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How to Choose a Bus Duct for High-Rise Buildings

By DHYN Engineering Team  ·  July 19, 2026

Quick answer: For a high-rise riser, you generally want a sandwich bus duct with copper conductors, IP54 or higher, fire barriers at each floor penetration, and plug-in tap-off boxes per floor. Size it from the total connected load with diversity factored in, and insist on IEC 61439-6 type test reports.

Risers are where bus ducts earn their keep, and also where specification mistakes get very expensive. Here is how we tell clients to spec one.

Start with the load, honestly

Add up the connected load per floor, apply a realistic diversity factor, and multiply by the number of floors. Residential towers usually land far below the sum of all breakers; oversizing the riser is just burning money in copper. A manufacturer who has done this before can sanity-check your diversity assumptions in a day.

Copper or aluminum

Copper carries more current in a smaller duct, and shaft space in a high-rise is expensive, so copper is the usual pick for risers. Aluminum works if the shaft has room and the budget is tight. Do not let anyone sell you aluminum for a cramped shaft without checking the dimensions twice.

Fire stopping is not optional

Every floor the duct passes through is a hole in your fire compartment. Specify fire barriers at each penetration, and if the local code requires it, a fire-resistant busway section for the escape-route supplies. This is the item inspectors check first, and the item cheapest suppliers quietly leave out.

Tap-off boxes per floor

Decide the rating and protection of each floor's box before production. Changing a box on site costs ten times what it costs in the factory. Think about metering now, not later; adding it afterwards on a live riser is miserable.

Protection rating and heat

IP54 is the floor for indoor shafts. Vertical runs also need a thought for heat rising with the duct itself and for spring hangers carrying the vertical weight. Ask the manufacturer how their hangers handle the full stack height; a 40-story riser is heavy.

The paperwork

IEC 61439-6 compliance, type test reports, and routine test certificates per section. Consultants ask for all three, and the consultants are right to ask. A supplier who hesitates on any of them is telling you something.