If I turn the ceiling fan on in my upstairs bedroom, the breaker for the dining room trips. The ceiling fan stays on. It has dimmable lights and I've determined that if I dim them to a lower level, no tripping occurs. Or if I turn on the fan only, no issues. Another ceiling fan in the dining room will cause the circuit for the electrical outlets to trip. The ceiling fan and the outlets are on different circuits. Why does it trip a totally different breaker? Other Info - I have a reef tank in my dining room. I upgraded the lights from 216 watts to 516 watts and the issue started occurring. There are two circuits in the dining room, one for the lights and one for the electrical outlets. The total draw of the tank equipment is about 900 watts. I have one lamp connected to the same circuit, but it's never on and hasn't been on at the time of the breaker tripping. The dining room electrical outlet circuit has a 20A breaker. House was built in 2010. I'm guessing this is related to something with AFCI, but I'm not sure whether explains the tripping of a breaker in a different room. I have 3 other ceiling fans in the house. One in each of the other bedrooms and one in the living room. None of these will cause any breakers to trip, even when on at the same time. The main difference between these fans and the one in the bedroom / one in the dining room, is that the other 3 fans all use CFL lights with lower wattage requirements. I've considered switching the lights in the two fans to CFL, but didn't want to do so until I understood this phenomenon and was sure it isn't indicating some sort of wiring fault. Thanks for your time.