Mike Dolt Enterprises
Mike Dolt Enterprises
User: kjroller, Location: Dawson Mn
Asked on: Thursday, March 27, 2025 at 5:10 pm EDT
Answered on: Thursday, March 27, 2025 at 5:12 pm EDT
Question: For some background im changing over from one generator to a new generator at work. I have a panel by the old one that feeds the emergency lights and I have a panel by the new one that will feed the emergency lights from now on. I turned the breaker off on the old generator but left the neutral and hot terminated in the panel. I turned on the breaker in the new panel hooked up normal to test it and the breaker instantly tripped. The panels are both on different seperatly derived systems but the neutral on both ends were still hook up so they were tied together. I unwired the terminations in the old panel turned the breaker on again and everything works. Is that neutral why my breaker was tripping? Thats what I was thinking please let me know what your thoughts are!
Yes, you are absolutely correct. The shared neutral between two separately derived systems (generators in this case) is almost certainly the reason for the breaker tripping. Here's a breakdown of why
Why the Shared Neutral Causes Problems
Neutral Current Paths
When you have two separate generators feeding power, each one establishes its own neutral-to-ground bond (creating a separately derived system). If you then connect the neutrals of these two systems together, you create a parallel path for neutral current.
Circulating Current
The problem is that the current from one generator will attempt to return through both its intended neutral AND the neutral connected to the other generator's system. This creates a circulating current loop.
Overcurrent and Tripping
The amount of current flowing through this shared neutral path can easily exceed the current rating of the breakers in either (or both) of the panels. This overcurrent is what causes your breaker to trip instantly.
In Summary Connecting the neutrals of two separately derived systems creates a ground loop and a parallel path for neutral current. This can lead to excessive current flow, which trips breakers and can potentially damage equipment. By disconnecting the neutral from the old generator panel, you eliminated the ground loop and allowed the new generator to operate as it should with its own properly bonded neutral.
Important Safety Considerations Never connect neutrals between separately derived systems (unless specifically designed and approved to do so). It is a dangerous practice that can lead to equipment damage, fire hazards, and even electrocution. Always verify grounding and bonding are correct when working with generators and electrical systems. This includes checking that each generator has its own appropriate neutral-to-ground bond and that there are no unintended connections between neutral and ground in other parts of the system. Double-check your work. Consult with a qualified electrician if you're unsure about any aspect of your generator setup.
Next Steps1. Document your changes
Clearly label the old panel as no longer connected to the generator and the new panel as the source for emergency lighting.2.
Remove the old generator connections
Remove the old generator connections completely. Simply disconnecting them is not enough because someone could come along later and reconnect them.3.
Verify proper grounding: Use a meter to verify that both panels are correctly grounded and that the neutral-to-ground bond is only present at the generator. Flag for review