12 V 线规与电流、回路长度

概述

使用此参考为 12 V 直流电路选择铜 AWG 线规，当design voltage drop is limited to 3% (0.36 V). The length in the table is the total circuit length: from the source to the load and back to the source. It is not the one-way distance.

这是一个电压降选择指南，不是规范载流量表。导体绝缘、安装lation method, ambient temperature, terminations, and local electrical rules can require a different conductor or overcurrent-protection rating.

How to Use the Table

1. 测量从电源到负载再返回的完整电流路径。
2. 选择该总长度的行和电路电流的列。
3. The intersecting value is the AWG size used by the source reference.

For example, a 15 ft total circuit carrying 15 A corresponds to 12 AWG. A 15 ft one-way run has a 30 ft total circuit length, so use the 30 ft row instead.

12 V Copper Wire Gauge Selection (3% Voltage Drop)

1 ft = 0.3048 m.

12 V Cable Table-Derived Maximum-Current Charts

These charts are calculated from the selection table above; they are not digitized copies of the original graphic. For each total circuit length and AWG, a plotted value is the highest current column in that row that specifies that AWG. If an AWG does not occur in a row, its point is blank rather than zero. The feet and metres charts show the same derived values.

Voltage-Drop Formula

For a two-conductor circuit, use the total circuit length directly:

$V_{\text{drop}} = I \times R_{1000} \times \frac{L_{\text{total}}}{1000}$

Where $I$ is current in A, $R_{1000}$ is the conductor DC resistance in $\Omega/1000\,\text{ft}$, and $L_{\text{total}}$ is the complete circuit length in ft. The resistance value must be in ohms, not milliohms.

Voltage Drop Calculator

The default resistance is 1.588 $\Omega/1000\,\text{ft}$ for 12 AWG solid copper at 20 °C. With the default 15 ft total circuit and 15 A load, the calculated drop is about 0.357 V (about 3.0%). Use manufacturer data for the actual conductor, temperature, and construction.

Important Limits

• Protect the conductor with correctly selected overcurrent protection. A fuse or circuit breaker cannot be chosen from AWG alone; use the applicable electrical code and the conductor manufacturer’s installation data.
• Resistance changes with conductor temperature and construction. Use the actual conductor’s published DC resistance when voltage drop is critical.
• If the chassis is used as a return path, include the resistance of the complete return path rather than assuming that only the supply conductor matters.
• This reference is for copper conductors in a 12 V system with a 3% voltage-drop design target. It does not replace code-required ampacity, derating, or termination checks.

参考资料

• Original source — Engineering ToolBox
• Virginia Department of Energy — copper-wire resistance table (20 °C)