An RCD in an EV charger is a residual current device: the circuit that compares the current flowing out to the car with the current coming back, and cuts the supply if some of it is leaking to earth. In many wallboxes and portable chargers, part of this protection is built into the charger itself, using a sensing coil, a measuring circuit and the charger’s own contactor. The rest may sit in the consumer unit or panel, depending on the design and local wiring rules.
Key Takeaways
- An RCD compares outgoing and returning current and disconnects on leakage.
- Inside a charger, a sensing toroid, electronics and the contactor do this job.
- Protection is often split between the charger and the consumer unit.
- Names differ by market: RCD and RDC-DD in IEC markets, CCID in North America.
What Is Physically Inside: The Parts of an RCD Function
| Part | What it does |
|---|---|
| Sensing toroid (current transformer) | A ring-shaped magnetic core that all live and neutral conductors pass through. If currents are balanced, their magnetic fields cancel; any imbalance means current is leaking elsewhere. |
| Measuring electronics | Amplify the imbalance signal and compare it with trip thresholds. Some sensors also detect smooth DC leakage, which needs a more advanced sensing method. |
| Control board | Decides when to stop charging and records the fault for the status light or app. |
| Contactor or relays | Open the live and neutral conductors to the car when a fault is detected. |
| Self-test circuit | Injects a small test current, often before each session, to confirm the sensor and switching path work. |
A stand-alone RCD in a consumer unit works on the same principle but uses its own mechanical trip mechanism and switch.
Built-In Protection vs the Device in the Panel
Protection is usually split between the charger and the fixed installation. A typical arrangement in IEC markets is a residual current device in the consumer unit plus DC leakage detection inside the charger. IEC 62955 defines this in-charger function as an RDC-DD (residual direct current detecting device) for Mode 3 charging. Which upstream device is then required is a matter for the installer and the wiring rules, such as BS 7671 in the UK; our article on RCD protection, Type A, Type B and 6 mA DC detection explains the types.
Portable chargers carry their protection in the in-cable box, because they plug into existing sockets. Our explainer on Mode 2 vs Mode 3 charging covers that difference.
RCD, RDC-DD, CCID: Names by Market
- UK and IEC markets: “RCD” for residual current protection in general; “RDC-DD” or “6 mA DC detection” for the DC function in the charger.
- North America: EV equipment uses a personnel protection function often called a CCID (charge circuit interrupting device), the EV counterpart of a GFCI. See our article on whether an EV charger needs GFCI protection.
- Datasheets: look for wording such as “leakage protection”, “residual current monitoring” or “DC 6 mA”, and the standard it refers to.
What an RCD Does Not Do
A residual current function protects against earth leakage. It does not replace overcurrent protection from the breaker, surge protection, or protection against a broken PEN conductor on certain UK supplies. Those are separate functions, sometimes combined in one product. If a charger trips repeatedly, do not bypass or swap protective devices yourself; have a qualified electrician investigate.
EVDANCE wallboxes and portable chargers include residual current protection matched to their market. Examples include the EV-ACT3204PE 22 kW wallbox for Type 2 markets and the EV-ACS3210E 32A Type 2 portable charger portable charger. Installers can request the protection details and installation manual through our distributor program.
Frequently Asked Questions
Why does my charger run a test before charging?
Many chargers self-test their leakage sensing and switching before each session. If the test fails, the charger refuses to start, which is the safe outcome.
Can I press a test button on a wallbox RCD?
Some units have one; follow the manual. Periodic testing of fixed installation devices is part of an electrician’s inspection.
Is a built-in RCD enough on its own?
It depends on the charger design and local rules. The installation manual states what upstream protection is required, and the installer must follow it.
Related Reading
- Why Does My EV Charger Keep Tripping the Breaker?
- Do Granny Chargers Have PEN Protection?
- Are Home EV Chargers Safe?
