Mike Dolt Enterprises
Mike Dolt Enterprises
User: DornElectric111, Location: Lockport, IL
Asked on: Tuesday, March 15, 2011 at 3:20 pm EDT
Answered on: Tuesday, May 14, 2024 at 2:50 am EDT
Question: I have a 3phase, 120-208volt sub-panel with separate neutral and ground terminal bars. The neutral bar has clearly overheated where the main neutral conductor is landed and has burnt about 4 branch circuit neutrals as well. Also in that same area of the neutral bar was a bonding wire from the feeder bonding bushing, which should have been landed on the ground bar instead. This panel has been in operation for years and supposedly the only work done recently to this business (an automotive lube center), was an upgrade to their neon signage (which is fed out of this sub-panel). Could the sign installer have somehow caused this overheating (possibly sending neon voltage back or ???) in combination with the incorrectly landed bonding wire or could the bonding wire alone have caused the heat? Also, the sign circuit may be part of a multi-wire branch circuit and I can not be positive the branch circuits are on different phases. I was inside this panel months ago and the neutral was definitely in good shape then. Can anybody help me determine this heat issue so that I can replace this panel and know with confidence the issue will not reappear?
Possible Causes of Overheating
Sign Circuit Overload: If the sign circuit was overdrawn, it could have caused excessive current to flow through the neutral conductor. Neon Voltage Backfeed: Neon signs use a high-voltage transformer, which could have backfed voltage into the panel's neutral. Bonding Wire Misconnection: The incorrectly landed bonding wire from the feeder bonding bushing could have allowed fault current to flow through the neutral bar. Loose Neutral Connection: A loose connection at the main neutral conductor or branch circuit neutrals could have increased resistance and caused the overheating. Aged or Corroded Neutral Bar: Over time, the neutral bar may have deteriorated or become corroded, leading to increased resistance and overheating.
Contributing Factors
Multi-Wire Branch Circuit: If the sign circuit is part of a multi-wire branch circuit, it is possible that the branch circuits were not on different phases, causing an imbalance in the neutral current.* Previous Work on Panel: Any recent work on the panel, such as the neon signage upgrade, could have introduced a new issue or disturbed existing connections.
Troubleshooting Recommendations
1.
Inspect Sign Circuit: Verify the load of the sign circuit and ensure it is not overloading the neutral conductor.2. Test Neon Voltage Backfeed: Use a voltmeter to check for voltage on the neutral conductor when the neon sign is operating.3. Relocate Bonding Wire: Move the bonding wire to the ground bar according to code requirements.4. Tighten Neutral Connections: Ensure that all neutral connections, including the main neutral and branch circuit neutrals, are tight and secure.5. Replace Neutral Bar: If the existing neutral bar is damaged or corroded, it should be replaced with a new one.6. Confirm Phase Balance: If the sign circuit is part of a multi-wire branch circuit, verify that the branch circuits are on different phases to balance the neutral current.By addressing these issues and implementing proper wiring practices, you can resolve the overheating problem and prevent it from reoccurring in the future. Flag for review