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Aluminum vs Copper Busway: Which Should You Choose?

By DHYN Engineering Team  ·  July 27, 2026

Quick answer: Copper conducts better and needs less space. Aluminum weighs about half as much for the same ampacity and costs far less, but you need roughly 1.6 times the cross section to carry the same current. Tight shafts and tight budgets pull in opposite directions: copper for cramped risers, aluminum for long horizontal runs where there is room. Both work fine if the joints are engineered properly.

This is the first real decision in any bus duct order, and it changes the price, the size, the weight and the installation crew's mood. Let me walk through the numbers the way we do when a customer asks us to quote both options.

The conductivity math

Copper is the reference point. On the IACS scale, annealed copper sits at 100 percent conductivity. Electrical grade aluminum comes in at about 61 percent. In resistivity terms, copper measures around 17.2 nΩ·m at 20 °C against roughly 28.2 for aluminum. Flip that around and you get the practical rule: an aluminum bar needs about 1.6 times the cross section to carry the same current at the same temperature rise.

Concretely, a copper bar of 100 × 10 mm (1000 mm²) matches up against something like 100 × 16 mm in aluminum. The duct grows, but not as dramatically as people fear, because the enclosure around it was never exactly skin tight anyway.

Size and weight pull in opposite directions

Copper is dense, 8.96 g/cm³. Aluminum is 2.70. Run the numbers on bars of equal conductance and the aluminum version weighs about half, despite the bigger cross section. So an aluminum bus duct comes out a size or two larger in each dimension, yet noticeably lighter per metre. Anyone who has humped 3-metre lengths of copper duct across a factory floor will tell you the crew notices. For long horizontal runs on steelwork, lighter is genuinely easier to hang and support.

What it costs

Copper trades at several times the price of aluminum per kilo, and the conductor is the single biggest material cost in a bus duct, often half or more of the total. Even after buying 60 percent more aluminum by cross section, the conductor material typically comes out 40 to 60 percent cheaper than the copper it replaces. On a large order that is real money. There is a second, quieter benefit: aluminum prices move less violently than copper. Anyone who quoted copper duct in a volatile month and watched the LME eat the margin knows what I mean.

Joints are where aluminum earns its bad reputation

Aluminum oxidizes fast, and aluminum oxide is an insulator. Left bare, a joint's contact resistance climbs over time, the joint runs hot, and the problem feeds itself. The fix is well established: tin or silver plating on the contact faces, done at the factory. The other issue is creep. Aluminum slowly deforms under sustained bolt pressure, so joints need spring (Belleville) washers and a specified torque, and some specs sensibly call for a re-torque check after the first year. Copper is simply more forgiving here, which is why old electricians trust it.

Thermal expansion deserves a mention too. Aluminum expands about 23 µm per metre per degree, copper about 17. On long runs with big temperature swings, the expansion fittings and joint design have to account for it. Any competent manufacturer does, but ask.

What the standards say

IEC 61439-6 does not care which metal you use. It cares about temperature rise limits, short-circuit withstand and dielectric performance, all verified by test. An aluminum bus duct that passes the same type tests is a legitimate product, not a cheap knockoff. On short-circuit duty, copper's mechanical strength helps against electrodynamic forces, but bracing and clamp design matter more than the metal itself.

Side by side

Property	Copper	Aluminum
Conductivity (% IACS)	100	~61
Resistivity at 20 °C (nΩ·m)	~17.2	~28.2
Cross section for same current	1.0×	~1.6×
Weight for same conductance	baseline	about half
Density (g/cm³)	8.96	2.70
Thermal expansion (µm/m·K)	~17	~23
Joint treatment	bare or tinned, forgiving	plating plus spring washers required
Conductor material cost	baseline	roughly 40–60% less
Duct size for same rating	smaller	one to two sizes up

How we advise customers

Cramped high-rise riser where shaft space costs money? Copper, almost every time. Long horizontal feeder across a factory with generous headroom and a tight budget? Aluminum, and enjoy the saving. Coastal or corrosive site? Tinned copper, or at minimum confirm the plating spec in writing. And whatever you do, never bolt copper directly to aluminum at an interface without a proper bimetallic transition or plated joint. Galvanic corrosion will find that connection, usually at 2 a.m. on a holiday weekend.

If you are genuinely torn, ask for both quotes. Any manufacturer with both lines running, us included, can price copper and aluminum versions of the same run in a day. The numbers usually make the decision for you.