Transformer Sizing Calculator for Wyoming
NEC 2017 transformer sizing math for EV charger installers working in Wyoming.
DCFC and large workplace EV deployments in Wyoming 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 2017 continuous-load multiplier.
Worked example for Wyoming
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. Wyoming's 90°F summer ambient does not directly derate the transformer, but it does push the secondary feeder ampacity down by 0.88× — so the secondary copper has to be sized accordingly.
Code & Utilities
The applicable code in Wyoming is the NEC 2017, which the state adopted in 2020. That includes Article 625 EVSE rules and the 125% continuous-load factor on charging branch circuits, though some 2020-cycle changes (like expanded EMS provisions) are not yet enforced statewide.
Major electric utilities serving Wyoming include Rocky Mountain Power, Black Hills Energy, Wyoming Rural Electric Cooperatives. Always verify the applicable tariff and any utility-specific requirements (CT cabinets, metering enclosures, demand limiters) at design time.
Climate & Ampacity
Wyoming's representative summer design ambient is around 90°F, which yields a 0.88× 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.
Wyoming takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Rocky Mountain Power early — interconnection lead times for new pad-mounts in Wyoming can run 6-12 months on commercial DCFC sites.