Box Fill Calculator for Wisconsin
NEC 2017 box fill math for EV charger installers working in Wisconsin.
Every EVSE installation in Wisconsin eventually hits a junction or device box — disconnects, splice points, pull boxes — all of which must satisfy NEC 2017 Article 314.16 fill rules.
Worked example for Wisconsin
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
The applicable code in Wisconsin is the NEC 2017, which the state 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.
Wisconsin's primary EV-relevant utilities are We Energies, Madison Gas & Electric, Wisconsin Public Service, Xcel Energy Wisconsin. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
In Wisconsin, the 88°F summer ambient drives a 0.88× 75°C ampacity correction. Bake this into every Level 2 and DCFC conductor pick before you commit to a wire size. 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.
Wisconsin 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 Wisconsin inspectors most often catch fill violations.