Fuses blow when you overload a circuit with too many appliances—like window air conditioners, microwaves, hair dryers, and toasters—and use several at once. Blown fuses are caused by a fault in a branch circuit from the breaker box to the problem device—not because of the overall capacity of your service. It may mean it’s time to consider an inspection to determine if you need an electrical upgrade to keep pace with your home’s demands.