3.7, 7.4, 11 or 22 kW home EV charging?

Three separate limits determine speed

Home charging power is limited by the building supply, wallbox and vehicle's on-board AC charger. The lowest limit wins. A 22 kW wallbox cannot force an 11 kW car to accept 22 kW, and an 11 kW car may charge more slowly if the connection or load-management system provides less current.

What the common ratings mean

Approximately 3.7 kW corresponds to 16 A single phase at 230 V, 7.4 kW to 32 A single phase, 11 kW to 16 A three phase at 400 V and 22 kW to 32 A three phase. These are nominal values for a simplified balanced load and do not replace an electrical design.

Calculate from daily energy, not marketing power

A driver covering 60 km/day at 20 kWh/100 km needs about 12 kWh returned to the battery, plus charging losses. Even a 3.7 kW supply can often replace that overnight. Higher power becomes useful for short dwell times, large daily distances, time-of-use windows or more than one EV.

Account for the whole home

The main breaker serves the property, not only the charger. Cooking, water heating, heat pumps and other loads can coincide with charging. Dynamic load balancing can reduce wallbox current when household demand rises, helping the installation stay within its agreed supply limit. Its operation and fail-safe configuration must be compatible with the meter and wallbox.

An illustrative charging session

Suppose usable battery capacity is 70 kWh and you add 60%: that stores 42 kWh. At a sustained input of 11 kW and 90% efficiency, the estimate is 42 ÷ 11 ÷ 0.90 ≈ 4.24 hours. This is a hypothetical example; confirm the actual vehicle capacity and phase-specific AC limit separately.

Do not size cables from a calculator

Main protection, cable cross-section, route length, installation method, voltage drop, earthing and residual-current protection require a site assessment. A charger setting that appears below the breaker rating is not by itself proof that the installation is safe or compliant.

A sensible selection process

Confirm the car's AC limit, measure typical daily energy, identify the available connection capacity and decide whether load balancing is needed. Then compare the slowest acceptable overnight case with the fastest technically supported case. This avoids paying for a rating the car or building cannot use.

Translate a power setting into an achievable overnight refill

At 7 kW input, six hours provides at most 42 kWh from the supply in a constant-power scenario. At an assumed 90% efficiency, that is 37.8 kWh stored. If household load management reduces the average input to 4 kW, the same window stores only 21.6 kWh. The wallbox label has not changed, but the possible refill has.

Check charger logs for actual power over the whole cheap period, not only the first minute. Compare the resulting input kWh with the next day’s energy need. If the car uses one phase, ask for a per-phase assessment: a low total household kW reading can still hide a heavily loaded phase. The calculation is a schedule check, not permission to increase circuit current.

Sources and scope

EIA: measuring electricity · Schneider Electric: apparent power. References explain units and technology; hypothetical examples use the site’s own model. Owner observations are not laboratory tests.