Why do the three phases matter?
The meter shows about 62 kW in total, below the 80 kW limit. But one of the three phases carries 116 A, the most the controller allows, close to its 125 A fuse.
Four of the cars charge on a single phase, and all four are on the same one, L1.
The questionHow can one phase be full while the total is fine?
16 A on each of three phases
16 A on a single phase
32 A on a single phase
the car park's supply; the controller keeps each phase at 116 A
Computed with 230 V per phase, the nominal value of the 230/400 V system; OCPP uses the same 230 V to turn power into current per phase. The fuse protects each phase on its own, so each phase has its own limit.
A composed example with a 125 A fuse per phase: seven three-phase cars draw 76 A on every phase, the pool car 16 A and six others 10 A each; four single-phase cars draw 40 A, all on L1. L1 is at 116 A, 93% of its fuse, while L2 and L3 have room.
Why some cars use one phase
The decides whether a car charges on one, two or three phases, and many manufacturers fit single-phase units. A single-phase car at 16 A draws 3.7 kW, all of it from one phase.
Two remedies
- . Charge points are connected in turns: the first with L1 first, the next with L2 first, the next with L3 first. Single-phase cars then spread over the three phases. lets a charger report this wiring order for each connector.
- Per-phase control. The controller counts every phase separately and keeps each one below its limit, as this one does. OCPP limits in amperes apply per phase, not to the sum of all phases. It protects the fuse, but it cannot use the room on L2 and L3 while every car also loads L1.
Connection rules also limit how unevenly the phases may be loaded. In Germany, for example, a grid operator requires single-phase charging equipment to stay within an imbalance of 4.6 kVA; above that, charging equipment has to be connected and operated on three phases, balanced.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
A single-phase car charges at 16 A. What power does it draw?
230 V × 16 A is about 3.7 kW, all from one phase.
What does phase rotation do?
Each charge point starts on a different phase, so a single-phase car lands on L1, L2 or L3 depending on where it parks.
Why can one phase be full while the total load is below the limit?
The total adds the three phases, but the protection works phase by phase.
- OCPP Open Charge Point Protocol: the open protocol between a charger and its operator's backend. EV charging fundamentals, stop 03 Glossary
- Onboard charger The converter in the car that turns AC from a wallbox or public AC charger into DC for the battery; its rating limits AC charging power. eMobility and EV basics, stop 04 Glossary
- Phase rotation Connecting charge points in turns, starting on L1, L2 or L3, so single-phase cars spread evenly over the three phases. Glossary
- IEC: IEC 60038:2009, IEC standard voltages, foreword: the 230/400 V system (free preview by VDE Verlag). https://www.vde-verlag.de/iec-normen/preview-pdf/info_iec60038%7Bed7.0%7Db.pdf. Checked 13 Oct 2026.
- Open Charge Alliance: OCPP 1.6 edition 2 (2017), section 2 Terminology (phase rotation), section 7.12 ChargingRateUnitType (amperes per phase, 230 V) and the ConnectorPhaseRotation key; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.
- AUTOHAUS (SP-X, Holger Holzer): Elektroauto-Technik: Warum einphasiges Laden nichts für Eilige ist, 28 November 2019. https://www.autohaus.de/nachrichten/elektroauto-technik-warum-einphasiges-laden-nichts-fuer-eilige-ist-2487912.html. Checked 13 Oct 2026.
- Open Charge Alliance: OCPP 1.6 edition 2 (2017), section 2 Terminology (phase rotation), section 7.12 ChargingRateUnitType (amperes per phase, 230 V) and the ConnectorPhaseRotation key; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.
- Open Charge Alliance: OCPP 1.6 edition 2 (2017), section 2 Terminology (phase rotation), section 7.12 ChargingRateUnitType (amperes per phase, 230 V) and the ConnectorPhaseRotation key; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.
- Stadtwerke Mühlacker (grid operator): Anschluss von Ladeeinrichtungen für Elektrofahrzeuge: maximum imbalance of 4.6 kVA, three-phase and balanced above. https://www.stadtwerke-muehlacker.de/sw-wAssets/docs/download/01Strom/18E-Mobilitaet/Anschluss-von-Ladeeinrichtungen-fuer-Elektrofahrzeuge.pdf. Checked 13 Oct 2026.