What is an Electrical Circuit Overload?

Have you ever flipped a switch on something electrical – lights, vacuums, technology, or an appliance – only for it to switch off suddenly? This means there’s an electrical circuit overload, and your home’s circuit breaker went into action. While it’s good to know that your circuit breakers are working properly to prevent house fires, it’s probably a good idea to make sure your circuit isn’t overloaded in the first place.

What’s a circuit?

It’s comprised of wiring, a breaker or fuse, and the electric devices you want to use (such as a hair dryer, lighting, or a vacuum). Each device uses a certain amount of electricity when it’s operating, adding to the total load on the circuit, but when you try to use more electricity than your circuit is made for, you get a circuit overload. This causes the breaker to trip, which shuts off the power supply to that circuit. This is an excellent way to prevent house fires. If there wasn’t a breaker, the overload would cause the wiring to overheat and possibly even melt, which could start a fire. But it shouldn’t be a regular occurrence.

Homes’ electrical systems are made for average use, but anyone can overload a circuit. It’s a good idea to know the basics about your house’s circuits to prevent overloads from happening.

What are the signs of overload?

The most obvious is when a breaker trips and the power shuts off when you’re trying to use it, but there are other, more subtle signs. These include:

  • Dimming lights.
  • Buzzing outlets or switches.
  • Warm outlets or switch covers.
  • Burning smells from or marks on outlet covers/switches. (This can also be a sign of other serious wiring issues!)
  • Power tools, appliances, or electronics aren’t as powerful as they once were.

It’s a good idea to learn which circuits power which devices or areas of your home. Doing this allows you to determine the safest load rate that each circuit can handle. For example, if your kitchen lights flicker when you turn on the toaster, this is a good sign that these are on the same circuit and you’re probably close to maxing out the power load on it.

How to Map Out Your Home’s Circuits

  1. Open your home’s breaker box and turn off one of the breakers with the number 15 or 20 on the switch. (Don’t worry about the switches with numbers higher than these; those are for more powerful appliances such as your oven, so you won’t be plugging things in on that circuit.) Write down where the circuit is on the panel so you can note it later.
  2. Walk through your home, flipping on the lights, ceiling fans, and other plug-in appliances. Write down which devices don’t have power and what room they’re in. Test each outlet with a voltage or receptacle tester (if you don’t have one, plug in a lamp) and write down which ones don’t work (and again, what room they’re in).
  3. Return to the breaker box and turn on the first breaker. Then turn off the next one in the row. Repeat the testing process on all the 15 and 20 circuits.
  4. Calculate how much power is being used by each device. Electricity is measured in watts; for example, a 100-watt light bulb uses 100 watts of electricity. Multiply the voltage (volts) and amperage (amps) and you get the wattage (1 volt x 1 amp = 1 watt). Add up the wattage of all the devices on each circuit. Light bulbs and many small appliances have labels listing their wattage, so list these number out. The voltage of most standard circuits is 120, so if a device only lists its amps, multiply that number by 120 to find the wattage.
  5. Compare the total wattage of each circuit to the load rating of that circuit. The circuits with 15 breakers are rated for 15 amps and the maximum load rating is 1,800 watts (120 volts x 15 amps = 1,800 watts). The 20 breakers’ load rates are for 20 amps, so their maximum load is 2400 (120 volts x 20 amps = 2,400 watts). If you use more than the maximum watts on any of these circuits, it’ll overload, the breaker will trip, and the power will shut off. (Remember though: reaching the maximum load rating isn’t the goal. A general rule of thumb is to not go above 80% of the maximum. For a 15-amp circuit, try not to go over 1440 watts on a 15-amp circuit or over 1920 for a 20-amp.)

If you find that you’re exceeding the maximum load rates for any of your circuits, there are a few things you can do to fix the problem. These options include:

Moving plug-in appliances to a less-used circuit.

Don’t turn on too many things at once on a given circuit (such as turning off the TV while you vacuum).

Replace incandescent or halogen light bulbs with LED or CFL (fluorescent) bulbs.

Install new circuits if needed for your lifestyle (for example, if you use a lot of power tools in your garage and it’s on a 15-amp circuit, you may want to upgrade it to 20 amps).