免费电线线径计算器
根据电流和距离选择合适的电线线径（AWG），免费线径计算器。
A
ft
%
Max Resistance Allowed
1.800 ohm/kft
Min Circular Mils0 CM
Max Resistance Allowed vs Circuit Amperage
公式
## Wire Gauge Selection **CM = 2 x K x I x D / Vdrop** Where K = 10.8 (copper resistivity constant), I is current in amps, D is one-way distance in feet, and Vdrop is the allowable voltage drop in volts. Compare the resulting circular mils to an AWG table to pick the minimum wire size.
计算示例
20A circuit, 50 ft run, 120V, 3% max drop.
- 01Allowable drop = 120 x 0.03 = 3.6V
- 02CM = 2 x 10.8 x 20 x 50 / 3.6 = 6,000 CM
- 0312 AWG = 6,530 CM, which satisfies the requirement
- 04Use 12 AWG copper wire.
常见问题
What is the NEC voltage drop recommendation?
The NEC recommends no more than 3% voltage drop on branch circuits, and no more than 5% total (feeder plus branch). These are recommendations, not hard code requirements.
Why multiply distance by 2?
Current must travel to the load and return, so the total conductor length is twice the one-way distance.
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