What is the difference between switchgear and switchboards?
Low-voltage metal-enclosed switchgear and low-voltage switchboards are products used to safely distribute power throughout a facility. Both assemblies utilize free-standing enclosures that house circuit breakers, bus bar and power cables. Both products may contain meters, relays, potential transducers, current transducers and transfer schemes for redundant power. However, that is where the similarities end.
Switchboards are typically constructed with a dead-front, open-chassis design with few or no internal barriers between the cables, circuit breakers and bus bar. When the switchboard dead-front is removed, all bus bar, cables and terminations are exposed.
Switchboards are tested per the UL 891 Switchboards standard and are normally composed of fixed-mounted molded case circuit breakers which comply with the UL 489 MCCB standard. Switchboards tend to be front-accessible which means the incoming and outgoing cable terminations can be accessed from the front so the assembly can be mounted against a wall. These differences result in a smaller footprint than a similar switchgear assembly that contains the same number of circuit breakers.
Switchboards also tend to be less expensive than switchgear. For example, fixed-mounted MCCBs are less expensive than draw-out power circuit breakers. However, MCCBs are not designed to be serviced and if the breakers are fix-mounted, the switchboard must be de-energized in order to replace them. Switchgear, on the other hand, contains draw-out power circuit breakers which can be removed from the equipment while it is energized and are designed to be fully serviceable.
Switchboards only have a 3 cycle short-time current withstand rating, versus a 30 cycle rating for switchgear. This is due to the fact that MCCBs also only have a 3 cycle short-time current withstand rating. This means that achieving selective coordination is more difficult since short-time delays cannot be programmed in to provide time for circuit breakers farther downstream to clear faults.
Certain arc-flash safety technologies are also not available in switchboards. Such technologies available only in low-voltage switchgear include Arc Quenching technology and arc-resistant construction.
In facilities that consume large amounts of power and facilities that require reliable power, switchgear and switchboards both play important roles. The switchgear may provide primary low-voltage power distribution and protection, often residing at the service entrance or on the secondary of a transformer substation, feeding power to various switchboards and low-voltage MCCs located throughout the facility which in turn feed smaller branch circuits such as lighting, HVAC and process-specific loads.