Had a 200 amp main breaker trip on a brand new panel in a Denver remodel last month. The whole house went dark right after we powered up.

That 200 amp main tripping right after power up is a classic sign. Wesley139 is right about checking lugs, but a loose factory connection usually causes heat damage over time, not an instant trip. An immediate trip like that points more to a dead short or a ground fault somewhere in the new wiring. I'd be looking real close at any home runs you just landed in that panel before it was energized.

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tara_williams16mo ago

Yikes, check the main lugs for a loose factory connection.

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wesley1396mo ago

Yeah, loose factory lugs. My buddy had that happen on a new build, turned out a leg was barely hanging on.

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