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 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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