With the launch of urban and rural power grid renovation projects in my country, more and more low-voltage power distribution systems are being equipped with electronic residual current circuit breakers (RCDs). How to ensure that the installed electronic residual current circuit breakers function properly for leakage protection, preventing malfunctions or failures to operate, and guaranteeing the safe and reliable operation of low-voltage power distribution systems is a crucial and important issue. [b]1 Functional Characteristics of Electronic Residual Current Circuit Breakers[/b] 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 operating 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. [b]2 Installation of Electronic Residual Current Circuit Breakers in TN Systems[/b] In power systems, one point is directly grounded, and the 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 line, the TN system can be divided into TN-S system, TN-C system and TN-CS system. (1) TN-S system with electronic residual current circuit breaker installed (taking three-pole four-wire or four-pole as an example): In the TN-S system, the neutral line and the protective line of the whole system are separated, as shown in Figure 1. When an electronic residual current circuit breaker (RCCB) is connected, during normal operation, [img=140,19]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/50.gif[/img]; during leakage, [img=142,22]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/50-2.gif[/img], the vector sum of the currents through the zero-sequence current transformer in the electronic RCCB is not zero. When the leakage current reaches a certain value, the electronic RCCB trips, cutting off the power supply. However, if the neutral line N is not connected to the power system, as shown in Figure 2, even if a leakage current occurs and reaches the leakage trip current, the electronic residual current circuit breaker will fail to operate and will not be able to provide leakage protection. [img=200,166]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t50.gif[/img] Figure 1 Correct Wiring [img=241,156]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t50-2.gif[/img] Figure 2 Incorrect Wiring (2) Installing Electronic Residual Current Circuit Breakers in TN-C Systems (Taking Three-Pole Four-Wire or Four-Pole as an Example): In a TN-C system, the neutral and protective earth conductors are combined. Connect the electronic residual current circuit breaker as shown in Figure 3. If a leakage occurs, it will provide protection. If the protective earth (PE) conductor of an electrical device is connected to the neutral (N) conductor at the load end of an electronic residual current circuit breaker (RCCB), as shown in Figure 4, if a leakage occurs, the leakage current will flow back to the RCCB through the PE conductor, causing the RCCB to fail to operate and lose its leakage protection function. [img=204,153]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t51.gif[/img] Figure 3 Correct wiring [img=222,159]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t51-2.gif[/img] Figure 4 Incorrect wiring (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 play the role of leakage protection. 3 Installing electronic residual current circuit breakers in TT systems Taking three-pole four-wire or four-wire as an example. The power system has one point of direct grounding. The exposed conductive parts of electrical equipment are connected to a grounding electrode unrelated to the power system grounding point through a protective grounding wire. According to the wiring method in Figure 5, it can play a protective role when leakage occurs. [img=195,171]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t51-3.gif[/img] Figure 5 Wiring diagram of TT system [b]4 Regarding the problem of incorrect connection of neutral line N[/b] 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 protects multiple electrical devices and the neutral line N of the downstream devices is repeatedly grounded, as shown in Figure 7, when a leakage occurs, part of the leakage current flows back to the power source through the ground, causing the electronic residual current circuit breaker to fail to operate and lose its leakage protection function. [img=194,175]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t51-4.gif[/img][font=SimSun][size=3] [/size][/font] Figure 6 Incorrect wiring [img=263,194]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/hubeidl/hbdl99/hbdl9903/image3/t51-5.gif[/img] Figure 7 Incorrect wiring In conclusion, when selecting an electronic residual current circuit breaker, it is essential to carefully analyze the grounding method of the power system and ensure correct wiring to prevent miswiring. Only then can the electronic residual current circuit breaker effectively provide leakage protection and avoid malfunctions or failures to operate, thus preventing unnecessary losses.