Troubleshooting Commercial Lighting Loads

Lighting loads are a major load for many large facilities. Evaluating these circuits is important for both energy conservation and power quality. Keep in mind that commercial lighting loads are wired single phase, with the loads connected from phase to neutral. Typically, the phase-to-phase voltage is 480V, with the phase-to-neutral voltage at 277V. Measurements must be taken at the lighting panel, one phase at a time, since power consumption and Power Factor could vary on each phase.

Some points to consider:

1. Power consumption: Excessive phase unbalance can cause voltage unbalance, which in turn can affect three-phase motor loads.

2. Power Factor: Ballast with low PF might have lower cost-of-purchase but higher cost-of-operation.

3. Total Harmonic Distortion: Current THD should be considered when selecting ballast, especially if there is a possibility of transformer overloading.

4. Voltage stability: Having the right power system measuring tools is important for good troubleshooting. For example, the sags and swells mode of the Fluke 43B Power Quality Analyzer (http://www.fluke.com/fluke/usen/Power-Quality-Tools/Single-Phase/Fluke-43B.htm?PID=56080) is especially useful for recording repetitive voltage sags, which can show up as flickering lights. Both current and voltage are monitored simultaneously. This helps us to tell if sags are downstream of the measuring point (load-related) or upstream (source-related). For example, if voltage sags while current swells, a downstream current inrush likely caused the sag. If both voltage and current sag, some event upstream caused the sags.

It could be an upstream load like a motor on a parallel branch circuit which drew down the feeder voltage. Or it could be source voltage related, for example, a lightning strike or breaker trip/reclosure on the utility distribution system.