Wire Size Calculator for Wisconsin
NEC 2017 wire size math for EV charger installers working in Wisconsin.
Wire sizing in Wisconsin is governed by NEC 2017 Table 310.16, with the state's 88°F summer ambient driving a 0.88× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for Wisconsin
A 70 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 70 A. In Wisconsin's 0.88× correction, that means picking a conductor whose 30°C-rated ampacity is at least 80 A. For copper THWN-2 in EMT, that typically lands at #4 AWG; aluminum requires one to two sizes larger.
Code & Utilities
The applicable code in Wisconsin is the NEC 2017, which the state adopted in 2020. That includes Article 625 EVSE rules and the 125% continuous-load factor on charging branch circuits, though some 2020-cycle changes (like expanded EMS provisions) are not yet enforced statewide.
Wisconsin's primary EV-relevant utilities are We Energies, Madison Gas & Electric, Wisconsin Public Service, Xcel Energy Wisconsin. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
In Wisconsin, the 88°F summer ambient drives a 0.88× 75°C ampacity correction. Bake this into every Level 2 and DCFC conductor pick before you commit to a wire size. Because the correction is below 0.9, conductors that "look fine" on a 30°C ampacity table will not carry their nameplate current here — always derate explicitly.
Wisconsin takeaway
Don't forget conduit-fill derating per NEC 310.15(C)(1) when more than three current-carrying conductors share a raceway — a common condition on multifamily and workplace EVSE home-run racks in Wisconsin.