In electric power distribution, a bus duct (also called busway) typically uses sheet metal, welded metal[1] or cast resin to contain and isolate copper or aluminium busbars for the purpose of conducting a substantial current of electricity. It is an alternative means of conducting electricity to power cables or cable bus.
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Originally a busway consisted of bare copper conductors supported on inorganic insulators, such as porcelain, mounted within a non-ventilated steel housing.[2]
Busways were produced due to request of the automotive industry in Detroit in the late s. Since that time, busways improved and became an integrated part of secondary network for industrial plants.[2]
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.[3] 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 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.[4] In addition to powering floor fixtures, busways can provide power to plug-in light fixtures and even IoT devices.[5]
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.[4] Bus ducts are building service penetrants that are required to be externally firestopped where they penetrate fire separations required to have a fire-resistance rating.
Busway, or Busduct, is a widely accepted method of distributing power since its first inception in ’s automotive industry, and is now used in a multitude of environments and sectors around the globe. Schneider Electric’s I-Line busway came to the market in the early ’s and Canalis busway followed in the early ’s.
What most don’t know is the wide variety of busway options available and the features and benefits they offer.
The first benefit most ask about is cost, and this is recognised through quick installation time, easy maintenance, and long-life span. Busway can be assembled in stages and energised as required, making installation planning much easier, and requiring less labour. Its compact size and 90-degree bends compared to cable means there is more space available for other services.
The second most considered benefit comes from what is called ‘de-centralised distribution’. Protection is no longer contained solely in the switchboard room but is distributed throughout the installation along the busway’s length. Among the obvious benefits are reduced switchboard footprint and protection closer to the loads.
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Other benefits may not be as immediately obvious, but are nevertheless important factors when considering busway options. These include better volt drop performance, lower heat rise therefore lower resistance, verified kA, IP and IK ratings, lower EMF emissions, and of course, a better environmental footprint recognised through performance efficiency and material impact.
Both Canalis and I-Line II aluminium busway have copper contact technology (also known as Bi-Metal), which means every connection point, bus to bus or plug-in unit connection, has silver plated copper contacts molecularly fused into the surface of the aluminium. This results in the low contact resistance performance of copper without the risk of delamination, making the aluminium product the go to in almost every case where cost and performance are considered.
Schneider Electric busways also benefits from its strong brand of current limiting circuit breakers installed inside the plug-in units – ComPact NS and ComPacT NSX MCCB’s and Acti9 MCB’s for final distribution. Performance of the busway Isc can also be enhanced significantly when protected by a current limiting device.
Peace of mind comes from the adaptability of the system as well as IEC-6 certification (ASTA Diamond and KEMA KEUR) of the busway and the plug-in units that connect to it. Compliance to AS/NZS-6 only requires environmental temperature consideration (de-rating for warmer states of AU), and adherence to local standards that apply. In the case of Australia this would be the AS.4: passive fire resistance level (FRL) standard, of which I-Line is thoroughly tested and assessed for both integral and internal earth for both copper and aluminium busway.
There are useful design tools available for busway, including catalogues full of information, a BIM busway plugin for Revit, volt drop calculators, spacing tools for I-Line, etc.
If you are looking for efficiencies in your installations distribution system, then consider busway.
Suitable for 1P or 3P lighting circuits including options for KNX or Dali, car park occupancy sensors or low power distribution (fused).
Most standardise on the KS range for this but is slightly more economical. Typical uses include underfloor power distribution or small workshop runs. Final distribution plug-in options only.
By far the most versatile offer in its amp range, with both sub and final distribution plug-in capability. Suitable for commercial and industrial environments its diversity spans from simple EV car charging to high density complex data center installs.
The backbone of any building, high power busway is used for transformer to switchboard, switchboard to switchboard, and main power distribution throughout the installation feeding local DB’s.
For harsh environments, typically used in infrastructure projects.
For more information on Schneider Electric’s full range of busway options, visit www.se.com/au/ or www.se.com/nz, or reach out to your local sales representative.
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