Selection and grounding requirements of lightning arrester

Lightning strike path of monitoring system

1. Direct lightning strike: Directly hitting a pole or equipment has the greatest damage.
2. Induction lightning: Thundercloud discharge induces surges on nearby lines and invades equipment along power lines and signal lines. This is the most common cause of damage.
3. Ground potential counterattack: A nearby lightning strike causes the ground potential to rise and counterattack the equipment through the ground wire.

Surge protector (SPD) type and installation location

Key points for selection

• Network lightning protector: Must support PoE (confirm support of af/at/bt and corresponding line sequence), Otherwise, abnormal power supply may occur.
• Transmission rate matching: For Gigabit networks, you need to choose a Gigabit lightning protector. A 100 Mbit lightning protector will limit the speed.
• Nominal discharge current In: General scenario ≥ 5kA (8/20μs), Areas prone to thunderstorms are more likely to be selected.
• Limit voltage (Up): The lower the better, it should be lower than the withstand voltage level of the protected equipment.
• Response time: Should be ≤ 25ns (nanoseconds).
• Interface and protection level: Outdoor installation requires IP65 or above.

Grounding requirements

• Ground resistance: General monitoring equipment room ≤ 4Ω; outdoor poles and equipment boxes ≤ 10Ω; areas with high soil resistivity can be relaxed and resistance reduction measures can be adopted.
• Equipotential bonding:The equipment casing, metal brackets, poles, lightning arrester ground wires, and wire conduits must be connected together and grounded uniformly. Avoid potential differences.
• Grounding wire: Sufficient cross-sectional area (generally ≥ 4mm², important areas ≥ 6mm²), Keep it as short and straight as possible and avoid loops (the inductive reactance under lightning current will significantly increase the residual voltage).
• Independent grounding vs joint grounding: Priority is given to joint grounding (connected to the building lightning protection grounding network), When making a ground net alone, pay attention to the safe distance from other ground nets.

Maintenance

• The lightning arrester has a deterioration indication window, which needs to be replaced when it turns red.
• Inspection once a year before the thunderstorm season.
• After the device is struck by lightning, even if it can still work, it is recommended to replace the lightning protection module.
• Ground resistance is measured and recorded once a year.