A load center is a metal-enclosed distribution panel containing circuit breakers that distribute, protect and control lighting and power circuits in residential and light commercial applications, including single-family homes, townhouses, apartment buildings, and small office buildings.
For most people, the home is an investment of a lifetime. It’s no place to compromise on electrical protection. That’s why nearly 40 years ago load centers and circuit breakers changed the way homes were protected replacing fuses with the convenience and safety of modern circuit breakers.
Load centers are typically rated 225 amps or less and 240 volts maximum and are intended for use in residential applications.
According to the NEC® definition, load centers are:
- Used to control light, heat, or power circuits.
- Placed in a cabinet or cutout box.
- Mounted in or against a wall.
- Accessible only from the front.
Load center has been called different names over the years—for example, a fuse box, breaker box, panelboard, or distribution panel.
Types of load centers
There are two types of load centers, main breaker type, and main lug type.
1. Main breaker load center
Main breaker load centers are suitable for use in service entrance applications. The incoming supply cables of the main breaker type load center are connected to the main breaker which in turn feeds power to the load center and its branch circuits. The main breaker disconnects power from the load center and provides overcurrent protection.
2. Main lug type load center
A main lug-type load center does not have a main circuit breaker. The incoming supply cables are connected directly to the main lugs and bus bars. Primary overload protection for the load center is not provided as an integral part of the load center. Main lug units are primarily used as a distribution panel where there is a main breaker upstream in the system. There are situations where a back-fed circuit breaker and a retainer clip (required by NEC®) are used to convert a main lug load center to the main breaker load center.
Main lug load centers are sometimes referred to as add-on, secondary or downstream panels. These panels are added when all circuit slots in the main breaker load center are full or when a remote panel is desired. For example, the main breaker load center might supply power to a main lug load center located in an area of the home used as a workshop. Main lug load centers are also fed from metering equipment when used in apartment installations.
Load center construction
There are several components that make up a load center. Load centers consist of an enclosure, interior, and trim.
The enclosure is typically cold-rolled (for indoor use) or galvanized steel (for outdoor use) and houses the other components. It is designed to provide component and personnel protection. Knockouts are provided to allow the user to install conduit or cabling as required. Approved cable clamps or conduit hubs are used in the holes to secure and protect the cable and conductors.
The interior consists of several components, including bus bars and neutral bars. Branch circuit breakers are fields added at the time of installation.
The trim assembly (dead front) is the front portion of the load center that covers the interior. The trim includes an access door and an adjustable upper pan. The trim/door provides access to the overcurrent devices while sealing off live parts and internal wiring from contact.