Cost-effective RCD & RDC-DD solution for Mode-3 EV Charger complying with IEC 61851-1

IEC s​​​​tandard reque​st for residual current protection at Mode-3 EV Charging

Configuration 3​​​​​

Type EV RCDs (Integrated Type-A RCBO/RCCB + RDC-PD) is a very safe and reliable protective measure, because it disconnect all live conductors in the occur of both AC and DC fault currents, as well as  works independent of charging controller and relays/contactors.  

Type EV RCDs benefits EV charger manufacturers from saving the high cost of testing the EV chargers in accordance with RCD and RDC-MD standards. For example, a EV charger can still reserve the connectors for DC RCS in the charging control board and go for a simplified mode-3 charger test about residual current protection via installing a type-EV RCBO/RCCB. The EV charger manufacturer can decides whether to test their charging controller as RDC-MD or mRCD depending on the sales ramp-up later.

Type EV/B RCDs also benefit installers and end-users. Electrician have been using RCBOs/RCCBs for years, thus there is a very low risk of wrong installation that results in electrical accidents. The end users can quickly notice the tripping of their type-EV RCBOs/RCCBs in the distribution boards.

Typical residual current protection configurations for mode-3 EV chargers following IEC 61851-1 request

Residual Current Protection for EV Charging 

Configuration 1​​​​​

DC residual current sensor alone (also called DC fault current sensor in some countries) is NOT a IEC62955 RDC-MD. However, it can be used to  configure a RDC-MD together with a specifically designed EV charging controller, which meets the DC fault current protection request defined in IEC 61851-1: 2017 and IEC 60364-7-722:2018. The charging controller can be viewed as monitoring module of RDC-MD, while DC RCS can be viewed as detection module of RDC-MD.

When a residual current sensor detecting both AC and DC fault current is used together with a specifically designed EV charging controller, it is feasible to configurate a type-EV mRCD – integrated type-A mRCD complying with IEC60947-2-(M) and RDC-MD complying with IEC62955. In this configuration, the protection against the fatal fault current of AC 30mA is provided by a coordinated activaties of RCS, Charging Controller and Relays/Contactors, which is less reliable than RCBOs or RCCBs that detect and trips independently. Therefore, we strongly advocate install at least a type-A RCBO or RCCB upstream of the EV charger, even your chargers tested as type-EV mRCD.

According to IEC61851-1: 2017 and IEC60364-7-222:2018, the appropriate measures for Mode-3 EV AC charging systems shall be 

    • Option 1: RCD Type B  (IEC60947-2 type-B mRCD/CBR or IEC62423 type-B RCCB)
    • Option 2: RCD Type A (IEC61008-1 type-A RCCB, IEC61009-1 type-A RCBO or IEC60947-2 type-A mRCD/CBR ) and RDC-DD (IEC62955 RDC-PD or RDC-MD)

RCDs and RDC-DD shall comply with the standards in the brackets. Also, it is explicitly stated by IEC60364-7-222:2018 that RCD shall disconnect all live conductors. In Option 2, it is fine to use relays to switch power off in the occur of DC fault current, but relays normally can not meet the standard request of disconnecting all live conductors in the occur of AC fault current. Therefore, it is highly recommended to install a type-A RCD inside or outside the EV charger housing for AC 30 mA fault current protection.

Configuration 2​​​​​

A RDC-MD that complies with IEC62955 can drive the relays or contacts to open position, which erase the risk of MCU mal-function in configuration 1. Moreover, relays or contacts used in this configuration MUST meet the switching time request defined in the RDC-MD technical datasheet.

It is feasible to meet both AC and DC fault current protection request defined in  IEC 61851-1 and IEC 60364-7-722 via implementing the protective configuration B of using a type-B or a type-EV mRCD (integrated type-A mRCD following IEC60947-2-(M) and RDC-MD following IEC62955)  together with a control device. However, the protection against fatal fault current of AC 30mA is provided by a coordinated activates of mRCD and control devices, which is less reliable than RCBOs or RCCBs that detect and trip independently. Therefore, we strongly advocate install at least a type-A RCBO or RCCB upstream of the EV charger.

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Design compact 3.5/7 kW EV Chargers with the help of BRCS-02 two-in-one sensor   

It is agreed by most EV charger manufacturers that a type-B RCBO/RCCB is too expensive to be afforded by end users. Also, the use of type-B RCBO/RCCB for home EV charging application brings extra efforts of adjusting sub/final power distribution system. (Our previous blog touched this topic). In order to meet residual current protection request defined in IEC 61851-1, EV charger manufacturers usually use the cost-effective solution of type-A RCD and RDC-DD, which is implemented with the following two design options.

The first option has been practiced by most of professional EV charger engineers - using EV charging controller, purely 6 mA DC leakage current sensor and relays/contacts to build RDC-DD complying with IEC 62955 standard. Outside the EV charger box, the users can select Type A RCBO/RCCB by their own, such as ABB F204 or Siemens 5SV3 that are affordable and widely available in the continental countries.

The second option is to configurate a type-A 30mA RCD and RDC-DD with a  type-A 30 mA & DC 6 mA leakage current sensor, a charging controller and relays/contacts. As a type-A 30mA RCD, the EV chargers can follow either IEC 61008-1 standard about type-A RCCB or IEC 60947-2-(M) about type-A mRCD. If a type-A 30 mA RCDs are installed upstream of EV chargers, then the EV chargers complying with type-A 30 mA RCD standard can provide back-up protection against electrical shock in the occur of external type-A RCD failure.

Our BRCS-01/02 series leakage current sensor have rated leakage current of type-A 30mA & DC 6 mA and purely DC 6mA, which facilitates customers to chose any of the two above design options. The BRCS-01/02 sensors are designed by BITUO’s experts with track records of designing world-class RCDs. And we carefully coordinate a supply chain that maintain Asia-and-Europe dual suppliers for critical components, in order to keep consistent performance of delivery and quality. Most importantly for EV charger manufacturers, there are five installation variants at BRCS-01 family for a quick integration of our sensors into your EV charger controllers as the following picture illustrated. Our offer helps EV charger manufacturers in all IEC countries mitigate delivery risk of critical components via maintaining high-standard suppliers from both Asia and Europe.

Compact AC EV chargers- either mode-2 IC-CPDs or mode-3 wallboxes- are favored by end users. Thus, EV charger engineers have been trying hard to design EV chargers as small as possible. The height of a 3.5/7 kW AC charger is often limited by the height of relays on the charging controller PCBA. Our enginners increased the height of BRCS-01 sensor housing to create BRCS-02 sensor that can not only fit an addional current transformer but also occupies the same space on charing controller PCBA as BRCS-01. The overall height of BRCS-02 is the same as BRCS-01, whose height is lower than the height of relays mostly used in charging controller.

BRCS-02 two-in-one sensor fits perfectly for 3.5/7 kW IC-CPDs and Wallboxes that comply with IEC/EN 62752 standard and IEC/EN 61851-1 standard. There are only five pins at the sensor - S1/S2 for current measurement and Vcc / GND / Trip / Test for redidual current detection.  The BRCS-02 sensor is very fast at detecting both AC and DC fault current, which faciliates the wide selection of main-circuit relays.