A circuit breaker is a safety device that automatically stops the flow of electricity when too much current runs through a wire. Think of it like an automatic shut-off switch that protects your home from electrical fires.

Here's why circuit breakers matter: when too many devices draw power from the same circuit, the wires can overheat and potentially start a fire. A circuit breaker detects this dangerous overload and instantly cuts the power by “tripping” or flipping to the off position. You might have seen this happen when someone runs a hair dryer, space heater, and microwave all at once: suddenly the lights go out in part of the house. That's the circuit breaker doing its job.

Before circuit breakers, homes used fuses, which burned out and had to be replaced each time. Circuit breakers can simply be reset by flipping them back on after you've unplugged some devices or fixed whatever caused the problem.

The term also applies to other systems with automatic stops. Stock markets use circuit breakers that temporarily halt trading if prices drop too quickly. Some machines have circuit breakers that shut them down if they overheat. In each case, the circuit breaker prevents small problems from becoming disasters by automatically breaking the connection before real damage occurs.