Grounding Conductor Calculator for Idaho
NEC 2020 grounding conductor math for EV charger installers working in Idaho.
EGC sizing in Idaho 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 Idaho
For a 100 A EVSE branch, Table 250.122 calls for a minimum #8 Cu equipment grounding conductor. If you upsize the phase conductors for voltage drop in Idaho's long runs, NEC 250.122(B) requires the EGC to be upsized proportionally.
Code & Utilities
Idaho currently enforces the NEC 2020 edition, adopted in 2021. 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.
Idaho's primary EV-relevant utilities are Idaho Power, Avista Utilities, Rocky Mountain Power. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Plan EV feeders against a 96°F ambient in Idaho — the resulting NEC 310.15(B) correction of 0.82× is what trims a #6 THWN-2 down to its true continuous rating. 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.
Idaho takeaway
On DCFC sites with parallel feeder sets, each parallel raceway needs its own full-size EGC — a detail inspectors in Idaho catch frequently on commercial submittals.