Ampacity Derating Calculator for Colorado
NEC 2023 ampacity derating math for EV charger installers working in Colorado.
Colorado's 90°F design ambient drives a 0.88× NEC 310.15(B)(1) correction at 75°C terminations — the single most-overlooked derate on hot-climate EV installs.
Worked example for Colorado
A conductor with a 30°C-rated ampacity of 75 A drops to roughly 66 A in Colorado ambient conditions. Stack a 0.8× conduit-fill adjustment (NEC 310.15(C)(1)) on top and that same conductor is only good for 52.8 A.
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
Never size off the 30°C column in NEC Table 310.16 for Colorado work — always start with the temperature-corrected number, then apply any conduit-fill adjustment.