WiremanWireman · Main breaker trips: troubleshooting for electricians · 2023 NEC ·
Main breaker trips
The whole panel goes dead. Find out if it’s the total load, a fault, heat at the lugs or the main itself.
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How it works
The main breaker protects the panel bus and the service conductors, so it sees the total current of every branch circuit on each leg. It should only trip on a sustained overload of the whole service, a fault that a branch breaker didn’t clear, or its own heat or failure. The line side of the main stays live when it’s off, so tightening its lugs or replacing it usually takes a utility disconnect.
Every question and answer in this guide. Tap “Step by step” to walk through it.
- When does the main trip?
- The moment it’s resetTurn every branch breaker off, then reset the main. Does it hold?
- It holdsTurn the branch breakers back on one at a time. Does one of them make the main trip?
- Yes, one circuit trips the mainA fault on one branch circuit
- All back on and it holdsTest: Measure the current on each service legExpect: Each leg well below the main’s rating; long-running loads should stay under 80% of it.
- A leg at or near the main’s ratingThe service is overloaded
- Both legs well below the ratingTest: Check the main and its lugs for heatExpect: No hot spot at the lugs, and the main about as warm as the loaded branch breakers.
- Lugs or conductor ends hot or discoloredLoose or failing service conductor connections
- Lugs normal, nothing unusualA weak or worn main breaker
- Trips with everything offA fault on the bus or a failed main
- It holdsTurn the branch breakers back on one at a time. Does one of them make the main trip?
- When several big loads runTest: Measure the current on each service legExpect: Each leg well below the main’s rating; long-running loads should stay under 80% of it.
- A leg at or near the main’s ratingThe service is overloaded
- Both legs well below the ratingTest: Check the main and its lugs for heatExpect: No hot spot at the lugs, and the main about as warm as the loaded branch breakers.
- Lugs or conductor ends hot or discoloredLoose or failing service conductor connections
- Lugs normal, nothing unusualA weak or worn main breaker
- After a long run, and the main feels hotTest: Check the main and its lugs for heatExpect: No hot spot at the lugs, and the main about as warm as the loaded branch breakers.
- Lugs or conductor ends hot or discoloredLoose or failing service conductor connections
- Lugs normal, nothing unusualA weak or worn main breaker
- Large commercial service with ground-fault protectionThe main’s ground-fault protection is tripping
- The moment it’s resetTurn every branch breaker off, then reset the main. Does it hold?