Transformer Sizing Calculator for Ohio
NEC 2017 transformer sizing math for EV charger installers working in Ohio.
DCFC and large workplace EV deployments in Ohio 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 Ohio
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. Ohio's 89°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
Ohio currently enforces the NEC 2017 edition, 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.
Ohio's primary EV-relevant utilities are AEP Ohio, Duke Energy Ohio, FirstEnergy, DP&L. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Ohio's representative summer design ambient is around 89°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.
Ohio takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with AEP Ohio early — interconnection lead times for new pad-mounts in Ohio can run 6-12 months on commercial DCFC sites.