We're doing a factory dismantle and rewire, and ran into a weird one today. Both electrical rooms have capacitor banks, and all MDP breakers have been de- energized except to the house lighting panel and a few others. Breaker feeding MCC-3 is off and locked out. We have detected voltage intermittently in the feeds to that MCC. Weird voltages too (A-B 200V, A-C 212V, B-C 12V, A-G 278V, B-G 76V, C-G 66V). All downstream switches and breakers are open on MCC-3, voltage persists, so it seems to be coming from the line side in the MDP. Cap bank breaker is open, as well as feed breaker to MCC-3. Levels seem too high for induction. Any other ideas? Also, voltage readings go to zeros for no discernible reason. Literally witnessed it tested at zero, left the site, and my guy called me back to show me the voltage reasons in- person. Where is this backfeed coming from?!?
Ghost voltage in an MCC
- Thread starter dweekly07
- Start date
ptonsparky
Tom
- Occupation
- EC - retired
Use low impedance meters.
A wiggy or solenoid type tester.
Have you inadvertently removed a system bonding jumper at a panel or transformer?
A wiggy or solenoid type tester.
Have you inadvertently removed a system bonding jumper at a panel or transformer?
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Probably a mistapped neutral somewhere. Turn off the panels you still have energized one by one to see if the voltage goes away, then if one panel seems to be the culprit, go through turning off six breakers at a time until a group is found, then narrow it down again. Divide and conquer!