The inability of a circuit breaker to close is a common fault. When encountering this fault, refer to the control wiring diagram (Figure 1) and check several key fault points. First, check the control fuses 1FU and 2FU, and the closing fuses 3FU and 4FU. Then, check if the changeover switch SA⑤-⑧ contacts are closed in the closed position, and if the circuit breaker auxiliary contact QF·1 is closed. Check if the closing contactor Q coil and closing coil r1 are burnt out. Finally, analyze mechanical faults. Below, I will analyze several common faults encountered during maintenance. [img=299,195]http://zszl.cepee.com/cepee_kjlw_pic/files/wx/ncdg/ncdg/ncdg99/ncdg9901/image1/t04.gif[/img] Figure 1 Control principle diagram of the electromagnetic operating mechanism of the circuit breaker. 1. If the green light is not on and the circuit cannot be closed, first check 1FU and 2FU, then check the QF.1 contact, and finally check the closing contactor coil. 2. If the green light is on but the circuit cannot be closed, it is generally because the control switch SA⑤-⑧ contact is not open or the closing contactor coil Q is burnt out and in a short-circuit state; there is also a fault in the closing power supply circuit: 3FU and 4FU are burnt out or the closing contactor contact Q.1 or Q.2 is burnt out and has poor contact. 3. The switch immediately separates after closing. 3.1 Resistor 2R is burnt out. When the switch is closed, the normally open contact QF.2 closes, and the power supply voltage directly connects to the trip coil r2 through the switch SA contact. Therefore, the switch immediately separates after closing, and resistor 2R needs to be replaced. 3.2 Mechanical reason: the holding mechanism failed to support the switch. 4. The switch can close under no-load but cannot close under load. The fact that the switch can close under no-load indicates that the control circuit and the closing power supply circuit are good. The main reason is that the main contacts of the circuit breaker are severely burned. When closing under load, the electric repulsion increases, and the closing electromagnet cannot push the roller to the closing position, so the switch cannot close. In this case, the switch should be disassembled and repaired.