Main Breaker
The single large breaker at the top of your panel that can disconnect the entire house, and whose rating (100, 150, 200 amps) defines your service size.
The main breaker is both the master shutoff and the nameplate of your electrical capacity. Everything downstream (the bus bars, every branch circuit) lives behind it, and its rating must match the service entrance conductors and the panel rating. When people say "we have 200-amp service," the main breaker is usually where they read that number.
It is also the one breaker homeowners should know how to find in an emergency: burning smell, sparking outlet, water in the panel area, flipping the main kills power to everything except the service conductors feeding it. Those stay live, which is why even a switched-off panel is not safe to open up.
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- Circuit Breaker : A resettable safety switch that cuts power automatically when a circuit draws more current than its wiring can safely carry, or when it detects a fault.
- Subpanel : A secondary breaker panel fed from the main panel, used to add circuit capacity or put breakers closer to where the power is used: garages, shops, additions, ADUs.
- Bus Bar : The rigid metal bars inside a panel that distribute power to the breakers.
- Double-Pole Breaker : A breaker occupying two panel spaces that connects across both hot bus bars to deliver 240 volts, used for dryers, ranges, AC units, EV chargers and other heavy loads.