Is An External Type-A 30mA RCD Still Needed, When There Is Built-In Type-A 30mA And DC 6 MA Protection At An EV Charger?

The IEC/EN 61851-1 standard specifies two optional residual current protection measures for Mode-3 EVSE (Electric Vehicle Supply Equipment) as follows:

• Option 1: RCD Type B (IEC 60947-2 Type-B mRCD/CBR or IEC 62423 Type-B RCCB)

• Option 2: RCD Type A (IEC 61008-1 Type-A RCCB, IEC 61009-1 Type-A RCBO, or IEC 60947-2 Type-A mRCD/CBR) combined with an RDC-DD (IEC 62955 RDC-PD or RDC-MD)

The Trend: Built-in vs. External Protection

Over the past few years, there has been a clear trend toward using Option 2 (Type-A RCD + RDC-DD) for home charging applications. The mainstream implementation approaches are illustrated in Diagram 1 (left) and Diagram 2 (middle) below. For instance, our BRCS residual current sensors are widely integrated by Mode-3 EVSE manufacturers.

However, some EVSE manufacturers advise users and installers that an external Type-A 30mA RCD is unnecessary if the EV charger features built-in Type-A 30mA and 6mA DC residual current protection, as illustrated in Diagram 3 (right).

Why Relying Solely on Built-in Protection is Risky

From an engineering perspective, relying exclusively on built-in Type-A 30mA protection—which typically consists of relays/contactors, a charging controller, and AC/DC residual current sensors—presents significant safety risks.

When reviewing the testing reports of EV chargers with built-in Type-A 30mA protection, they often state compliance with "Partial Testing Items in IEC 61008-1." This indicates that EV chargers declaring built-in Type-A 30mA protection are unlikely to be as robust as a fully tested, traditional DIN-rail Type-A 30mA RCD.

The Superiority of Dedicated DIN-Rail RCDs

A traditional DIN-rail Type-A 30mA RCD is engineered and rigorously tested to withstand the harsh climatic conditions defined in IEC 61008-1 or IEC 61009-1, including highly acidic and humid environments. Some professional manufacturers even test their RCDs against severe SO2 conditions.

Furthermore, a dedicated Type-A 30mA RCD can trip within 40ms in the event of a residual current during the switch-on stage. This rapid response feature is not always guaranteed by the built-in protection of EV chargers. If an electrician or user unintentionally switches on the upstream MCB during a fault (as seen in Diagram 3), the lack of rapid tripping could lead to electrical accidents.

Conclusion

Type-A 30mA protection is a critical component of electrical safety. A traditional DIN-rail Type-A 30mA RCD is highly affordable (typically 20-30 USD/EUR) and benefits from decades of manufacturing refinement to ensure maximum reliability.

While having built-in Type-A 30mA protection at the EV charger serves as an excellent backup, the external Type-A 30mA RCD should never be removed from the installation.