Power connections
Copper vs Aluminum Busbars: Conductivity, Section, and Joints
Use copper when the section cannot grow. Use 6101 aluminum when the design can take a larger bar and the weight matters.
On this page
Use copper when the enclosure cannot accept a larger bar. Use 6101 aluminum when the design can grow the section and the weight matters. Storm Power Components, as of October 20, 2026, says a 5 inch by 1/4 inch aluminum bar matches the temperature rise of a 4 inch by 1/4 inch copper bar, which is a 27 percent increase in width, and that a 4 inch by 3/8 inch aluminum bar matches that same copper bar, which is about a 50 percent increase in thickness. The same page states that 6101 aluminum offers 56 percent of copper's conductivity at half the weight of copper.
Which conductor the pages are talking about
The comparison is alloy to alloy. Storm's aluminum page names 6101 as the aluminum alloy it is describing. The Pryor, Schlobohm, and Brownell paper hosted on Storm's site uses cold-worked electrolytic tough pitch copper similar to ASTM B187, alloy C11000, at a nominal 98 percent conductivity on the International Annealed Copper Standard. The paper says pure aluminum is too soft for these assemblies. It describes alloy 1350, the older electrical-conductor grade, as 61 percent of copper's conductivity and weaker in mechanical properties. It describes 6101, hardened by heat treatment, as the predominant aluminum busbar alloy in that paper, at 56 percent of copper's conductivity.
Storm fabricates custom aluminum and copper busbar and says silver or tin electroplating for aluminum joints is available in-house. The manufacturer comparison lists other shops and the constructions they publish. This page does not assign a current rating to a bar Storm has not sized.
Section, weight, and the two ways to grow an aluminum bar
Storm's page gives two conversion methods for equal temperature rise and says the table is a guideline. The design may need more or less material, and Storm says thermal testing should validate the choice. The width method adds surface area, which Storm ties to heat leaving the bar. The thickness method adds metal with less change in exposed surface.
| Method on the Storm page | Copper section in the example | Aluminum section in the example | What the page says changed |
|---|---|---|---|
| Increase width 27 percent | 4 inch by 1/4 inch | 5 inch by 1/4 inch | Same temperature rise, wider aluminum bar. |
| Increase thickness about 50 percent | 4 inch by 1/4 inch | 4 inch by 3/8 inch | Same temperature rise, thicker aluminum bar. |
| Double the area by width | 4 inch by 1/4 inch, used as the starting bar | 8 inch by 1/4 inch | Capacity up by about 87 percent. |
| Double the area by thickness | 4 inch by 1/4 inch, used as the starting bar | 4 inch by 1/2 inch | Capacity up by about 45 percent. |
Storm uses those last two rows to make a point about shape. Both changes double the cross section of the starting bar. The page says there is a 42 percent difference in the ampacity of the two examples, because the wider bar has more surface for heat to leave. A buyer who matches square inches and stops there misses that split. Ask which temperature rise and which orientation the quote used. This page does not pick a rise for the equipment.
The Pryor paper, opened October 20, 2026, prints a property table and says the figures come from GE properties and material bulletins B11B4 for copper and B12H60 for aluminum. For the same conductivity, the table sets copper's cross section at 100 and aluminum's at 156, and it sets copper's weight at 100 and aluminum's at 54. Raw tensile strength in that table is 50,000 lb/in2 for copper and 32,000 lb/in2 for aluminum. The same table then lists tensile strength for the same conductivity as 50,000 lb for both, which is the paper's equal-ampacity comparison, not a second test of the raw alloys. Specific resistance at 20°C is 10.6 ohms cir/mil ft for copper and 18.52 for aluminum. The paper also calculates densities of 559 lb/ft3 for copper and 169 lb/ft3 for aluminum, and it says one pound of aluminum has the same electrical capability as 1.85 pounds of copper at the 56 percent conductivity ratio.
Storm's phrase is half the weight. The paper's equal-conductivity weight is 54 against 100. Those statements sit near each other and they are not the same number. Keep the drawing's mass, and keep Storm's 56 percent conductivity line as Storm's line. The paper has no publication date in the text. The file path on Storm's site includes 2025. Treat the table as the paper's table, not as a new lab result from October 20, 2026.
Joints, expansion, and plating
Storm's aluminum page, as of October 20, 2026, says aluminum's thermal expansion and contraction is 42 percent higher than copper, and that the difference raises the chance that fasteners between bars loosen. The Pryor table lists the coefficient of expansion as 16.6 for copper and 23 for aluminum, in units of per degree C times 10 to the minus 6. The paper's prose calls aluminum's coefficient 42 percent greater than copper's. Use Storm's 42 percent sentence as Storm's current page, and use 16.6 and 23 as the paper's table. Do not average them into a new coefficient.
Both pages put the joint finish on the request. Storm says corrosion affects copper and aluminum, names hydrogen sulfide and extreme temperature as examples, and says silver or tin electroplating is the finish it offers in-house for that problem. The paper says oxides of aluminum are a poorer contact than oxides of copper, and that a low-resistance aluminum joint depends on plating. It says a bolted connection of unplated aluminum to copper is discouraged, and that most aluminum-to-copper joints plate one or both faces with silver or tin. Tin is the finish the paper discusses for hydrogen sulfide, where it says silver and bare copper corrode. Tin, nickel, and silver on copper are specified the same way: name the finish and where it stops.
Storm says it can provide torque sequence and washer information. The aluminum page does not print a torque value or a washer part number. The paper discusses Belleville washers and says some UL standards, including busway standard UL 857, do not require a Belleville spring on an aluminum joint when tensile strength is at least 20,000 psi. It also says 6101-T63 has a tensile strength of 27,000 psi. This guide did not open the current UL 857 text, so that sentence stays the paper's account. Ask the supplier which hardware the quote includes.
What the quote has to name
A conductor swap is a drawing change. Send the revision, the alloy, the section, the space the bar is allowed to occupy, the joint finish, and the environment. If the bar is still undecided, say so, and ask for copper and 6101 aluminum as separate lines. The custom copper request covers fabrication details that stay in force after the metal is chosen.
- Drawing number and revision.
- Alloy: C11000 copper, 6101 aluminum, or the specification the design already uses.
- Cross section, and whether width or thickness is the dimension that can grow.
- Temperature-rise basis, if the design has one.
- Joint finish, and whether the mating bar is copper or aluminum.
- Hydrogen sulfide or another atmosphere the site has.
- Quantity and the date.
Questions before changing the metal
Does the same cross section carry the same current?
Storm's examples say no for equal temperature rise. The 4 inch by 1/4 inch copper bar in that table is paired with a wider or thicker aluminum bar. The paper's cross-section row, 100 for copper and 156 for aluminum at the same conductivity, is the same kind of statement. A catalog ampacity for one copper size is not an aluminum ampacity.
Which weight figure should the request use?
Use a calculated mass from the drawing, or the figure the supplier prints for that bar. Storm's half-weight line and the paper's 54-versus-100 line are both published comparisons of the materials. They are not a shipping weight for a bent, plated bar with holes.
Can the joint stay bare?
Storm's page treats silver or tin as the answer for the corrosion and contact problem it describes on aluminum. The paper discourages unplated aluminum against copper. If the drawing leaves the faces bare, say that in the request and ask what the quote will plate.
Sources
The dimension examples, the 56 percent conductivity line, the half-weight line, and the 42 percent expansion line are from Storm's aluminum page, opened October 20, 2026. The alloy names, the property table, and the UL 857 remark are from the Pryor paper on that same site. Cost percentages in the paper were left out because they track commodity prices and the PDF text has no publication date. No bar was weighed or heated for this note.