EV Charger Load Calculator for Washington
NEC 2020 ev charger load math for EV charger installers working in Washington.
Sizing an EV charger circuit in Washington starts with NEC 2020 Article 625 — the EVSE branch must be sized to 125% of the continuous load. Hot-climate mild-band states like Washington (87°F design ambient) also force a 0.88× ampacity correction at 75°C terminations.
Worked example for Washington
For a 48 A Level 2 charger on a 240 V single-phase circuit, the OCPD is sized to 60 A (48 × 1.25 = 60.0 A, rounded up to the next standard breaker). The conductor must carry 60 A after Washington's 0.88× correction — that typically lands at #6 AWG copper THWN-2 for a residential garage run, with conduit fill checked separately if you're stacking multiple home runs.
Code & Utilities
The applicable code in Washington is the NEC 2020, which the state adopted in 2023. 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.
Washington's primary EV-relevant utilities are Puget Sound Energy, Seattle City Light, Avista Utilities, Snohomish PUD. 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 87°F ambient in Washington — 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.
Washington takeaway
Always cross-check the EVSE manufacturer's listed maximum overcurrent rating; Puget Sound Energy may also have specific service-upgrade or load-management requirements you'll need to coordinate before final inspection.