How to Check the Amp Size of a House's Electrical Service

Check the capacity of the service entry cable, which leads to the main electrical panel of your house. Sometimes the cable is labeled with the amp capacity. If not, measure the cable's width -- 60-amp cables are 3/4 to 7/8 inches wide. One hundred-amp cables measure are 1 inch wide, 150 amp cables are 1 1/4 inches wide and 200 ampere capacity cables are 1 to 1 1/2 inches wide.

Check the panel rating, which should be on the inside of the door to the main electrical panel. The label will contain information like the catalog number, the model number and type, and the rating. If your label is inside the panel, contact an electrical professional to remove the panel to determine the rating, as it can be dangerous to remove if you aren't trained.

Check the capacity of the main disconnect. Most homes have only one main disconnect, which will be a switch that is much larger than all the other switches in your panel. Most often, this switch will be labeled as "Main." The amps of the main disconnect will be labeled on the switch. If your house has a split-buss panel, where this isn't a single disconnect, disregard this step.

Use the smallest amp measurement as the capacity rating for your house. For example, if the service entry cable measures 150 amps, the panel label rating is 200 amps and the main disconnect capacity is 200 amps, the electrical capacity of your house is considered 150 amps. If your house has a split-buss, use only the entry cable and panel label to determine the capacity of your house.