Troubleshooting commercial lighting loads


Commercial lighting loads are a major load for large facilities. Troubleshooting them can often be challenging but it's important to evaluate these circuits for both 1) energy conservation and 2) power quality purposes. They 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 need to 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: I've found the sags and swells mode of the Fluke 43B to be especially useful for recording repetitive voltage sags which can show up as flickering lights. Both current and voltage are monitored simultaneously. This helps me 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.

I hope this helps!

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