Small switch boxes with residual current devices

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1. **Definition and Composition**

- Small switch boxes with residual current devices are electrical equipment used for controlling and protecting electrical circuits. They mainly consist of a box body, circuit breakers (switches), and residual current devices. The box body is usually made of metal or plastic materials, which play a role in protecting and fixing the internal components. The circuit breaker is used to turn on and off the circuit under normal circumstances and can automatically trip when the circuit is overloaded or short-circuited, thus protecting the safety of the lines and equipment. The residual current device is specifically designed to detect leakage current. When the residual current (leakage current) in the circuit reaches the set value, it will quickly cut off the circuit to prevent electric shock to people and electrical fires and other accidents caused by leakage.

2. **Working Principle**

- The core component of the residual current device is the zero-sequence current transformer. Under normal circumstances, the inflow and outflow of current in the circuit are balanced, and the zero-sequence current transformer cannot sense the current. When a leakage phenomenon occurs, for example, when a person touches the shell of a leaking electrical appliance, a part of the current will flow into the earth through the human body, resulting in an imbalance between the inflow and outflow of current in the circuit. At this time, the zero-sequence current transformer will sense this residual current and amplify its signal. When the residual current reaches the set action current value of the residual current device (usually 30 mA, etc.), the tripping mechanism inside the residual current device will act, causing the circuit breaker to trip and thus cutting off the circuit.

3. **Installation Points**

- **Position Selection**: It should be installed in a dry and well-ventilated place, avoiding installation in damp, corrosive gas-containing or mechanically vulnerable positions. Meanwhile, it should be convenient for operation and maintenance. Generally, the installation height is preferably 1.3 - 1.5 meters from the bottom edge to the ground.

- **Connection Method**: When connecting the circuit, it is necessary to ensure that the input and output lines are connected correctly. The incoming line should be connected to the power supply side, and the outgoing line should be connected to the load side. The cross-sectional area of the connecting wire should meet the rated current requirements of the switch box, and the connection should be firm to avoid loose connections. For the residual current device, the threading method of its zero-sequence current transformer should be operated correctly according to the instructions. Generally, all the phase wires and the neutral wire should be threaded through the transformer together.

4. **Precautions for Use**

- **Regular Inspection**: The switch box should be inspected regularly, including checking the tripping function of the circuit breaker and the leakage action function of the residual current device. The normal operation of the residual current device can be detected by the test button. Generally, the test should be carried out once a month.

- **Load Matching**: The power of the connected load should be within the rated power range of the switch box to avoid overloading operation. If it is necessary to connect high-power electrical appliances, it is necessary to first check whether the rated current of the switch box meets the requirements. Otherwise, it may cause the circuit breaker to trip frequently or damage the equipment.

- **Fault Handling**: If the switch box trips, the cause of the fault should be checked before reclosing. For the tripping of the residual current device, it is necessary to check whether there is leakage, such as leakage of electrical equipment, damage to the line, etc. For the tripping of the circuit breaker, it is necessary to check whether there is overload or short circuit. Only after the fault is eliminated can the switch box be reclosed.

5. **Application Scenarios**

- Small switch boxes with residual current devices are widely used in households, construction sites, temporary power consumption sites, and so on. In households, they can be used to control socket circuits, lighting circuits, etc., providing guarantee for the electrical safety of family members. In temporary power consumption sites such as construction sites, they can effectively prevent electric shock accidents of construction workers caused by leakage and ensure construction safety.