11 kW or 22 kW wallbox connected on a single phase: how much charging power is left?
A wallbox with 11 or 22 kW is normally intended for a three-phase connection. If it only runs on one phase, the available charging power drops considerably. The rule of thumb is:
Charging power = voltage × current × number of phases
On a single phase, around 230 volts are available. What matters then is whether the wallbox is operated at 16 or 32 amps.
Key points at a glance
- 11 kW wallbox on a single phase: around 3.7 kW.
- 22 kW wallbox on a single phase: technically up to 7.4 kW, but usually limited to 3.7 kW in Austria.
- For new installations, a three-phase connection is almost always the better basis.
Short answer: 11 kW and 22 kW on one phase
| Wallbox rated power | Usual design | Single-phase charging power |
|---|---|---|
| 11 kW | 3 × 16 A | approx. 3.7 kW at 1 × 16 A |
| 22 kW | 3 × 32 A | approx. 7.4 kW at 1 × 32 A |
Important for Austria: the permissible phase imbalance is generally limited to 16 A, or around 3.7 kW, per phase. Charging on a single phase at 32 A or 7.4 kW is therefore not automatically permitted and must be clarified with your electrician and, if necessary, the grid operator.
Why does an 11 kW wallbox only deliver 3.7 kW on a single phase?
An 11 kW wallbox is designed for 16 A per phase:
- Phase L1: 230 V × 16 A = 3.7 kW
- Phase L2: 230 V × 16 A = 3.7 kW
- Phase L3: 230 V × 16 A = 3.7 kW
Together, that makes around 11 kW. If only one phase is connected or the vehicle only uses one, the share of one phase remains: 230 V × 16 A = around 3.7 kW. This is not a fault of the wallbox – it only delivers what is possible via the available phases.
What does a 22 kW wallbox deliver on a single phase?
A 22 kW wallbox is designed for 32 A per phase:
- Phase L1: 230 V × 32 A = 7.4 kW
- Phase L2: 230 V × 32 A = 7.4 kW
- Phase L3: 230 V × 32 A = 7.4 kW
On three phases, that is around 22 kW. On a single phase, it could technically deliver up to 7.4 kW. In Austria, however, this power is usually not approved for continuous use because of the phase imbalance limit – so in practice the limit here is also around 3.7 kW.
3.7 kW, 7.4 kW, 11 kW or 22 kW compared
| Connection type | Current | Theoretical charging power |
|---|---|---|
| single-phase | 16 A | approx. 3.7 kW |
| single-phase | 32 A | approx. 7.4 kW |
| three-phase | 16 A | approx. 11 kW |
| three-phase | 32 A | approx. 22 kW |
These are technical maximum values. The actual charging power also depends on the vehicle, charging cable, circuit protection, installation and any load management.
The vehicle has a say too
Many current electric cars have a three-phase 11 kW onboard charger and charge at a maximum of 11 kW even on a 22 kW wallbox. Many plug-in hybrids and some electric cars only charge on a single phase – in that case, depending on the vehicle and installation, the power is often 2.3 or 3.7 kW.
| Vehicle | Wallbox | Possible charging power |
|---|---|---|
| single-phase, 16 A | 11 or 22 kW | approx. 3.7 kW |
| three-phase, 16 A | 11 or 22 kW | approx. 11 kW |
| three-phase, 32 A | 22 kW | approx. 22 kW |
| single-phase, 32 A | 22 kW | technically up to 7.4 kW – check in advance in Austria |
We explain why plug-in hybrids in particular charge so slowly in Why won't my plug-in hybrid charge at full power?
How long does charging take?
With 60 kWh of usable battery capacity, the theoretical charging times are roughly as follows:
| Charging power | Time from 0 to 100%* |
|---|---|
| 2.3 kW | approx. 26 hours |
| 3.7 kW | approx. 16 hours |
| 7.4 kW | approx. 8 hours |
| 11 kW | approx. 5.5 hours |
| 22 kW | approx. 2.75 hours |
* In practice, there are charging losses, and the vehicle often reduces power towards the end.
For overnight charging, 3.7 kW is often enough: in ten hours, theoretically around 37 kWh are added. For short parking times or several vehicles, however, a three-phase connection has a clear advantage.
Why three-phase is usually the better solution
A three-phase connection distributes the power evenly across all three line conductors. This relieves the grid and enables significantly more charging power. For new installations, a five-core, three-phase connection is therefore almost always the right basis – even if your current car only charges on a single phase.
Especially with 22 kW, you should check:
- Is the house connection sufficiently dimensioned?
- Is the supply cable suitably sized and protected?
- Does the power need to be notified to or approved by the grid operator?
- Can the vehicle actually charge at 22 kW AC?
- Is dynamic load management required?
- What single-phase charging power is permitted at the site?
Conclusion
An 11 kW wallbox delivers around 3.7 kW on a single phase. A 22 kW wallbox could technically deliver up to 7.4 kW, but in Austria single-phase charging is usually limited to 16 A, or 3.7 kW. How fast your car charges therefore depends on the grid connection, installation, wallbox settings and, above all, your vehicle's onboard charger. Always have the specific setup checked by a qualified electrician before buying.
Frequently asked questions
Does an 11 kW wallbox charge at 11 kW on a single phase?
No. The rated power is only available on three phases at 16 A per phase. On a single phase, around 3.7 kW remains.
Can a 22 kW wallbox charge at 7.4 kW on a single phase?
Technically yes, if the wallbox, vehicle, cable and circuit protection support 32 A. In Austria, however, this is not automatically permitted and must be checked in advance.
Does a car that charges on a single phase need a different wallbox?
No. It also charges on a three-phase 11 or 22 kW wallbox, but then only uses one phase.
Why does my car only charge at 3.7 kW on a 22 kW wallbox?
Possible reasons include a single-phase 16 A onboard charger, a limit set in the wallbox, the installation or load management. The phase imbalance limit in Austria can also be the deciding factor.
