Transformer Sizing Calculator for South Carolina
NEC 2017 transformer sizing math for EV charger installers working in South Carolina.
DCFC and large workplace EV deployments in South Carolina 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 South Carolina
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. South Carolina's 94°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 South Carolina is the NEC 2017, which the state adopted in 2018. 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.
Major electric utilities serving South Carolina include Duke Energy Carolinas SC, Dominion Energy South Carolina, Santee Cooper. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
South Carolina's representative summer design ambient is around 94°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.
South Carolina takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Duke Energy Carolinas SC early — interconnection lead times for new pad-mounts in South Carolina can run 6-12 months on commercial DCFC sites.