A circuit must be a closed loop of wiring. Electricity flows from a power source, through the circuit to the different outlets and switches, then back to the source. Circuits are designed to handle a certain amount of electricity. There are safety measures in place like fuses and circuit breakers that are designed to stop the flow if there is too much electricity on the circuit.

Switches are like manual circuit breakers—the either complete or break an electrical circuit. In the “off” position the electrical contacts inside the switch can’t meet. When you flip the switch to the “on” position, the contacts connect and allow electricity to flow through.