Wire Size Calculator for California
NEC 2023 wire size math for EV charger installers working in California.
Wire sizing in California is governed by NEC 2023 Table 310.16, with the state's 95°F summer ambient driving a 0.88× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for California
A 60 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 60 A. In California's 0.88× correction, that means picking a conductor whose 30°C-rated ampacity is at least 69 A. For copper THWN-2 in EMT, that typically lands at #6 AWG; aluminum requires one to two sizes larger.
Code & Utilities
California currently enforces the NEC 2023 edition, adopted in 2023. 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.
Major electric utilities serving California include Pacific Gas & Electric (PG&E), Southern California Edison, San Diego Gas & Electric, LADWP, SMUD. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Plan EV feeders against a 95°F ambient in California — the resulting NEC 310.15(B) correction of 0.88× 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.
California 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 California.