What Causes Breakers to Trip or Fuses to Blow?

We all have an electrical control box located in or on our home, outside or in the back of a closet somewhere. These boxes receive the electricity from the pole outside or an underground source and distribute the power to various areas inside our home. The boxes contain circuit breakers or fuses if it is an older home.

If you are replacing fuses or find yourself wandering outside or climbing into the back of an out of the way closet in the dark to “flip” a breaker back on, chances are, you are overloading a circuit. What does that mean?

Normally, if you are tripping breakers or blowing fuses it will be because you’ve plugged in an appliance that draws too many amps for the circuit. Normal household electrical outlet circuits are 15 to 20 amps and are divided into areas or zones in the home, such as: “kitchen outlets” or “bedroom outlets”. Standard household appliances such as mixers, clock radios, televisions, phone chargers, etc. only use a small percentage of the amperage and very rarely max out the circuit causing a blown fuse or tripped breaker.

In my personal experience, space heaters and blow dryers have been items that often cause a circuit overload. A typical portable space heater is usually 500, 750, 1000 or 1500 watts. A simple formula can be used to determine the amperage of an appliance;

Wattage / voltage = amperage

Example: a 1500 watt space heater operated on a standard 120 volt outlet

1500 watt / 120 volt = 12.5amps

We can see that if this space heater is operated on a 15 amp circuit with just a few other items drawing the other 2.5 amps available, “poof”, out go the lights. Usually a space heater will have a “low” setting that is about Ã?½ the wattage. The example below shows that this will allow the heater to operate with less likelihood of causing breaker or fuse problems:

750 watt/ 120 volt = 6.25 amps

The heater will probably not be as effective, but it will operate at least without causing problems.

If a larger household appliance such as a refrigerator or washing machine suddenly begins to trip breakers or blow fuses, it’s probably time to call a repairman for that appliance because something has caused it to begin to operate differently and use more amperage. This could become a fire hazard if left unchecked.