Residual current circuit breaker is a kind of switch which can act automatically when the leakage current exceeds the preset value. The commonly used residual current circuit breakers are divided into voltage type and current type, and the current type is divided into electromagnetic type and electronic type. Voltage type residual current circuit breaker is used in low voltage power network with ungrounded neutral point of transformer. Its characteristic is that when people get an electric shock, there is a relatively high voltage between the zero line and the ground, which causes the relay to act and the power switch to trip. Current mode residual current circuit breaker is mainly used in low voltage distribution system with transformer neutral grounding. Its characteristic is that when a person gets an electric shock, a leakage current is detected by the zero sequence current transformer, which makes the relay act and the power switch turn off.
The following is a brief introduction to the two faults encountered in the use of residual current circuit breakers and their solutions. The details are as follows:
Fault 1: the residual current circuit breaker tripped as soon as it was put into operation
（1） If the three-phase power line, including the zero line, does not pass through the zero sequence current transformer in the same direction, correct the wiring.
（2） The circuit with residual current circuit breaker and the circuit without residual current circuit breaker are electrically connected, and the two circuits can be separated.
（3） There is one fire and one ground load in the line, so it is enough to eliminate such load.
（4） The working zero line passing through the zero sequence current transformer has the phenomenon of repeated grounding, so the repeated grounding should be eliminated.
（5） The residual current circuit breaker itself is faulty and should be replaced.
Second, the operation of the residual current circuit breaker is misoperated
（1） It is caused by over-voltage. For example, the circuit breaker can act when the switching overvoltage occurs in the line. At this time, the time-delay or impulse voltage non action type residual current circuit breaker can be selected, the resistance capacitance absorption circuit can be installed between the contacts to suppress the overvoltage, and the overvoltage absorption device can also be put into the line.
（2） Electromagnetic interference. If there is magnetic equipment or high-power electrical equipment nearby, the installation position of residual current circuit breaker should be adjusted to keep away from such electrical components.
（3） Circulation influence. If two transformers operate in parallel, they have their own grounding. Because the impedance of the two transformers cannot be completely equal, it will generate circulating current in the grounding wire and cause the circuit breaker to act. Just remove one grounding wire. In addition, if the same transformer supplies power to the same load through two parallel circuits, the currents in the two circuits can not be exactly the same, and circulation may also occur. Therefore, the two circuits should be operated separately.
（4） The insulation resistance of working zero line is reduced. When the insulation resistance of the working zero line is reduced, if the three-phase load is unbalanced, a relatively large working current will appear on the zero line and flow to other branches through the human ground, so that the leakage current can appear on each leakage circuit breaker and make the circuit breaker misoperate.
（5） Improper grounding. If the zero line is repeatedly grounded, it will cause the misoperation of the residual current circuit breaker.
（6） Overload or short circuit. If the residual current circuit breaker has short-circuit protection and over-current protection at the same time, misoperation will occur when the setting current of the over-current protection release is not appropriate. At this time, the setting current value can be adjusted.