EV Charger RCD Selection: Type B vs. Type F vs. Type EV (IEC 62955 & IEC 62423)

For electrical engineers and installers, the rapid expansion of Electric Vehicle (EV) infrastructure presents a specific protection challenge: DC fault currents. Unlike standard household loads, the rectification circuits within EV On-Board Chargers (OBC) can generate smooth DC leakage currents in the event of a fault.

If not properly isolated, these DC currents can blind upstream Type A Residual Current Devices (RCDs), rendering the entire electrical installation unsafe.

This engineering guide analyzes the three compliant protection strategies defined by IEC 60364-7-722 and IEC 61851-1: using a Type B RCD, a Type F RCD (with specific conditions), or the newer “Type EV” (RDC-DD) approach. We will examine the technical distinctions between IEC 62423 and IEC 62955 to determine the optimal selection for safety, compliance, and cost-efficiency.

The “Blinding” Effect: Why Type A is Insufficient

The fundamental issue in EV protection is the magnetic saturation of the sensing core in standard RCDs. A standard Type A RCD (commonly used in residential and commercial circuits) uses a toroidal transformer optimized for 50/60Hz AC and pulsating DC.

When smooth DC current (DC current with less than 10% ripple) flows through this toroid, it creates a constant magnetic flux. If this DC leakage exceeds 6mA, it can shift the operating point of the magnetic core into saturation. Once saturated, the core cannot detect the alternating magnetic field generated by a life-threatening AC earth fault. The RCD becomes “blind” and will not trip, leaving users unprotected against electric shock.

Therefore, international standards mandate that any EV charging point must be protected by a device that disconnects the supply in case of DC fault current ≥ 6mA.

Defining the Contenders: Type B vs. Type F vs. Type EV

1. Type B RCD (IEC 62423)

The Type B RCD is the most robust solution. It contains two detection systems: a standard fluxgate for AC/pulsating DC and a separate high-frequency electronic detection circuit for smooth DC.

• Capabilities: Detects sinusoidal AC, pulsating DC, and smooth DC residual currents. Also detects currents at frequencies up to 1000Hz (critical for detecting switching frequency leakage from inverters).
• Tripping Threshold: Typically 30mA AC and 60mA DC. (Note: While the standard allows up to 2x IΔn for DC, VIOX Type B breakers often trip earlier for enhanced safety).
• Application: Required for three-phase chargers where DC leakage can be smooth, and for installations requiring maximum uptime and selectivity.

2. Type F RCD (IEC 62423)

The Type F RCD is an enhanced Type A. It offers better immunity to nuisance tripping from surge currents and can detect residual currents with mixed frequencies (up to 1kHz).

• Limitation: Crucially, Type F does not detect smooth DC.
• EV Application: You cannot use a Type F RCD alone for EV charging. It must be paired with an RDC-DD (Residual Direct Current Detecting Device) that handles the 6mA DC detection.

3. Type EV / RDC-DD (IEC 62955)

Often marketed as “Type EV,” this is technically a Residual Direct Current Detecting Device (RDC-DD). It is specifically designed to prevent Type A upstream RCDs from being blinded.

• Function: It monitors the circuit for smooth DC leakage.
• Threshold: It must trip at 6mA DC.
• Standards: Governed by IEC 62955.
• Variants:
  • RDC-MD (Monitoring Device): Detects leakage and signals the EV charger’s contactor to open. If the contactor contacts weld, protection fails.
  • RDC-PD (Protective Device): Includes its own disconnection mechanism (similar to a circuit breaker).

For a deeper understanding of how these devices fit into broader commercial systems, refer to our guide on Commercial EV Charging Protection.

Technical Comparison Matrix

The following table summarizes the detection capabilities and standard compliance for each device type.

*IEC 62423 allows the DC tripping current to be up to 2 times the rated AC residual current (IΔn). For a 30mA device, this is 60mA DC. However, the device itself is designed to withstand this DC level without blinding.

IEC 62955 vs. IEC 62423: Which Standard Applies?

The choice between an IEC 62423 compliant device (Type B) and an IEC 62955 device (RDC-DD) often depends on the charging hardware and the installation environment.

Scenario 1: The “Integrated” Approach (IEC 62955)

Many modern AC wallboxes (7kW – 22kW chargers) come with built-in 6mA DC detection. This is an RDC-DD compliant with IEC 62955.

• Requirement: You must install a Type A RCD upstream in the distribution board to handle AC faults.
• Pros: Lower component cost in the panel.
• Cons: If the charger’s internal detection fails, the Type A RCD upstream is at risk of blinding. Maintenance involves replacing the entire charger PCB rather than a DIN-rail component.

Scenario 2: The “External Protection” Approach (IEC 62423)

Using a DIN-rail mounted Type B RCD (or Type B RCBO) in the distribution board.

• Requirement: No additional RDC-DD is needed inside the charger. The Type B RCD handles AC, pulsating DC, and smooth DC faults.
• Pros: Centralized maintenance, higher reliability, immune to external DC interference, clear indication of fault type (on advanced models).
• Cons: Higher initial component cost.

Selection Decision Framework

When specifying protection for a project, follow this logic to ensure compliance with IEC 60364-7-722:

1. Check the Charger Datasheet: Does the EVSE (Electric Vehicle Supply Equipment) declare a built-in RDC-DD compliant with IEC 62955?
   • YES: You may use a Type A (or Type F) RCD/RCBO in the panel.
   • NO: You must use a Type B RCD in the panel.
2. Check Upstream Selectivity:
   • If you install a Type B RCD for the charger, ensure the upstream main RCD is not a Type A. A DC fault passing through the Type B could blind an upstream Type A. Ideally, the EV circuit should be connected parallel to other circuits, not downstream of a general Type A RCCB, or the main switch should be Type B (rare/expensive) or non-RCD (if TN-C-S/TN-S permits).
3. Consider Commercial Environments:
   • In commercial settings with multiple chargers, the cumulative leakage (even below 6mA per charger) can be problematic. Type B RCDs are preferred for durability and to avoid relying on the varied quality of internal charger electronics.

Cost vs. Safety Analysis

For high-value assets and critical infrastructure, the Type B RCD remains the engineering preference due to its independence from the charger’s internal electronics. For mass residential rollouts, the Type A + RDC-DD model is the economic standard.

FAQ

Q: Can I use a Type AC RCD for EV charging?
A: No. Type AC RCDs are prohibited for EV charging in most jurisdictions (including under IEC 60364-7-722) because they cannot detect pulsating DC, which is common in EV rectification circuits.

Q: If I have a Type B RCD, do I need an earth rod?
A: The RCD type dictates leakage detection, not earthing arrangements. However, for PME (TN-C-S) supplies, you may still need an open-PEN detection device or an earth rod, regardless of whether you use a Type B or Type A RCD.

Q: What is the difference between RDC-MD and RDC-PD?
A: Both are defined in IEC 62955. An RDC-MD monitors leakage and tells a contactor to open (cheaper, integrated). An RDC-PD has its own protection (switching) mechanism, making it safer if the contactor welds shut.

Q: Can I use a Type B RCD downstream of a Type A RCD?
A: Generally, no. Ideally, RCDs should be coordinated. If a DC fault occurs, it flows through both. The downstream Type B will trip, but the DC current might have already blinded the upstream Type A, disabling it for other circuits. Best practice is to connect the EV circuit in parallel or ensure the upstream device is also Type B (or time-delayed Type S, if appropriate for the system earthing).

For more information on selecting the right circuit protection for your projects, explore our guides on Electrical Derating Factors and Types of Circuit Breakers.