What Is a Bus Duct (Busway)? Types, Benefits and Applications
July 19, 2026 | DHYN ELEC GROUP CO.,LTD.
If you've ever looked inside the electrical shaft of a tall building, you've probably seen one: a flat metal trunk running floor to floor, feeding power to every level. That's a bus duct. Electricians also call it a busway or a busbar trunking system. Whatever the name, the idea is the same. Instead of pulling dozens of heavy cables through trays and conduits, you run one prefabricated assembly with copper or aluminum busbars sealed inside a metal housing.
How it works
The busbars inside carry current from the transformer or main switchboard along the route. Wherever you need to draw power, you clamp or plug a tap-off box onto the duct. No shutdown, no new cable run from the distribution board. That plug-and-play structure is the real difference from cable wiring, and it's the reason contractors keep choosing it for big jobs.
The four types you'll run into
Sandwich (compact) bus duct is the one you'll see most often indoors. The bars are packed tight with epoxy film insulation, so the duct stays small and sheds heat well. Ratings go up to 6300A.
Air-insulated bus duct leaves gaps of air between the bars. It's a bit bulkier but easy to maintain, and a lot of older industrial plants still run it.
Resin cast busway seals the conductors completely in epoxy. With IP68 protection it goes where other types can't: outdoors, tunnels, ships, anywhere wet or corrosive.
Lighting busway is the small one, built for lighting circuits and light loads in supermarkets, workshops and parking garages.
Why contractors pick it over cable
Ask anyone who has installed both, and the first thing they'll mention is speed. Prefab sections bolt together. There's no pulling, no dressing, no terminating dozens of cable ends. On a busy site that alone can cut weeks off the schedule.
Then there's the day-two problem. Buildings change. Tenants move, machines get relocated, and with cable every change means a new pull from the panel. With a busway you plug in a tap-off box at the nearest point and you're done.
The duct is also far more compact than the cable tray it replaces, which matters when shaft space costs money. Flat busbars keep impedance and voltage drop low on long runs, the metal enclosure handles fault currents better than a bundle of cables ever will, and if the layout changes completely, you can unbolt the sections and use them again. Try that with cable.
Where it gets used
Anywhere large currents have to move reliably: high-rise residential and office towers, malls, hospitals, data centers, factories, airports. In a tall building the duct usually runs vertically through the electrical shaft, with tap-off units feeding each floor.
Picking the right one
Start with rated current and conductor material. Copper carries more in less space; aluminum costs less. Then look at the environment: IP54 is fine for a dry indoor shaft, but outdoors or in a wash-down area you'll want IP65 or a cast resin unit at IP68. Check fire performance requirements and make sure the product is built and tested to IEC 61439-6. A decent manufacturer will walk you through all of this if you send them your single-line diagram.
DHYN ELEC GROUP CO.,LTD. builds sandwich bus ducts, resin cast busways and custom busbar trunking systems for projects around the world. Talk to us about your project and we'll come back with a design and a quote.