How it Works: Electrical Breaker Panels
The job of the breaker panel is to distribute the incoming power to the separate circuits throughout a home’s electrical system.
Synopsis: The job of an electrical breaker panel is to distribute power to the different circuits in a house’s electrical system, and to do so in a way that reduces the risk of an electrical fire. Here, electrician Cliff Popejoy identifies the different parts of an electrical breaker panel and explains how they work.
The National Electrical Code (NEC) calls breaker panels, panel boards, a name given to the earliest whole-house electrical systems—including those with switches and screw-in, Edison-type fuses— which were mounted on wooden or asbestos panels.
By the mid-1960s, breakers had almost completely replaced Edison-type fuses in new construction, so the old panel-mounted fuse boxes gave way to the metal breaker panels that are still being used today.
Although the panel shown here is based on modern NEC requirements, older service/ main panel configurations may differ. That doesn’t mean your old electrical panel necessarily requires an upgrade. If an old panel meets code requirements appropriate for when it was installed, the workmanship was good, and the panel has been maintained, then an upgrade is not required.
The job of the breaker panel is to distribute the incoming power to the separate circuits throughout a home’s electrical system, and to reduce the risk of a fire if something goes wrong with the wiring. Here’s how it works.
Beneath the metal cover and beyond the wires and breakers, the design of your home’s main breaker panel is simple. Although configurations vary based on panel size, type, and brand, the basic components are similar.
1. Main lugs- These threaded connectors are the main point of connection between incoming electricity and the panel that distributes the power to the house. If the utility is connected, these lugs are live.
2. Main circuit breaker- This is the master switch for the breaker panel. It shuts off the power to everything downstream, including the hot bus bars and all breakers mounted to them.
3. Hot bus bars- These metal bars, typically made of aluminium or copper, are mounted to the panel on plastic insulators and have tabs that connect with and channel electricity to the clips on the back of the branch circuit breakers. Each of the two conductors feeds one side of the hot bus-bar section.
4. Neutral bus bars- The role of the neutral bus bars, which are typically strips of aluminium bored with holes to secure and connect wires, is to act as a hub for the neutral wires returning from each circuit in the panel, completing the loop of electricity. Some panels may have just one neutral bus bar.
5. Ground bars- These metal bars are the central safety hub for the panel and the ground wires for circuits connected to the panel. They create a direct path for errant power to be discharged safely to the earth.
To access a diagram of an electrical breaker panel and learn the flow of power, click the View PDF button below.
From Fine Homebuilding #257