Wire Size Calculator for Oklahoma
NEC 2020 wire size math for EV charger installers working in Oklahoma.
Wire sizing in Oklahoma is governed by NEC 2020 Table 310.16, with the state's 99°F summer ambient driving a 0.82× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for Oklahoma
A 100 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 100 A. In Oklahoma's 0.82× correction, that means picking a conductor whose 30°C-rated ampacity is at least 122 A. For copper THWN-2 in EMT, that typically lands at #2 AWG; aluminum requires one to two sizes larger.
Code & Utilities
Oklahoma currently enforces the NEC 2020 edition, adopted in 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 Oklahoma, you'll most often interconnect with OG&E, Public Service Company of Oklahoma, Western Farmers Electric Cooperative. 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 99°F ambient in Oklahoma — 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.
Oklahoma 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 Oklahoma.