With the commencement of urban and rural power grid renovation projects in China, more and more low-voltage power distribution systems are being equipped with electronic residual current circuit breakers (RCDs). Ensuring that these installed RCDs provide effective leakage protection, preventing malfunctions or failures to trip, and guaranteeing the safe and reliable operation of low-voltage power distribution systems is a crucial and important issue. 1. Functional Characteristics of Electronic Residual Current Circuit Breakers Electronic residual current circuit breakers mainly consist of a circuit breaker, a zero-sequence current transformer, electronic amplification and triggering components, and a residual current trip unit. They feature high sensitivity, stable performance, and overload and short-circuit protection functions. Their main technical indicators include rated voltage Ua, rated current In, rated residual operating current IΔn (rated residual operating current), and rated ultimate short-circuit breaking capacity. 2. Installation of Electronic Residual Current Circuit Breakers in TN Systems In a power system, one point is directly grounded. Exposed conductive parts of electrical installations are connected to this grounding point via a protective conductor. According to the connection method of the neutral line and the protective conductor, the TN system can be divided into TN-S system, TN-C system and TN-CS system. (1) Installing electronic residual current circuit breaker in TN-S system (taking three-pole four-wire or four-pole as an example): In the TN-S system, the neutral line and the protective conductor of the whole system are separate, as shown in Figure 1. Connect the electronic residual current circuit breaker and it will run normally. (2) Installing electronic residual current circuit breaker in TN-C system (taking three-pole four-wire or four-pole as an example): In the TN-C system, the neutral line and the protective conductor of the whole system are combined. Connect the electronic residual current circuit breaker as shown in Figure 3. If leakage occurs, it can play a protective role. For example, connect the protective conductor PE of the electrical equipment to the neutral line N of the load end of the electronic residual current circuit breaker, as shown in Figure 4. If leakage occurs, the leakage current flows back to the electronic residual current circuit breaker through the PE line, causing the electronic residual current circuit breaker to fail to operate and lose the leakage protection function. (3) In a TN-CS system, the neutral and protective conductors of some lines are combined. The wiring of the electronic residual current circuit breaker is the same as in Figure 1, which can provide leakage protection. 3. Installing electronic residual current circuit breakers in TT systems Taking a three-pole four-wire or four-wire system as an example. One point of the power system is directly grounded. The exposed conductive parts of the electrical equipment are connected to a grounding electrode unrelated to the power system grounding point through a protective grounding wire. The wiring method is shown in Figure 5. When leakage occurs, it can provide protection. 4. Regarding the problem of incorrect neutral line N connection Whether it is a TN system or a TT system, if the neutral line N of the load end of the electronic residual current circuit breaker is repeatedly grounded, as shown in Figure 6, when the load is unbalanced, the current on the neutral line flows into the ground through the grounding wire, causing the electronic residual current circuit breaker to malfunction and fail to work properly. For example, if an electronic residual current circuit breaker (RCCB) protects multiple electrical devices, and the neutral line N of these devices is repeatedly grounded (as shown in Figure 7), when a leakage current occurs, a portion of the leakage current flows back to the power source through the ground, causing the RCCB to fail to trip and lose its leakage protection function. In conclusion, when selecting an electronic RCCB, it is essential to carefully analyze the grounding method of the power system and ensure correct wiring to prevent misconnections. Only then can the RCCB effectively provide leakage protection and avoid malfunctions or failures to trip, resulting in unnecessary losses.