Ampacity Derating Calculator for Texas
NEC 2020 ampacity derating math for EV charger installers working in Texas.
Texas's 101°F design ambient drives a 0.82× NEC 310.15(B)(1) correction at 75°C terminations — the single most-overlooked derate on hot-climate EV installs.
Worked example for Texas
A conductor with a 30°C-rated ampacity of 130 A drops to roughly 106.6 A in Texas ambient conditions. Stack a 0.8× conduit-fill adjustment (NEC 310.15(C)(1)) on top and that same conductor is only good for 85.3 A.
Code & Utilities
The applicable code in Texas is the NEC 2020, 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.
In Texas, you'll most often interconnect with Oncor Electric Delivery, CenterPoint Energy, AEP Texas, Austin Energy, CPS Energy. Their make-ready, time-of-use, and demand-charge structures vary widely; pull the specific tariff before sizing service equipment.
Climate & Ampacity
Texas's representative summer design ambient is around 101°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.
Texas takeaway
Never size off the 30°C column in NEC Table 310.16 for Texas work — always start with the temperature-corrected number, then apply any conduit-fill adjustment.