Transformer Sizing Calculator for Maryland
NEC 2020 transformer sizing math for EV charger installers working in Maryland.
DCFC and large workplace EV deployments in Maryland 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 Maryland
A 350 kW DC fast charger draws roughly 421 A at 480 V three-phase. Applying the 125% continuous-load factor (350 × 1.25 ≈ 438 kVA), then rounding up to the next standard transformer rating gives a 450 kVA minimum. Maryland'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
EV installations in Maryland are governed by the 2020 National Electrical Code, in force since 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.
In Maryland, you'll most often interconnect with BGE, Pepco, Delmarva Power, Potomac Edison. Always verify the applicable tariff and any utility-specific requirements (CT cabinets, metering enclosures, demand limiters) at design time.
Climate & Ampacity
In Maryland, the 91°F summer ambient drives a 0.88× 75°C ampacity correction. Bake this into every Level 2 and DCFC conductor pick before you commit to a wire size. 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.
Maryland takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with BGE early — interconnection lead times for new pad-mounts in Maryland can run 6-12 months on commercial DCFC sites.