lookup |
Using non-standard or unregistered graphical symbols in safety-critical documentation (e.g., emergency shutdown systems, fire protection) creates legal and operational liability. In the event of an incident, the use of non-compliant symbols can be construed as negligence in design documentation. Always audit symbol libraries for IEC 81714 compliance in safety-related applications.
For organizations developing product documentation for international markets, IEC 81714 compliance is particularly important. Symbols that are intuitive to engineers in one cultural context may be confusing in another. The classification system and design rules in IEC 81714 provide a neutral, internationally accepted framework that transcends language and cultural barriers, making technical documentation truly global.
Frequently Asked Questions
Q: Can I create a custom symbol that does not exist in the IEC library?
A: Yes, but you must follow the design rules in IEC 81714-2 and submit it through the appropriate national standards body for registration and classification per IEC 81714-3. This ensures global consistency and prevents duplicate symbols with conflicting meanings.
A: Yes, but you must follow the design rules in IEC 81714-2 and submit it through the appropriate national standards body for registration and classification per IEC 81714-3. This ensures global consistency and prevents duplicate symbols with conflicting meanings.
Q: How does IEC 81714 relate to ISO 14617?
A: ISO 14617 adopted the IEC 81714 framework for graphical symbols and extended it into additional domains. The two standards are closely aligned, and symbols designed under IEC 81714 are generally compatible with ISO 14617 requirements.
A: ISO 14617 adopted the IEC 81714 framework for graphical symbols and extended it into additional domains. The two standards are closely aligned, and symbols designed under IEC 81714 are generally compatible with ISO 14617 requirements.
Q: Are digital (screen-based) symbols treated differently from printed symbols?
A: IEC 81714 primarily addresses printed documentation, but its design principles apply equally to digital displays. Additional considerations for digital use include minimum pixel resolution, anti-aliasing behavior, and contrast ratios for backlit displays.
A: IEC 81714 primarily addresses printed documentation, but its design principles apply equally to digital displays. Additional considerations for digital use include minimum pixel resolution, anti-aliasing behavior, and contrast ratios for backlit displays.
