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.
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. |
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| Bus Isolation | Bus is in the same compartment as the overcurrent devices | Bus is in the same compartment as the overcurrent devices; insulating barriers may be provided as an option, to separate horizontal and vertical bus from OPDs | Full metal barriers between OPDs and horizontal and vertical buses | Full metal barriers between OPDs and horizontal and vertical buses | Full metal barriers between OPDs and buses |
| Bus Insulation | Bus is insulated from the enclosure but no surrounding insulation is provided | Insulating barriers are optional between sections; insulated bus is an option | Insulated bus is standard; as an option, buses may be fully isolated | Insulated bus is standard | Isolated bus is standard |
| Overcurrent Protective Devices (OPDs) | All overcurrent devices are fixed, mounted in the same compartment; draw-out OPDs are not available | OPDs may be either group-mounted, individually-mounted or draw-out | OPDs are standard as draw-out | OPDs are standard as draw-out | OPDs are standard as fixed |
| OPD Types | Molded-case or insulated-case breakers or fused switches only | OPDs may be molded-case breakers, insulated-case breakers, fused switches, bolted pressure fused switches, power air circuit breakers | Only power air circuit breakers | Vacuum circuit breakers,fused air interrupter switches, or SF-6 circuit breakers | Vacuum 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 enclosure | Enclosures are normally intended for installation indoors; weather-proof enclosures or protected-aisle installations may be provided for exterior installations | Enclosures are normally intended for installation indoors; weather-proof enclosures or protected-aisle installations may be provided for exterior installations | Enclosures are normally intended for installation indoors; weather-proof enclosures or protected-aisle installations may be provided for exterior installations | Enclosures 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% rated | Maximum 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% rated | Main bus ampacities range from 2,000 to 6,000 amps and are all 100% rated | Main bus ampacities range from 1,200 to 3,000 amps and are all 100% rated | Main bus ampacities are typically 600 amps |
| Relative Cost * | Aluminum Bus: 100 Copper Bus: 135 | Copper bus: 250 | Copper 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 buildings | Service entrance equipment in larger commercial, some institutional and grouped residential facilities | Service entrance equipment in industrial and health-care facilities | Medium voltage service entrance equipment in large commercial, industrial, institutional, and health-care facilities | Primary protection and disconnection means for underground distribution and services in campus-type installations |
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