Current Capacity of Wires and Traces

I’ve been looking at the maximum current ratings of both wires and traces and have had a hard time finding good numbers.  So this is a collection of what I’ve found but limited to the ranges that I normally use.  There are lots of very advanced calculators online but I had difficulty finding a nice clear chart.  So I hope this helps others or at least helps me next time I need to look it up. The formula for external trace width is: I = 0.048 * dT^0.44 * A^0.725 as given in the ANSI / IPC-2221/IPC-2221A design standards which I have taken from here.  The internal trace width is about half of this since it cannot dissipate heat as well.  As you can see from the formula, this is all dependent on the allowable temperature rise.  Since circuit boards generally shouldn’t get above 105 degrees Celsius, you can use that and a knowledge of what temperature the board will be before you plug it in to determine what is allowable.  Most of the time, a 30-40C rise would be fine, but I like to factor in some safety.

Trace Current – 1oz copper

 Trace Width (mils) Amps, 10C rise Amps, 20C rise Amps, 30C rise Amps, 40C rise
6 0.61 0.83 0.99 1.13
8 0.75 1.02 1.22 1.39
10 0.89 1.20 1.44 1.63
12 1.01 1.37 1.64 1.86
14 1.13 1.53 1.83 2.08
16 1.25 1.69 2.02 2.29
18 1.36 1.84 2.20 2.50
20 1.47 1.99 2.38 2.70
25 1.72 2.34 2.79 3.17
30 1.97 2.67 3.19 3.62
35 2.20 2.98 3.56 4.05
40 2.42 3.29 3.93 4.46
50 2.85 3.86 4.62 5.24
60 3.25 4.41 5.27 5.98
70 3.63 4.93 5.89 6.69
80 4.00 5.43 6.49 7.37
100 4.71 6.38 7.63 8.66

TraceCurrentOneOz.png

Trace Current – 2oz Copper

Below is a table and chart for PCBs with 2oz of copper per square foot.  I’ve put this in since OSHpark now offers this at the same cost as a 1oz board.

 

Trace width (mils) Amps, 10C rise Amps, 20C rise Amps, 30C rise Amps, 40C rise
6 1.01 1.37 1.64 1.86
8 1.25 1.69 2.02 2.29
10 1.47 1.99 2.38 2.70
12 1.67 2.27 2.71 3.08
14 1.87 2.54 3.03 3.44
16 2.06 2.79 3.34 3.79
18 2.24 3.04 3.64 4.13
20 2.42 3.29 3.93 4.46
25 2.85 3.86 4.62 5.24
30 3.25 4.41 5.27 5.98
35 3.63 4.93 5.89 6.69
40 4.00 5.43 6.49 7.37
50 4.71 6.38 7.63 8.66
60 5.37 7.29 8.71 9.88
70 6.01 8.15 9.74 11.05
80 6.62 8.98 10.73 12.18
100 7.78 10.55 12.61 14.32

TraceCurrentTwoOz.png

Wire Current

For wires, there are numerous charts, but they used terms that I always had to look up and included lots of very large and very small wires that I will never need.  The values in this chart are taken from here where they use terms like “Chassis Wiring” and “Power Transmission” that may be common to others but confuse me.  I’ve relabeled them “Amps in Air” to denote the current for the wire surrounded by air and “Amps in Bundle” for wires that are in a bundle and cannot dissipate heat as well.

AWG Amps in Air Amps in Bundle
10 55 15
12 41 9.3
14 32 5.9
16 22 3.7
18 16 2.3
20 11 1.5
22 7 0.92
24 3.5 0.577
26 2.2 0.361
28 1.4 0.226
30 0.86 0.142
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