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Importance of RCD in EV chargers

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What is RCD

RCD (residual current device) is a safety production device used to check and prevent electrical leakage in EV chargers. Electrical be cut down to prevent accidents when RCD detects electricity abnormality.

How RCD works

1. Normal working conditions:

  • In the electrical circuit, electric in L line(also ask Live line), pass load, into N line(Neutral line) returned。
  • In normal conditions, the quality of into and out electricity is the same, so RCD can not any actions.

2. Fault condition (leakage current occurs):

  •  If someone’s device happens to Insulation damage， electric current can through the body or the ground leakage, then the current in the Live (L) and neutral (N) wires is no longer equal.
  • The CT (Current Transformer) inside the RCD detects this unbalanced current and cuts off the power supply immediately to protect the user from electric shock or prevent a fire.
Joint Tech EVL006 with RCD Protection Device
Joint Tech EVL006 with RCD Protection Device

What does the RCD consist of?

The RCD mainly consists of the following components:

1. CT, Current Transformer

  • CT consists of an iron core and two wire circles, connected to the L wire and N wire.
  • Normally, the current in the live and neutral wires is equal and opposite in direction, and the magnetic fields generated in the transformer balance each other out, with the total magnetic flux being zero.
  • If the electric currents are unbalanced (e.g., leakage currents appear), a change in magnetic flux occurs in the iron core, resulting in the induction of a voltage signal.

2. Detect and trigger circuit

  • RCD also consists of an operational amplifier (Op-Amp)and comparator, etc. It analyses the signal from the current transformer.
  • If it detects the leakage current over the default value (e.g. 30mA or 6mA DC), it will trigger the relay to operate.

3. Disconnecting mechanism (relay)

  • After the electronic triggering, the relay disconnects the charging circuit and cuts off the power supply to prevent electric shock or device damage.

RCD triggering system

The triggering of RCD mainly depends on two important factors:

1. The amount of leakage current

The nominal action value of RCDs:

  • 30mA ( Human Body Protection ): protects from serious electric shock and is suitable for homes and offices.
  • 100mA / 300mA ( Device Protection): it is suitable to protect against the risk of fire and is usually used in industrial equipment.
  • 6mA DC (for EV charger): specifically detects DC leakage to avoid RCD not working.

2. Response time

  • Regular RCD (no delay): Disconnect in 10-30ms at 30mA leakage current.
  • Delayed RCD (S-type): 300mA leakage current, disconnect within 500ms to prevent the false trigger.

Importance of RCD in EV chargers

1. Prevention of electric shock accidents

  • During the EV charging process, cable, socket, charging system and other components may suffer from leakage currents due to aging, insulation damage or grounding faults.
  • The RCD can monitor leakage current in real time and quickly disconnect the power supply when the value is out of the safety range, preventing the user from electric shock.

2. Preventing fires and electrical accidents

  • The long time of the leakage current may cause the device’s internal temperature to increase, causing a fire.
  • The RCD can cut off circuits in time before the current reaches a dangerous level, avoiding fire risks.

3. Protection of EV charging equipment

  • DC Fast Charging (DCFC) and AC Chargers have a lot of electronic components inside, and if leakage current occurs, it is possible to damage equipment or cause control system anomalies.
  • The RCD can prevent circuit boards, power modules, and other critical components from being damaged and improve the charging pile lifespan.

4. Meeting the international safety standards

All countries have strict safety requirements for EV charging equipment, such as:

 

  • IEC 61851 (international standard): EV charging equipment is required to have an RCD protection function.
  • IEC 62752 (IC-CPD mobile charging equipment): requires a DC fault detection function.
  • UL 2231 (North American Standard): Requires RCD can detect AC and DC leakage current.
  • BS 7671 (UK IET Wiring Regulations): Recommends Type B RCDs or Type A + 6mA DC detection devices at EV charging points.
  • VDE 0100-722 (German Standard): specifies RCD protection requirements for EV charging.

Conclusion

RCD is an indispensable safety protection device in EV chargers, which can effectively prevent the risks of electric shock, fire and damage to electrical equipment. According to different EV charging scenarios, different RCD types (Type A, Type B or Type A + 6mA DC detection) should be chosen to ensure the compliance and safety of the charging pile.

 

As technology advances, smart RCDs and higher standard protection mechanisms will be gradually promoted to further enhance the safety and user experience of EV charging.

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