Wire Size Calculator for New Hampshire
NEC 2020 wire size math for EV charger installers working in New Hampshire.
Wire sizing in New Hampshire is governed by NEC 2020 Table 310.16, with the state's 87°F summer ambient driving a 0.88× correction factor at 75°C terminations per Table 310.15(B)(1).
Worked example for New Hampshire
A 100 A continuous EV branch needs a conductor whose corrected ampacity meets or exceeds 100 A. In New Hampshire'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
New Hampshire currently enforces the NEC 2020 edition, adopted in 2022. 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.
New Hampshire's primary EV-relevant utilities are Eversource New Hampshire, Unitil, New Hampshire Electric Cooperative. Each has its own service-upgrade timeline, EV rebate availability, and metering rules — confirm them before quoting commercial work.
Climate & Ampacity
New Hampshire's representative summer design ambient is around 87°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.
New Hampshire 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 New Hampshire.