电压降

概述

电压降发生在电流流过导体电阻时，降低了负载处可用的电压。国家电气规范 (NEC) 建议将分支电路的电压降限制在 3%，总电压降（馈线加分支）限制在 5%。准确的电压降计算有助于选择正确的导体尺寸，并确保设备在其额定电压范围内运行。

关键公式

欧姆定律方法：

$\Delta V = I \times R$

其中导体的电阻为：

$R = \frac{\rho \times 2L}{A}$

系数 2 考虑了单相电路中的供电和回流两个导体。

圆密尔方法：

$\Delta V = \frac{K \cdot P \cdot L \cdot I}{A}$

此形式使用以 Ω·圆密尔/ft 为单位的特定电阻率 K 和以圆密尔为单位的导线面积 A，避免了单独进行电阻率换算。

简化铜公式：

$\Delta V = f \cdot I \cdot L$

其中 f 为下方导体表中预计算的系数（每安培每 1000 ft 的伏特数），I 为以安培为单位的负载电流，L 为以英尺为单位的单向导线长度。

变量

特定电阻率（K 值）

计算器

单位换算器

Source Examples

Example - Voltage Drop: for a single-phase copper circuit, voltage drop is calculated from conductor resistance, current, and one-way length with the return path included by the phase constant. Example - Specific resistivity and Voltage Drop: use the material K value in ohm-circular-mils per foot with conductor area in circular mils to avoid mixing SI and AWG units.

Copper Conductor Voltage Drop Factors

还原的原始源表

以下表格还原自原始来源页面，以保留完整的参考数据。

Copper Conductor - Voltage Drop

工程要点

• Temperature matters. Conductor resistance rises with temperature. Use the higher K value for circuits operating above 121 °F (49 °C).
• Parallel conductors. For parallel runs, divide the total current by the number of parallel paths and calculate each path separately.
• NEC recommendations. The NEC (NFPA 70) suggests a maximum 3% voltage drop on branch circuits and 5% total (feeder plus branch combined).
• Aluminum conductors. Aluminum has roughly 1.6× the resistivity of copper; the K values and factors above reflect this difference.
• Conduit and skin effect. At higher frequencies or in ferromagnetic conduit, effective resistance increases. The formulas here assume DC or 60 Hz in non-ferrous raceways.
• Simplified formula limits. The factor-based method is calibrated for copper at standard building-wire temperatures. For aluminum or elevated-temperature designs, use the circular-mils formula with the appropriate K value.

参考资料

• Engineering ToolBox — Voltage Drop