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Tray & Cable Vs. Bus Duct

Distributing electric power in a factory or commercial building has to be secure, flexible and cost-effective. In some cases, running power cables on cable trays is the best solution. For other applications, a bus duct system designed for the particular location may offer the best setup. The optimum solution depends on the voltage, the current, the physical environment, the number of circuits and the power required.

Physical Protection
- In a rough environment, the protection of electrical installations from physical damage is a priority. Cables in cable trays are susceptible to damage from machinery striking the cables, and from dropped items. Cables may be run in conduits, or the cable tray may be covered to help prevent potential damage. With a bus duct, current-carrying bus bars are located in a grounded metal enclosure. The metal enclosure protects the bars, while the bars themselves are more resistant to damage.
Installation
- It is less expensive to run cables on cable trays than to design and install bus ductwork. When an installation requires a large number of cables due to high currents, it may be difficult to run the necessary trays due to space limitations. Cables with very high current capacities are inflexible and difficult to install. Cable terminations are sources of failure due to heat build-up and mechanical failure. For high current installations, bus duct is often the better and sometimes the only solution.
Short Circuit
- Short-circuit currents are lower in installations that include long cable runs. Cables have a higher impedance than corresponding lengths of bus bar and limit short-circuit currents. For high voltage and high power applications, short-circuit protection via adequately-rated circuit breakers may be a major cost factor. Since calculating short-circuit currents is an element in the initial design of power distribution installations, these calculations can affect the choice of cables over bus duct.
Cost
- Bus duct is cost-effective for transferring large quantities of power from one location through a rough environment to another central location. It is more expensive for transferring numerous small circuits in an installation. Cables on cable trays are a flexible, low cost solution for such multi-circuit distributions, even if they require additional measures for physical protection. The solution with the lowest cost and highest installation quality uses bus duct to get the power to a particular floor or factory location, then uses cable on trays for the final distribution.

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