Bus duct and power cable are two common ways to distribute high-current electricity from a source to a load. Bus duct uses prefabricated enclosed conductors, while cable uses flexible insulated conductors pulled through supports or conduit. This guide compares the two options and explains when each is the better choice.
What Is Bus Duct?
Bus duct, also called busway, is a factory-assembled system of rigid conductors enclosed in a metal housing, with plug-in points for tap-offs. It is designed for currents typically above 400 A and provides a modular, factory-tested alternative to power cable for high-current feeders.
What Is Power Cable?
Power cable is a flexible, insulated conductor used to transmit electrical power. For high-current applications, multiple single-core cables are often paralleled (two or three per phase) and routed on cable ladders, in trays, or through conduit. Cable is the traditional solution for almost any current level.
Bus Duct vs Cable: Main Comparison
| Factor | Bus Duct | Power Cable |
|---|---|---|
| Current range | 400 A – 6300 A | Any (multiple cables in parallel) |
| Installation | Fast, modular | Slower, labor-intensive |
| Footprint | Compact | Larger for high current |
| Heat dissipation | Better (open design) | Limited by bundling |
| Tap-offs | Easy, any position | Fixed junction boxes |
| Expansion | Simple, add sections | Difficult, re-pull |
| Initial cost (high current) | Often lower | Often higher |
| Maintenance | Periodic re-torque | Visual inspection |
| Fire resistance | Optional (fire-rated busway) | Available (fire-rated cable) |
When to Choose Bus Duct
Bus duct is typically the better choice in the following situations:
- High current, typically 800 A to 6300 A.
- Long horizontal or vertical runs, especially in high-rise risers.
- Frequent or planned future expansion with new tap-offs.
- Limited installation space, such as tight ceiling cavities or riser shafts.
- Projects where installation speed is critical, since bus duct modules are quickly bolted together.
- Buildings where the load may grow over time, because adding a tap-off is much easier than re-pulling cable.
When to Choose Power Cable
Power cable remains the right choice in many situations:
- Low to medium current, typically below 800 A.
- Short runs where the labor cost of pulling cable is low.
- Highly curved or twisted routing where rigid bus duct is impractical.
- Underground distribution, where cable is more easily buried than bus duct.
- Hazardous areas requiring certified cable glands, where bus duct may not be available.
- Existing installations where adding bus duct would be disruptive.
Cost Comparison
Initial cost depends on the current level, run length, and local labor rates. As a general rule:
- For currents below 400 A, cable is usually cheaper.
- For currents between 400 A and 800 A, the two options are similar in cost.
- For currents above 800 A, bus duct becomes increasingly cost-effective as the current rises.
Total cost of ownership should also include installation labor, maintenance, and the cost of future expansion. Bus duct often wins on lifecycle cost for high-current applications.
Installation Comparison
Bus duct is supplied as factory-built straight sections, elbows, tees, and tap-off units. The pieces are bolted together on site, requiring only basic tools and trained workers. A typical bus duct run can be installed in a fraction of the time of a comparable cable run.
Power cable requires cable drums, pulling equipment, supports, terminations, and jointing. Installation is more labor-intensive and weather-sensitive. The result is more variable and depends heavily on the skill of the installation crew.
Heat Dissipation and Voltage Drop
Bus duct uses open or ventilated housings that allow heat to dissipate efficiently, supporting higher current density at lower temperature rise. Cable runs, especially when multiple cables are bundled together, can suffer from mutual heating and reduced current-carrying capacity.
Voltage drop in bus duct is generally lower than in cable for the same current and length, because of the larger cross-section and shorter current path. This can be a deciding factor for long runs in high-rise or large plant installations.
Maintenance and Reliability
Bus duct requires periodic joint re-torqueing (typically once a year for the first year, then every two to three years) and visual inspection of tap-off units. Power cable requires visual inspection of terminations, supports, and insulation condition.
Both systems are reliable when properly installed and maintained. Bus duct failure is often related to loose joints, while cable failure is often related to insulation aging or termination problems.
How to Choose
Use this short checklist to decide between bus duct and cable:
- What is the design current? Above 800 A usually favors bus duct.
- What is the run length? Long runs favor bus duct for voltage drop and installation speed.
- Is the route complex? Complex routing favors cable.
- Is future expansion expected? Expansion favors bus duct.
- What is the available space? Tight spaces favor bus duct.
- What is the local labor cost? High labor cost favors bus duct.
- What does the local code or consultant recommend? Always follow local practice and standards.
Frequently Asked Questions
Can bus duct replace cable entirely?
For high-current feeders, yes. For branch circuits and final distribution, cable remains the standard. Most installations use a combination: bus duct for the main feeder and cable for branches.
Is bus duct more expensive than cable?
For low currents, yes. For currents above 800 A, bus duct is often cheaper in initial cost and significantly cheaper in installed cost. Lifecycle cost usually favors bus duct for high current.
What is the typical lifespan of bus duct vs cable?
Both can last 25 to 30 years or more with proper installation and maintenance. Bus duct benefits from factory-controlled quality; cable lifespan depends heavily on installation quality and environmental conditions.
Can I mix bus duct and cable in the same installation?
Yes. Many installations use bus duct for the main transformer-to-switchboard feeder and cable for all other runs. The transition is made at the switchboard or distribution panel.
What is the best choice for a data center?
Data centers typically use bus duct for the main UPS-to-room feeders and tap-off units for each row of server racks. This gives fast installation, easy expansion, and good heat dissipation.
Are there applications where cable is mandatory?
Yes. Underground feeders, hazardous areas, and highly curved routes typically require cable because bus duct is not available in suitable form. Mobile equipment and portable tools also use cable.
Source Bus Duct and Cable Systems from BANGE Electric
BANGE Electric provides integrated electrical distribution and cable system solutions, including bus duct (air-insulated, compact, fire-resistant, and smart) and complementary cable tray systems. We support specification customization, consistent quality control, export packaging, and reliable international supply.
To receive a quotation, send us your current level, run length, environment, and destination port.