Is It Safe To Use Voltage-Dependent Type-EV Or Type-B RCDs For Mode-3 EV Charging?

It is argued that voltage-dependent (VD) RCDs might not be able to perform functionally under AC 50V - leaving a protection blind range of 14 V to the AC 36V safe voltage for humans. This article provides a in-sight view about applying VD RCDs for E

Before answering the question, the author prepares some basic knowledge about the construction of type-EV RCDs (type-A RCD + IEC 62955 RCD-PD) and type-B RCDs. Almost all the type-EV / B RCDs sold in the market contain PCBA (electronic parts) inside the housing, because the fluxgate technology used to detect smooth DC leakage current has to be designed with MCU. The low-voltage protection industry categorizes type-EV/B RCDs as follows.

• Voltage-dependent structure (purely electronic design without VI part): both the type-A 30mA and smooth DC fault current detection is implemented with Fluxgate technology

• Hybrid structure (mix of electromagnetic and electronic design): The type-A protection part is voltage-independent, whereas the smooth DC fault current protection part is voltage-dependent

The above text clarifies that there are no voltage-independent (VI) type-EV RCDs or type-B RCDs with only electromagnetic design. Perhaps we’d better redefine the question as follows whether it is safe to use voltage-dependent (VD) Type-EV or Type-B RCDs with purely electronic design for Mode-3 EV Charging?

Firstly, the application of type-EV/B RCDs with purely VD structure for mode-3 charging is in full compliance with IEC requirements. The mode-3 EV charging-related standards (IEC 61851-1 and IEC 60364-7-222) widely used in IEC countries allows using type-EV or Type-B RCDs with purely electronic design. Both type-B CBR and type-B mRCD with purely electronic design (IEC 60947-2) and type-B RCCB / RCBO with hybrid design (IEC 62423) can meet the residual current protection request defined in IEC 61851-1 and IEC 60364-7-222. For type-EV RCDs, it is acceptable to design type-A part either in VI structure following IEC61008-1 and IEC61009-1 or in VD structure following IEC61008-1, IEC61009-1, and IEC60947-2.

Secondly, the main-stream design of EV chargers makes it safe to use type-EV/B RCDs with purely VD structures. People might argue that VD RCDs might not be able to perform functionally under AC 50V – leaving a protection gap of 14 V to the 36V safe voltage for humans. However, most of EV chargers contain under/over-voltage protection that stops charging in the event of an abnormal voltage supply, which significantly mitigates the risk of voltage-dependent RCD failure.

Thirdly, the design of the final power distribution system in most IEC countries also contributes to the safe use of VD type-EV/B RCDs with purely VD structure for mode-3 charging. For example, a VI type-A RCCB is usually installed at the incoming line of an in-door distribution board (or named consumer units) in most continental countries. Even in the extremely low-possibility scenario of an under-voltage power supply of 36~50V and EV charging without over/under-voltage (OV/UV) protection, the VI type-A RCCB at the main incoming line of an in-door distribution board can provide protection against the electrical shock of 36~50V AC. Another example is protection design in China. AOV/UV protection device must be installed at in-door distribution according to JGJ-242 standard. The OV/UV protection device can switch off the power supply in case the main voltage drops below the defined threshold, which significantly mitigates the risk of voltage-dependent RCD failure. In the UK, BS 7671 requires PEN fault protection for mode-3 EV charging which can also contribute to managing the risk.

To sum up, the author thinks it safe to use VD Type-EV or Type-B RCDs with purely electronic design for Mode-3 EV charging. Actually, the very challenge we see is whether the type-EV/B RCDs with purely VD structures can be designed, manufactured, and tested fully in accordance with the standards. E.g. there is a trend that EV charger manufacturers to design the charging controllers as a type-EV RCD following IEC61008-1 / IEC 60947-2 (Type-A RCCB / Type-A mRCD) and IEC 62955 (RDC-PD) – using relay or contacts, AC/DC leakage current sensor, charging controller MCU and other electronic components to design a type-EV RCD rather than installing a type-EV RCD of DIN-rail design. With in-depth experiences in RCD designing and manufacturing, our team believes it is not an easy task for EV charger manufacturers to ensure every charger provides consistent performance of residual current protection during large manufacturing. Therefore, BITUO teams offer a wide range of value-added services for EV charger manufacturers, such as technical support in integrating our AC/DC leakage current sensor into the charging controller properly, testing and verifying your design of EV charger as type-EV RCD, and even consultation about automated RCD testing.