Transformer Sizing Calculator for North Carolina
NEC 2017 transformer sizing math for EV charger installers working in North Carolina.
DCFC and large workplace EV deployments in North 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 North 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. North Carolina's 92°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 North Carolina are governed by the 2017 National Electrical Code, in force since 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 North Carolina include Duke Energy Carolinas, Duke Energy Progress, Dominion Energy NC. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Plan EV feeders against a 92°F ambient in North Carolina — the resulting NEC 310.15(B) correction of 0.88× is what trims a #6 THWN-2 down to its true continuous rating. 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.
North Carolina takeaway
Coordinate primary-side voltage, impedance, and fault-current specs with Duke Energy Carolinas early — interconnection lead times for new pad-mounts in North Carolina can run 6-12 months on commercial DCFC sites.