Breaker Sizing Calculator for Iowa
NEC 2020 breaker sizing math for EV charger installers working in Iowa.
Every EVSE branch in Iowa is treated as a continuous load per NEC 2020 Article 625 — the OCPD must be sized at 125% of the EVSE's listed maximum draw.
Worked example for Iowa
A 80 A continuous EV load requires a breaker rated 100 A (80 × 1.25 = 100.0 A, rounded up to the next standard size). The conductor downstream must carry that 100 A after Iowa's 0.88× ampacity correction.
Code & Utilities
EV installations in Iowa are governed by the 2020 National Electrical Code, in force since 2021. 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 Iowa include MidAmerican Energy, Alliant Energy Iowa, Iowa Association of Municipal Utilities. Always verify the applicable tariff and any utility-specific requirements (CT cabinets, metering enclosures, demand limiters) at design time.
Climate & Ampacity
Plan EV feeders against a 91°F ambient in Iowa — 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.
Iowa takeaway
Use a 100%-rated breaker only when the panel and breaker are both listed for 100% continuous duty — otherwise the 125% rule applies. Iowa inspectors enforce this rigorously on Article 625 work.