How is lightning protection and grounding implemented for high-mast lights?
Due to their significant height, high-mast lights are susceptible to lightning strikes; therefore, a comprehensive lightning protection and grounding system must be designed. The primary measures are as follows:
1. Air-termination device (lightning rod): Install an air-termination rod (typically stainless steel or galvanized round steel) measuring 1–2 meters in length at the top of the mast to conduct lightning current to the ground via a down-conductor. The rod should extend at least 1 meter above the highest luminaire on the light assembly.
2. Down-conductor: Utilize the metal mast body itself as a natural down-conductor (requiring a steel thickness of ≥4 mm and electrical continuity). Install a grounding terminal at the base of the mast.
3. Grounding device: Install a ring-shaped grounding electrode (galvanized flat steel -40×4 or copper-bonded steel) around the mast foundation at a burial depth of ≥0.6 meters, welding it to the foundation's reinforcing steel. Grounding resistance requirements: ≤10 Ω for general areas; ≤4 Ω (or even ≤1 Ω) for critical locations (airports, ports, hazardous chemical zones). If natural grounding resistance is insufficient, install additional artificial grounding electrodes (e.g., 2.5-meter copper-bonded steel rods).
4. Surge Protective Device (SPD): Install a Type 1 or Type 2 SPD at the incoming power terminal of the control cabinet to protect against induced lightning and switching overvoltages. The SPD's voltage protection level should be ≤2.5 kV.
5. Equipotential bonding: Establish equipotential bonding for the mast, control cabinet enclosure, cable metal sheaths, and metal components of the lifting system to prevent potential differences during a lightning strike.
6. Electrical isolation: Use fiber-optic cables or shielded twisted-pair cables for signal lines (e.g., dimming, monitoring) and install signal SPDs.
7. Periodic inspection: Measure grounding resistance and check SPD status annually before the rainy season to ensure the lightning protection system remains intact.
During the design phase, a design institute with appropriate lightning protection qualifications should be commissioned to perform calculations and produce drawings.
