6063-T6 tubular bus pipe is seamless aluminium pipe used as a rigid conductor in substations, switchyards and generator connections. It combines about 53 % IACS conductivity with enough strength to span between insulators, and its round shape keeps corona low at high voltage. This guide covers sizes with calculated weights and resistance, the standards that apply, how 6063 compares with 6101 and 6061, and the design points engineers check.
In an air-insulated substation, rigid bus connects transformers, breakers, disconnectors and line bays. Rigid tubular bus replaces stranded conductors where spans are short to medium, where clearances must be held precisely, and where low maintenance and a tidy layout matter.
A tube is efficient for this job. Alternating current crowds towards the outer surface of a conductor (skin effect), so the metal at the centre of a solid bar carries little current; a tube puts all its metal where it works. The round section also has the same stiffness in every direction, and a smooth large diameter lowers the surface voltage gradient that causes corona discharge, radio interference and audible noise at higher voltages.
6063-T6 seamless pipe in ANSI schedule 40 dimensions is the most widely used bus tube in North America and many export markets. It offers a practical balance: conductivity of about 53 % IACS, a guaranteed yield of around 170 MPa to carry its own weight, ice and short-circuit forces between supports, and good weldability to aluminium bus fittings.
| Alloy and temper | Conductivity (typical) | Strength | Specification | When used |
|---|---|---|---|---|
| 6063-T6 | About 53 % IACS | Yield min about 172 MPa (25 ksi) | ASTM B241 (seamless pipe) | General outdoor substation bus; the usual default |
| 6101-T6 / T61 / T63 / T64 | About 55 – 59 % IACS, by temper | Lower to similar, by temper | ASTM B317 (bus conductor) | Where higher conductivity outweighs strength, such as generator and indoor bus |
| 6061-T6 | About 43 % IACS | Yield min about 241 MPa (35 ksi) | ASTM B241 | Long spans or high short-circuit forces where strength governs |
| 1350 / 1060 tube | About 61 – 62 % IACS | Low | Conductor-grade specifications | Short, well-supported runs and flexible connections |
ASTM B317 is the specification written specifically for extruded aluminium bus conductors, and it covers 6101. 6063-T6 bus pipe is normally supplied as seamless pipe to ASTM B241 with conductivity confirmed by test. Read our 6101 bus pipe guide and 6061 bus pipe guide for those options.
Dimensions follow ANSI/ASME B36.10 pipe schedules. Area and weight are calculated from nominal OD and wall with a density of 2.70 g/cm³; DC resistance is calculated at 20 °C for 53 % IACS. Use these values for early design; final ratings should come from the conductor manufacturer's data and a calculation to IEEE 605 or your national code.
| NPS | OD (in / mm) | Wall (in / mm) | Area (in²) | Weight (lb/ft) | Weight (kg/m) | DC resistance at 20 °C (µΩ/m) |
|---|---|---|---|---|---|---|
| 1 | 1.315 / 33.4 | 0.133 / 3.38 | 0.494 | 0.578 | 0.86 | 102.1 |
| 1¼ | 1.660 / 42.2 | 0.140 / 3.56 | 0.669 | 0.782 | 1.16 | 75.4 |
| 1½ | 1.900 / 48.3 | 0.145 / 3.68 | 0.799 | 0.935 | 1.39 | 63.1 |
| 2 | 2.375 / 60.3 | 0.154 / 3.91 | 1.075 | 1.257 | 1.87 | 46.9 |
| 2½ | 2.875 / 73.0 | 0.203 / 5.16 | 1.704 | 1.994 | 2.97 | 29.6 |
| 3 | 3.500 / 88.9 | 0.216 / 5.49 | 2.228 | 2.607 | 3.88 | 22.6 |
| 3½ | 4.000 / 101.6 | 0.226 / 5.74 | 2.680 | 3.135 | 4.67 | 18.8 |
| 4 | 4.500 / 114.3 | 0.237 / 6.02 | 3.174 | 3.714 | 5.53 | 15.9 |
| 5 | 5.563 / 141.3 | 0.258 / 6.55 | 4.300 | 5.031 | 7.49 | 11.7 |
| 6 | 6.625 / 168.3 | 0.280 / 7.11 | 5.581 | 6.530 | 9.72 | 9.0 |
| 8 | 8.625 / 219.1 | 0.322 / 8.18 | 8.399 | 9.827 | 14.63 | 6.0 |
Schedule 80 has thicker walls for the same outside diameter. It carries more current and resists higher short-circuit forces, at the cost of extra weight on the insulators.
| NPS | OD (in / mm) | Wall (in / mm) | Area (in²) | Weight (lb/ft) | Weight (kg/m) | DC resistance at 20 °C (µΩ/m) |
|---|---|---|---|---|---|---|
| 1 | 1.315 / 33.4 | 0.179 / 4.55 | 0.639 | 0.747 | 1.11 | 78.9 |
| 1¼ | 1.660 / 42.2 | 0.191 / 4.85 | 0.881 | 1.031 | 1.54 | 57.2 |
| 1½ | 1.900 / 48.3 | 0.200 / 5.08 | 1.068 | 1.250 | 1.86 | 47.2 |
| 2 | 2.375 / 60.3 | 0.218 / 5.54 | 1.477 | 1.728 | 2.57 | 34.1 |
| 2½ | 2.875 / 73.0 | 0.276 / 7.01 | 2.254 | 2.637 | 3.93 | 22.4 |
| 3 | 3.500 / 88.9 | 0.300 / 7.62 | 3.016 | 3.529 | 5.25 | 16.7 |
| 3½ | 4.000 / 101.6 | 0.318 / 8.08 | 3.678 | 4.304 | 6.41 | 13.7 |
| 4 | 4.500 / 114.3 | 0.337 / 8.56 | 4.407 | 5.157 | 7.68 | 11.4 |
| 5 | 5.563 / 141.3 | 0.375 / 9.52 | 6.112 | 7.151 | 10.65 | 8.2 |
| 6 | 6.625 / 168.3 | 0.432 / 10.97 | 8.405 | 9.834 | 14.64 | 6.0 |
| 8 | 8.625 / 219.1 | 0.500 / 12.70 | 12.763 | 14.932 | 22.23 | 4.0 |
Metric bus tubes are also widely used, particularly for 66 – 500 kV substations designed to IEC practice, with outside diameters from about 60 mm to 250 mm and above and walls of about 4 – 15 mm. Send the OD and wall thickness and we will confirm availability.
| Element | Min % | Max % |
|---|---|---|
| Silicon (Si) | 0.20 | 0.60 |
| Iron (Fe) | — | 0.35 |
| Copper (Cu) | — | 0.10 |
| Manganese (Mn) | — | 0.10 |
| Magnesium (Mg) | 0.45 | 0.90 |
| Chromium (Cr) | — | 0.10 |
| Zinc (Zn) | — | 0.10 |
| Titanium (Ti) | — | 0.10 |
| Others, each / total | — | 0.05 / 0.15 |
| Aluminium (Al) | Remainder |
| Property | 6063-T6 value | Note |
|---|---|---|
| Tensile strength | 207 MPa (30 ksi) min; about 241 MPa typical | ASTM B241 / B221 minimum |
| Yield strength (0.2 %) | 172 MPa (25 ksi) min; about 214 MPa typical | |
| Elongation | 8 – 12 % | Depends on wall thickness |
| Electrical conductivity | About 53 % IACS | Volume conductivity at 20 °C |
| Resistivity | About 0.0325 Ω·mm²/m | At 20 °C |
| Temperature coefficient of resistance | About 0.0035 per °C | Approximate, at 20 °C |
| Density | 2.70 g/cm³ | |
| Thermal expansion | 23.4 µm/m·°C | About 23 mm per 10 m for a 100 °C change |
| Modulus of elasticity | 68.9 GPa | Used for deflection and vibration calculations |
The old figure of 2.75 g/cm³ sometimes quoted for 6063 density is incorrect; the registered value is about 2.69 – 2.70 g/cm³.
Current rating depends on allowable temperature rise, ambient temperature, wind, solar gain and surface emissivity. A weathered or painted surface radiates heat better than bright metal. Ratings are calculated to IEEE 605 or the national equivalent.
The bus must carry its own weight, ice and wind between supports within a deflection limit, often expressed as a fraction of the span. A larger diameter is the most effective way to increase stiffness.
Fault currents create large electromagnetic forces between phases. The tube, insulators and fittings must withstand them; Schedule 80 or 6061-T6 is used where forces are high.
Wind can set long tubes vibrating. Damping conductors (stranded cable inside the tube) or proprietary dampers are installed on longer spans.
Aluminium expands about twice as much as steel. Expansion fittings or sliding supports are needed so the bus does not load insulators as temperature changes.
At higher voltages the surface gradient must stay below the corona onset level. Larger diameters, smooth surfaces and corona caps or bells at tube ends are used.
A typical example: an outdoor 132 kV substation uses 4 in Schedule 40 6063-T6 tube for its main bus, supported on post insulators, with welded or bolted fittings, damping cable on the longer spans and expansion fittings at regular intervals.
Pure aluminium conducts better but is too soft to span between insulators without sagging. 6063-T6 keeps about 53 % IACS conductivity while giving a minimum yield of about 172 MPa.
6101 is a conductor alloy with slightly higher conductivity (about 55 – 59 % IACS depending on temper) and is covered by ASTM B317. 6063-T6 is stronger than the high-conductivity 6101 tempers and is the common choice for outdoor substation bus.
It depends on the allowed temperature rise, ambient temperature, wind and surface condition. Published ratings for this size are typically in the low thousands of amperes; calculate the rating for your conditions to IEEE 605 or ask the conductor supplier for rated tables.
Bus pipe for substations is normally seamless extruded pipe to ASTM B241, which gives uniform properties around the circumference. Welded tube is not usually accepted for high-voltage bus.
No. 6063 resists outdoor corrosion without coating. Contact areas may be plated, and some designers paint the tube to raise emissivity and current rating.
Yes. Metric outside diameters and walls for IEC-style substations can be supplied; send the OD, wall and length.
Send the size, schedule, length, quantity and destination. We will reply with availability, certification and a delivered price.
