Ampacity Derating Calculator for Virginia
NEC 2020 ampacity derating math for EV charger installers working in Virginia.
Virginia's 92°F design ambient drives a 0.88× NEC 310.15(B)(1) correction at 75°C terminations — the single most-overlooked derate on hot-climate EV installs.
Worked example for Virginia
A conductor with a 30°C-rated ampacity of 130 A drops to roughly 114.4 A in Virginia ambient conditions. Stack a 0.8× conduit-fill adjustment (NEC 310.15(C)(1)) on top and that same conductor is only good for 91.5 A.
Code & Utilities
The applicable code in Virginia is the NEC 2020, which the state adopted in 2021. 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.
In Virginia, you'll most often interconnect with Dominion Energy Virginia, Appalachian Power, Old Dominion Electric Cooperative. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Plan EV feeders against a 92°F ambient in Virginia — 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.
Virginia takeaway
Never size off the 30°C column in NEC Table 310.16 for Virginia work — always start with the temperature-corrected number, then apply any conduit-fill adjustment.