Voltage Drop Calculator

Calculate the voltage drop for installing wire at certain lengths.

Jackson Location

425 E. Washington Ave | Jackson, MI 49203
(800) 686-9301 | (517) 782-9301

Adrian Location

1153 W. Beecher Street | Adrian, MI 49221
(800) 589-9301 | (517) 263-5500

Voltage Drop Calculator


This should be the line-to-line voltage for multi-voltage and 3 phase systems. For a 120/240V single phase system select 240V. For other single phase systems select the line-to-neutral voltage.

Wire or Cable

These are uncoated copper or aluminum conductor sizes with CU/AL 60C Ampacity listed at 30C ambient for reference.

NEC tables assume 75C operating temperature. If conductor is oversized a lower temperature can be used but this temperature should always be higher than ambient. This value only used for adjusting conductor resistance.

See NOTE 1 below






  • 1. Examples for parallel runs: 120/240V single phase system with single black-red-white conductors (installed in single conduit) select "single set of conductors", 120/208V 3phase system with 2 conductors per phase and neutral (installed in 2 parallel conduits) select "2 conductors per phase in parallel", dc system with 3 positive and 3 negative conductors select "3 conductors per phase in parallel".
  • 2. Voltage drop for ac systems should total no more than 5% under full load conditions. Drop may be significantly larger during surge or motor starting conditions -- sometimes in the 15% to 25% range if other devices on the system can withstand this momentary dip. Voltage drop for dc systems should be designed as low as possible or less than 2%.
  • 3. For most 120/240V systems using cables of adequate ampacity, voltage drop is not a concern unless cable lengths are well over a hundred feet.