What causes a high-mast light's light source to be only partially illuminated?
It is easier to troubleshoot a high-mast light where the source is only partially illuminated (i.e., some lights are on while others are off) than one where the entire mast is dark. The causes and solutions are as follows:
1. Circuit control issues: High-mast lights are typically divided into multiple circuits, each controlled independently. If an entire circuit fails to light up, check that circuit's circuit breaker, contactor, fuse, and control wiring. For example, the outer ring of lights might be designed to switch off late at night to save energy; check the time-switch settings.
2. Cable or wiring faults: If some lights on the same circuit are on while others are off, the fault likely lies in the junction box inside the light assembly or in the branch cable. Open the junction box and check for loose or burnt terminals. Use a multimeter to measure the voltage at the faulty light's terminals; if there is no voltage, trace the cable to locate the break.
3. Damaged LED driver: If a specific light fails to turn on despite receiving proper power, the driver is likely damaged. Replace it with a driver of the same model.
4. Open circuit in series-connected LEDs: In fixtures where multiple LEDs are connected in series, the failure of a single LED chip can cause the entire fixture to go dark. Inspect the LED chips for black spots. Replace the faulty chip or the entire module.
5. Contactor contact issues (stuck or disconnected): If a contactor engages but the main contacts fail to make a proper connection (e.g., loss of one phase), it can cause malfunctions in some of the lights. Measure the voltage at the contactor's output terminals using a multimeter.
6. Surge Protection Device (SPD) breakdown: A failed SPD can cause leakage current to ground, tripping the circuit breaker or causing a voltage drop. Remove the SPD to test the circuit. During troubleshooting, it is recommended to lower the light assembly to the ground and check the input voltage and driver status of each fixture individually for efficient fault localization.
