The Importance of RCD in EV Chargers

Leakage protection for EV charger use Residual Current Device (RCD) to detect and quickly disconnect hazardous AC and DC leakage currents from the charger, preventing electric shock and fire. These RCDs must be sensitive to both AC and smooth DC residual currents due to the electronic components in EV chargers, with standards like IEC 62955 requiring DC 6mA detection for some systems. Solutions range from Type B RCDs, which detect all current types, to built-in AC/DC fault monitoring sensors in the charger itself.

Why RCD protection is Necessary

Personal Safety:

Prevents electric shock to the user by quickly shutting off power if current leaks from the charger or cable.

Equipment Protection:

Protects critical components within the charging equipment, like circuit boards and power modules, from damage caused by leakage currents.

Fire Prevention:

Helps prevent fires by detecting and mitigating the causes of hazardous current leakage.

Types of Leakage Current

AC and Pulsating DC: Generated by the charger's rectifier/inverter circuits.

Smooth DC: Also produced by two-phase/three-phase rectification and filtering within the charger's power module.

How Leakage Protection Works

1. Monitoring:

The system continuously monitors the current flowing through the charging circuit.

2. Detection:

If current "leaks" from the cable or charger and does not return through the expected path, it indicates a fault.

3. Disconnection:

An RCD or similar device detects these abnormal AC and DC residual currents and rapidly disconnects the power supply, stopping the fault from progressing.

Key Standards & Components

IEC 61851:

The international standard for EV charging equipment, requiring RCD protection.

IEC 62955:

Specifies requirements for Residual Direct Current Detecting Devices (RDC-DDs) for detecting hazardous DC residual currents, often at 6mA.

RCDs (Residual Current Devices):

Safety devices used to detect leakage current.

Type B RCDs:

Required for high-safety applications as they detect AC, DC, and pulsating DC fault currents.

RDC-DD/RCM (Residual Current Monitoring):

Specialized devices that detect residual DC currents, like the 6mA requirement in IEC 62955.

Integration in EV Chargers

External RCDs:

A Type B RCD can be installed in the electrical panel to protect the charging point.

Integrated Protection:

Many modern chargers and charging cables (IC-CPDs) have built-in leakage protection, including integrated RCD modules or leakage current sensors that monitor and provide DC fault detection directly within the charging device.