Electrostatic discharge and LED luminaires

ESD Mitigation Guideline

Effective ESD mitigation is critical to safeguard sensitive electronic equipment such as LED lighting.

This article provides guidelines and procedures for effectively mitigating Electrostatic Discharge (ESD) on structures such as bridges, specifically focusing on components such as plastic covers and luminaires installed on metal stays. This article aims to prevent damage to sensitive electronic equipment such as LED lighting, ensure the safety of personnel, and maintain the integrity of the bridge's electrical systems.

All conductive elements of any structure (such as a bridge) must be adequately grounded and bonded to provide a safe path for static charges to dissipate. This process requires a Comprehensive Grounding System where the entire metallic structure of the installation including the framework, cable ladders, luminaire mountings, etc. should be grounded to the earth. This implies a network of grounding rods and conductors that provide a low-resistance path for static charges to dissipate safely into the ground. All structural steel elements, railings, and other large metallic components should be interconnected and bonded to the primary bridge ground.

Additional bonding is necessary within the installation for key, vulnerable equipment racks, cable trays, and any potentially live sub-structure of the Electrostatic Discharge (ESD) sensitive devices. ESD-sensitive devices should be electrically bonded properly together. This ensures that there are no significant differences in electrical potential between various parts of the structure, preventing sparks from jumping between them.

ESD Mitigation Requirements

• Metal Stays require direct grounding, continuity testing, and corrosion protection.

Ensure each metal stay is directly connected to the comprehensive grounding system of the bridge structure. This connection should be made using low-resistance bonding jumpers or clamps. Regularly test the electrical continuity of the metal stays to the main ground point to ensure an uninterrupted path for static dissipation. Protect all grounding and bonding connections on metal stays from corrosion using appropriate coatings or enclosures to maintain low resistance over time.

• Luminaires mounted on metal stays require grounding, shielded cabling, insulation integrity, and conductive mounting hardware.

All metallic housings of luminaires installed on metal stays must be securely bonded to the stay itself, thereby connecting them to the comprehensive grounding system. Utilize shielded cables for power and data transmission to light luminaires to minimize electromagnetic interference (EMI) and provide an additional path for static dissipation. The shield must be properly grounded at both ends (if applicable and according to design specifications) or at the source. Ensure that the insulation of all wiring associated with the lights is intact and free from damage to prevent accidental contact with energized conductors or static buildup. Use conductive mounting hardware where possible, ensuring it establishes a good electrical connection between the luminaire and metal stay.

• Luminaires mounted on plastic covers require specific mitigation measures.

Anti-static materials: Specify and use plastic covers made from anti-static or static-dissipative materials. These materials are formulated to prevent the buildup of static charge. Use static-dissipative plastics (surface resistivity 10^6–10^9 ohms/sq) for covers where feasible.

Conductive coatings and treatments: If standard plastics must be used, apply anti-static sprays or conductive coatings to the surfaces of the plastic covers to allow static charges to dissipate. Regular re-application may be necessary based on product specifications and environmental conditions.

Proximity to grounded surfaces: Design the installation so that plastic covers are in close proximity to, or in direct contact with, grounded metallic surfaces. This allows for induction-based dissipation of charges.

Humidity control: Maintain an appropriate relative humidity level (typically 40-60%) in enclosed environments near sensitive electronics, as higher humidity can naturally reduce static buildup. (Note: This is often less feasible for open bridge environments but relevant for enclosed control rooms).

Bonding of fasteners: If plastic covers are secured with metallic fasteners, ensure these fasteners are bonded to the underlying grounded metal structure to help dissipate any charge that might accumulate on the surface of the plastic or in the immediate vicinity.

Installation Procedures

Before installation, inspect all components (metal stays, lights, plastic covers, grounding cables, bonding jumpers) for damage, corrosion, or defects that could impede ESD mitigation.

Grounding system verification

Before installing any components, verify the integrity and continuity of the main bridge grounding system.

Bonding connections

• Clean contact surfaces thoroughly to ensure low-resistance connections.
• Install bonding jumpers between adjacent metal sections of the bridge structure, metal stays, and light fixture housings as per design specifications.
• Ensure all connections are tight and secure, using appropriate torque settings for fasteners.

Cable management

• Route cables neatly and away from sharp edges or potential pinch points.
• Ensure shielded cables are properly terminated and grounded.
• Avoid tight bends that could damage cable insulation.

Plastic cover installation

• Handle plastic covers carefully to avoid unnecessary friction.
• If using anti-static sprays, apply them as per manufacturer instructions.
• Ensure any conductive fasteners are properly installed and bonded to the grounded structure.

Maintenance and Inspection

Conduct regular visual inspections semi-annually (or more frequently in harsh environments) for:

• Corrosion on grounding and bonding connections.
• Loose or damaged bonding jumpers.
• Damaged cable insulation.
• Degradation of anti-static coatings on plastic covers.

Conduct electrical continuity testing annually (or as required by local regulations), perform electrical continuity tests on:

• All grounding and bonding connections to ensure resistance is below specified limits.
• Metal stays to the main ground.
• Light fixture housings to the main ground.

Reapply anti-static coatings to plastic covers as recommended by the manufacturer or when performance degrades.

Maintain detailed records of all inspections, tests, and maintenance activities.

Training

All personnel involved in the design, installation, maintenance, and inspection of bridge components covered by this article shall receive comprehensive training on:

• The principles of ESD and its potential hazards.
• The specific ESD mitigation measures detailed in this article.
• Proper use of tools and equipment for ESD-safe practices.
• Emergency procedures in case of an ESD-related incident.

Documentation

All ESD mitigation designs, installation records, inspection reports, test results, and maintenance logs shall be documented and maintained for the lifespan of the bridge components.

Safety

• Always follow general electrical safety procedures when working with bridge lighting and electrical systems.
• Use appropriate Personal Protective Equipment (PPE).
• Ensure lockout/tagout procedures are followed before performing any work on energized systems.
• Be aware of environmental conditions (Eg: humidity, weather) that may affect ESD risks.

Glossary

Bonding: The practice of intentionally connecting two or more conductive objects with a conductor to equalize electrical potential between them.

Electrostatic Discharge (ESD): The sudden flow of electricity between two electrically charged objects caused by contact, an electrical short, or dielectric breakdown.

Floating Metal: Any conductive material that is not connected to a ground path and therefore has no path to release its charge. Floating metal can build up a static charge causing damaging discharges to nearby sensitive components. 

Grounding (Earthing): The process of connecting an electrical circuit or electrical equipment to the Earth, providing a low-resistance path for electric currents to dissipate safely.

Metal Stays: Structural tension members, often steel cables or rods, used to support the bridge deck or towers.

Plastic Covers: Non-conductive enclosures or shields used for various purposes, such as protecting components or aesthetic finishes.

Further Reading

The Electrostatic Discharge Association provides a variety of useful resources including webinars, articles, FAQs, and beginner-friendly guides that explain the fundamentals of ESD and effective mitigation and protection techniques.

 YouTube offers many tutorials and straightforward videos about ESD and LED lighting including mitigation approaches.

Still Have Questions?

If you still have questions about ESD Contact us. We are happy to help.