NEC Voltage Drop
Unlike ampacity, the NEC frames voltage drop as an informational recommendation rather than a numbered rule. Here is what that distinction means in practice.
Open the NEC looking for a hard, numbered voltage drop limit the way you'd find one for conductor ampacity, and you won't find it presented the same way. That's not an oversight — it's a deliberate structural choice in how the NEC is written, and it matters for how you should actually treat the limit on a real project.
The NEC's voltage drop guidance — commonly cited as 3% for a branch circuit and 5% combined with the feeder — appears in the code as an Informational Note (formerly called a Fine Print Note, or FPN), attached to sections like 210.19(A) and 215.2(A). Informational Notes are explicitly explanatory, not enforceable requirements in the way a numbered code section is.
Despite not being a hard NEC rule, the 3%/5% figures are so widely adopted by local jurisdictions, utilities, and engineering specifications as a firm requirement that treating them as optional is a real professional risk. Many Authorities Having Jurisdiction (AHJs) enforce these percentages as if they were numbered code sections, and plenty of engineering specs cite them directly as contract requirements.
Certain applications tighten this further regardless of the general NEC guidance — motor branch circuits sensitive to starting torque, and PV/solar DC circuits (Article 690) where even a small percentage compounds into meaningful lost energy production over a system's 25-year lifespan, typically pushing installers toward a 1-3% target rather than the general 3-5%.
Check your run against the applicable limit in the NEC Voltage Drop calculator.