What is a Busway? Definition and Classification of Busway Systems

A busway, also known as a busbar trunking system, is a high-efficiency, safe, and energy-saving power distribution device widely used in buildings and industrial sectors. It consists of copper or aluminum conductors supported by non-combustible insulating materials and enclosed in a metal casing. Busways have become essential in electrical distribution systems in high-rise buildings, factories, and other facilities. Compared to traditional conduit wiring systems, busways offer greater flexibility, ease of modification, and enhanced aesthetics in construction projects.

This article will provide a detailed overview of the types of busways and guidelines for busway selection, offering valuable insights for electrical designers.

1. Definition and Classification of Busways

1.1 What is a Busway?

In low-voltage electrical distribution design, a busway is a critical component of the distribution trunk system. According to the Chinese national standard GB7251.6-2015 “Low-voltage switchgear and controlgear assemblies—Part 6: Busbar trunking systems (Busways),” a busway is defined as:

Busway: An enclosed assembly formed by a conductor system, used for power distribution and control for all types of loads. It is suitable for industrial, commercial, and similar applications. The conductor system is enclosed in a duct, trunking, or similar casing, with busbars insulated and supported by insulating materials.

1.2 Types of Busways

Busways can be classified based on their structure or usage environment:

By Structure:
- Air Insulated Busway: The busbars are insulated by air and protected by a metal casing. Due to its reliance on air convection for cooling, this type of busway is less efficient at heat dissipation and is thus more suitable for low-current applications.

- Compact Insulated Busway: The busbars are wrapped with solid insulation materials and tightly enclosed in a metal casing. Compact busways are more efficient at conducting heat and are ideal for high-current applications.

By Usage Environment:
- Standard Busway: Non-fire-resistant and non-flame-retardant busway, used in ordinary electrical loads. In the event of a short circuit, it can pose a fire risk as the flames may spread through connected busways.

- Flame-Retardant Busway: The flame does not spread to other sections of the busway during a fire, as both the metal casing and insulating materials are flame-retardant.
- Fire-Resistant Busway: Maintains circuit integrity for a specified period under fire conditions. Fire-resistant busways are insulated with fireproof or flame-retardant materials and must pass the type tests defined in JB/T10327-2011 “Fire-Resistant Busbar Trunking Systems” to ensure their performance in fire scenarios.

2. Key Considerations for Busway Selection

When selecting a busway, several factors should be considered to ensure optimal performance:

Installation Location:
- Indoor Environments: For specialized indoor environments, such as high-capacity substations, busways with a protection rating of IP30 can be used to enhance heat dissipation. For standard indoor applications, such as electrical shafts and distribution rooms, busways with at least IP40 protection should be chosen for safety.
- Humid or Splash-Prone Areas: In environments with potential exposure to water, a busway with at least IP54 protection is necessary to ensure reliable operation during splashes.
- Outdoor and Corrosive Environments: For areas exposed to water, sea spray, or corrosive conditions, resin-insulated busways or reinforced casing busways should be selected to ensure durability and protection.
Current Rating: The rated current (IN) of the busway should be selected based on the operational current (IB) and the technical specifications of the product, including heat dissipation and price considerations. Aluminum alloy low-impedance compact busways with excellent heat dissipation and low energy consumption are currently popular in the market. The current rating must conform to the manufacturer’s standard busway product specifications.

By considering these factors, you can choose the most suitable busway for your specific needs, ensuring both safety and efficiency in your electrical distribution system.

What is a Busway? Definition and Classification of Busway Systems