6061-T6 Aluminium Tubular Bus Pipe

What is 6061 tubular bus pipe?

A rigid bus is a self-supporting conductor carried on post insulators. Tubes are used rather than solid bars because, for alternating current, current crowds towards the surface (skin effect), so the hollow centre of a solid bar adds weight and cost without carrying much current. A tube also has a high section modulus for its weight, which is what lets it span between supports.

Three aluminium alloys dominate tubular bus. 6063-T6 is the most common outdoor bus alloy, with about 53 % IACS conductivity. 6101-T6 conducts slightly better and is often used indoors and in generating stations. 6061-T6 has the lowest conductivity of the three but the highest strength, with a minimum yield around 29 % above 6063-T6. Engineers choose it where mechanical loads, not ampacity, set the conductor size.

6061 vs 6063 vs 6101 bus conductor

For the same size, 6061 has about 20 % higher DC resistance than 6063, so it runs warmer at the same current. In practice the bus designer checks ampacity (temperature rise) and mechanical stress for each alloy and size, and picks the smallest conductor that satisfies both, following a method such as IEEE 605.

6061 bus pipe: Schedule 40 data

Dimensions follow standard pipe sizes (ANSI H35.2 / ASME B36.10). Weights use a density of 0.098 lb/in³; DC resistance is calculated at 20 °C for 43 % IACS. AC resistance at 60 Hz is only slightly higher for these sizes because the walls are thin compared with the skin depth.

6061 bus pipe: Schedule 80 data

Calculated values for guidance. Current ratings depend on ambient temperature, allowable temperature rise, sun, wind, emissivity and phase spacing, so they are not given here; size the bus to IEEE 605 or the applicable national practice.

Metric bus tubes, such as 80/72, 100/90, 120/110 and 150/136 mm (OD/ID), are used in many IEC markets and can be supplied in 6061-T6 to EN 755 tolerances.

Composition and mechanical properties

Design and installation points

• Thermal expansion: a 100 m bus run that warms by 40 °C grows by about 94 mm; use expansion fittings or flexible connectors
• Aeolian vibration: long, light tubes can vibrate in steady wind; damping cable or dampers inside the tube are common
• Welding: joints welded on site with ER4043 lose some T6 strength in the heat-affected zone, so welds are placed near supports where bending stress is low
• Connections: clean contact surfaces, use contact compound and bolted or compression fittings rated for aluminium; tin or silver plating reduces contact resistance at copper interfaces
• Drainage: drill drain holes at low points so condensation does not collect and freeze inside the tube
• Corona: at high voltage, the outside diameter and end caps must be large and smooth enough to keep surface gradient below corona onset

Supply forms, lengths and finishes

Related bus conductor pages

6061 aluminum bus pipe: frequently asked questions