Switchboards play the important role of distributing incoming electrical power to smaller downstream loads and facilitate the means for switching, circuit protection, and metering. In commercial buildings, utility power is first brought to a service entrance switchboard before feeding several other switchboards, transformers, panelboards or other electrical loads throughout the facility.
The service entrance is usually the boundary between the facility and the electric utility supplying power. It consists of the conductors and all necessary power control and safety equipment. The service section of a switchboard houses the incoming power source, whether cable and conduit or bus duct, and the main disconnecting means (circuit breaker or switch) with overcurrent protection.
In many applications, the service section will also contain the utility owned watt-hour meter (usually referred to as the utility metering compartment) along with ammeters and voltmeters for the system operator. When incoming power lines enter a switchboard from underground, a separate pull section may be required for the cable or busway to pass before connecting with the main lugs of the switchboard.
The distribution section is where power from the service section is divided into feeders and branch circuits. Current passes along busbars to one or more distribution sections from which individual branch and feeder circuits are tapped.
Each branch or feeder circuit has its own disconnect and overcurrent protection device (either a circuit breaker or fused switch) which forms the connection between the busbars and the feeder or branch circuits. Downstream loads are usually fed by cable and conduit but may also connect directly to metal-enclosed busways.
Switchboards are typically installed close to a wall and are front accessible only but can be constructed to access from both sides. Rear access switchboards provide easier access for construction and maintenance, but they are typically larger and require more clearance than front access only.