Wire Size Calculator for Michigan
NEC 2017 wire size math for EV charger installers working in Michigan.
Wire sizing in Michigan 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 Michigan
A 60 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 60 A. In Michigan's 0.88× correction, that means picking a conductor whose 30°C-rated ampacity is at least 69 A. For copper THWN-2 in EMT, that typically lands at #6 AWG; aluminum requires one to two sizes larger.
Code & Utilities
EV installations in Michigan are governed by the 2017 National Electrical Code, in force since 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.
In Michigan, you'll most often interconnect with DTE Energy, Consumers Energy, Indiana Michigan Power. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Michigan's representative summer design ambient is around 88°F, which yields a 0.88× ampacity correction factor at 75°C terminations per NEC 310.15(B)(1). 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.
Michigan 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 Michigan.