Grounding Conductor Calculator for Illinois
NEC 2020 grounding conductor math for EV charger installers working in Illinois.
EGC sizing in Illinois follows NEC 2020 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 Illinois
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 Illinois's long runs, NEC 250.122(B) requires the EGC to be upsized proportionally.
Code & Utilities
EV installations in Illinois are governed by the 2020 National Electrical Code, in force since 2022. That includes Article 625 (Electric Vehicle Power Transfer System) requirements: 125% continuous-load sizing on EVSE branch circuits, GFCI protection at outdoor receptacles, and provisions for energy management systems on shared circuits.
In Illinois, you'll most often interconnect with ComEd, Ameren Illinois, MidAmerican Energy. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Illinois's representative summer design ambient is around 91°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.
Illinois takeaway
On DCFC sites with parallel feeder sets, each parallel raceway needs its own full-size EGC — a detail inspectors in Illinois catch frequently on commercial submittals.