Transformer Sizing Calculator for Virginia
NEC 2020 transformer sizing math for EV charger installers working in Virginia.
DCFC and large workplace EV deployments in Virginia 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 2020 continuous-load multiplier.
Worked example for Virginia
A 240 kW DC fast charger draws roughly 289 A at 480 V three-phase. Applying the 125% continuous-load factor (240 × 1.25 ≈ 300 kVA), then rounding up to the next standard transformer rating gives a 300 kVA minimum. Virginia's 92°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 Virginia is the NEC 2020, which the state adopted in 2021. 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.
In Virginia, you'll most often interconnect with Dominion Energy Virginia, Appalachian Power, Old Dominion Electric Cooperative. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Plan EV feeders against a 92°F ambient in Virginia — the resulting NEC 310.15(B) correction of 0.88× is what trims a #6 THWN-2 down to its true continuous rating. 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.
Virginia takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Dominion Energy Virginia early — interconnection lead times for new pad-mounts in Virginia can run 6-12 months on commercial DCFC sites.