Wire Size Calculator for Massachusetts
NEC 2023 wire size math for EV charger installers working in Massachusetts.
Wire sizing in Massachusetts is governed by NEC 2023 Table 310.16, with the state's 88°F summer ambient driving a 0.88× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for Massachusetts
A 100 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 100 A. In Massachusetts's 0.88× correction, that means picking a conductor whose 30°C-rated ampacity is at least 114 A. For copper THWN-2 in EMT, that typically lands at #2 AWG; aluminum requires one to two sizes larger.
Code & Utilities
The applicable code in Massachusetts is the NEC 2023, 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.
Major electric utilities serving Massachusetts include Eversource Energy, National Grid, Unitil Massachusetts. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
Massachusetts's representative summer design ambient is around 88°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.
Massachusetts takeaway
Don't forget conduit-fill derating per NEC 310.15(C)(1) when more than three current-carrying conductors share a raceway — a common condition on multifamily and workplace EVSE home-run racks in Massachusetts.