Check how much voltage a run will lose, for example to a detached garage, shop, well pump or EV charger.
Rough estimate only. Uses DC resistance from NEC Chapter 9 Table 8 (uncoated copper, aluminum, 75°C). Single-phase: VD = 2 × L × R × I / 1000. Three-phase: VD = 1.732 × L × R × I / 1000. Real drop also depends on conductor temperature, power factor and raceway. The code's 3% / 5% figures are recommendations (informational notes), not requirements, except in specific cases.
How much voltage drop is acceptable?
A common design target is no more than 3% on a branch circuit and 5% total for feeder plus branch circuit. Motors, well pumps and EV chargers are happier with less.
Common questions
What is a good voltage drop percentage?
A common target is 3% or less for a branch circuit and 5% or less combined with the feeder.
General information for California homes under the California Electrical Code (based on the NEC). Local rules and inspectors can vary. Not a substitute for an on-site inspection. Never work inside a panel, at the meter or on live circuits.