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{{Short description|Low resistance electrical conductor for high current transmission and distribution}}
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[[Image:T_ratings_oldest_trick_in_the_book_002.png|thumb|right|5000 [[ampere]] [[copper]] and 4000 A [[aluminium]] bus ducts]]

In [[electric power distribution]], a '''bus duct''' (also called '''busway''') typically uses [[sheet metal]], welded metal<ref>{{Cite web |title=Isolated Phase Bus Duct |url=https://www.stacelectric.com/products/isolated-phase-bus-duct/ |access-date=2024-01-04 |website=Stace |language=en-US}}</ref> or cast resin to contain and isolate [[copper]] or [[aluminium]] [[busbar]]s for the purpose of conducting a substantial [[Electric current|current]] of electricity. It is an alternative means of conducting electricity to [[power cable]]s or cable bus.

Originally a '''busway''' consisted of bare [[copper]] [[Electrical conductor|conductor]]s supported on inorganic insulators, such as [[porcelain]], mounted within a non-ventilated steel housing.<ref name="The IEEE Standards Association 2013">{{cite web | title=IEEE 3001.5-2013 - IEEE Recommended Practice for the Application of Power Distribution Apparatus in Industrial and Commercial Power Systems | website=The IEEE Standards Association | date=2013-12-11 | url=https://standards.ieee.org/findstds/standard/3001.5-2013.html | access-date=2018-01-09}}</ref>

==History==
Busways were produced due to request of the automotive industry in Detroit in the late 1920s. Since that time, busways improved and became an integrated part of [[secondary network]] for industrial plants.<ref name="The IEEE Standards Association 2013"/>

==Construction==
<gallery>
T_ratings_oldest_trick_in_the_book_004.png|Section of [[aluminium]] bus duct with sandwiched bus bars
T_ratings_oldest_trick_in_the_book_005.png|Innards of bus duct showing [[plastic]] wrappings of sandwiched [[busbars]] and hollow plastic tube spacers.
T ratings oldest trick in the book 006.png|Individual [[busbar]] wrapping
File:Pre-wired steel strut.png| Bus duct, also called busway, is available with (3) finger-safe #8AWG copper wires in steel housing.
</gallery>
Some bus ducts are rectangular similar to [[cable tray]], but have thicker, [[cold-formed steel]] side rails and thinner [[sheet metal]] coverings. Others can be circular.<ref>{{Cite web |title=Isolated Phase Bus Duct |url=https://www.stacelectric.com/products/isolated-phase-bus-duct/ |access-date=2024-01-04 |website=Stace |language=en-US}}</ref> Busbars inside may be separated with distinct and even gaps between them, or “sandwiched” together.

Typically, individual busbars are wrapped or coated with a non-conducting, [[Covalent bond|covalent]] material, such as [[plastic]] or (in older systems) [[electrical tape]].

At the connection point, busbars flare out to enable connection to the next segment.

A plug-in bus duct system or busway can have disconnect switches and other devices mounted on it, for example, to distribute power along a long building. Many forms of busway allow plug-in devices such as switches and motor starters to be easily moved; this provides flexibility for changes on an assembly line, for example.<ref name=AEH11>Terrel Croft, Wilford Summers (ed)''American Electricians Handbook Eleventh Edition'', McGraw-Hill 1987, {{ISBN|0-07013932-6}}, pages 9-114 through 9-132</ref> In addition to powering floor fixtures, busways can provide power to plug-in light fixtures and even IoT devices.<ref>{{Cite web |title=Why busSTRUT|url=https://busstrut.com/why-busstrut/|access-date=2024-01-13 |website=busSTRUT|language=en-US}}</ref>

Feeder busway is used to interconnect equipment, such as between a transformer and a switchgear line up.  A variant type is a low-impedance busway, which is designed to have lower voltage drop by virtue of close spacing of bus bars, which reduces inductive reactance. 
 
A trolley busway provides power to equipment that must be frequently moved.  The busway is open at the bottom, and a movable collector assembly "trolley" is used to connect between the fixed bus bars in the busway and the cable connected to moving equipment.<ref name=AEH11/>
Bus ducts are building service [[Penetrant (mechanical, electrical, or structural)|penetrants]] that are required to be externally [[firestop]]ped where they penetrate fire separations required to have a [[fire-resistance rating]].

== See also ==
* [[Bus (computing)]]
* [[Busbar]]
* [[Isolated-phase bus]]
* [[Duct (flow)]]

== References ==
{{Reflist}}

==External links==
{{commonscat|Bus ducts}}
* [http://www.merriam-webster.com/dictionary/bus%20duct Merriam Webster Definition of Bus Duct]
* [https://www.youtube.com/watch?v=gvyfq-mY54o YouTube Bus Duct Installation]
* [https://www.youtube.com/watch?v=SAEyN8fw29E YouTube Bus Duct Construction and Installation]
* [http://ulstandards.ul.com/standard/?id=857 Underwriters Laboratories Standard UL857 abstract]
* [https://standards.ieee.org/findstds/standard/C37.23-2003.html IEEE C37.23 Standard For Metal Enclosed Bus]
* [https://standards.ieee.org/findstds/interps/C37.23-1987.html Interpretations for IEEE Std C37.23-1987 IEEE Guide for Metal-Enclosed Bus and Calculating Losses in Isolated-Phase Bus]
* [http://standards.ieee.org/develop/project/3004.7.html IEEE P3004.7 - Recommended Practice for the Protection of Power Cables and Busway Used in Industrial and Commercial Power Systems]
* [http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4158073&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D4158073 IEEE Busway Short Circuit Testing Procedures]
* [http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=7035409&newsearch=true&queryText=bus%20duct IEEE Mathematical model of high voltage sandwich bus duct]


[[Category:Electric power systems components]]
[[Category:Electrical wiring]]