Busways are efficient, safe, and energy-saving power transmission devices widely used in various buildings and industrial fields. Busways can be classified based on different criteria, such as structure, purpose, and conductor material. Typically made of copper or aluminum conductors insulated with non-flammable materials and installed in metal casings, busways have become an essential wiring method in high-rise buildings, factories, and power systems. Traditional conduit wiring presents significant challenges during installation and modifications, making it nearly impossible to simplify distribution changes. In contrast, busways allow for easier adjustments and can enhance building aesthetics. Below is a detailed introduction to busway classification and selection, intended as a reference for electrical designers.

01 Definition and Classification of Busways

1. Definition of Busways

In building electrical low-voltage distribution design, busways are a crucial part of low-voltage distribution trunk systems. According to the national standard GB7251.6-2015, “Low-voltage switchgear and controlgear assemblies – Part 6: Busbar trunking systems (busways),” busways are defined as enclosed conductor systems that distribute and control electrical energy for all types of loads. Suitable for industrial, commercial, and similar applications, busways consist of conductors housed in channels or similar enclosures, with insulation materials providing spacing and support.

2. Classification of Busways

Busways are primarily classified into two main types based on structure: air-type and compact-type.

Air-Type Busways: Insulation is provided by air between the busbars, with a metal casing enclosing the busbars and their insulators as a unit. Air-type busways rely on air convection for heat dissipation, making them suitable for smaller current specifications due to limited cooling effectiveness.

Compact-Type Busways: Each busbar is wrapped in solid insulation material, packed tightly together, and then protected with a metal casing. Compact-type busways utilize conductive heat dissipation, which significantly enhances cooling performance compared to air-insulated busways, making them ideal for high-current applications.

Busways are also classified by usage environment into three main categories: standard busways, flame-retardant busways, and fire-resistant busways.

Standard Busways: Designed for general load distribution, these busways are neither flame-retardant nor fire-resistant. They can pose a fire hazard if a short circuit occurs, as the fire may spread through connected busways.

Flame-Retardant Busways: In case of fire, the flame does not spread along the busway. Both the metal casing and insulation materials must be flame-retardant.

Fire-Resistant Busways: Designed to maintain circuit integrity for a specified time under fire conditions. Fire-resistant busways generally use non-combustible insulation materials, though some use flame-retardant materials. They must pass type testing per the national standard JB/T10327-2011 to verify fire resistance and other electrical performance criteria, ensuring reliable power supply under fire conditions.

Fire-resistant busways can be further classified by insulation type into air-insulated and compact-insulated fire-resistant busways:

Air-Insulated Fire-Resistant Busways: Utilize air as the insulation medium with fire-resistant properties.

Compact-Insulated Fire-Resistant Busways: Employ heat-resistant insulation materials packed tightly together with fire-resistant properties.

02 Selection Criteria for Busways

When selecting a busway, several key factors must be considered:

Installation Environment: First, assess the casing’s protection level, followed by the impact of building structure on the busway's shape, mounting brackets, and span requirements.

For indoor specialized workplaces, such as large-capacity substations, an IP30 busway may be used to enhance cooling performance.

For general indoor applications, such as vertical shafts and distribution rooms, IP40 busways are recommended to ensure safety.

In damp indoor environments or locations with splashing water, an IP54 or higher rating is needed to ensure normal operation despite water exposure.

For outdoor or specialized environments (e.g., splash-proof, seawater-resistant, or corrosive settings), resin-insulated busways are preferred.

Current Rating: When selecting the rated current (IN) for the busway, consider the technical performance, cooling effectiveness, and cost. Currently, low-impedance, compact-insulated busways with aluminum alloy casings are popular due to their excellent cooling performance and low energy consumption. The rated current should match the required working current (IB) based on the manufacturer’s standard current levels.