Grounding Conductor Calculator for Michigan
NEC 2017 grounding conductor math for EV charger installers working in Michigan.
EGC sizing in Michigan follows NEC 2017 Table 250.122, indexed off the upstream OCPD rating, with parallel rules for parallel sets and increased-conductor adjustments under 250.122(B).
Worked example for Michigan
For a 40 A EVSE branch, Table 250.122 calls for a minimum #10 Cu equipment grounding conductor. If you upsize the phase conductors for voltage drop in Michigan's long runs, NEC 250.122(B) requires the EGC to be upsized proportionally.
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
On DCFC sites with parallel feeder sets, each parallel raceway needs its own full-size EGC — a detail inspectors in Michigan catch frequently on commercial submittals.