Ampacity Derating Calculator for Utah
NEC 2023 ampacity derating math for EV charger installers working in Utah.
Utah's 99°F design ambient drives a 0.82× NEC 310.15(B)(1) correction at 75°C terminations — the single most-overlooked derate on hot-climate EV installs.
Worked example for Utah
A conductor with a 30°C-rated ampacity of 95 A drops to roughly 77.9 A in Utah ambient conditions. Stack a 0.8× conduit-fill adjustment (NEC 310.15(C)(1)) on top and that same conductor is only good for 62.3 A.
Code & Utilities
Utah currently enforces the NEC 2023 edition, adopted in 2024. 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.
Utah's primary EV-relevant utilities are Rocky Mountain Power, Murray City Power, Logan Light & Power. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Utah's representative summer design ambient is around 99°F, which yields a 0.82× ampacity correction factor at 75°C terminations per NEC 310.15(B)(1). 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.
Utah takeaway
Never size off the 30°C column in NEC Table 310.16 for Utah work — always start with the temperature-corrected number, then apply any conduit-fill adjustment.