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# Built-in RDC-DD / RCD for EV Chargers
A guide for electronic engineers and purchasers on built-in residual current protection in EV chargers, covering product selection, integration, and testing.
### ⚡ Quick Answers
What is an RDC-DD? [BRCS]
**RDC-DD** stands for **Residual Direct Current Detecting Device**. It is specifically designed for Mode 3 electric vehicle (EV) charging in compliance with the **IEC 62955** standard. Its primary function is to ensure the proper functionality of upstream Type A or Type F RCDs, even in the presence of smooth DC residual currents exceeding 6 mA.
According to IEC 62955:2018, RDC-DDs are categorized into two types:
* **RDC-MD (Residual Direct Current – Monitoring Device):** Primarily used for monitoring DC residual currents. It prevents Type A or Type F RCDs from malfunctioning (blinding) due to DC leakage above 6 mA.
* **RDC-PD (Residual Direct Current – Protection Device):** Provides comprehensive protection. In addition to handling DC residual currents above 6 mA, it also protects against AC residual currents and pulsating DC residual currents.
**The Key Difference:** The primary difference between an RDC-MD and an RDC-PD lies in their protection capabilities. While the RDC-MD effectively monitors DC leakage to protect upstream RCDs, it does *not* offer protection against AC or pulsating DC residual currents. Therefore, it is unsuitable for directly protecting human life on its own.
Because of this specific monitoring role, engineers often refer to the RDC-MD as a **DC RCM (Residual Current Monitor)**.
What is the difference between an RDC-DD and a Type B RCD? [BRCS]
The primary differences lie in how they respond to various types of residual currents, particularly smooth DC currents and high-frequency composite currents.
The table below compares the responses of **RDC-MD** (one type of RDC-DD), **RDC-PD** (the other type of RDC-DD), and **Type B RCD**:
| Residual current form | RDC-MD | RDC-PD | Type B RCD |
| ---------------------------------------------------------- | --------- | --------- | ----------- |
| Sinusoidal AC residual current | N | Y | Y |
| Pulsating DC residual current | N | Y | Y |
| Smooth DC direct currents | Y (3-6mA) | Y (3-6mA) | Y (15-60mA) |
| Composite residual currents with frequencies up to 1000 Hz | N | N | Y |
**Notes:**
1. **Tripping Thresholds for Smooth DC:** Type B 30mA RCDs respond to smooth DC residual currents ranging from 15mA to 60mA ($$0.5 I\_{\Delta n}$$ to $$2 I\_{\Delta n}$$, where $$I\_{\Delta n} = 30mA$$). In contrast, RDC-DD devices respond to much lower smooth DC currents, specifically between 3mA ($$0.5 I\_{\Delta dc}$$) and 6mA ($$I\_{\Delta dc}$$).
2. **High-Frequency Currents:** Composite residual currents with frequencies up to 1000 Hz are generally not found in EV charging systems where the onboard charger (OBC) is properly isolated.
Why do most EV charger manufacturers prefer built-in RDC-DDs over Type B RCDs for Mode-3 charging? [BRCS]
**A:** While some engineers assume that RDC-DDs are simply cheaper to manufacture than Type B RCDs, cost is actually not the core factor. When implemented with proper sensors, the manufacturing costs of both solutions are comparable.
The real reason RDC-DD dominates Mode-3 EVSE design is the **simplicity of electrical installation** and the prevention of a critical safety hazard known as the **DC blinding effect** in residential power grids.
Here is the technical breakdown of why the RDC-DD + Type A RCD combination is preferred:
**1. The "Blinding" Hazard in Residential Panels** In a typical home installation, an EV charger equipped with a built-in Type B RCD is usually connected to a dedicated MCB (Miniature Circuit Breaker) branch within the distribution board. If the main incoming power supply of the house uses a general Type-A or Type-AC 30mA RCBO/RCCB, a severe safety risk emerges.
If a smooth DC fault current between 6mA and 15mA occurs on the EV charger branch, the charger's Type B RCD will *not* trip (since its DC tripping threshold is 15\~60mA). Instead, this specific 6\~15mA DC current will flow back into the household grid and **"blind" the main upstream Type-A/AC RCD**. If other MCB branches—such as those for bathroom outlets or kitchen appliances—rely on this main Type-A/AC RCD for leakage protection, the blinding effect completely disables their safety mechanism, posing a hidden and lethal danger to the entire household.
**2. The Installation Hassle of Type B Solutions** To mitigate this extreme risk when using an EV charger with a Type B RCD, installers are forced to use one of two complex approaches:
* **Approach A:** Replace the main upstream household Type-A/AC RCD with an expensive Type B RCD.
* **Approach B:** Rewire the distribution board so the EV charger's power supply bypasses the main RCD (connecting its incoming power supply directly to the incoming terminal of the upstream RCD).
**3. The RDC-DD Advantage** Neither of the above approaches is ideal for residential applications due to high installation costs and inconvenience. By integrating an **RDC-DD** (which strictly trips at 6mA DC) into the EVSE, manufacturers ensure that the upstream Type A RCD is perfectly protected from DC blinding. This configuration efficiently meets **IEC 61851-1** requirements while keeping the end-user's electrical installation safe, simple, and cost-effective.
Should I design a Built-in RDC-PD or an RDC-MD for my AC EV charger? [BRCS]
**A:** While an **RDC-PD** (Protection Device) sounds ideal because it combines AC, pulsating DC, and 6mA DC detection with mechanical switching in a single unit, **we generally do not recommend attempting a built-in RDC-PD design.**
To qualify as an RDC-PD, the device must be suitable for isolation and fully comply with the stringent requirements of **IEC 61008-1** or **IEC 61009-1** (as outlined in Annex O of IEC 62955:2018). In practice, achieving this full compliance on a PCBA is extremely challenging due to the physical and electrical limitations of standard PCB-mounted power relays.
**The Practical Approach: Two Viable Alternatives** Therefore, a more accurate question is: *Should I design a built-in Type-A mRCD & RDC-MD combination, or should I opt for a built-in RDC-MD design?*
Due to varying local policies, installation habits, and power distribution setups, we recommend making this decision based on your target market:
* **Option 1: Built-in Type-A mRCD (IEC 60947-2) & RDC-MD (IEC 62955)**
* **Commonly used in:** Markets that can accept voltage-dependent RCDs for household applications, like the UK, Nordic countries, China and India.
* **Option 2: Built-in RDC-MD (IEC 62955) Only**
* **Commonly used in:** Markets that do not accept voltage-dependent RCDs for household applications, such as European continental countries like Germany, France, Italy and Austria.
*(💡 **Learn More:** To understand the technical differences between these two types of residual current devices, check out our detailed blog post:* [*Can Voltage-Dependent RCDs Provide Sufficient Protection?*](https://www.bituo-technik.com/can-voltage-dependent-rcds-provide-sufficient-protection/)*)*
What standards should we declare for the "integrated" or "built-in" residual current protection on our EV charger's Declaration of Conformity (DoC)? [BRCS]
For Mode-3 EVSE (AC EV Charger) manufacturers integrating our residual current sensors onto a PCBA, we highly recommend declaring conformity based on **IEC 60947-2** and **IEC 62955**.
Drawing on our expertise since the introduction of IEC 62955 in 2018, we consistently advise using one of the following declarations, depending on your hardware design:
* **Option A:** Built-in Type-A mRCD (IEC 60947-2) & RDC-MD (IEC 62955)
* **Option B:** Built-in RDC-MD (IEC 62955)
**Why avoid IEC 61008-1?** We strongly advise against declaring your built-in solution as a standard Type-A RCCB (IEC 61008-1) or RDC-PD unless your assembly strictly fulfills all their specific mechanical and electrical criteria.
Electrical safety authorities in Europe and Asia closely scrutinize EVSE compliance. Using the recommended options above accurately reflects your integrated architecture and ensures smooth market entry.
Do your AC/DC residual current sensors have independent IEC 62955 RDC-DD certification and reports from an accredited independent test laboratory? [BRCS]
Yes, for the first product in our BRCS family. However, for subsequent models, we focus on system-level compliance.
The first product in our BRCS family—the BRCS01-\*-H1—was actually the world's first residual current sensor to obtain TÜV certification back in 2019. We are happy to provide this certificate and its test report upon request.
For subsequent products in the BRCS family, we no longer conduct expensive, standalone third-party certifications for every single model. Instead, we rely on our **rigorous internal testing, combined with integration testing by our pilot customers and the successful certification of their complete charging stations**. Here is why:
* **System-Level Mandate**: According to the IEC 62955 standard, the sensor must be validated as part of a complete system. In the context of an AC EV charging station's integrated leakage protection, this "system" includes the sensor, the charging control board's power supply, the MCU, the relays, and auxiliary components on the board.
* **No Exemption**: A standalone component certificate cannot exempt your final product (the charging station) from system-level testing. If you review our original BRCS01-\*-H1 TÜV report, you will see it was also tested as a combination with other components.
* **Real-World Validation:** Beyond our internal tests, new products are validated through integration by our pilot customers. Their EV chargers have successfully passed complete built-in RCD / RDC-DD tests at recognized testing institutions. With years of successful application, our sensors have been widely integrated by customers across Europe and Asia.
With a well-engineered charging controller design, passing the IEC 62955 tests for a Residual Direct Current Detecting Device (RDC-DD)—**whether configured as an RDC-PD (Protection Device) or an RDC-MD (Monitoring Device)**—is straightforward. If you encounter any challenges during your integration and design process, please feel free to contact our engineering team for support.
Why do testing laboratories reject standalone IEC 62955 reports for the sensor and insist on testing it within our complete EV charging station? [BRCS]
This is a standard industry requirement because **IEC 62955 evaluates residual direct current protection or monitoring as a complete, integrated system**, rather than an isolated component.
As mentioned, this system includes the sensor, the charging control board's power supply, the MCU, the relays, and auxiliary components on the board.
When you integrate a sensor into a new charging station, testing labs must evaluate the whole assembly because **hardware variables**—such as any changes in the PCBA layout, power supply design, or surrounding components—can significantly impact the overall function of the system (including its Electromagnetic Compatibility / EMC performance).
Therefore, reputable certification bodies (such as TÜV, DEKRA, and SGS) will not accept a sensor's historical test report that was conducted using a specific, different controller. To ensure true safety and compliance, the sensor must be tested as an integrated part of your specific, complete charging system.
How to understand the 85°C maximum operating temperature? [BRCS]
The 85°C specified in the datasheet refers to the **maximum ambient operating temperature**, not the device's surface temperature.
**Detailed Explanation:**
* **Designed for Real-World Load:** The 85°C rating already accounts for the additional temperature rise when the charger is operating under load. In actual applications, high-current traces on the PCB directly underneath the sensor can sometimes exceed 90°C.
* **Ample Redundancy:** While our sensor is designed and its components are selected to fully cover the -40°C to 105°C range, we conservatively specify 85°C as the maximum ambient temperature. This approach ensures straightforward reliability and ample redundancy under actual load conditions, avoiding the controversial "no-load" 105°C claims made by some manufacturers.
* **High Heat Resistance:** There are no concerns about the device's casing getting too hot or melting. The plastic housing of the sensor is designed to withstand temperatures up to **150°C**.
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