Residual current devices (RCDs) can be classified according to their protective functions, structural features, installation methods, operating methods, number of poles and wires, and operating sensitivity. This description primarily focuses on their classification by protective function and application, generally categorized into three types: residual current relays (RCDs), residual current circuit breakers (RCCBs), and residual current sockets (RCCBs).
1. A residual current relay (RCD) is a device that detects and judges leakage current but does not have the function of cutting off or connecting the main circuit. An RCD consists of a zero-sequence current transformer, a trip unit, and auxiliary contacts for output signals. It can be used in conjunction with high-current automatic switches as the main protection for low-voltage power grids or for monitoring leakage, grounding, or insulation in main circuits.
2. A residual current circuit breaker (RCCB) not only connects or disconnects the main circuit like other circuit breakers but also has the function of detecting and judging leakage current. When leakage or insulation failure occurs in the main circuit, the RCD can connect or disconnect the main circuit based on the judgment result. It can be used in conjunction with fuses and thermal relays to form a fully functional low-voltage switching element.
3. A residual current device (RCD) socket is a power socket that can detect and judge leakage current and cut off the circuit. Its rated current is generally below 20A, the leakage current is 6-30mA, and it has high sensitivity. It is often used for the protection of handheld power tools and portable electrical equipment, as well as in civilian places such as homes and schools.
