Electrical projects often involve taking devices out of boxes and opening up existing circuits. For these reasons, it is imperative to know how to turn a circuit breaker off in order to safely work on a project. Shutting off the circuit that you're working on and then testing the circuit will ensure that you won't be electrocuted. Electrical safety should be your number one concern for the welfare of yourself and your family.
Locate the Electrical Panel
Before you can work on an electric device or circuit, you'll need to find your home's electrical panel. Once there, open the panel door and look at the panel schedule on the door. There is a list of the circuits there and it should be labeled with the locations that each breaker feeds. For instance, circuit #2 may feed the furnace. Look the panel schedule over and find the circuit that you're trying to find. If, however, the electrician that wired your house didn't mark the panel, you'll have to find the circuit by the old trial-and-error method.
Understanding the Panel
The breaker panel is comprised of a main breaker and many branch circuit breakers. The breakers are labeled by odd numbers on the left side of the breaker panel and even numbers on the right side. To help you understand, the left side from the top towards the bottom would be 1, 3, 5, etc... Likewise, the right side would be labeled 2, 4, 6, etc... This is critical in locating the proper breaker in order to turn off the right circuit.
A circuit breaker is designed with a switch in order to turn a circuit on and off. When the breaker is in the off position, the switch will be positioned towards the outside of the panel. When the breaker is in the on position, the switch will be positioned towards the center or inside of the panel.
After You Turn Off a Circuit Breaker
I cannot stress this enough! After you have turned off the breaker that you believe controls the circuit that you are working on, test the circuit with a circuit tester to be certain that indeed it is off. Safety first! Don't take any chances. Implement safety procedures to prevent electrical shock. Electricity kills and you don't want to be electrocuted, trust me!