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Load centers are commonly used in residential and small commercial applications. Since nearly every house in America has one, they are the least expensive way to accommodate circuit breakers. The breakers themselves are usually less expensive because they are mass-produced and simply plug into the load center bus.\u00a0 Load centers are primarily intended for applications up to 240V and are normally only rated up to 225A. At those ratings, they are shallow enough to recess into a 2×4 stud wall and narrow enough to fit between studs on 16″ centers. With larger, surface mount enclosures, one manufacturer offers load centers rated up to 600A. Also, voltages up to 277V can be obtained, but are not common.<\/p>\n
Both load centers and panelboards are mounted in cabinets \u201c. . . provided with a frame, mat, or trim in which a swinging door or doors are or can be hung.\u201d [NEC<\/i>\u00a0100]\u00a0\u00a0As required in\u00a0NEC<\/i>\u00a0408.38, they also have dead fronts, meaning that there are no \u201c. . . live parts exposed to a person on the operating side of the equipment\u201d [NEC<\/i>100]. Normally, panelboards are used for voltages up to 600V, but higher voltage ratings are also available. Panelboards can be rated for up to 1,200A. Smaller panelboards can accommodate plug-in or bolt-on breakers. Larger panelboards only utilize bolt-on breakers and can have a standard thermal-magnetic trip or electronic trip breakers with adjustable settings. Panelboards are deeper than load centers. The wall into which a recessed panelboard is mounted must be constructed using 2×6 studs. Panelboards rated 600A, and higher are deeper and surface mounted on the wall.<\/p>\n
Switchboards.\u00a0<\/b>Switchboards are defined in the\u00a0NEC\u00a0<\/i>as \u201cA large single panel, frame, or assembly of panels on which are mounted on the face, back, or both, switches, overcurrent, and other protective devices, buses, and usually instruments. These assemblies are generally accessible from the rear as well as from the front and are not intended to be installed in cabinets\u201d [NEC\u00a0<\/i>100].<\/p>\n
Switchboards are similar to panelboards in that they are normally rated for up to 600V, but they can handle higher fault currents than panelboards and load centers. They are floor mounted and are deeper than panelboards, usually starting at 18″ deep. Since switchboards are larger and more expensive than panelboards, they are seldom used for bus ratings less than 1200A and can be rated for up to 5,000A. Both bolt-on breakers and draw-out breakers can be installed inside a switchboard line-up. Often, just access to the front is required, but rear and side access may also be required.<\/p>\n
<\/p>\n Switchgear.\u00a0<\/b>The\u00a0NEC\u00a0<\/i>identifies switchgear as: \u201cAn assembly completely enclosed on all sides and top with sheet metal (except for ventilating openings and inspection windows) and containing primary power circuit switching, interrupting devices, or both, with buses and connections. The assembly may include control and auxiliary devices. Access to the interior of the enclosure is provided by doors, removable covers, or both.\u201d<\/p>\n Switchgear is the largest of the three. It can be rated for up to 38 kV and can have current ratings up to 6,000A.\u00a0\u00a0Normally draw-out breakers are used, and therefore, access to the front and rear of the gear is required. Switchgear is tested to a different UL standard than panelboards and switchboards.\u00a0\u00a0Because the breakers in switchgear are each in their own compartment, the gear is rated to withstand a short circuit condition for up to 30 cycles. Panelboards and switchboards are only rated to withstand a short circuit condition for up to 3 cycles.<\/p>\n Switchgear often utilizes draw-out breakers. These breakers can be detached from the bus and removed for maintenance or replacement without shutting down the main or affecting the other breakers in the gear lineup.\u00a0 With moving parts, a draw-out breaker does need to be maintained on a regular basis to ensure that the mechanisms are adequately lubricated and will function properly when required. Working with the breaker energized also requires particular attention to potential arc fault dangers, and personal protective equipment must be utilized.<\/p>\n <\/p>\n Factors that drive decisions about which type of gear to use include economics, space constraints, utility service requirements, ability to shut down the facility, and the electrical system size (voltage and current ratings).<\/p>\n \u00a0<\/span><\/p>\n The following table provides a comparison of the various aspects of the different styles of gear.\u00a0\u00a0Note that the\u00a0NEC<\/i>\u00a0does not limit the use of any gear types to particular voltages or current ranges. These are products that the electrical gear manufacturers have created to meet the\u00a0Code<\/i>\u00a0requirements and the needs of the electrical construction industry. This table is based on gear ratings and sizes by ABB, Eaton, and Schneider Electric for equipment commonly used in residential and commercial facilities. Industrial facilities may use gear by other manufacturers with additional ratings and sizes.<\/p>\n<\/a><\/a>When One Type Of Gear Is Preferred Over The Others<\/h2>\n
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Panelboard, Switchboard, Switchgear Comparison Table<\/b><\/h2>\n