Glossary
The vocabulary our guides assume, defined once. Every definition here is the one the articles use.
- AC / DCAlternating current / direct current
The grid supplies AC. A battery stores DC. Something has to convert between them: at home the car does it internally, which is why home charging speed is capped by the car. At a DC fast charger the station does it instead, which is why those are large and expensive.
- Ampacity
How much current a conductor can carry continuously without exceeding its temperature rating. It depends on the metal, the insulation, the installation method and the ambient temperature — not on the wire gauge alone.
- CCSCombined Charging System
A DC fast-charging connector that adds two high-power DC pins below an AC connector — J1772 in North America, Type 2 in Europe. It is a fast-charging standard, not a home-charging one.
- Charging losses
The gap between what your meter records and what reaches the battery — conversion, cabling and thermal management, typically 10 to 15%. Your bill is based on the meter, so cost should always be computed from metered energy.
- Continuous load
A load expected to run at its maximum for three hours or more. EV charging qualifies. US practice limits a continuous load to 80% of the circuit rating, which is why a 40 A circuit gives 32 A of charging and a 60 A circuit gives 48 A.
- Dedicated circuit
A circuit serving one appliance and nothing else, run from its own breaker. Required for a Level 2 charger: sharing the circuit means the charger and the other load can add up past what the wire can carry.
- EVSEElectric Vehicle Supply Equipment
The formal name for the box on the wall. It is not a charger in the strict sense — it switches power on safely and tells the car how much current is available. The actual charger is inside the car.
- J1772
The five-pin AC connector used by most non-Tesla vehicles in North America. Every AC home charger in the region either has this plug or adapts to it. Identifiable by the latch lever on top.
- kWKilowatt
A rate — how fast energy moves. It describes charging speed. A 7.7 kW charger delivers energy at 7.7 kW for as long as it runs.
- kWhKilowatt-hour
A quantity — how much energy. It is what a battery holds and what your utility bills you for. One hour at 7.7 kW delivers 7.7 kWh.
- Level 1 / Level 2
Level 1 is a standard household outlet — about 1.4 kW in North America, adding roughly 3 to 5 miles of range per hour. Level 2 is a 240 V dedicated circuit, typically 7.7 to 11.5 kW. Level 2 is not automatically necessary; overnight parking time often makes Level 1 sufficient.
- Load calculation
An electrician's arithmetic totalling a home's existing electrical demand to determine what capacity is left. It is the step that decides whether a charger needs a service upgrade — and a free breaker slot is not a substitute for it.
- NACSNorth American Charging Standard
Tesla's connector, opened up and adopted across the North American industry. Smaller than J1772 and it carries both AC and DC on the same pins.
- NEMA 14-50
A 240 V, 50 A receptacle originally intended for electric ranges, widely used for plug-in EV chargers. Receptacle quality matters here more than people expect: a cheap one under a continuous load is a known failure point.
- Onboard charger
The AC-to-DC converter inside the vehicle, and the real limit on home charging speed. If it accepts 7.7 kW, an 11.5 kW wall unit still delivers 7.7 kW. Not the same specification as the car's DC fast-charging peak.
- Three-phase supply
Three alternating currents offset from one another, common in European homes and rare in North American ones. It makes 11 kW charging routine without a service upgrade, which is why the "how many amps" question barely arises in Europe.
- Time-of-use (TOU)
A tariff where the price of electricity varies by hour — expensive at the evening peak, cheap overnight. Because a parked car is a flexible load, moving to one is usually the single largest saving available to a home charger, often halving cost per mile.