Layout Lowdown for Major Electrical Equipment

Distribution equipment may be divided into several categories: distribution panels, switchboards and switchgear. These categories, in turn, can be divided into units for interior or exterior installations. Distribution panels are typically surface wall-mounted panels that are about 12 in. × 36 in.

09/01/2004


Distribution equipment may be divided into several categories: distribution panels, switchboards and switchgear. These categories, in turn, can be divided into units for interior or exterior installations. Distribution panels are typically surface wall-mounted panels that are about 12 in. × 36 in. in plan. Switchboards are free-standing distribution equipment that may be mounted against a wall or out away from the wall in the event the equipment requires rear access for maintenance procedures. Switchgear, as defined by ANSI, has the overcurrent protective devices (OPD) mounted in a metal-enclosed compartment, separate from the internal, current-carrying buses. As noted in the chart, however, the degree of isolation, barriers required and bus insulation provides differences in the safety and robustness of the equipment.

Electrical Distribution Equipment

Distribution Panels Switchboards 600-Volt Switchgear Medium-Voltage Switchgear 5 kV, 15 kV, 24 kV Pad-mounted Medium-Voltage Switchgear
* Costs are relative and based on comparable equipment and options. The figure starts with the simplest device as a cost of "100" with the others being a multiple of that cost.
** Relative costs between 600-volt and medium-voltage equipment may not be directly compared in this chart.
Bus Isolation Bus is in the same compartment as the overcurrent devicesBus is in the same compartment as the overcurrent devices; insulating barriers may be provided as an option, to separate horizontal and vertical bus from OPDsFull metal barriers between OPDs and horizontal and vertical busesFull metal barriers between OPDs and horizontal and vertical busesFull metal barriers between OPDs and buses
Bus Insulation Bus is insulated from the enclosure but no surrounding insulation is providedInsulating barriers are optional between sections; insulated bus is an optionInsulated bus is standard; as an option, buses may be fully isolatedInsulated bus is standardIsolated bus is standard
Overcurrent Protective Devices (OPDs) All overcurrent devices are fixed, mounted in the same compartment; draw-out OPDs are not availableOPDs may be either group-mounted, individually-mounted or draw-outOPDs are standard as draw-outOPDs are standard as draw-outOPDs are standard as fixed
OPD Types Molded-case or insulated-case breakers or fused switches onlyOPDs may be molded-case breakers, insulated-case breakers, fused switches, bolted pressure fused switches, power air circuit breakersOnly power air circuit breakersVacuum circuit breakers,fused air interrupter switches, or SF-6 circuit breakersVacuum circuit breakers, fused air interrupter switches, or SF-6 circuit breakers, according to options and manufacturer
Environment May be provided in indoor or rain-tight enclosureEnclosures are normally intended for installation indoors; weather-proof enclosures or protected-aisle installations may be provided for exterior installationsEnclosures are normally intended for installation indoors; weather-proof enclosures or protected-aisle installations may be provided for exterior installationsEnclosures are normally intended for installation indoors; weather-proof enclosures or protected-aisle installations may be provided for exterior installationsEnclosures are normally intended for installation outdoors and are fully weather-proof
Ampacities Maximum ampacity-1,200 or 2,000 amps according to the manufacturer; main bus is 80% ratedMaximum ampacity-2,000 to 6,000 amps according to the manufacturer and style of equipment; main bus may be 80% or 100% rated, based on whether the OPDs are 80 or 100% ratedMain bus ampacities range from 2,000 to 6,000 amps and are all 100% ratedMain bus ampacities range from 1,200 to 3,000 amps and are all 100% ratedMain bus ampacities are typically 600 amps
Relative Cost * Aluminum Bus: 100 Copper Bus: 135Copper bus: 250Copper bus: 400**vacuum CBs: 450 **fused air SWS: 250 **SF-6: 350**100
Application Service entrance equipment in smaller commercial facilities or distribution equipment in larger buildingsService entrance equipment in larger commercial, some institutional and grouped residential facilitiesService entrance equipment in industrial and health-care facilitiesMedium voltage service entrance equipment in large commercial, industrial, institutional, and health-care facilitiesPrimary protection and disconnection means for underground distribution and services in campus-type installations





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