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DC Wire Size Chart

Author: Emma Clarke, Reference Desk4 min readReviewed

Low-voltage DC is governed by voltage drop, not ampacity, because a 3 percent drop at 12 volts is only 0.36 volts. A 20 amp load 10 feet away needs 12 AWG at 12 volts; the same load 25 feet away needs 8 AWG. Double the voltage to 24 volts and the same run drops to 12 AWG again, which is why larger systems use higher voltages.

Electrical. Based on ABYC E-11, NEC 310.16, ISO 10133.

12 volt DC wire size chart

Sized for 3 percent voltage drop, which is the limit for critical circuits under ABYC E-11 and a sensible target for anything running electronics. Length is the one-way run, since the calculation already doubles it for the return conductor.

Minimum copper AWG at 12 V DC for 3 percent voltage drop, by current and one-way length in feet.
Amps5 ft10 ft15 ft20 ft25 ft30 ft40 ft
518161412121010
1016121010886
15141088664
20121086644
2512866442
3010864422
4010644221/0
50864221/02/0
100621/02/03/04/0-

24 volt DC wire size chart

At 24 volts the same 3 percent is 0.72 volts of allowable drop, so every cell in this table is one to two sizes smaller than the 12 volt chart. It is the practical argument for 24 or 48 volt systems on anything with long runs.

Minimum copper AWG at 24 V DC for 3 percent voltage drop.
Amps5 ft10 ft15 ft20 ft25 ft30 ft40 ft
518181616141412
1018161412121010
15161412101088
2016121010886
30141088664
5012866442
100864221/01/0

Amp capacity of wire by gauge

Voltage drop usually sets the size on DC, but the conductor still has to carry the current without overheating. These are the limits for a single conductor in free air at 30 degrees C for the small sizes DC work uses; inside a bundle or a conduit derate them.

Ampacity for copper conductors, small sizes, free air.
AWGmm²Amps, chassis wiringAmps, in bundle
220.3375
200.52117.5
180.821610
161.312213
142.083217
123.314123
105.265533
88.377346
613.310160

The voltage drop formula

VD = 2 x K x I x L / CM, where K is 12.9 for copper, I is amps, L is one-way length in feet and CM is the conductor area in circular mils. The 2 accounts for the return conductor.

Rearranged to find the wire you need: CM = 2 x K x I x L / VD, where VD is the drop you will accept, so 0.36 volts for 3 percent of 12. Then pick the next AWG size up from the circular mil area.

Emma Clarke, Reference Desk editor at Compel GroupEmma ClarkeReference Desk

Emma looks after the reference charts and calculators. Every figure is copied from the named standard on the page rather than generated, and each page shows the date it was last checked. When a value looks wrong, the standard wins and the page gets fixed.

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Reference

DC Wire Size Chart questions

What size wire for 30 amps at 12 volts?
10 AWG up to 5 feet, 8 AWG to 10 feet, 6 AWG to 15 feet and 4 AWG to 25 feet, all at 3 percent voltage drop. Ampacity alone would allow 10 AWG for the whole run; voltage drop is what pushes the size up.
Why does DC need thicker wire than AC for the same amps?
Because 3 percent of 12 volts is only 0.36 volts. The same current over the same run causes the same drop in volts, but at 12 volts that drop is a much larger share of the supply. At 230 volts AC the same run would drop well under 1 percent.
How many amps can 22 AWG carry?
About 7 amps as a single chassis wire in free air, or 5 amps inside a bundle. It is signal and small-load wire, not power wire.
Is 10 gauge wire good for 30 amps?
For ampacity yes, 10 AWG carries 30 amps in most installations. On a 12 volt DC run it will only hold 3 percent drop out to about 5 feet, so length decides whether 10 AWG is enough.

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