Circuit breakers are designed to prevent the wiring in a house from overheating and catching fire. The breaker is sized according to the anticipated load and the size of the wiring it serves. Circuit breakers conduct electricity when in the closed (complete circuit) position. When amperage flow exceeds the rated capacity of the breaker, it trips (opens) and breaks the circuit, de-energizing it. The breaker can be reset to the closed position once the cause of the overload is rectified. Frequent tripping and resetting will fatigue the breaker and eventually reduce its capacity, artificially lowering the breaker's amperage rating. Circuit breakers can be replaced with common tools and basic mechanical skill.
Replacing the Main Breaker
De-energize the circuit. Electrical service must be interrupted outside the house as this is the main breaker. The interrupt is in a locked meter box, and in many cases the box is the property of the power company. Contact your local power company for assistance.
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Remove the cover on the breaker box. Remove the 2 screws that connect the 2 big, black wires to the main breaker. Bend the wires outward to prevent them from contacting anything in the panel.
Pry up one side of the breaker carefully with a flat screwdriver. Grab the breaker and roll it outwards as it comes free. The breaker should come out easily and now be free of the breaker box.
Insert the new breaker and push it in to snap into place. The breaker will lay flat and be in a plane with the other breakers. Turn the new breaker "off' (open).
Install the 2 big, black wires onto the new circuit breaker. Torque the screws firmly but do not overtighten or strip them. Re-establish electrical service to the house and observe the breaker box for arcing or smoke. Reset the main breaker to "on" (closed) and verify that you have power to the house circuits. Replace the breaker box cover.