Transformer Sizing Calculator for Utah
NEC 2023 transformer sizing math for EV charger installers working in Utah.
DCFC and large workplace EV deployments in Utah typically need a dedicated 480 V three-phase service, which means sizing a pad-mount or dry-type transformer against the connected charger load plus the NEC 2023 continuous-load multiplier.
Worked example for Utah
A 180 kW DC fast charger draws roughly 217 A at 480 V three-phase. Applying the 125% continuous-load factor (180 × 1.25 ≈ 225 kVA), then rounding up to the next standard transformer rating gives a 225 kVA minimum. Utah's 99°F summer ambient does not directly derate the transformer, but it does push the secondary feeder ampacity down by 0.82× — so the secondary copper has to be sized accordingly.
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
Coordinate primary-side voltage, impedance, and fault-current specs with Rocky Mountain Power early — interconnection lead times for new pad-mounts in Utah can run 6-12 months on commercial DCFC sites.