EV charging glossary

Short, direct answers to the terms that come up when choosing a home EV charger.

Breaker sizing (the 125% rule): EV charging is a continuous load, so the US electrical code requires the circuit breaker to be rated at least 125% of the charger’s output current: a 40 A charger needs a 50 A breaker, a 48 A charger a 60 A breaker.
Dual-input (Level 1/Level 2) charger: A dual-input charger is a portable unit that runs on both a 120 V household outlet (Level 1) and a 240 V outlet (Level 2), usually via swappable plug adapters — one device for home, travel, and backup.
ENERGY STAR certified EVSE: ENERGY STAR certification for EV chargers (EVSE) verifies low energy waste when the charger is idle — certified units draw dramatically less standby power, saving roughly $25+ per year, and the EPA publishes their tested specs in a public dataset.
Hardwired vs plug-in installation: A hardwired charger is permanently wired to its circuit; a plug-in charger connects to a 240 V outlet. Hardwiring supports higher amperage (above 48 A it is required) and is more weather-robust, while plug-in units are portable and easier to replace.
J1772 (SAE J1772): J1772 is the standard North American connector for AC (Level 1 and Level 2) charging, used by nearly every non-Tesla EV sold before 2025. Teslas can use J1772 chargers with the adapter included with the car.
J1772-to-NACS adapter: A J1772-to-NACS adapter lets an EV with a NACS (Tesla-style) port charge from a standard J1772 home charger. Tesla includes one with every vehicle; other NACS-port EVs typically ship with one too.
kW vs amps: Amps measure current; kilowatts measure power, which is what actually determines charging speed. At 240 V, power in kW is amps × 240 ÷ 1000 — so a 48 A charger delivers 11.5 kW.
Level 1 charging: Level 1 charging means plugging an EV into a standard 120 V household outlet. It delivers roughly 1–1.9 kW, adding about 3–5 miles of range per hour — enough for short commutes but slow for anything else.
Level 2 charging: Level 2 charging uses a 240 V circuit — like an electric dryer — to charge an EV at 3.3 to 19.2 kW, adding roughly 20–60 miles of range per hour. It is the standard for home charging.
Miles of range per hour: Miles of range per hour expresses charging speed in practical terms: how much driving distance the battery gains each hour. It equals charging power (kW) × vehicle efficiency (miles per kWh) — typically 25–45 miles per hour on a home Level 2 charger.
NACS (North American Charging Standard): NACS is Tesla’s charging connector, standardized as SAE J3400, now being adopted across the US industry. It handles both AC home charging and DC fast charging through one compact plug.
NEMA 14-50 outlet: The NEMA 14-50 is a 240 V, 50 A four-prong outlet — the same type used by electric ranges and RV parks — and the most common outlet for plug-in Level 2 EV chargers, supporting up to 40 A of continuous charging.
Onboard charger (OBC): The onboard charger is the AC-to-DC converter built into every EV. It — not the wall unit — sets the maximum AC charging speed: a car with a 7.2 kW onboard charger charges at 7.2 kW even on a 19.2 kW home station.
Smart (networked) charger: A smart charger connects to Wi-Fi (or Ethernet/cellular) and adds app control: scheduling for off-peak rates, energy tracking, load management, and participation in utility demand-response programs.
Standby power draw: Standby power is what a charger consumes while plugged in but not charging — typically 1–8 W. At 5 W standby, a charger burns about 44 kWh a year doing nothing; the best certified units draw under 1 W.