Tracing cause of an arc


Senior Member
Got called to flickering lights at school today. Opened up a 208/120V panelboard and discovered one lug was roasted. We ripped it apart and changed the guts on site to make them happy but we still need to find the CAUSE of the problem. Legs are labeled BLACK RED BLUE.
Blue leg was the one burned up. Checked voltage and amperage on all 3 legs and nothing was out of wack. Short of tracing and testing every circuit on that leg, what could help us speed up the process of identifying the problem circuit? I still hear the faint sound of an Arc on the leg every couple of minutes but cannot find the source. Would an IR gun tell me anything? Anyone have some experience with troubleshooting these kind of issues?


Senior Member
NE (9.06 miles @5.9 Degrees from Winged Horses)
Electrical Contractor
Poor connection.

Did you do FOP across the connection? Use a good meter to check the voltage drop across breaker or connections. You will be looking for milivolts. A thermal imaging camera or even simple laser thermometer would find the hot spot as well.

You may have an additional breaker that was damaged by the original problem. Check them all for discoloring on the stabs. Use a camera or the FOP method.