Transformer Sizing Calculator for Indiana
NEC 2020 transformer sizing math for EV charger installers working in Indiana.
DCFC and large workplace EV deployments in Indiana 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 Indiana
A 180 kW DC fast charger draws roughly 217 A at 480 V three-phase. Applying the 125% continuous-load factor (180 × 1.25 ≈ 225 kVA), then rounding up to the next standard transformer rating gives a 225 kVA minimum. Indiana's 90°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 Indiana 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.
Major electric utilities serving Indiana include Duke Energy Indiana, AEP Indiana Michigan Power, NIPSCO, Indianapolis Power & Light. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Indiana's representative summer design ambient is around 90°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.
Indiana takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Duke Energy Indiana early — interconnection lead times for new pad-mounts in Indiana can run 6-12 months on commercial DCFC sites.