Transformer Sizing Calculator for Maine
NEC 2020 transformer sizing math for EV charger installers working in Maine.
DCFC and large workplace EV deployments in Maine 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 Maine
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. Maine's 84°F summer ambient does not directly derate the transformer, but it does push the secondary feeder ampacity down by 0.94× — so the secondary copper has to be sized accordingly.
Code & Utilities
The applicable code in Maine is the NEC 2020, which the state adopted in 2023. 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 Maine, you'll most often interconnect with Central Maine Power, Versant Power, Maine Public Utilities Commission Cooperatives. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Maine's representative summer design ambient is around 84°F, which yields a 0.94× ampacity correction factor at 75°C terminations per NEC 310.15(B)(1). The correction is mild but still NEC-required; document it on the load calc so your inspector sees that 310.15(B) was applied.
Maine takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Central Maine Power early — interconnection lead times for new pad-mounts in Maine can run 6-12 months on commercial DCFC sites.