Bus duct types
A bus duct or busway can conduct currents up to 5000 A in copper and 4000 A in aluminum within an insulated metal enclosure, offering a compact alternative to conventional cables. The main types differ by their connection method and application: feeder, plug-in, trolley, and low impedance.
Main types of bus ducts
Section titled “Main types of bus ducts”| Type | Typical rated current | Typical rated voltage | Conductor material | Distinctive feature |
|---|---|---|---|---|
| Feeder busway | 4000 A – 5000 A | 600 V / 1000 V (low voltage), up to 15 kV (medium voltage) | Copper or aluminum | Fixed connection between transformers and distribution panels; no intermediate insertion points. |
| Plug-in busway | 100 A – 5000 A | 600 V / 1000 V | Copper or aluminum | Taps with pluggable switches or starters along the busway, facilitating load redistribution. |
| Trolley busway | 60 A – 800 A | 600 V | Copper or aluminum | Open bottom for a mobile pick-up that supplies moving equipment, such as cranes or assembly lines. |
| Low impedance busway | 1600 A – 5000 A | 600 V / 1000 V | Copper | Bars very close together to reduce inductive reactance and voltage drop; suitable for long runs. |
Construction features
Section titled “Construction features”Bars are manufactured with a controlled spacing of 3 mm to 6 mm / 0.12 in to 0.24 in between phases in a sandwich design, individually wrapped with insulating plastic material and housed in a galvanized steel enclosure that guarantees structural rigidity. The joining ends incorporate widened busbars that facilitate mechanical and electrical coupling using high-strength bolts.
Advantages over conventional wiring
Section titled “Advantages over conventional wiring”Space reduction in cable trays of up to 50% compared to equivalent configurations with multiple single-conductor cables. The stacked arrangement of bars minimizes mutual inductance and, in the case of low impedance busways, can reduce inductive reactance by up to 40% compared to standard busways of similar cross-section. The modular construction allows adding or relocating load points in plug-in busways without interrupting the main supply.
Typical applications
Section titled “Typical applications”- Automotive industry: the origin of busway is in Detroit at the end of the 1920s, where flexible distribution was required for changing assembly lines.
- Data centers and hospitals: low impedance busways maintain stable voltage levels on long runs (> 100 m / 328 ft) with high density of critical loads.
- Steel plants and shipyards: trolley busways supply overhead cranes and mobile machinery with currents up to 800 A.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum current a copper bus duct can carry?
Section titled “What is the maximum current a copper bus duct can carry?”A copper bus duct can reach 5000 A, enough to supply several low voltage distribution panels from a single transformer. For higher currents, parallel configurations or isolated phase bus ducts are used.
How much voltage drop is avoided with a low impedance bus duct?
Section titled “How much voltage drop is avoided with a low impedance bus duct?”By reducing inductive reactance by approximately 40% compared to a standard bus duct, the voltage drop per unit length can be limited to less than 2% for a run of 100 m / 328 ft operating at full load.
What is the maximum length of a straight section of bus duct without support?
Section titled “What is the maximum length of a straight section of bus duct without support?”Standard sections are manufactured in modules of 3 m / 10 ft length. These modules are joined by bolted flanges and, once installed, are supported at intervals of 1.5 m to 2.4 m / 5 ft to 8 ft depending on the bus duct weight and seismic loads.
What is the main advantage of plug-in bus duct over a fixed wiring system?
Section titled “What is the main advantage of plug-in bus duct over a fixed wiring system?”It allows tapping currents from 100 A to 5000 A at any point along the bus duct using pluggable connection boxes, which facilitates reconfiguration of production areas without the need to run new cables every time a layout is changed.
In what voltage range do industrial bus ducts operate?
Section titled “In what voltage range do industrial bus ducts operate?”Most low voltage bus ducts operate at 600 V / 1000 V. There are medium voltage versions that reach 15 kV, used in overhead distributions or in connections between generators and park transformers.
How much does an aluminum bus duct weigh approximately compared to a copper one?
Section titled “How much does an aluminum bus duct weigh approximately compared to a copper one?”For the same capacity of 4000 A, the aluminum bus duct weighs about 30% less than a copper one, although it requires a larger cross-section. This lightness reduces support requirements and facilitates handling on site.