A switchboard can consist of a single vertical structure or multiple structures depending on the number and sizes of the loads being powered.
A main structure will contain the main disconnects or main lugs and will often contain utility and/or customer metering equipment and surge protection.
Cabling can enter directly into the main structure or through a dedicated pull structure. Pull structures are commonly used in service entrance switchboards. Cables can enter the structure from the floor (bottom entry) or from above (top entry.)
Distribution structures divide and send power to branch circuit protection devices and then to branch circuits to power downstream loads. Power flows from the main structure to the distribution structure via cross bus.
In most installations, switchboards are mounted close to a wall and are front accessible only. If required, the switchboard can be constructed to allow both front and rear access. Rear access switchboards provide easier access for installation and maintenance, but they are typically deeper than front access only switchboards.
The primary components of a switchboard structure are the frame, bus, overcurrent protective devices, instrumentation, enclosures and exterior covers. The switchboard frame is the metal skeleton that houses all the other components. The bus, which is either copper or aluminum, is mounted within this frame. The bus distributes power from the incoming cable conductors to the branch circuit devices. A horizontal bus distributes power to each switchboard section. In contrast, a vertical bus distributes power to the circuit protection devices within an individual section.