Classification of residual current circuit breakers

Residual current devices (RCDs) can be classified according to their protection function, structural features, installation method, operation mode, number of poles and wires, and operating sensitivity. This description primarily focuses on their classification by protection function and application, generally categorized into three types: residual current relays, residual current switches, and residual current sockets.

1. A residual current relay 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.

When there is leakage current in the main circuit, because the auxiliary contacts and the main circuit switch's trip unit are connected in series, the auxiliary contacts activate the trip unit, disconnecting the air switch, AC contactor, etc., causing it to trip and cutting off the main circuit. The auxiliary contacts can also activate audible and visual signal devices to issue a leakage alarm signal, reflecting the insulation status of the line.

2. A residual current circuit breaker (RCCB) is a switching element that not only connects or disconnects the main circuit like other circuit breakers, but also detects and judges leakage current. When leakage or insulation failure occurs in the main circuit, the RCCB 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.

Currently, this type of RCCB is the most widely used. RCCBs on the market are commonly categorized according to their functions as follows:

(1) Only has leakage protection and power-off function; it must be used in conjunction with fuses, thermal relays, overcurrent relays, and other protective elements.

(2) Also has overload protection function.

(3) Also has overload and short-circuit protection functions.

(4) Also has short-circuit protection function.

(5) Also has short-circuit, overload, leakage, overvoltage, and undervoltage functions.

3. A residual current circuit breaker (RCCB) is a power socket that can detect and judge leakage current and disconnect 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 mobile electrical equipment, as well as in civilian places such as homes and schools.