Transformer Sizing Calculator for Delaware
NEC 2020 transformer sizing math for EV charger installers working in Delaware.
DCFC and large workplace EV deployments in Delaware 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 Delaware
A 150 kW DC fast charger draws roughly 180 A at 480 V three-phase. Applying the 125% continuous-load factor (150 × 1.25 ≈ 188 kVA), then rounding up to the next standard transformer rating gives a 200 kVA minimum. Delaware's 91°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 Delaware is the NEC 2020, which the state adopted in 2022. 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.
Delaware's primary EV-relevant utilities are Delmarva Power, Delaware Electric Cooperative, Delaware Municipal Electric. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Plan EV feeders against a 91°F ambient in Delaware — 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.
Delaware takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Delmarva Power early — interconnection lead times for new pad-mounts in Delaware can run 6-12 months on commercial DCFC sites.