Lately, there's been a rash of lighting problems. These have included dim lighting, flickering lights, ballast failure, and lamp failure. The last two issues are particularly puzzling, because the ballast are only a few years old and the lamps are on a relamping program and nowhere near their expected end of life.
After replacing a few ballasts and lamps based on the idea that sometimes things just happen, it now has become clear that something is causing these failures. The plant manager wants you to find that cause and fix it. What are some possible clues that will help you, and where should you start troubleshooting?
Look at your calendar. That's your first clue. During winter, moisture condenses inside raceway that's exposed to the cold. With April showers, you might not get May flowers but you certainly get even more moisture.
Conductors immersed in moisture inside a raceway can leak power to ground. Especially if they've been damaged by a transient voltage event. The dim lighting and the flickering indicate this may be what's going on. On a circuit that exhibits problems, look at the voltage with a recording DMM and test for ground leakage with a ground leakage tester.
You probably don't trend insulation resistance test readings, or even take them, on 277V lighting conductors. It's hard to draw anything conclusive from a single reading, but perform this test anyhow. At the very least, it will help dry out the insulation. Hi-potential testing will also do that.
If any portion of the lighting raceway runs on or in exterior walls, install drains and/or reroute the raceway to prevent similar problems next spring.