Box Fill Calculator for Utah
NEC 2023 box fill math for EV charger installers working in Utah.
Every EVSE installation in Utah eventually hits a junction or device box — disconnects, splice points, pull boxes — all of which must satisfy NEC 2023 Article 314.16 fill rules.
Worked example for Utah
A 4-11/16" square × 2-1/8" deep box has a 42.0 in³ volume. Each #6 Cu conductor counts as 5.0 in³. With a 2-conductor + EGC EVSE branch landing in the box plus a device, you consume roughly 15-20 in³, leaving plenty of headroom — but a 60 A multi-port pull box can fill quickly with #4 or #2 AWG conductors.
Code & Utilities
Utah currently enforces the NEC 2023 edition, adopted in 2024. 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.
Utah's primary EV-relevant utilities are Rocky Mountain Power, Murray City Power, Logan Light & Power. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Utah's representative summer design ambient is around 99°F, which yields a 0.82× 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.
Utah takeaway
Always run box-fill math when the EVSE disconnect lives more than a few inches from the unit itself — that intermediate junction is where Utah inspectors most often catch fill violations.