Why do cables get thicker at higher power?
The technician holds two cables side by side: the light Type 2 cable from the hotel car park and the DC cable of charger 1.
The DC cable is heavy, and two thin hoses run inside it. A cooling unit in the charger hums.
The questionWhy does more power need a thicker or cooled cable?
Computed: current equals power divided by voltage. A car with an 800-volt battery takes 300 kW at the same current a 400-volt car needs for 150 kW.
Computed: the heat in a conductor equals current squared times resistance. Double the current, four times the heat.
Thicker, or cooled
A cable has to carry its current without overheating. Two ways lead there:
- More copper. A larger cross-section carries more current, but the cable gets thicker and heavier, and harder to handle.
- Thermal management. Sensors in the connector watch the temperature, and in cooled designs a circuit carries the heat away. The cable can stay thin enough to handle.
The IEC specification for such DC cable assemblies covers up to 500 A at up to 1,500 V. An AC charge point of 22 kW, by comparison, draws about 32 A on each of three phases at 230 V.
Why voltage helps
Cars with an need half the current for the same power. The cable carries less, and the heat falls to a quarter. The IEC specification names both levers: more charging power needs a higher voltage, a higher current, or both, and the higher current is what calls for thermal management.
The battery side of this is the subject of eMobility and EV basics, stop 04.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
What does a charging cable have to be sized for?
Heat depends on current and resistance. The same current at a higher voltage means more power through the same cable.
The current through a cable doubles. What happens to the heat?
Heat equals current squared times resistance, so twice the current gives four times the heat.
Why can an 800-volt car charge at high power with less cable heat?
Current equals power divided by voltage. Half the current means a quarter of the heat.
- 800-volt battery A battery with a system voltage of around 800 V instead of around 400 V; for the same power it needs half the current, so cables and contacts heat up less. Glossary
- LEIFIphysik (FWU Institut für Film und Bild): Grundwissen: Elektrische Leistung, P = U · I and P = R · I². https://www.leifiphysik.de/elektrizitaetslehre/elektrische-energie/grundwissen/elektrische-leistung. Checked 13 Oct 2026.
- LEIFIphysik (FWU Institut für Film und Bild): Grundwissen: Elektrische Leistung, P = U · I and P = R · I². https://www.leifiphysik.de/elektrizitaetslehre/elektrische-energie/grundwissen/elektrische-leistung. Checked 13 Oct 2026.
- IEC (free preview by VDE Verlag): IEC TS 62196-3-1:2020, DC vehicle connector, inlet and cable assembly with a thermal management system: introduction and scope. https://www.vde-verlag.de/iec-normen/preview-pdf/info_iects62196-3-1%7Bed1.0%7Den.pdf. Checked 13 Oct 2026.
- IEC (free preview by VDE Verlag): IEC TS 62196-3-1:2020, DC vehicle connector, inlet and cable assembly with a thermal management system: introduction and scope. https://www.vde-verlag.de/iec-normen/preview-pdf/info_iects62196-3-1%7Bed1.0%7Den.pdf. Checked 13 Oct 2026.
- 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.
- IEC (free preview by VDE Verlag): IEC TS 62196-3-1:2020, DC vehicle connector, inlet and cable assembly with a thermal management system: introduction and scope. https://www.vde-verlag.de/iec-normen/preview-pdf/info_iects62196-3-1%7Bed1.0%7Den.pdf. Checked 13 Oct 2026.