Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC 62491:2008 — Industrial Systems — Labelling of Cables and Cores
Industrial systems, installations and equipment and industrial products — Labelling of cables and cores
Cost-Benefit Principle
The standard explicitly advises that additional labelling should be limited to the necessary minimum and kept as short as practicable. Each additional character represents cost across potentially thousands of cables in a large installation.
The standard explicitly advises that additional labelling should be limited to the necessary minimum and kept as short as practicable. Each additional character represents cost across potentially thousands of cables in a large installation.
Important Consideration
Labelling must be designed to survive the full lifecycle of the installation — from assembly through production, service, and maintenance. The standard recommends considering environmental factors such as temperature, humidity, UV exposure, and chemical resistance when selecting labelling materials.
Labelling must be designed to survive the full lifecycle of the installation — from assembly through production, service, and maintenance. The standard recommends considering environmental factors such as temperature, humidity, UV exposure, and chemical resistance when selecting labelling materials.
Engineering Insight
Implementing IEC 62491 labelling from the design phase dramatically reduces commissioning time. The standard approach of combining identification, connection, and signal labelling into a coherent system means that any technician can trace, verify, and troubleshoot wiring without relying on institutional knowledge.
Implementing IEC 62491 labelling from the design phase dramatically reduces commissioning time. The standard approach of combining identification, connection, and signal labelling into a coherent system means that any technician can trace, verify, and troubleshoot wiring without relying on institutional knowledge.
Introduction and Rationale for Cable Labelling Standards
In large industrial installations, equipment skids, and control panels, hundreds or even thousands of cables and cores must be identified, terminated, and maintained over decades of service life. Without a consistent labelling system, commissioning becomes a nightmare, troubleshooting is slow, and maintenance errors can lead to costly downtime or safety incidents. IEC 62491, published in 2008, provides a comprehensive framework for the labelling of cables and cores in industrial systems.
The standard recognizes that while cable manufacturers provide basic core colour-coding and alphanumeric designation, these are often insufficient in complex systems with many cores of the same colour or many cables serving similar functions. Additional labelling fills this gap, but the standard wisely cautions that additional labelling will cause additional cost, usually increasing with the number of characters in the labelling string.
Labelling Rules and Identification Systems
IEC 62491 establishes three main categories of labelling for cables and cores: identification labelling, connection labelling, and signal labelling. Identification labelling provides a unique identifier for each cable or core within the system. Connection labelling indicates the termination points at both ends, and may be applied at the local end, remote end, or both ends. Signal labelling describes the electrical function or signal carried by the cable or core.
The standard specifies that designated cable core colours (per IEC 60757) should be used as the primary identification method. When the number of cores exceeds the available colour combinations, additional alphanumeric labelling becomes necessary. The rules address: general requirements for labelling, use of designated cable cores, and use of additional labelling.
Connection and Signal Labelling Best Practices
For connection labelling, the standard defines three approaches: local-end labelling (showing only the local termination point), remote-end labelling (showing only the remote destination), and both-end labelling (showing both local and remote information). Both-end labelling is generally preferred for complex systems where maintenance personnel may not have access to complete documentation.
Signal labelling goes a step further by incorporating functional information such as signal type (e.g., 24V DC, 4-20mA, E-STOP), signal number, and cable number. This approach enables cross-disciplinary communication across process engineering, software engineering, electrical engineering, mechanical/fluid engineering, and control engineering teams.
| Labelling Type | Content | Application | Example |
|---|---|---|---|
| Identification | Unique cable/core ID | Both ends of every cable | CBL-1023 / W-45A |
| Connection (local) | Terminal number at local end | Source end of cable | TB-12:34 |
| Connection (remote) | Terminal number at far end | Destination end | JBOX-7:A12 |
| Signal | Function + signal type | Both ends for critical signals | E-STOP / 24V-DC |
Frequently Asked Questions
Q: What is the difference between identification labelling and signal labelling?
Identification labelling assigns a unique identifier to each cable or core for tracking purposes. Signal labelling describes the electrical function (e.g., emergency stop, 4-20 mA loop, 24 V DC power). Both are complementary and serve different purposes in the maintenance lifecycle.
Q: When should both-end connection labelling be used?
Both-end labelling is recommended for complex systems where maintenance personnel may not have immediate access to wiring diagrams, or where cables pass through multiple junction boxes or intermediate termination points.
Q: Does IEC 62491 specify the physical format of labels (size, material)?
The standard provides guidelines on content and structure but refers to environmental conditions (per IEC 60721) for material selection. Labels must be legible, durable, and resistant to the environmental conditions expected throughout the installation lifecycle.
Q: How does cable labelling relate to functional safety standards like IEC 61508?
Proper cable labelling is an important aspect of the overall safety lifecycle. In safety-related systems, clear identification of safety-critical signals (e.g., emergency stop circuits) helps prevent maintenance errors that could compromise functional safety.
