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Busway vs Bus Duct vs Busbar: What Is the Difference?

By DHYN Engineering Team  ·  September 15, 2026

Quick answer: A busbar is the metal conductor. A bus duct encloses busbars in a protective metal housing. A busway is the complete prefabricated system: sections, joints, elbows, end feeds and tap-off units. Many buyers use "bus duct" and "busway" for the same product family; a busbar is only the conductor inside.

These three words show up together on drawings, quotations and site meetings, often as if they mean the same thing. They do not. The difference matters when you compare prices, write a specification, or decide whether a future production line can be connected without shutting down the whole floor.

What is a busbar?

A busbar is the current-carrying metal bar, usually copper or aluminum. It sits inside switchgear, distribution boards, transformers and busway sections. Its job is simple: collect power from one point and distribute it to several circuits with low resistance.

Copper carries more current for the same cross-section and handles joint stress well. Aluminum is lighter and cheaper, but it needs a larger section for the same ampacity. If you are comparing conductors, our guide to aluminum vs copper busbars covers the real trade-offs. At the joint, plating matters too; tinned or silver-plated copper keeps contact resistance stable over time.

A busbar by itself is not a complete distribution system. It has no enclosure, no joint kit, no defined ingress protection rating, and no safe way to add a branch circuit unless the surrounding equipment was designed for it. Think of it as the working metal inside the system, not the system itself.

What is a bus duct?

A bus duct is a group of busbars mounted inside a metal enclosure. The enclosure protects people from live parts and protects the conductors from dust, moisture and accidental impact. Traditional bus duct was often air-insulated: the bars sat on insulators with clearance between phases, and the enclosure was built around a fixed route.

That older meaning still appears in power plants and heavy industry. You may see non-segregated phase bus duct between a transformer and switchgear, segregated phase duct where metal barriers separate phases, or isolated phase bus on large generators. These are engineered feeders for high current, point-to-point power transfer. They are strong, but they are not designed for frequent branch connections along the run.

In everyday low-voltage purchasing, "bus duct" is also used as the general product name for what many manufacturers now call busway. That is why the word causes confusion. The enclosure alone does not make the product modular; the design of the joints, tap-off points and accessories does.

What is a busway?

A busway is a factory-built electrical distribution system made from enclosed busbar sections. IEC 61439-6 uses the term "busbar trunking system." UL 857 and NEMA BU 1 use "busway" in North America. In practice, the product includes straight lengths, elbows, tees, joints, end feed units, supports and plug-in tap-off boxes.

Modern low-voltage busway usually comes in two construction styles. A sandwich busway wraps each conductor in insulation and presses the bars closely together inside the housing. This keeps the section compact and reduces impedance. A cast resin busway seals the conductors in epoxy resin, which is useful for outdoor, wet or corrosive sites; we compared both in cast resin busway vs sandwich busway.

The feature that changes daily operation is the tap-off point. A plug-in busway lets you connect a breaker box or fused switch along the run. A feeder busway moves power from one end to the other without outlets. Most buildings use both types, which we explain in feeder busway vs plug-in busway.

Busway vs bus duct vs busbar: side-by-side

Item	Busbar	Bus duct	Busway
What it is	Bare or plated conductor	Conductors inside a metal enclosure	Complete prefabricated distribution system
Main job	Carry and distribute current inside equipment	Move bulk power along a protected route	Distribute power with factory-built sections and branches
Typical insulation	Air, heat shrink or equipment insulation system	Air spacing or solid insulation	Epoxy coating, polyester film or cast resin
Branch power	Only inside the host equipment	Usually fixed, point-to-point	Plug-in tap-off units along the run
Flexibility	Low	Low to medium	High; sections and tap-offs can be relocated
Typical location	Switchgear, panelboards, battery systems	Transformer to switchgear, generator feeders, heavy industry	Risers, factories, data centers, commercial buildings
Relevant standards	IEC 61439-1 as part of an assembly	Project specification; IEC 61439-6 when it is a busbar trunking system	IEC 61439-6, UL 857, NEMA BU 1

Which one should you specify?

Inside switchgear or a panel

Use busbar. It is part of the equipment design, and the cabinet provides the enclosure, clearances and protection. This is not the place to improvise a field-built duct.

Between a transformer and switchboard

Use a feeder bus duct or feeder busway. The route is fixed, the current is high, and the short-circuit rating matters more than frequent outlets. Check the available fault current before comparing prices. Our article on bus duct short-circuit ratings explains Icw and Ipk in plain terms.

Around a building or production floor

Use plug-in busway where loads will move or grow. The first installation may cost more than cable tray, but adding a machine later takes a tap-off box instead of a new conduit run. In a data center, metered tap-offs also make branch-circuit monitoring much easier.

Outdoors or in harsh areas

Do not rely on the words "bus duct" or "busway" to tell you the protection level. Check the IP rating and the joint design. IP54 may suit a dry indoor riser. Outdoor runs, tunnels and chemical plants often need IP65 or a resin-cast design; IP54 vs IP65 vs IP68 busway gives the rating differences.

What buyers should check before comparing quotes

Two suppliers can both offer a 1600 A "bus duct" and quote very different products. Ask for these items before you compare the bottom line:

• Rated current after ambient temperature and mounting-position derating, not just the catalog number.
• Rated short-time withstand current and duration, such as 50 kA for 1 second, plus peak withstand current.
• Conductor material, plating and temperature rise test data under IEC 61439-6 or the project standard.
• Housing material, IP rating, fire barrier options and whether tap-off units include breakers, meters or communication modules.
• Installation scope: supports, joint torque, expansion fittings, firestopping and commissioning tests.

If the run is long, include voltage drop in the comparison. A cheaper section can lose more energy every hour it operates. We walk through the calculation in bus duct voltage drop calculation.

Common mistakes with these terms

The first mistake is writing "busbar" on a purchase requisition when the project actually needs a complete busway system. The second is treating all enclosed bus products as equal, even though one may be air-insulated feeder duct and another may be compact plug-in busway. The third is comparing material price only. Factory-built busway often wins on labor because sections arrive measured, drilled and ready to bolt together.

We also see specifications copied between projects without checking the environment. A dry office riser and a coastal wastewater plant should not receive the same housing finish or IP rating. The name on the quote tells you less than the test data behind it.

FAQs

Is a bus duct the same as a busway?

In many low-voltage catalogs, yes. People use both names for an enclosed busbar trunking system. Strictly speaking, busway describes the complete modular system, while bus duct can also mean older fixed, air-insulated feeders. Check the drawings and the standard instead of relying on the name.

Is busbar trunking a busway?

Yes. "Busbar trunking system" is the IEC term used in IEC 61439-6. "Busway" is common in North American standards and project documents. Both refer to factory-built enclosed sections with joints and accessories.

Can a busbar be used outside an enclosure?

Only where the equipment design and electrical code allow it. A bare busbar needs clearance, guarding and a controlled environment. For distribution through a building, use an enclosed bus duct or busway.

Which is better: busway or cable?

For large currents, long runs and changing loads, busway is usually easier to install and expand. For small branch circuits, cable is still the practical choice. Our bus duct vs cable comparison goes through cost, voltage drop and installation time.

Bottom line

The busbar carries the current. The bus duct protects it in an enclosure. The busway turns those parts into a modular distribution system. Once those roles are clear, the selection becomes easier: fixed feeder or flexible distribution, indoor or outdoor, sandwich or resin, and what fault rating the system must survive.

If you are comparing options for a real project, send us the single-line diagram, route length, ambient conditions and load list. We can size the run and tell you whether feeder busway, plug-in busway or a resin-cast electrical busduct system fits the job better.