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Understanding Different Types of RCDs and Their Importance in EVSE Chargers

Residual Current Devices (RCDs) play a crucial role in ensuring electrical safety by quickly disconnecting the power supply when they detect an imbalance between the live and neutral currents. As Electric Vehicle Supply Equipment (EVSE) chargers become increasingly common, it's essential to understand the different types of RCDs and why choosing the right one is vital for safe and efficient charging.

Types of RCDs

There are several types of RCDs, each designed for specific applications and environments. Here are the most common types:

Type AC

Type AC RCDs are the most basic and were the most widely used type however we are moving across to Type A within consumer units (Fuse box). They are designed to detect alternating current (AC) leakage to earth and provide protection against electrical shock. However, they are not suitable for all applications, particularly when dealing with electric vehicle chargers.

Warning: As stated within BS7671:2018+A2:2022 531.3.3 - RCD Type AC shall only be used to serve fixed equipment where it is known that the load current contains no DC components.

Type AC RCD will be blinded by any DC components which will prevent it from operating when any connected circuits require it to do so on safety grounds.

Type A
Type A RCDs are more advanced and capable of detecting both alternating current (AC) and residual pulsating direct current (DC) leakage. This makes them suitable for a wider range of applications, including EVSE chargers, which may produce DC leakage due to their internal electronics.
Type B
Type B RCDs are the most versatile and can detect all types of fault currents, including AC, DC, and smooth DC. While they offer the highest level of protection, they are also the most expensive and are typically used in specialized industrial applications which in turn means they are not readily available.

Identifying Each Type of RCD

You can identify the type of RCD by examining the diagrams or markings on the device itself. Here's how to identify each type:

Type AC
Type AC RCDs typically have a symbol that resembles a sine wave (~). This symbol indicates that the device is designed to detect alternating current (AC) leakage to earth.
Type A
Type A RCDs usually feature two symbols: one that resembles a sine wave (~) and another that looks like a straight line with a series of dots (· · ·). The sine wave symbol indicates AC detection, while the line with dots represents the device's ability to detect pulsating DC leakage.
Type B
Type B RCDs often have a combination of symbols, including a sine wave (~), a line with dots (· · ·), and sometimes a symbol that resembles a straight line with no dots (—). These symbols indicate the device's ability to detect AC, pulsating DC, and smooth DC fault currents.
Diagram
 

 

Why a Minimum of Type A RCDs are Essential for EVSE Chargers

When it comes to EVSE chargers, using the right type of RCD is crucial for ensuring safety and compatibility.

Note: While you can use Type B and Type F RCDs most often due to costing and availability reasons Type A is the go-to for all installers.

Here's why Type A RCDs are recommended for EVSE installations:

EVSE chargers often have electronic components that can produce DC leakage as can the connected vehicles themselves. Type A RCDs are capable of detecting this type of leakage, providing an additional layer of safety compared to Type AC RCDs.

Compliance with Standards

Many electrical codes and standards now require the use of Type A RCDs for EVSE installations. Using the correct type of RCD ensures compliance with these regulations, reducing the risk of non-compliance penalties and ensuring that the installation meets safety standards.

Avoiding Issues

Using a Type AC RCD with an EVSE charger can lead to compatibility issues and potential safety hazards. AC-only RCDs cannot detect DC leakage, leaving the installation unprotected against certain fault conditions.

Warning: As stated within BS7671:2018+A2:2022 531.3.3 RCD Type AC shall only be used to serve fixed equipment where it is known that the load current contains no DC components.

Conclusion

Choosing the right type of RCD is crucial for ensuring the safety and reliability of EVSE charger installations. While Type AC RCDs offer basic protection against AC leakage, they are not suitable for EVSE applications due to their inability to detect DC leakage. Type A RCDs, on the other hand, provide comprehensive protection against both AC and DC faults, making them the preferred choice for EVSE installations.

By understanding the different types of RCDs and their applications, you can ensure that your EVSE charger installation is safe, compliant, and efficient. Always consult with a qualified electrician or installer when selecting and installing RCDs to ensure that they meet the specific requirements of your EV charging system.