Why Built-in RDC-DDs are the Preferred Choice for EV Charging over Type B RCDs

Feb 17, 2023 | Applications, Technology

IEC 61851-1:2017 (Electric vehicle conductive charging system – Part 1: General requirements) requires the detection of smooth DC leakage current above 6 mA for AC EV charging to ensure electrical protection. Both Type B RCDs and RDC-DDs can be used for smooth DC leakage current detection, individually complying with IEC 62423 / 60947-2 and IEC 62955. In a related blog post, we explored where the smooth DC leakage current comes from.


However, built-in RDC-DDs have been more widely used than Type B RCDs for EV charging since IEC 62955:2018 (product standard for RDC-DD) came into effect four years ago. In this blog post, our experts explain why built-in RDC-DDs are more favored than Type B RCDs for EV charging applications.


What are Built-in RDC-DDs?

RDC-DD stands for Residual Direct Current Detecting Device, and it is used for Mode 3 charging of electric vehicles. An RDC-DD compliant with IEC 62955:2018 can detect smooth DC residual currents above 6 mA and ensure that the type A/F RCDs’ proper functionality is not impaired. The RDC-DD disconnects the power supply to the EV when it detects a smooth residual direct current equal to or above 6 mA.


There are two types of RDC-DDs in practical applications: independent RDC-DDs and built-in RDC-DDs. An independent RDC-DD can disconnect all live conductors in case of DC leakage currents, while a built-in RDC-DD’s function is provided by coordinated activities among the DC leakage current sensor, the EV charging controller, and the relays/contactors.

Built-in RDC-DD and Independent RDC-DD


What is a Type B RCD?

Type B RCDs, such as Type B RCBO and Type B RCCB, are mainly used for protection against sinusoidal AC residual current, pulsating DC residual current, composite residual currents with frequencies up to 1000 Hz, and smooth DC direct currents. They can be installed in the circuit feeding the EV charger to detect smooth DC leakage current.


Factors Influencing the Selection of Built-in RDC-DDs or Type B RCDs for EV Charging

Our experienced experts believe that three major factors influence the selection of built-in RDC-DDs or Type B RCDs for EV charging, leading to the widespread use of built-in RDC-DDs:


  • Competition: Both built-in RDC-DDs and Type B RCDs are safe and reliable from a technical perspective, and both are allowed by the standard. However, Type B RCDs are much more expensive than built-in RDC-DDs. For EV charger manufacturers, the cost of a Type B RCD solution is at least three times higher than a built-in RDC-DD.
  • Maintenance: It is accepted to remotely reset the control device after the DC smooth current disappears. A built-in RDC-DD consisting of a DC leakage current sensor, an EV charging controller, and control/relays facilitates this remote re-closing function. However, it is difficult to achieve this function with a Type B RCD due to its combined detection and tripping of AC and DC leakage current.
  • Installation: As we discussed in our previous post, if there is a Type-AC/A RCD installed upstream of the Type B RCD newly added for EV chargers, electricians have to change the in-coming power supply of the Type B RCD, from the out-going terminal of the upstream Type-AC/A RCD to the in-coming terminal of the upstream Type-AC/A RCD. Another method is to replace the upstream Type-AC/A RCD with a Type B RCD. A built-in RDC-DD at an EV charger simplifies the extra re-wiring or investment compared to a Type B RCD.


Bituo’s AC/DC Leakage Sensors for Built-in RDC-DD Design at EV Chargers

Bituo offers a range of AC/DC leakage current sensors that facilitate the built-in RDC-DD design at AC EV chargers, providing a reliable and cost-effective solution for EV charging protection. Among Bituo’s sensor portfolio, BRCS01/02 has been widely used with proven records in IEC markets, and BRCS03 is to be launched in April, which will further enhance the performances and provide both 5V and 12V interface.


Bituo AC/DC Leakage Current Sensors for Mode-2/3 EV Chargers


Final Words

In summary, while both built-in RDC-DDs and Type B RCDs can be used to detect smooth DC leakage current in EV charging applications, the use of built-in RDC-DDs is more widespread due to their lower cost, easier maintenance, and simpler installation compared to Type B RCDs.


If you’re interested in learning more about residual current monitoring and protection technologies, or need assistance with the right solution for your specific needs, feel free to contact us anytime. Our experienced team is always ready to help you find the best solution for your EV charging protection needs.


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