Definition
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, over current and other protection devices, buses, and usually instruments.
Theory
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
Buses
As the NEC® definition states, switchboards include buses, which are metal bars mounted inside the switchboard to conduct power to the switchboard’s devices.
Instrumentation
The NEC® definition of a switchboard also indicates that the switchboard may have instrumentation. This instrumentation often includes one or more meters designed to accept signals from sensors and other equipment and display representative values for power monitoring and management.
Another characteristic of a switchboard identified in the NEC® definition is that it may be installed away from a wall to provide access to the rear of the switchboard. Keep in mind, however, that this is not a requirement of all switchboards.
When a particular device is connected but not in use, only the minimum amount of power must be supplied to that device. The power supply to the board must be turned off when it is opened for maintenance. It prevents the operator working on the plate from being electrocute. The main source of power supply within the switchboards are bare busbars. Therefore, if an individual has to work in distribution tables that are active, appropriate precautions must be taken before working on it. One should wear protective gloves, eyeglasses, shoes, rubber mats when working on the live electrical dashboard.
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.
