What is RCD?
RCD stands for “Residual Current Device,” also known as a “Residual Current Circuit Breaker” or “RCCB.”
It is a low-voltage safety device designed to detect and disconnect residual currents in an electrical circuit. RCDs are primarily used to prevent accidents, fires, and equipment damage caused by leakage currents and to detect and disconnect various types of ground faults. When electrical equipment experiences a leakage current, the RCD automatically trips and cuts off power, thereby preventing equipment damage and personal injury.
RCDs are widely promoted and mandated for use in low-voltage electrical networks by countries worldwide and the International Electrotechnical Commission, which establishes electrical installation and usage regulations.
The principle of its operation involves the detection of abnormal current and voltage signals generated when electrical equipment experiences leakage. The RCD detects these signals and triggers the actuator mechanism to quickly disconnect the power, providing residual current protection.
Types
RCDs are primarily classified into Type A and Type B.
- Type AC Residual Current Devices
- Type AC RCDs are designed to protect against sinusoidal leakage currents at the mains frequency. They provide reliable protection against both sudden and slow-rising sinusoidal leakage currents.
- Type A Residual Current Devices
- Type A RCDs encompass the characteristics of Type AC RCDs and provide additional protection against pulsating direct currents, superimposed smooth direct currents up to 6mA, and smooth residual currents. They ensure disconnection in the presence of these types of currents.
- Type B Residual Current Devices
- Type B RCDs include the features of Type A RCDs and provide protection against sinusoidal alternating currents up to 1000Hz and below, superimposed smooth direct currents, pulsating direct currents superimposed with smooth residual currents, pulsating direct currents generated by rectifier circuits, and smooth residual currents. Only Type B RCDs can provide protection in the event of direct current leakage.
Please note that the classification of RCDs may vary in different regions or countries, and it is important to refer to the specific standards and regulations applicable in your location.
In cases where the EV supply equipment is equipped with an AC socket-outlet or vehicle connector in accordance with IEC 62196 (all parts), protective measures against DC fault current must be implemented. The suitable measures are as follows:
Type B RCD, or Type A RCD in combination with appropriate equipment that guarantees disconnection of the power supply when DC fault current exceeds 6 mA.
IEC 61851-1 determines the requirement of RCD:
- Type B
- Type A + 6mA smooth DC protection
IEC 62955 details the form of RCD:
In the context of electric vehicle charging stations, the application of residual current devices (RCDs) can be divided into two scenarios:
- RCD at the output of the charging station:
RCDs are installed at the output circuit of the charging station primarily to protect the charging equipment and prevent potential harm to electric devices and individuals caused by current leakage. In this case, the type of RCD used is crucial because the battery of an electric vehicle and the AC-DC conversion circuit are significant sources of direct current leakage. Therefore, protection against smooth direct current residual currents is essential.
- RCD at the input of the charging station:
RCDs are used at the input side of the charging station to protect the charging station itself and subsequent electrical devices from leakage currents in the power grid. Different types of RCDs can be selected for this purpose. In the industry, RCBO (Residual Current Circuit Breaker with Overcurrent Protection) is commonly used.
RCBO
RCBO is a combination electrical protection device that integrates two functions: residual current protection and overload protection. It performs similar functions to an RCD by detecting residual currents in the circuit. Additionally, RCBO incorporates overload protection features similar to fuses or miniature circuit breakers (MCBs). When the current in the circuit exceeds the rated value, the RCBO automatically trips, cutting off the circuit to prevent wire overload, equipment damage, or fire hazards.
RCBO provides protection against both residual currents and overload conditions, making it widely used in electrical systems as a crucial component to ensure electrical safety.
How RAEDIAN uses RCD to protect charging safety:
RAEDIAN RCD Approach
RAEDIAN’s RCD solution adopts the most validated and approved method that endorsed by most of the certification lab and agency.
Method C is implemented in NEO/NEX/NORA
Method C is most popular solution for residential and semi-public because:
- External RCD is easy to recover when nuisance trips occur
- Size of the wallbox could be reduced
- Internal 6mA DC RCM could be programmed to re-close when the fault current disappears, nuisance-trip-proof
RAEDIAN Type B implementation
For Method C, Type B RCBO could be installed upstream of the wallbox to provide the maximum protection over DC and high frequency fault current.
The external Type B RCBO and internal DC residual current detection will work simultaneously.
RAEDIAN offer its own power distribution unit ECPC Unit,
CDU-40B-S is the model that integrated Type B RCBO as well as Type 2 SPD to provide maximum protection for your EV and wallbox.
At the output of the charging station:
RAEDIAN charging stations are equipped with an integrated Residual Current Monitor (RCM), which fully complies with the standards of IEC 62955:2018. The RCM detects residual currents of 6mA and above for smooth direct currents, and 30mA and above for alternating currents and pulsating direct currents. When such currents are detected, the charging process is stopped, and a fault alarm is issued.
Before each charging session, the built-in RCM undergoes a self-check.
The action characteristics of the built-in RCM do not affect the protective functionality of the front-end RCBO. Both systems work together to provide comprehensive detection and protection against residual currents.
At the input of the charging station:
RAEDIAN explicitly states that RCBO (Residual Current Circuit Breaker with Overcurrent Protection) should be installed at the input of the charging station. The specific requirements are as follows:
