Mike Dolt Enterprises
Mike Dolt Enterprises
User: cammronz, Location: Michigan
Asked on: Thursday, March 24, 2011 at 8:58 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:14 am EDT
Question: Let me start by apologizing for the size of this beforehand. I'm going to do my best to explain my issue as thoroughly as possible.I'm working in a Govt. building that has had multiple additions over the years and the electrical work does not look pretty. The issue I'm having is a GFCI(brkr 24) tripping only when another s/p(brkr 8) standard(non GFCI or AFCI), is on. I turn off the s/p brkr 8 and the GFCI brkr 24 will no longer trip. I unplug everything fed from s/p brkr 8 and the GFCI brkr 24 will no longer trip. s/p brkr 8 never trips.I traced out the wiring and found that the neutral for s/p brkr 8 is shared with the neutral for the GFCI brkr 24. They tie in together, about 100 ft through conduit bends after the GFCI brkr 24. And both hots are in the same conduit run.I tried disconnecting the hot for the s/p brkr 8 at the first available junction box and it will still trip the GFCI brkr 24. This is also the same location that the neutral all tie in together.My thoughts are that because of the shared neutral, after the GFCI brkr 24, the GFCI brkr 24 is detecting the 5/1000 of an amp difference coming from the s/p brkr 8 in the conduit run within the first 100 ft.I am slightly skeptical of this and before I start running new wires into a run that is almost at it's max wire capacity. I wanted to verify that this is a possibility and the most likely of problems.
Possible Cause
It is highly likely that the shared neutral between the GFCI breaker (24) and the standard breaker (8) is causing the issue.
Reasoning
A GFCI breaker monitors the current flow in the hot and neutral conductors and trips if there is a significant imbalance between them. When the standard breaker (8) is turned on, its load current flows through the shared neutral back to the GFCI breaker (24). If there is any resistance or impedance in the neutral conductor within the conduit run where the two neutrals are tied together, it will cause a voltage drop. This voltage drop will result in a current imbalance between the hot and neutral conductors at the GFCI breaker (24), causing it to trip.
Troubleshooting Steps
To confirm that this is the issue, you can try the following: Disconnect the neutral wire from the GFCI breaker (24) and connect it to a known good neutral (such as a nearby junction box). If the GFCI breaker no longer trips when the standard breaker (8) is turned on, then it confirms that the shared neutral is the issue.
Solution
To resolve the issue, you will need to separate the neutral wires for the GFCI breaker (24) and the standard breaker (8). This can be done by running a new neutral wire from the GFCI breaker to the load or by installing a separate neutral bar in the panel.
Note:
Before running new wires, check the conduit capacity to ensure that it can accommodate the additional wires. If the conduit is full, you may need to consider alternative routing options. Flag for review