Voltage Drop Calculator
Calculate voltage drop for a circuit using NEC Chapter 9 conductor resistance. Enter your load current, one-way run length, wire size, and material — get the drop in volts and as a percentage of source voltage instantly.
How it works
WireCoder uses NEC Chapter 9, Table 8 DC conductor resistance (75°C). For single phase, voltage drop = 2 × I × R × L; for three phase it uses the √3 line-to-line factor. The 3% guideline (NEC 210.19 informational note) is flagged automatically.
Frequently asked questions
What is an acceptable voltage drop?
The NEC recommends a maximum 3% drop on branch circuits and 5% total (feeder + branch). WireCoder flags results over 3%.
Does this work for aluminum wire?
Yes — choose copper or aluminum; the calculator uses the correct Table 8 resistance for each.
Single phase vs three phase?
Single phase applies a factor of 2 (out-and-back); three phase applies √3 (≈1.732).