6101 Aluminium Busbar: Tempers, Sizing and Specification

Why 6101 is the standard busbar alloy

A busbar is judged on three things: how much heat it generates per ampere, whether it stays straight and tight at its joints for decades, and how much it costs and weighs. 6101 scores well on all three.

Pure EC aluminium (1350) conducts slightly better, but it is soft and creeps under bolt pressure, so its joints loosen over time unless carefully designed. General-purpose alloys such as 6063 and 6082 are stronger but their conductivity is not guaranteed and is noticeably lower. 6101 sits deliberately between them: its chemistry keeps manganese, chromium and other conductivity-killing elements at trace levels, and its ageing treatments are tuned to deliver a published minimum conductivity with useful strength.

For switchgear, busway and panel builders this means a predictable product. When a 6101-T61 bar is certified to ASTM B317, its conductivity will be at least 57 % IACS at 20 °C, and its tensile and yield strengths will meet set minimums for its thickness. That predictability is what allows designers to rely on temperature-rise test results from one batch to the next.

6101 busbar tempers and minimum properties

All conductor tempers of 6101 are solution heat-treated and aged. Moving from T6 towards T64 over-ages the alloy: strength falls, conductivity and bendability rise. The table lists the specified minimums for extruded bar.

Specified minimums for extruded rod, bar, tube, pipe and profiles for electric conductors, from the Aluminum Association property-limit table that ASTM B317/B317M follows (inch values converted). T65 has both minimum and maximum limits so that bending behaviour is repeatable. Confirm against the current edition of the standard for contract use.

6101 chemical composition (wt %)

The 0.03 % caps on manganese and chromium are the critical lines on a 6101 certificate. A bar extruded from ordinary 6063 billet can look identical but will not reach the B317 conductivity minimums, so check the certified analysis as well as the measured conductivity.

Sizing 6101 busbar against copper

Common North American bar sizes are given in inches. The table compares 6101-T61 (57 % IACS) with C11000 copper (taken as 100 % IACS) of the same size: mass per metre and calculated DC resistance per metre at 20 °C.

For equal DC resistance, a 6101-T61 bar needs about 1.75 times the cross-section of copper. In practice the equal-temperature-rise ratio is smaller, because the larger aluminium bar has more surface area to shed heat. Two rules of thumb are widely used for converting a copper design:

1. Widen the barKeep the thickness and increase the width by roughly a quarter to a third, for example replacing a 1/4 × 4 in copper bar with 1/4 × 5 in aluminium.
2. Thicken the barKeep the width and increase the thickness by about half, for example 3/8 × 4 in aluminium for 1/4 × 4 in copper.
3. Verify by testConfirm the rating by temperature-rise testing of the assembly, for example to IEC 61439-1 or UL 857 for busways. Bar orientation, spacing, enclosure ventilation and AC skin effect all change the result.

Even after upsizing, the aluminium bar typically weighs about half as much as the copper bar it replaces.

Types of 6101 busbar

Designing joints that stay cool

Most busbar failures start at joints, not in the bar. Aluminium forms a hard oxide film within seconds of exposure and creeps slowly under constant pressure; good joint design deals with both.

• Prepare the surface: wire-brush or abrade the contact area under a jointing compound and assemble immediately, or use factory-plated (tin or silver) contact areas.
• Keep pressure constant: use high-strength bolts with conical (Belleville) spring washers or thick flat washers. Plain split washers do not maintain load as the aluminium creeps.
• Use enough overlap: overlap length of several bar thicknesses and multiple bolts spread current evenly; follow your design standard.
• Avoid bare copper-to-aluminium contact: plate one or both surfaces, or use bimetallic transition plates, to prevent galvanic corrosion in humid conditions.
• Retorque or inspect: thermographic inspection after commissioning finds any high-resistance joint before it fails.
• Weld where suitable: TIG- or MIG-welded joints with ER4043 filler eliminate contact resistance entirely for permanent connections.

Supply range, tolerances and processing

Bend radii depend on temper: T64 and T65 take the tightest flatwise and edgewise bends, while T6 needs the most generous radius. Agree a sample bend on the first delivery if the bar will be formed on automated equipment.

Where 6101 busbar is used

How to specify 6101 busbar

1. Standard and temperFor example "6101-T61 to ASTM B317/B317M".
2. Section and lengthThickness × width, edge form, length or drawing.
3. ConductivityState the minimum % IACS at 20 °C if higher than the standard minimum.
4. Finish and fabricationPlating type and thickness, holes, bends, insulation.
5. Documents and shippingEN 10204 3.1 certificate with chemistry, mechanicals and conductivity; EXW, FOB, CIF or DAP; export packing with interleaving.

Related busbar pages

6101 aluminium (aluminum) busbar: FAQ