Wire Size Calculator for Colorado
NEC 2023 wire size math for EV charger installers working in Colorado.
Wire sizing in Colorado is governed by NEC 2023 Table 310.16, with the state's 90°F summer ambient driving a 0.88× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for Colorado
A 70 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 70 A. In Colorado's 0.88× correction, that means picking a conductor whose 30°C-rated ampacity is at least 80 A. For copper THWN-2 in EMT, that typically lands at #4 AWG; aluminum requires one to two sizes larger.
Code & Utilities
The applicable code in Colorado is the NEC 2023, which the state 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.
Colorado's primary EV-relevant utilities are Xcel Energy Colorado, Colorado Springs Utilities, Tri-State Generation. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
In Colorado, the 90°F summer ambient drives a 0.88× 75°C ampacity correction. Bake this into every Level 2 and DCFC conductor pick before you commit to a wire size. 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.
Colorado 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 Colorado.