Wire size calculator: inlets, transfer switches, EV chargers
Copper AWG from load, voltage, length and allowed voltage drop. NEC 310.16 (75 °C) ampacity, Chapter 9 Table 8 resistance.
FAQ
What wire do I need for a 50 A generator inlet?
A 50 A inlet needs conductors rated for 50 A: AWG 6 copper NM-B/UF-B (60 °C column) or AWG 8 THWN in conduit (75 °C). For long runs the calculator shows when a size larger is needed to stay under 3 % drop.
What wire size for a 48 A EV charger?
Continuous loads are sized at 125 %: 48 A × 1.25 = 60 A → AWG 6 THWN in conduit (65 A at 75 °C) or AWG 4 NM-B (60 °C column) on a 60 A breaker; larger for long runs.
Is 3 % or 5 % voltage drop the limit?
The NEC recommends (not requires) 3 % for branch circuits and 5 % total. Generators and sensitive electronics behave better at 3 %.
Estimate for copper conductors; aluminum, conduit fill, ambient temperature and local amendments change the answer. Have a licensed electrician verify.