Designing the Supply Panel for an Electric Vehicle Charging Station
EV charging supply panel: In an electric vehicle charging supply panel every charging point needs its own circuit, residual current protection of at least type A must be combined with a means of detecting 6 mA of smooth direct current leakage, cables must be sized for 100 percent continuous duty, and total installed power should be matched to the connection limit through dynamic load management.
Contents
- Load Profile and the Effect of Continuous Duty
- Protection per Circuit: Breaker and Residual Current Device
- Earthing, PEN Conductor Failure and Surge Protection
- Cable Sizing, Voltage Drop and Cable Routes
- Load Management, Metering and Expandability
- Key takeaways
- Frequently asked questions
- Related articles
Charging stations present a load profile very different from an ordinary socket outlet: they draw current close to the rated value continuously for hours. As a result both the thermal sizing and the residual current protection approach of a charging panel differ from those of a standard distribution board. This article sets out the design rules for an EV charging supply panel within the framework of IEC 61851 and IEC 60364-7-722.
Load Profile and the Effect of Continuous Duty
For cable and device selection a charging point is treated as a continuous load, meaning the circuit must be able to carry its rated current for hours. Diversity factors applied in ordinary distribution cannot be used on charging circuits on their own, although total power may be limited where dynamic load management supervises several points. Because continuous current raises terminal and breaker temperature, the internal heat load calculation must be carried out and ventilation added where needed. The derating table of the breaker against ambient temperature should also be checked.
Protection per Circuit: Breaker and Residual Current Device
As a rule, every charging point should have its own circuit and its own protective devices so that a fault at one point does not affect the others. Residual current protection requires at least a 30 mA type A device, but because the power electronics in the vehicle can produce smooth direct current leakage above 6 mA, a specific measure is mandatory: either a type B device is used, or it is documented that 6 mA DC detection is built into the charger. For overcurrent protection a type C curve breaker is the typical choice and must be coordinated with the maximum short circuit current permitted by the charger.
Earthing, PEN Conductor Failure and Surge Protection
In TN-C-S systems a broken PEN conductor can leave the body of a vehicle at a dangerous potential, so PEN fault detection must be provided either within the charger or by a voltage monitoring relay inside the panel. Some countries accept an alternative of installing a dedicated earth electrode at the charging point. Because outdoor charging points are exposed to lightning and switching surges, a type 1 or type 2 surge protective device should be planned in the main panel and a type 2 device at the charging point. Separate signal surge protection should also be considered for communication and payment system lines.
Cable Sizing, Voltage Drop and Cable Routes
| Protection topic | Requirement | Application note |
|---|---|---|
| Overcurrent | Breaker per circuit | Type C curve is the typical choice |
| Residual current | At least 30 mA type A | A separate device per charging point |
| DC leakage | 6 mA detection | Type B RCD or a function inside the charger |
| PEN conductor failure | Voltage monitoring or dedicated electrode | Critical in TN-C-S systems |
| Surge protection | Type 2 SPD | Type 1 may also be needed outdoors |
| Continuous duty | 100 percent continuous load | Diversity factors do not apply alone |
Charging points are usually located far from the panel, in different corners of a car park, which makes voltage drop the governing constraint; a limit between 3 and 5 percent at continuous full load should be targeted. For underground routes the cable type and burial depth are assessed together with the installation method correction factors for current capacity. The cable compartment should be designed with spare ducts and terminal capacity for future charging points. Where aluminium cable is used, lug and terminal compatibility and torque values deserve particular attention.
Load Management, Metering and Expandability
Ten charging points in a car park rarely operate at full power simultaneously, and dynamic load management measures the instantaneous consumption of the building and reduces charging power automatically, which avoids increasing the connection capacity. This requires an energy analyser at the incomer and a controller in the panel that communicates with the chargers. Where billing is needed, MID approved meters must be used and meter and analyser data forwarded to the management system over Modbus or OCPP. If the panel is designed with spare module space for at least twice the initially installed number of points, the cost of the second phase falls noticeably.
Key takeaways: EV charging supply panel
- Give every charging point its own circuit — A fault at one point must not interrupt charging at the others.
- Verify 6 mA DC leakage detection — Use a type B RCD or document that the function exists inside the charger.
- Size circuits as continuous loads — Charging current lasts for hours, so diversity factors cannot be applied on their own.
- Protect the connection capacity with load management — Measuring instantaneous demand and reducing charging power avoids a supply upgrade.
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
Why is a type B residual current device discussed for charging stations?
The charging electronics inside the vehicle can produce leakage containing a smooth direct current component under fault conditions. That component can saturate and blind a type A device, removing the protective function altogether. The standard therefore requires a measure against smooth DC leakage above 6 mA, which may be either a type B device or a DC detection module built into the charger.
How much connection capacity do a given number of points need?
With a static approach the total is simply the number of points multiplied by the power of each, which grows quickly: ten 22 kilowatt points mean 220 kilowatts. With dynamic load management the connection capacity is limited to what the building already has and charging power is shared automatically. In most car parks this allows two or three times as many points to be installed without upgrading the supply.
Can a charging panel be installed outdoors?
It can, provided the degree of protection and mechanical strength are selected accordingly; outdoors typically calls for at least IP54 and IK08 or above depending on the impact risk. Enclosures exposed to direct sunlight heat up quickly, so shading or ventilation is needed. Because of condensation risk, a heater with a hygrostat is a valuable measure for the service life of the electronic boards during winter.
Related articles
- Residual Current Device Types: The Difference Between AC, A, F and B
- Cable Sizing and Voltage Drop Calculation
- Surge Protective Device (SPD) Selection: Type 1, Type 2 and Type 3
- EV Charging Station Distribution Board: Protection and Load Management
- All technical articles
Devpan designs supply panels for your electric vehicle charging infrastructure with per-circuit protection, dynamic load management and expandability in mind, and delivers them verified. Let us plan the electrical infrastructure of your charging project together. Related Devpan solution: DevBox sub-distribution board.
