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Is RCD Type B Better Than RCD Type A + RDC-DD for EV Charging?

Is RCD Type B Better Than RCD Type A + RDC-DD for EV Charging?

Han, Xiang | Bituo Technik

IEC 61851-1:2017 and IEC 60364-7-222:2018 specify the protective measures against residual current for Mode-3 EV AC charging systems as follows:

  • Option 1: RCD Type B complying with IEC 62423 or IEC 60947-2

  • Option 2: RCD Type A complying with IEC 61008-1, IEC 61009-1, or IEC 60947-2 and RDC-DD complying with IEC 62955

People might ask what the difference between the two protective measures is. The following table shows the protective difference between Option 1 and Option 2:

Protective Measure

Fault current detected

Protective Difference

Option 1: RCD Type B (I∆n  = 30mA)


  • Sinusoidal AC residual current

  • Pulsating DC residual current

  • Composite residual currents with frequencies up to 1000 Hz

  • Smooth DC direct currents  per IEC 62423 / IEC60947-2


  • According to IEC 62423 / IEC60947-2, Type B RCDs shall operate in response to a steady increase of smooth direct residual current limits of 0.5 I∆n  to 2 I∆n (I∆n =30 mA for EV charging application)

  • Composite residual currents with frequencies up to 1000 Hz SHALL NOT exist in an EV AC charging system when OBC is designed with an appropriate isolation scheme.

Option 2: RCD Type A (I∆n  = 30mA) and RDC-DD (I∆dc = 6mA)

  • Sinusoidal AC residual current

  • Pulsating DC residual current

  • Smooth DC direct currents  per IEC 62955

  • According to IEC 62955, the Standard value of rated residual operating current  (IΔdc) is 6 mA, while the standard value of residual non-operating current (IΔndc) is 0,5 I∆dc (3mA).

The tripping range of a Type B 30mA RCD for smooth direct residual current is between 15mA and 60mA, while the tripping range of an RDC-DD for smooth direct residual current is between 3mA and 6mA. The following diagram shows a Type-B RCD of 30mA installed at the final power distribution system. This Type B RCD of 30mA does not trip in the event of a 6mA ~ 15mA DC fault current – such as the DC fault current brought by an OBC insulation fault. However, the DC fault current within 6mA ~ 15mA can impair the function of the upstream Type AC/A RCD.

Diagram showing a Type B RCD (30mA) installed in a final power distribution system, with a 6mA to 15mA DC fault current flow through the Type B RCD branch that could potentially impair the functionality of an upstream Type AC/A RCD.

To mitigate the risk of upstream Type AC/A RCD blinding, the following installation approaches for Type B RCDs are usually used:

  • Approach A: Replace the upstream  type-AC/A RCD with a type-B RCD

  • Approach B: Change the incoming power supply of the type-B RCD from the outgoing terminal of the upstream  type-AC/A RCD to the incoming terminal of the upstream  type-AC/A RCD

For home charging applications, neither Approach A nor Approach B is a good solution from the perspective of product cost and installation convenience. Therefore, there is a clear trend of using the combination of  RCD Type A and RDC-DD for residual current protection for home EV charging.

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