Voltage Drop Calculator

Estimate conductor voltage drop for a copper or aluminum run — single or three phase — and check it against the NEC's 3% recommendation for branch circuits. Enter your load, run length, and wire size to see the drop, the end voltage, and whether you're within spec.

Inputs

Mode

Phase

System Voltage (V)

Load Current (A)

One-Way Run Length (ft)

Wire Size

Conductor

Power Factor

0.85 typical; 1.0 = resistive

Operating Temp (°C)

75°C base

Raceway (AC R/X)

Power factor + operating temperature are live (resistive K-method). Per-raceway reactance (Table 9 R/X) is pending — until then PF applies to the resistive drop only.

Results

Enter inputs to calculate

Method: VD = (K × I × L × multiplier) ÷ circular mils, using resistivity of 12.9 (copper) / 21.2 (aluminum) Ω·cmil/ft at 75°C; multiplier 2 for single phase, √3 for three phase. The 3% branch-circuit figure is an NEC recommendation (FPN), not a hard code limit. Verify against the governing edition of the NEC for your jurisdiction.

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