Voltage Drop Calculator

Source

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

Length of cable in feet (one-way distance):

Load

Load current in amperes:

Calculate

Results

Estimated voltage drop: See NOTE 2 below

NOTES:

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.