How to Size Electrical Service Panels

An electrical service panel acts as a branching point that splits the incoming electrical service into smaller amperages for individual circuits throughout a building.
Depending on the building's intended use, such as a residential home or a barn, the size of the service panel required varies. There are several considerations to make when choosing a service panel ranging from price to capacity. Whether upgrading or replacing, sizing a service panel correctly prevents power outages and wasted investment.

Step 1

Determine the amperage requirements of the building. Detached garages and barns often require little in the way of power capacity and are well suited for low-amperage service panels ranging from 40 to 60 amps. A residential home, however, is usually serviced with 100 to 200 amps of electrical power.

Step 2

List the electrical devices that will be installed within a building. For an attached garage, for example, items to consider include electrical power tools, lighting and motors. Residential homes have varied electrical needs. However, within a home there are few devices that use large amperages for an extended period of time. For example, a residential dryer or air conditioner may use large-amperage motors but only run for several minutes every hour or two.

Step 3

Add the total amperages needed within the building. For example, a 50-amp motor, 15 amps worth of lighting and a 30-amp air conditioner within a garage would add up to 95 amps. This is the maximum amperage capacity required for the service panel.

Step 4

Take the operational duration of devices into account. Residential homes often have 100-to-150-amp service panels installed. This is despite having well over 200 to 300 amps worth of devices installed within a home. If many of the high-amperage devices operate for only a short time per day, they can be given far less weight in the final determination of the service panel capacity.

Step 5

Choose a service panel capacity that covers, at a minimum, the continuous power load within the house (lighting, water heater and ranges) and can operate one or two of the high-power items simultaneously.

About the Author

Heather Lindsay is a stained glass artist who holds a master's degree in library science, a bachelor's degree in anthropology with a minor in art, and has enjoyed working in special libraries with photograph collections.