Electrical Apparatus magazine, March 2003 Low Voltage Busway: An Overview

The most flexible and economical means of electric power distribution within buildings, particularly when total current reaches 800 amperes at 600 volts or below, is often low-voltage busway. Its application is governed by NEMA Standard BU 1, UL 857, and Article 368 of the National Electrical Code. It consists of a metal channel enclosing bus bar conductors of copper or aluminum, in standard lengths of 1.5 to 6 meters, usually suspended from ceilings but also usable as vertical risers.

A common version is "feeder" busway used to transmit power from one area to another. Individual phase, neutral, and ground bars may be insulated and stacked together ("sandwich" construction), or left bare and spaced apart by insulating supports. The sandwich design minimizes circuit reactance and voltage drop, and limits arc migration during a fault. However, inspection is difficult; bar insulation can deteriorate; and the busway itself does little to limit short-circuit current.

Also common, particularly in factory production areas, is "plug-in" busway. It allows attachment of power taps or plugs at intervals along its length, supplying individual loads that are easily moved as processes or machines are changed. A variation permits direct mounting of overhead lighting fixtures to the busway. Taps may involve simple receptacles or a variety of control devices such as circuit breakers or motor starters. Circuit protective devices in such accessories need careful coordination with those protecting the busway, as well as any in the individual loads.

Installation should provide ample support. Ceiling hangers are required every 1.5 meters. These must also allow for horizontal expansion and contraction of busway during load swings (typically 1 to 2 centimeters per 30 meters of length). Some types of vertical busway may allow internal spread of fire and smoke, requiring fire barriers at each floor through which they pass.

Standards such as NEMA BU 1.1, NFPA 70B, and ANSI/NECA 408 offer guidelines for busway maintenance. Annual inspection is suggested, to look for loose joints, moisture contamination, obstructed ventilation, or overheating (infrared scanning is recommended). 

Industry news...

Featured Technical Article
March 2003

On this page is a summary of the Electrical Apparatus March 2003 featured technical article, by Richard L. Nailen, P.E. , "Low Voltage Busway: An Overview" Niederspannungs-schienenverteiler: eine Übersicht ... Le bus à basse tension: un aperçu ... El Bus de Bajo Votalje

To order backissues which contain the foreign language summaries and the full article, call 312-321-9440 or visit our online webstore. See also links to additional technical summaries, below.

For our international readers, summaries of the technical articles are provided in German, French and Spanish. (Summaries do not appear when the article is U.S.-specific.)

 

Advertising for the August Electrical Apparatus closes July 12 (Classified ads close July 16.)