When the breaker maintenance procedure says "inspect contacts," do more than just verify their presence. Before examining the breaker contacts, inspect the breaker cubicle. If the breaker operated under load, then there's a good chance you'll see "welding slag" on the bottom or walls of the enclosure. The metallic particles may not be readily visible, so shine a light at various angles to help spot these.
Because this metal coating is not part of the original design, it needs to be removed after sufficient lockout/tagout. Use a soft-bristled brush and vacuum; make slow strokes with the brush so you aren’t creating any clouds of metal particles. If the material still won't come off, make a note to clean the enclosure during the next outage rather than use volatile solvents when the surrounding switchgear is energized.
