IEC 61666-2021 PDF

Full title and description

St IEC 61666-2021 — Industrial systems, installations and equipment and industrial products — Identification of terminals within a system. This consolidated edition (IEC 61666:2010+A1:2021, Ed. 2.1) sets out general principles and designation rules for identifying terminals of objects within a system across technical domains (electrical, mechanical, process, building services, etc.).

Abstract

Provides a framework for creating terminal designations and terminal designation sets, explains structuring principles (function and location aspects), gives examples illustrating use of designations, and clarifies that product marking requirements are outside the scope. The 2021 amendment expands examples and aligns terminology with IEC/ISO system‑structuring principles.

General information

• Status: Active.
• Publication date: 16 June 2021 (consolidated edition including Amendment 1, issued 2021-06-16).
• Publisher: International Electrotechnical Commission (IEC).
• ICS / categories: 01.080.30 (Graphical symbols and technical product documentation area).
• Edition / version: Edition 2.1 (IEC 61666:2010+A1:2021 — consolidated version; often shown as Ed.2.0 + Amendment 1, 2021).
• Number of pages: 66 (consolidated CSV edition).

Scope

This International Standard establishes general principles for the identification of terminals of objects within a system and is applicable across all technical areas (for example mechanical engineering, electrical engineering, construction engineering and process engineering). It supports systems built from different technologies or combinations of technologies. The standard provides rules and examples for composing terminal designations but does not set requirements for how terminal designations must be marked directly on products.

Key topics and requirements

• Principles for composing terminal designations (structure, syntax and use of designation sets).
• Separation of aspect-based information (function aspect, location aspect) when forming terminal identifiers.
• Guidance and worked examples illustrating terminal designations in typical installations and multi-technology systems.
• Definition and use of terminal designation sets to manage groups of related terminal identifiers.
• Alignment of terminology and structuring principles with ISO/IEC system structuring standards (e.g., ISO/IEC 81346 series).
• Clarification that product marking requirements (how to print or affix marks on hardware) are excluded from this publication.

Typical use and users

Used by electrical and control engineers, panel builders, instrumentation and wiring designers, technical authors and document controllers, CAD/drawing specialists, system integrators, and manufacturers of terminal blocks and enclosures. The standard is used to create consistent terminal lists, wiring diagrams, control-panel documentation and to support automated documentation workflows in engineering projects.

Related standards

Closely related to the ISO/IEC system‑structuring series (ISO/IEC 81346) and referenced in implementations and national/adopted versions (for example EN 61666:2010/A1:2021 and national adoptions such as BS EN 61666 etc.). IEC 61666 is treated as a horizontal standard for terminal identification and is aligned with IEC Guide 108 system principles.

Keywords

terminal identification, terminal designation, terminal designation set, wiring diagram, system structuring, function aspect, location aspect, IEC 61666, ISO/IEC 81346, control panel documentation

FAQ

Q: What is this standard?

A: An international standard that defines general principles and rules for identifying terminals of objects within technical systems to ensure consistent, unambiguous terminal designations across documentation and systems.

Q: What does it cover?

A: Composition and structuring of terminal designations, use of designation sets, examples showing function and location aspects, and guidance on applying the principles across different technologies. It does not prescribe how designations must be physically marked on products.

Q: Who typically uses it?

A: Electrical and control engineers, panel builders, instrument technicians, CAD and documentation authors, system integrators, and product manufacturers involved in wiring and terminal documentation.

Q: Is it current or superseded?

A: The consolidated edition IEC 61666:2010+A1:2021 (Ed. 2.1) was published 16 June 2021 and is active; it incorporates Amendment 1 (2021) to the 2010 edition. The consolidated status and edition details are recorded by the IEC webstore.

Q: Is it part of a series?

A: It is a horizontal standard and is intended to be used in conjunction with system‑structuring publications such as the ISO/IEC 81346 series and relevant national/adopted standards (EN adoptions and national versions).

Q: What are the key keywords?

A: Terminal identification; terminal designation; designation set; function aspect; location aspect; system structuring; wiring documentation.