BendCraft Pro
Voltage Drop Calculator
Enter your circuit current, one-way distance, source voltage, and conductor to check voltage drop against the 3% recommended limit — for single-phase or three-phase circuits.
Results are estimates. Verify against your local jurisdiction and the NEC 2026 (NFPA 70). BendCraft Pro is not affiliated with the NFPA. The 3% limit is a widely used field recommendation, not a mandatory NEC requirement.
How voltage drop is calculated
Voltage drop grows with current and distance, and shrinks as conductor size (circular mils) increases. Single-phase circuits use a round-trip multiplier of 2 (current flows out and back through two conductors); three-phase circuits use √3 instead, reflecting the phase-to-phase geometry rather than phase-to-neutral.
The 3% figure isn't a hard NEC rule — the NEC's own informational notes recommend keeping combined voltage drop (feeder + branch circuit) under 5%, with no more than 3% on either segment alone, for reasonable equipment efficiency. This calculator uses that 3% per-segment convention as its reference point.
Frequently asked questions
Is 3% voltage drop a code requirement?
No — it's a widely followed performance recommendation from NEC informational notes, not a mandatory rule. Some engineers use 2% for sensitive equipment. Always check your local jurisdiction's specific requirements.
Why does aluminum need a bigger conductor than copper?
Aluminum has a higher resistivity than copper (roughly 1.6× at the same size), so an aluminum run needs a larger circular-mil area to match copper's voltage drop performance at the same length and current.
What distance should I enter — one-way or round-trip?
Enter the one-way distance from source to load. The formula's multiplier (2× for single-phase, √3× for three-phase) already accounts for the return path — don't double it yourself.
Need conduit fill too?
BendCraft Pro for iOS pairs voltage drop with conduit fill, all 10 bend types, and PDF reports you can hand off on-site.