Breaker Sizing Calculator for Ohio
NEC 2017 breaker sizing math for EV charger installers working in Ohio.
Every EVSE branch in Ohio is treated as a continuous load per NEC 2017 Article 625 — the OCPD must be sized at 125% of the EVSE's listed maximum draw.
Worked example for Ohio
A 40 A continuous EV load requires a breaker rated 50 A (40 × 1.25 = 50.0 A, rounded up to the next standard size). The conductor downstream must carry that 50 A after Ohio's 0.88× ampacity correction.
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
Use a 100%-rated breaker only when the panel and breaker are both listed for 100% continuous duty — otherwise the 125% rule applies. Ohio inspectors enforce this rigorously on Article 625 work.