Busbar Trunking Systems: Busway, Rigid Bar and Cable Compared

A busbar trunking system, usually called busway, is a factory-built run of copper or aluminium conductors inside a metal housing, supplied in sections with tap-off points at intervals along its length. Instead of pulling several parallel cable sets through a building and terminating each one, you bolt sections of trunking together and plug loads into the outlets provided. It is a distribution system rather than a component, and that is the distinction that decides most specifications.

The confusion around the term is worth clearing first. A busbar is a conductor — a bar of copper or aluminium. Busbar trunking is the finished product built around those conductors: housing, insulation, joints, expansion provisions, fire barriers and tap-off outlets. The same bar material appears in both, in completely different roles.

How a busway run is built

Two constructions dominate. In a sandwich system the conductors are laid flat against each other with thin insulation between them, so the whole assembly is compact and the conductors are close together. In an air-insulated system the bars are held apart on supports inside a larger housing, with air as the main dielectric.

The sandwich form gives a smaller cross-section and lower reactance for the same current, which matters on long runs and on systems with high fault levels. The air-insulated form runs cooler at the joints and is easier to inspect, which matters where maintenance access is limited. Neither is universally better; the choice follows the run length, the ambient temperature and how the client expects to maintain it.

Every run needs the same supporting decisions regardless of construction: conductor material and cross-section, the short-circuit withstand the housing must survive, the degree of protection against dust and water, fire barrier sections where the run crosses a compartment wall, and expansion joints where the building moves.

Busway, cable or rigid bar?

This is the decision buyers actually face, and it is usually framed as a cost question when it is really a question about how often the layout will change.

The pattern is consistent. Busway wins where current is high and tap-offs are frequent, because it removes both the parallel cable sets and the repeated termination labour. Cable wins where the run is short, the current is modest, or the route has more bends than the trunking range can accommodate. Rigid bar is not really a competitor to either — it is what you use inside the panel that feeds them.

Where busway stops making sense

• Low current. Below a few hundred amps the housing and joint cost dominates, and a cable tray is simply cheaper.
• Short or complex routes. Every change of direction uses a factory fitting. A route with many bends and level changes accumulates fittings that cost more than the straight sections.
• Corrosive or wet environments. The housing and joints need a protection rating that suits the location, and that rating has a price. In aggressive atmospheres a sealed enclosure is often the better answer.
• One-off layouts that will never change. The reconfiguration advantage is the main justification for the premium. If nothing will ever move, you are paying for an option you will not use.

Tap-off outlets and busway plugs

The tap-off is where busway earns its reputation. Outlets are provided at intervals along each section — commonly on one or both sides — and a plug-in box with its own protective device is fitted wherever a load is required. Outlets not in use stay covered.

Two numbers decide whether the system works in practice. The first is outlet spacing: too wide and every load needs a separate run of cable from the nearest plug, which defeats the purpose. The second is the rating of each tap-off against the protective device you intend to fit, because the plug-in box must be able to carry and protect that circuit without exceeding the trunking rating.

Ask for the outlet schedule with the quotation, not after. It is the single document that shows whether the layout you have drawn can actually be built from standard sections.

What YOMIN supplies

To be precise about scope: YOMIN manufactures the conductor side of this picture — rigid copper and aluminium busbar in insulated and bare forms for fixed installations, battery packs and switchgear, laminated busbar for compact high-current links, flexible busbar where vibration or tolerance take-up is needed, and aluminium busbar with EL-600 insulators for support structures. We do not supply the busway housing and tap-off system itself, and we would rather say so than quote into a specification we cannot fill.

A typical rigid bar order is specified by material (copper or aluminium), cross-section, whether it is insulated, the drilling pattern for the joints, and the quantity. The copper bus flat range covers copper and aluminium in rigid insulated form with a minimum order of 50 pieces, manufactured in Zhejiang, China.

What to send with a busbar enquiry

• Material and cross-section — copper or aluminium, and the bar dimensions.
• Insulation — bare, epoxy-coated, heat-shrink sleeved or laminated. State the rated voltage the insulation must hold.
• Joint detail — hole diameter and spacing, and whether the joint faces are tinned.
• Quantity and length — per piece and total, with the cut length tolerance that matters to your assembly.
• Application — switchgear, battery pack or fixed distribution, because that sets the mechanical support expectations.

Send those five items and a quotation is usually a matter of days rather than a design cycle. Send a drawing instead and you will get questions back about all five.

Frequently asked questions

What is the difference between a busbar and busbar trunking?

A busbar is the conductor itself, a bar of copper or aluminium used to carry current inside equipment. Busbar trunking, also called busway, is a finished distribution system built from those conductors inside a metal housing, supplied in sections with tap-off points along its length.

When is busway cheaper than cable?

Busway rarely wins at low current or on a short run. It wins where current is high, where tap-offs are frequent, or where the layout will change: the labour of pulling and terminating several parallel cable sets usually outweighs the material cost difference at that point.

Can tap-off points be added to busway after installation?

On most systems yes, that is the main operational advantage. Tap-off outlets are provided at intervals along the run, and a plug-in box is fitted where a load is needed. The outlets that were not ordered as plugs remain covered until used.