1. Why Outdoor Signal Cables Need Protection

Outdoor signal cables connect field equipment with monitoring and control systems. They may carry measurement signals, communication data, or control information between different parts of an industrial installation.

Examples include:

• Instrumentation cables connecting field sensors to control panels.
• Communication cables linking outdoor equipment with monitoring systems.
• Control cables connecting equipment across different installation areas.
• Signal connections between external devices and indoor electronic systems.

When these cables are exposed to electrical disturbances, connected equipment may experience transient voltages beyond its intended operating conditions.

The actual risk depends on factors such as cable routing, installation exposure, connected equipment, grounding arrangements, and the electrical characteristics of the circuit. Therefore, protection should be evaluated according to the specific installation rather than assuming every outdoor cable has the same level of risk.

2. How Lightning-Induced Surges Can Reach Industrial Equipment

Lightning-related surges can affect connected electrical systems through different mechanisms. Understanding these mechanisms helps engineers identify the relevant protection points.

Conducted Surges

A conducted surge travels through an electrically connected path. Lightning current or associated electrical disturbances can introduce transient overvoltages into connected conductive systems, potentially affecting equipment linked to those paths.

For example, an outdoor instrument connected to a control panel through a signal cable may create an electrical path between the field installation and indoor equipment.

Electromagnetically Induced Surges

Lightning produces rapidly changing electromagnetic fields. These fields can induce transient voltages in nearby conductive loops and cables, depending on their routing, geometry, and exposure.

Long cable runs and exposed installations should therefore be evaluated as part of the overall electrical protection design.

Differences in Electrical Potential

During a lightning event, different parts of an installation may temporarily experience different electrical potentials. If interconnected equipment is not appropriately considered within the grounding and bonding arrangement, these differences can contribute to electrical stress across connected interfaces.

The appropriate mitigation measures depend on the installation design and applicable engineering requirements.

3. Which Parts of an Industrial Installation Should Be Evaluated?

A useful assessment considers the entire connection between the outdoor equipment and the system it serves.

This table identifies areas for technical evaluation. It does not establish that every installation requires the same protective devices or configuration.

4. How Surge Protective Devices Help Protect Signal Circuits

Surge protective devices (SPDs) are designed to limit transient overvoltages and divert surge currents according to their design and installation conditions. Selecting the appropriate device requires understanding the circuit being protected.

For signal and instrumentation circuits, engineers should consider the following:

• Signal characteristics: Identify the signal type and relevant electrical operating parameters.
• Equipment compatibility: Confirm that the protective device is suitable for the connected equipment and circuit.
• Installation location: Evaluate where the signal cable enters the building, panel, or protected equipment area.
• Grounding and bonding: Ensure the installation arrangement is compatible with the selected protection system.
• Coordination: Review how the proposed device works with other protection measures in the wider installation.

LES offers surge protection solutions for electrical protection applications. Explore the surge protective devices range to learn more about the product category.

The correct selection should be based on the actual installation requirements and relevant technical documentation.

5. Why Earthing and Bonding Matter

Surge protection should not be considered independently of the grounding and bonding arrangement. These elements form part of the wider electrical protection design.

Earthing establishes an electrical connection to the earth, while bonding connects conductive parts to help manage potential differences within the installation.

For industrial facilities, engineers should review:

• The existing earthing arrangement.
• Connections between relevant conductive components.
• Bonding of applicable equipment and installation parts.
• The grounding requirements of the selected SPDs.
• The relationship between signal protection and the wider lightning protection system.

The objective is to develop a coordinated protection arrangement that considers the installation as a whole rather than relying on a single component.

For related solutions, visit the earthing and grounding systems section of the LES website.

6. Practical Engineering Considerations for Outdoor Cable Protection

Before selecting protective equipment, engineers should collect information about the installation and its connected circuits.

Review the Cable Route

Identify where the cable runs, whether it passes through exposed areas, and where it enters buildings or control panels. Cable routing can influence exposure to electromagnetic disturbances and should be considered during the assessment.

Check Equipment Specifications

Review the operating voltage, signal type, connection arrangement, and relevant equipment withstand specifications. These details help establish the requirements for compatible protection.

Evaluate Existing Protection

Identify existing SPDs, grounding connections, bonding arrangements, and other relevant protection measures. This helps engineers understand the current installation before recommending modifications.

Consider Applicable Standards

The IEC 62305 series addresses lightning protection, while the IEC 61643 series covers surge protective devices and related applications. Engineers should confirm the applicable parts, editions, and project requirements before specifying a system.

Where relevant, the installation must also meet applicable Indian electrical requirements and project specifications.

Prepare Information for a Technical Assessment

When discussing industrial signal cable protection, provide the technical team with relevant information, such as:

• The type of industrial facility.
• The equipment connected to the outdoor signal cable.
• The signal and operating specifications, where available.
• The approximate cable route and installation environment.
• Existing surge protection and grounding arrangements.
• Available electrical drawings or equipment documentation.

This information helps establish the scope of the technical discussion. The final protective arrangement should be determined through an appropriate engineering assessment.

You can also explore the control and instrumentation protection products available through LES.