Bituo provide RCDs and RDC-DD for IEC Market  
What Is An RCD & RDC-DD?

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​Residual current devices (RCDs) – that usually cut off the power supply in case of detecting an imbalance of the electrical current flow, thus providing protection against electrocution and electrical fires. It is one of the widely used measures to protect people and equipment against leakage current. Typical RCDs used in industries and household application are listed as follows: 


  • RCCB (IEC/EN 61008-1, IEC/EN 62423): Residual current protection only, thus MCB must be installed additionally for overcurrent and short-circuit protection 


  • RCBO (IEC/EN 61009-1, IEC/EN 62423): MCB + residual current protection. It is usually seen in two structures - An integrated device or MCB in association with RC-Unit 


  • RC-Unit (IEC/EN 61009-1)): An add-on module for MCBs to provide residual current protection function in addition to overcurrent and short-circuit protection   


  • RDC-DD (IEC 62955): A device to be used to protect a Type-A RCD from being negatively impacted by DC fault current equal to or above 6 mA at Mode-3 EV Charging 


  • RCM (IEC/EN 62020): A device designed to monitor residual currents and indicate by the alarm. It is NOT intended to provide protection


  • mRCD (IEC 60947-2 (M)):  A residual current module used in conjunction with a MCB or MCCB to provide residual current protection. A shunt trip or under-voltage release may be used additionally. 


Residual Current Devices​ 

& Residual Direct Current Detection Devices 

Which Type Of RCD Should Be Used?

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​Residual current devices (RCDs) – that usually cut off the power supply in case of detecting an imbalance of the electrical current flow, thus providing protection against electrocution and electrical fires. It is one of the widely used measures to protect people and equipment against leakage current. Typical RCDs used in industries and household application are listed as follows: 




RCD TypeFault current detectedTypical types of load


- Sinusoidal AC residual current


Resistive, capacitive, inductive loads. 

Immersion heater, oven/hob with resistive heating elements, electric shower, tungsten/halogen lighting, etc



- Sinusoidal AC residual current

- Pulsating DC residual current


Single-phase with electronic components

Single phase inverters, class 1 IT & multimedia equipment, power supplies for class 2 equipment, appliances such as washing machines, lighting controls, induction hobs etc.


* Type A is also suitable for Type AC applications.



- Sinusoidal AC residual current

- Pulsating DC residual current
- Composite residual currents with frequencies up to 1000 Hz 


Frequency controlled single-phase equipment/appliances

Appliances such as a washing machine that is frequency controlled, some class 1 power tools, some air conditioners using variable frequency speed drives


* Type F is also suitable for Type AC and Type-A applications.



- Sinusoidal AC residual current

- Pulsating DC residual current
- Smooth DC direct currents per IEC 62955


Mode-3 EV chargingAC EV charging where both AC 30mA (A-type) protection and DC fault current>6mA detection are requested by IEC 61851-1 & IEC 60364-7-722


* Type EV is also suitable for Type AC and Type A applications



- Sinusoidal AC residual current

- Pulsating DC residual current
- Composite residual currents with frequencies up to 1000 Hz
- Smooth DC direct currents 


Three phase electronic equipment

Inverters for speed control, ups, mode-3 EV charging, Photo voltaic, Power Electronic Converter Systems, industrial machines, cranes


 * Type B is also suitable for Type AC, Type A Type F, and Type EV applications.


In order to speed up the protection upgrading in the segment of renewable energy and e-mobility, Bituo offers some high-performance standard residual current devices (RCDs) against smooth DC fault current and high-frequency fault current and residual direct current detection devices (RDC-DDs) complying with IEC 62955.

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Why is protection against DC fault current above 6mA needed for AC EV charging?

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Inside the blue line of the following picture is the electrical diagram of a typical onboard charging system(OBC). Various factors - such as vibrating and aging – might result in insulation fault of OBC at the car. During charging, It is the insulation fault at DC/DC converter part of OPC that leads to smooth DC current, which impairs the function of type-A RCD at the AC power supply side. In other words, both the response time and the response level of type-A RCD can be negatively affected in the occur of DC fault currents above 6 mA. In the worst case, a type-A RCD will no longer prevent people against electrical shock. 







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However, the product standard about detecing DC fault current above 6mA has been missing till 2018. Thanks to the newly published IEC62955:2018 (Residual direct current detecting device ((RDC-DD)) to be used for mode 3 charging of electric vehicles), the design and testing of a RDC protection device now shall follow the specification defined in the standard. The IEC62955:2018 is like a fine calibrated ruler to check a RDC protection device, which fundamentally raises the bar of human protection in the EV charging infrastructure.


To know more about how to design a EV charger fully complying with redidual current protection defined in IEC 61851-1 and IEC 60364-7-722, click here

Email：info@bituo-technik.com   ​​​
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