How to Calculate Voltage Drop
120V circuit, 20A load, #12 copper wire, 75 ft one-way. Drop = 5.94V (4.95%) -- exceeds the 3% NEC recommendation. Upsizing to #10 gives 3.1%, and #8 gives 1.94%.
Frequently Asked Questions
What is an acceptable voltage drop?
NEC recommends no more than 3% for branch circuits and 5% total. Most electricians target under 3%.
How far can you run 12-gauge wire?
At 20A on 120V with 3% max: about 53 ft one-way. At 15A: about 70 ft. Longer runs require upsizing.