Grounding Conductor Calculator for Wisconsin
NEC 2017 grounding conductor math for EV charger installers working in Wisconsin.
EGC sizing in Wisconsin 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 Wisconsin
For a 50 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 Wisconsin's long runs, NEC 250.122(B) requires the EGC to be upsized proportionally.
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
On DCFC sites with parallel feeder sets, each parallel raceway needs its own full-size EGC — a detail inspectors in Wisconsin catch frequently on commercial submittals.