I recently replaced our main load center with a larger one. I was planning to use the old, smaller panel as a sub panel in an addition we are building.
After removing the breakers from the old panel, I noticed some discoloration on the bus bar, where the breakers attach. The panel and all breakers were Square D QO brand. The contacts on the breakers don't seem to have this.
Is this panel still safe to use? What causes this? Should I use some electrical contact cleaner on the bar?