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Busway Hangers: What Types Exist and How Far Apart Should They Go?

By DHYN Engineering Team  ·  September 16, 2026

Quick answer: Support a horizontal busway at least every 3 m (10 ft), with a hanger within about 600 mm of every joint, elbow and tap-off unit. Vertical risers stand on spring hangers at each floor, spaced up to about 5 m (16 ft) apart, so the spring absorbs both the weight and the thermal expansion. These are the numbers NEMA BU 1 and most manufacturers publish, and the manufacturer's instruction always overrides the rule of thumb. The failures we see are almost never bad busway; they are missing or wrongly chosen supports. (Answer time: September 16, 2026)

A 1600 A copper busway weighs somewhere between 25 and 35 kg per meter, depending on the housing. A 30-meter riser is a ton of copper hanging in a shaft, and every gram of it is carried by hardware that somebody selected in a hurry. Support design looks like a detail. It decides whether joints stay torqued, whether the duct stays straight, and whether the run survives its own thermal cycling. Here is how we tell customers to think about it.

The hanger types you will actually meet

For horizontal runs there are two clamp styles, and the difference matters. A flatwise hanger grips the duct lying flat, the orientation with the wider face horizontal; it is the natural choice under a ceiling. An edgewise hanger holds the duct on edge, which is how you fit a big feeder through a congested ceiling void alongside pipework. Same duct, different clamp, different clearance envelope. Where two or more runs travel together, a trapeze of channel on threaded rods carries them side by side and keeps the spacing the electrical designer assumed.

Vertical shafts use a different animal entirely. Spring hangers (also sold as riser supports) bolt to the floor or shaft wall at each level and carry the duct on calibrated springs. Plain rigid wall brackets still appear along the riser, but their job is only to keep the duct aligned and take lateral loads. If a rigid bracket ends up carrying weight, something above it has gone wrong.

Spacing rules that hold up in practice

The baseline most catalogs publish: horizontal runs supported at maximum 3 m (10 ft) intervals, vertical risers at up to 5 m (16 ft). Schneider's I-Line documentation, for instance, states exactly those two figures. But the spacing that actually fails installations is not the headline number, it is the exceptions around it:

Location	Rule of thumb	Why
Straight horizontal run	Every 3 m (10 ft) max	Limits sag and joint bending moment
At a joint	Hanger within ~600 mm either side	The joint is the weakest section; unsupported joints flex and loosen
Elbows, tees, offsets	Support on each leg, close to the fitting	Fittings weigh more and collect eccentric loads
Tap-off / plug-in units	Independent support for units above ~25 kg	A breaker box hanging off the duct twists the housing
Vertical riser	Spring hanger each floor, max 5 m apart	Carries weight while allowing expansion
Transformer / switchgear flange	Support the first section independently	Equipment connections must not carry duct weight

One sentence belongs in every specification: supports per the manufacturer's installation manual, not per habit. The bus duct installation guide covers where this fits in the overall sequence.

Why vertical risers need springs, not rigid rods

Copper expands about 16.5 µm per meter per kelvin; aluminum around 23. A 30 m riser cycling 40 K between cold mornings and full load grows roughly 20 to 28 mm. If the riser is clamped rigidly top and bottom, that growth has nowhere to go, so it goes into joint stress, bowed sections and eventually hot joints. Spring hangers compress and extend with the duct, keeping the supported weight roughly constant while the metal moves. Size the springs for the actual duct weight per floor, set them per the maker's chart at commissioning, and never let a rigid bracket below a spring hanger take load. Our article on vertical vs horizontal bus duct runs goes deeper into riser design, including the fire barriers at each floor.

Anchors, rods and the building above

Hangers attach to structure, not to whatever happens to be overhead. Threaded rod is typically M10 or 3/8 inch and up, sized against the run weight with a safety factor, and anchored into concrete slab or steel beam. Anchoring to metal deck, ceiling grid or another trade's trapeze is a classic site shortcut and a classic failure. In seismic zones the support layout is a calculated design, not a spacing rule: bracing intervals, rod stiffeners and connection details come from the seismic submittal, and skipping them voids exactly the certification the project was bought for.

The support mistakes we keep finding

Sagging mid-span sections because someone stretched 3 m into 5 m to save rods. Rigid all-thread drops on vertical risers, which turns thermal expansion into joint damage within a year or two. No hanger near a joint, so the joint carries a bending load it was never designed for and shows up hot on the first thermal scan. Cable tray or small pipe clipped to the busway hanger, adding load nobody calculated. Plug-in units left hanging off the duct with no independent support. And the quiet one: hangers installed but never re-checked after other trades adjusted their services around the duct. Most of these announce themselves in the first year as loose joints or distorted housings, which is why the annual maintenance checklist starts with a straightedge and a thermal camera. A busway's most common problems trace back to supports more often than to the busway itself.