Wire Size Calculator for Idaho
NEC 2020 wire size math for EV charger installers working in Idaho.
Wire sizing in Idaho is governed by NEC 2020 Table 310.16, with the state's 96°F summer ambient driving a 0.82× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for Idaho
A 50 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 50 A. In Idaho's 0.82× correction, that means picking a conductor whose 30°C-rated ampacity is at least 61 A. For copper THWN-2 in EMT, that typically lands at #6 AWG; aluminum requires one to two sizes larger.
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
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 Idaho.