Calculating a Circuit Breaker Load

man working on a circuit breaker box
  • 2 hours
  • Intermediate
  • 10
What You'll Need

A circuit breaker can easily malfunction and cause a number of problems if the electrical system gets overloaded. This can result in the power getting cut throughout the home. This problem is not only difficult to deal with, but the sudden loss of house power will also damage the electronics in the home. For this reason, it is important to ensure that the load the circuit breaker will be handling is appropriate. This can be done with a few simple calculations.

Step 1 - Make a Rough Blueprint

The best way to get started is by drawing a rough blueprint of the home. Remember to include all the rooms with electrical outlets in them. You can choose any room as the starting point and make a list of all the electrical appliances which are plugged into the outlets. However, exclude anything that is plugged into a dedicated outlet. This is usually a plug which is equipped with a reset button and can mostly be found in bathrooms and kitchens. Generally, these should not be included when calculating the load for the breaker.

Step 2 - Note the Wattage Being Used

Once you have made a list of the items that are not plugged into any dedicated outlets, note the amount of wattage they use. You can find the wattage of appliances either on the back of the appliances’ spec plates or in the owner’s manual. When noting the wattage of these electrical appliances, it is important to include the wattage of ceiling fans and lights as well. This is because these are sure to be used a great deal on the same circuit and not taking them into consideration can result in quite an overload for the breaker.

Step 3 - Calculate the Wattage

pushing buttons on a calculator and taking notes

You will then have to calculate the wattage which is in use in all the rooms. This can be done by adding the wattage of each of the items plugged in and the lights and ceiling fans too. Once you get the total of the wattage being used, open the circuit panel and note the amperage of every circuit breaker. It is important that each room is correlated to a circuit breaker and accordingly labelled. The amperage of every circuit breaker is usually marked with a white number on the switches of the circuit breaker. These generally range from 15- 25.

To calculate the maximum wattage of the circuit breaker, multiply the amperage by 120V. For instance, a circuit breaker that has 15 amp will have a maximum wattage of 1800 watts. You will then have to compare the total wattage for every room with that room’s maximum circuit breaker wattage.

Generally, it is recommended to avoid drawing over 80% of any circuit’s total wattage. For an easier calculation of this value, you can simply multiply the maximum wattage of the breaker by 0.8. This will give you the ideal percentage range that the circuit breaker will be capable of handling.