What protection measures are required for high-mast lighting circuits?
High-mast lighting circuits must be equipped with multiple protection measures to ensure electrical safety and equipment longevity:
1. Overload protection: Each circuit (e.g., outer ring lights, inner ring lights) should be equipped with a thermal-magnetic circuit breaker rated at 1.25 to 1.5 times the load current.
2. Short-circuit protection: Circuit breakers must feature an instantaneous short-circuit trip function.
3. Earth leakage protection: Outdoor high-mast lights must be installed with a Residual Current Device (RCD) featuring an operating current of ≤30mA and an operating time of ≤0.1 seconds. Installation is mandatory for TT systems.
4. Surge protection: A Type 2 Surge Protective Device (SPD) should be installed in the control box, with a nominal discharge current of 10kA (8/20μs) and a maximum discharge current of 20kA. In areas prone to lightning, the addition of a Type 1 SPD is recommended.
5. Over-voltage protection: A Metal Oxide Varistor (MOV) should be connected in parallel at the driver input to prevent voltage spikes.
6. Under-voltage protection: Some smart drivers include under-voltage protection, automatically shutting down when the voltage drops below 85% of the rated value to prevent excessive current caused by under-voltage operation.
7. Thermal overload protection: Contactors should be paired with thermal relays to prevent prolonged overloading of the motor (lifting system).
8. Grounding protection: The light mast, control box enclosure, and cable metal armor must all be reliably grounded, with a grounding resistance of ≤4Ω. All protective devices should be sourced from reputable brands, and their operational reliability should be tested regularly. A well-designed high-mast lighting circuit should be capable of automatically cutting off power during various abnormal conditions to safeguard both equipment and personnel.
