Voltage Drop Calculator
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Formula: Vdrop = I × R_wire × 2 (round trip)
Voltage Drop Calculator
Voltage drop is the reduction in voltage along a wire due to its resistance. Excessive voltage drop can cause equipment malfunction and energy waste.
Conversion Formula
Vdrop = I × R_wire × 2 (round trip)
Vdrop = I × (resistance per foot × length × 2). The ×2 accounts for the return path.
Step-by-Step Examples
20A, 100ft, 12AWG, 120V = 6.36V (5.3%)
20 × 0.00159 × 200 = 6.36V
Frequently Asked Questions
What is an acceptable voltage drop?
The NEC recommends no more than 3% for branch circuits and 5% total for feeder + branch combined.
Why multiply wire length by 2?
Current flows to the load and back, so the total wire length is twice the one-way distance.
How do I reduce voltage drop?
Use a larger wire gauge, shorten the wire run, or reduce the current draw.