The main electrical service delivered to your house from the electrical utility company has a total available capacity, measured in amps, or amperes. Most homes have an electrical service of between 100 to 200 amps. Amperage is a measurement of the volume of electricity flowing through wires, and this measurement can vary between 30 amps in very old homes that have not been updated to as much as 400 amps in a very large home with extensive electric heating systems.
Knowing the size of a house’s electrical service can help you know if an update is needed or if the service is large enough to handle an update, such as a remodeled kitchen or room addition.
How Electrical Current Reaches Your Home
Electrical service reaches your home from the power utility through two 120-volt service wires that offer a combined 240 volts of power (voltage is a measurement of electricity’s pressure or rate of flow). The main electrical service reaches your home either through overhead service wires that enter a service mast and pass down through an electrical meter into your home or through underground wires that also pass through an electrical meter. The first stop for the electrical service once it enters your home is the main service panel.
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What the Main Service Panel Does
The main service panel is the distribution center that splits the main electrical service into individual branch circuits that run through your home to power the lights, outlets, and individual appliances. The main service panel is usually a gray metal box located somewhere along the inside surface of an exterior wall. It is often found in a utility area, such as a garage, basement, or furnace room. When it is located in a finished living space, it is sometimes contained inside a finished cabinet mounted on the wall. Service panels also can be located outdoors, typically on an exterior house wall.
The main service panel includes two hot bus bars that run side-by-side down the panel. The bus bars are fed by a large breaker called the main breaker. Each bus bar carries 120 volts. A branch home circuit connected to just one bus bar will deliver 120 volts of power, while a circuit connected to both bus bars will deliver 240 volts of power.
Fuse Box vs. Circuit Breaker Panel
In most homes, the main service panel uses circuit breakers that control and protect the individual circuits. Circuit breakers are specially designed safety switches that prevent individual branch circuits from drawing more power than the circuit wires can safely handle. Virtually all homes built since the early 1960s use circuit breakers as the power distribution method. Older homes also have circuit breaker panels if their electrical service was updated after 1960.
Where an electrical service was installed before the early 1960s and has not been updated, it may use a different style of power distribution—a fuse panel, which protects individual circuits with screw-in or cartridge fuses.
The use of fuse panels and circuit breaker panels for residential wiring follows a historical pattern:
- 30-amp fuse panel: Installed before 1950, these service panels provide only 120-volt current. Such a service provides insufficient power for modern usage and generally needs to be updated.
- 60-amp fuse panel: Installed from 1950 to about 1965, 60-amp fuse panels provide 240 volts of power but are still insufficient for most homes. An update is usually needed.
- Circuit breaker panel: Since the early 1960s, homes have generally been wired with circuit breaker panels that provide 240-volt current. Early services may provide 60 amps of power, while large houses built today may have 200 amps or more of power. Homes with 60-amp or 100-amp service often require an electrical service update during major remodeling or expansion projects.
Source: The Spruce