How to use residual current monitors to ensure electrical safety when charging electric vehicles
with IEC 62752 (Mode 2), IEC 62955 (Mode 3), and UL 2231. Each RCM has one operation LED and one fault LED. The four- pin JST connector simplifies the installation: pins 1 and 2 are for the 12-volt power supply, pin 3 is for external function testing, and pin 4 is an open-drain switching output to drive an external disconnector such as a cutoff relay, at up to 100 mA and 24 volts (maximum) (Figure 4).
The product is fully compliant with IEC 62955. RCM20-03: The RCM20-03 is a residual current monitor intended for the detection of DC and AC residual currents in 50 Hz/60 Hz AC installations. It is intended for Mode 2 Electric Vehicle Charging Stations, to disconnect the supply to the Electric Vehicle under DC and AC fault current condition. The product is fully compliant with IEC 62752, and can also be used for IEC 62955 applications where 30 mA AC fault detection is required.
For integration in a larger device circuit, the following RCM modules presented are also available as open-frame systems: ■ RCM14-01_SYS_V , RCM14- 01_SYS_H ■ RCM14-03_SYS_V , RCM14- 03_SYS_H ■ RCM14-04_SYS Each system consists of a solderable sensor pc board and a separate current transformer (Figure 6).
Conclusion AC-sensitive Type-A RCDs are common installation standards in building electrical systems, but they cannot protect against DC residual current hazards in EV charging circuits. As shown, the RCM14 series can perform the DC residual current monitoring required in ICCB charging cables (Mode 2) and EV charging stations (Mode 3). Featuring only four connection pins, system designers can easily and cost-effectively implement the compact RCM module or the open-frame system in their EVSE.
Figure 5: RCM14-01 adds monitoring of DC residual currents ≥ 6 mA to AC-sensitive Type-A RCDs in building electrical systems. (Image source: Littelfuse, Western Automation)
RCM14-01: 6 mA DC RCM module according to IEC 62955, 14 millimeter (mm) aperture The RCM14-01 residual current monitor detects DC fault currents in 50 Hz/60 Hz AC systems. It is developed for use in Mode 3 charging stations for EVs (IEC 62955 standard) to interrupt the charging circuit of the EV in the event of a DC fault current ≥ 6 mA. This detector adds DC residual current monitoring function to existing Type-A and Type-F RCDs of the building’s electrical system in a cost-effective and simple manner (Figure 5). RCM14-03: 6 mA DC/30 mA AC RCM module according to IEC 62752, 14 mm aperture The RCM14-03 is intended for use in ICCB or integrated protection devices for EVs in charging Mode 2
to interrupt the supply to the EV in the event of an AC or DC fault. RCM14-04: 56 mA DC/20 mA AC RCM module according to UL 2231- 2, 14 mm aperture The RCM14-04 module detects AC and DC fault currents in 60 hertz (Hz) AC installations. It is designed for use in Charging Circuit Interrupting Device (CCID) EV charging station applications where it interrupts the supply to the EV in the event of an AC and/or DC residual current condition. RCM20-01: The RCM20-01 is a residual current monitor intended for the detection of DC residual currents in 50 Hz/60 Hz AC installations. It is intended for Mode 3 Electric Vehicle Charging Stations, to disconnect the supply to the Electric Vehicle under DC residual fault current condition.
Figure 4: The RCM14 series modules have two status LEDs and are easy to connect via the four-pin JST connector. (Image source: Littelfuse)
Figure 6: The RCM14-04_SYS modules are open-frame systems consisting of a sensor pc board and a current transformer. (Image source: Littelfuse, Western Automation)
These active RCMs can also be used to detect AC and/or DC residual currents in single-phase or multi-phase DC installations. Single-phase operation limits the load current to 100 A, while three- phase operation is at 40 A. They can handle load current pulses up to 3000 A.
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