Residual Current Devices (RCDs) are electrical safety devices designed to protect people and property from the dangers of electrical shocks and fires. They work by constantly monitoring the current flowing through a circuit and interrupting it if an imbalance or fault is detected. There are different types of RCDs available on the market, each with specific features and applications. In this article, we will discuss the four main types of RCDs: Type AC, Type A, Type F, Type B.
Type AC RCD
Type AC RCDs are the most common type of RCDs used in residential and commercial applications. They are designed to detect and interrupt alternating current (AC) faults, such as those caused by accidental contact with live wires, defective appliances, or damaged insulation. Type AC RCDs can detect imbalances in the current as low as 30 milliamps (mA) and interrupt the circuit within 0.1 seconds, providing reliable protection against electric shock.
Please note, that in most instances Type AC RCDs are no longer suitable in the UK (and across parts of the world). This is due to their protective function prone to being affected by any piece of electrical equipment that may contain DC components within the load current. For more information see our bulletin on “Type AC RCDs and the effects of DC leakage current”
Type A RCD
Type A RCDs are more sensitive than Type AC RCDs and can detect both AC and pulsating direct current (DC) faults. They are designed to protect against the risks of indirect contact with live parts, such as when using power tools or handling electrical equipment in damp or wet conditions. Type A RCDs can detect imbalances up to 6 mA of DC leakage and interrupt the circuit within 0.1 seconds, providing higher levels of safety in potentially hazardous environments.
Type F RCD
Type F RCDs are designed to protect against the risks of fire caused by electrical faults. They are more sensitive than Type AC and Type A RCDs and can detect both AC and high-frequency AC faults, such as those caused by arc faults in electrical circuits. Type F RCDs can detect imbalances up to 10 mA of DC leakage and interrupt the circuit within 0.1 seconds, providing early warning of potential fire hazards.
Type B RCD
Type B RCDs are the most advanced type of RCDs and can provide protection against all types of electrical faults, including AC, DC, pulsating DC, and smooth DC faults. They are designed for use in high-risk environments, such as medical facilities, laboratories, and data centres, where even small electrical faults can have serious consequences. Type B RCDs provide the highest levels of safety and protection.
Choosing the right type of RCD for your application is essential to ensure optimal protection against electrical hazards. Type AC RCDs are suitable for most residential and commercial applications, although are being phased out due to their proclivity to be negatively impacted by DC leakage current. Type A devices are therefore becoming the de facto device of choice for most applications, while Types F, and B RCDs are designed for more specific environments and hazards.