The National Electrical Code® (NEC) defines a switchboard as a large single panel, frame, or assembly of panels on which are mounted, on the face, back, or both, switches, overcurrent and
other protection devices, buses, and usually instruments.
As this definition indicates, switchboards enclose various devices. For example, the following illustration shows two switchboard sections, an incoming or service section and a distribution section that provides power to feeder and branch circuits. Circuit breakers mounted in these sections provide overcurrent protection. Some switchboards use fusible switches instead of circuit breakers
Switchboard Standards
Switchboards are built according to standards set by Underwriters Laboratory (UL 891) and the National Electrical Manufacturers Association (NEMA PB2). Basic requirements for switchboards are also covered in National Electrical Code® Article 408.
Switchboard Construction
There are multiple elements that make up a switchboard. Included in the list of elements are a frame, buses, overcurrent protective devices, service metering, and outer covers.
Frame
The frame of the switchboard houses and supports the other components.
Buses
A bus is a conductor or set of conductors that serves as a common connection for two or more circuits. Switchboard buses are constructed from metal bus bars which are mounted inside the switchboard to conduct power to various devices.
Overcurrent Protective Devices
Operator components are mounted on the front side of the switchboard. This includes overcurrent protective devices, such as circuit breakers and disconnect switches. These devices are mounted to the bus bars using straps connected to the line side of the devices.
Outer Covers
Cover panels are installed on the switchboard so that no live parts are exposed to the operator. The front cover is referred to as the dead front. The panels are also used as trim to provide a finished look to the switchboard. A product information label identifies the switchboard type, catalog number, and voltage and current ratings.
References :
- siemens COURSES: Basics of Switchboards