September 2005

What's This?-Service Entrance Panel

Known as the breaker panel, fuse box or switch box, the service entrance panel (SEP) is the heart of your home's or business's electrical system.

After the electricity comes off Walton EMC lines and through your meter, it's routed to the SEP through of a large cable. This large cable serves as the electrical trunk line into the building and power branches out when it gets to the SEP. That's where the term “branch circuits” originated in describing a building's many individual electrical pathways.

This branching allows smaller wires to be used in the building's distribution system.   The electrical load is spread out among many smaller wires instead of a few large ones.

The most important function of the SEP is safety. The SEP is full of devices that keep branch circuit wires from becoming overloaded. Overloading leads to excessive heat and possible fire.

Modern SEPs use circuit breakers to limit electric current flow.  Fuses were common years ago, but are now used in limited applications.

The main advantage of circuit breakers over fuses is that they can be used over and over again. Once a fuse is blown, it's no good.

It's important you know the location of your SEP and keep it clear so it's easily accessible in an emergency. Most SEPs are located in a basement or utility room.   Don't lock doors that prevent entry to the room containing the SEP.

It's also a good idea to make sure each breaker is correctly labeled so you know which branch circuit it powers.

Smaller 120-volt circuit breakers for general circuits take up one space in the SEP and have a single handle. Larger 240-volt breakers that power appliances like stoves, air conditioners and water heaters, will look like double breakers and have two handles tied together to operate as one.

Besides breakers on individual circuits, your SEP has a main breaker.  This breaker shuts off all power to the building when operated. It may be located at the top of the inside SEP in an older installation or in a disconnect box on the outside of the building next to the electric meter in newer construction.

In the event of an electrical emergency or fire, it's probably quickest and simplest to shut off the main breaker instead of trying to figure out which branch circuit to shut down.

See how a circuit breaker works.

More Information:  University of Missouri Extension

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