电压降计算器

简化公式（本工具采用，只计电阻、忽略电抗）：

单相：Vd = 2 × L × I × R ÷ 1000

三相：Vd = √3 × L × I × R ÷ 1000

Simplified (resistance only): single-phase Vd = 2 × L × I × R / 1000; three-phase Vd = √3 × L × I × R / 1000, where L is in m, I in A and R in Ω/km.

完整公式（供参考，含电抗项）：

单相：Vd = 2 × L × I × (R·cosφ + X·sinφ) ÷ 1000

三相：Vd = √3 × L × I × (R·cosφ + X·sinφ) ÷ 1000

Full formula (with reactance): Vd = 2 (or √3) × L × I × (R·cosφ + X·sinφ) / 1000, where X ≈ 0.08 Ω/km for low-voltage cables and cosφ defaults to 0.8.

简化模型适用声明：本工具 R 取工作温度电阻，R_work = R20 × 1.2（20℃→70℃ 温升修正）。一般 120mm² 以下低压线路电阻分量占主导，简化误差可接受；大截面、长距离项目应以完整公式核算。

Scope: the simplified model ignores reactance and suits low-voltage runs up to about 120 mm² where resistance dominates. For large sections or long runs, verify with the full formula.

导体电阻表（20℃ 直流电阻，Ω/km，参考 IEC 60228）：

规范参考 / References：计算方法参考 GB/T 16895 与 IEC 60364；导体电阻参考 IEC 60228；美国用户可参考 NEC Chapter 9 Table 8。压降判定限值：照明 3%、动力 5%。计算结果仅供参考，实际工程以当地规范为准。

References: GB/T 16895 and IEC 60364 for the calculation method, IEC 60228 for conductor resistance, and NEC Chapter 9 Table 8 for US users. Limits: 3% for lighting, 5% for power circuits. Results are for reference only.