Power connections
Copper Busbar Ampacity: Which Temperature-Rise Column to Use
Match the drawing's rise to the column on the C11000 chart. A 30°C rise, a 50°C rise, and a 65°C rise are three different currents for the same bar.
On this page
Use the 30°C column when the design is held to a 30°C rise, the 50°C column for a 50°C rise, and the 65°C column for a 65°C rise. On Storm's C11000 chart, as of October 21, 2026, a 1/16 inch by 1/2 inch bar is 103 A, 136 A, and 157 A at those three rises. A 1/4 inch by 4 inch bar on the same chart is 1250 A, 1700 A, and 1950 A. The chart is 60 Hz, emissivity 0.4, indoors, 40°C ambient, horizontal on edge, and free from external magnetic influences. Copper.org says an energy-efficiency design should use a 30°C rise or less, and that rises above 65°C are not recommended.
The conditions printed with the chart
Storm's chart is titled for copper alloy C11000. The note above the table says the ampacities are for bus bars with an emissivity of 0.4, observed on samples exposed for 60 days in an industrial environment. The footnote says the values apply to typical in-service conditions: indoors, 40°C ambient, a horizontal run on edge, and free from external magnetic influences. The current columns are 60 Hz ampacity for a 30°C rise, a 50°C rise, and a 65°C rise. Each rise also has a skin-effect ratio at 90°C. The table credits the Copper Development Association.
Copper.org's busbar page, opened the same day, describes ampacity tables for rectangular busbars of Copper No. 110, calculated at a nominal 99 percent IACS, listed for 60 Hz at rises of 30, 50, and 65°C. It says Table 1 is for an emissivity of 0.4 after 60 days in an industrial environment. It says that for energy-efficiency considerations the design should be based on a 30°C rise above ambient, or less, and that temperature rises above 65°C are not recommended. The ampere values in the rows below are copied from Storm's chart.
Three sizes on the chart
The 1/16 inch by 1/2 inch row, read as thickness by width, has an area of 0.0312 square inches and a weight of 0.121 pounds per foot. Skin-effect ratio is 1.00 in all three rise columns. Ampacity is 103 A at 30°C rise, 136 A at 50°C rise, and 157 A at 65°C rise. Storm's understanding article uses this size as the example: 136 A expects a 50°C rise at 60 Hz, and the area is 0.0312 square inches. The same article says the DC resistance heading is microohms per foot at 20°C and that this thinnest bar is 264.0 microohms per foot. The chart cell in that column is 264.0.
The 1/8 inch by 1 inch row has an area of 0.125 square inches and a weight of 0.483 pounds per foot. DC resistance cell is 65.8. Skin-effect ratio is 1.01 in each rise column. Ampacity is 270 A at 30°C rise, 360 A at 50°C rise, and 415 A at 65°C rise.
The 1/4 inch by 4 inch row has an area of 1.00 square inch and a weight of 3.86 pounds per foot. DC resistance cell is 8.23. Skin-effect ratio is 1.12 at the 30°C column, 1.11 at the 50°C column, and 1.10 at the 65°C column. Ampacity is 1250 A, 1700 A, and 1950 A. That cross section is the 4 inch by 1/4 inch copper bar in the copper and 6101 aluminum comparison. That page compares section and weight for an equal temperature rise. It does not assign these chart currents. The currents here apply to the copper bar under the chart's horizontal-on-edge conditions.
| Thickness x width | Area and weight | 30°C rise | 50°C rise | 65°C rise |
|---|---|---|---|---|
| 1/16 x 1/2 in | 0.0312 in², 0.121 lb/ft | 103 A, skin 1.00 | 136 A, skin 1.00 | 157 A, skin 1.00 |
| 1/8 x 1 in | 0.125 in², 0.483 lb/ft | 270 A, skin 1.01 | 360 A, skin 1.01 | 415 A, skin 1.01 |
| 1/4 x 4 in | 1.00 in², 3.86 lb/ft | 1250 A, skin 1.12 | 1700 A, skin 1.11 | 1950 A, skin 1.10 |
Mounting, work hardening, and testing
The footnote limits the columns to a horizontal run on edge. Storm's understanding article says flat mounting changes the convection that on-edge bars get, and that bars packed close together change how the middle bar sheds heat. A flat bar, or a stack, is outside the footnote. The article also says work hardening from bending, stamping, or hole punching raises resistance around those features, so the chart estimate moves.
The same article says an ampacity chart is a guide, and that a part's performance is confirmed by thermal testing. Copper.org points designers who already know an ampacity to its Table 1 to verify the size, and it separates DC ampacity from the 60 Hz columns because of skin effect. This page does not size a bus. It matches a named rise, on a named size, to the current Storm prints for those conditions.
What to put on the drawing note
- Alloy. This chart is C11000.
- Thickness and width, in the chart's order.
- The rise the design uses: 30°C, 50°C, or 65°C.
- Ambient. The footnote uses 40°C indoors.
- Mounting. The footnote is a horizontal run on edge.
- 60 Hz, when the current column is the AC column.
Questions about the column
Which rise should a new drawing name?
Copper.org says an energy-efficiency design should use a 30°C rise or less, and that rises above 65°C are not recommended. On the 1/16 by 1/2 inch row that is the difference between 103 A and 157 A. On the 1/4 by 4 inch row it is the difference between 1250 A and 1950 A. Name the rise the equipment specification already uses. The chart then has one column.
Does the 60 Hz column apply to DC?
The ampere columns are labeled 60 Hz. Storm's article says the DC concern on the chart is resistance per foot and voltage drop, and it gives 264.0 microohms per foot for the thinnest bar at 20°C. Copper.org says DC ampacity can differ from the AC ampacity because of skin effect. Use the 60 Hz column for 60 Hz. Ask for the DC figure when the bus is DC.
Can the same amperes be used for a bar mounted flat?
The footnote says horizontal run on edge. Storm's article treats flat mounting as a different cooling case. A drawing that mounts the bar flat needs a current for that mounting. The three columns above are the on-edge currents.
Sources
Ampere values, areas, weights, skin-effect ratios, emissivity, and the installation footnote are from Storm's C11000 chart. The 136 A example, the 264.0 microohm-per-foot sentence, and the testing limit are from Storm's understanding article. The 30°C design sentence, the 65°C limit, the 99 percent IACS line, and Copper No. 110 are from copper.org. Pages were opened October 21, 2026.