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Leakage protection switch selection and operation management - Database & Sql Blog Articles
The leakage protection device is a critical grounding protection system designed to prevent electrical accidents caused by shocks and leaks. When the leakage current in a circuit or electrical equipment exceeds the device's set value, or when a person or animal is at risk of electric shock, it quickly disconnects the power supply, preventing the accident from escalating and ensuring the safety of both people and equipment. Therefore, the correct selection and proper maintenance of the leakage protection switch are essential technical and management measures for safe electricity use in rural areas.
First, the selection of the leakage protection device should be based on the system's protection mode, usage purpose, installation location, voltage level, the leakage current of the controlled circuit, and the grounding resistance of the electrical equipment.
1. **Selecting Based on Protection Purpose**
- **Direct Contact Protection**: This type of protection prevents electric shocks that occur when a person directly touches a live conductor. In such cases, the device must act within 0.1 seconds due to the high risk involved. The action current is determined by the body's voltage and resistance, and the device cannot limit the current passing through the body. Thus, fast-acting devices with inverse time characteristics (as per IEC standards) are required.
- **Indirect Contact Protection**: This protects against dangerous voltages appearing on exposed metal parts when equipment is damaged. The operating current (IΔn) of the device should be chosen based on the equipment’s grounding resistance (R) and allowable contact voltage (U). The formula IΔn ≤ U/R is used to determine the appropriate setting. For fixed equipment with 220V or 380V, if the grounding resistance is below 500Ω, a device with an operating current of 30–50 mA and a response time under 0.1 seconds is suitable. If the grounding resistance is lower than 100Ω, a higher current range (200–500 mA) can be used. For critical equipment, a time-delayed device may be considered to avoid unnecessary power interruptions.
2. **Choosing Based on Installation Location**
Leakage protection devices are typically installed in low-voltage lines (380/220V). In places where metal parts are easily touched, and grounding is not properly implemented, it is recommended to install the device according to indirect contact protection standards. In wet environments, where skin resistance is reduced, a more sensitive device with an operating current between 15–30 mA and a response time of less than 0.1 seconds is ideal.
3. **Considering Normal Leakage Current**
While a lower operating current increases sensitivity, all circuits have some normal leakage current. To ensure stable operation, the selected device’s operating current must be greater than the circuit’s normal leakage current. For example:
- For single-phase lighting circuits: IΔn ≥ IH / 2000
- For three-phase systems: IΔn ≥ IH / 1000
In rural areas, where insulation levels are often poor and leakage currents are higher, careful consideration is needed. The leakage current increases with the number of households connected, so multi-stage protection is recommended. The first stage should have a maximum leakage current of 100 mA, while the second stage should be between 30–75 mA, and the final stage (last-level protection) should be around 15–30 mA to protect individuals.
After installation, effective management is crucial to ensure the device remains functional. Regular checks, monthly testing, and professional maintenance are necessary. In case of unexpected tripping, the cause should be identified before reactivating the system. Faulty devices must be replaced promptly, and unauthorized adjustments should be avoided. Testing should only be done using approved equipment, and direct contact with live conductors is strictly prohibited.
In summary, the proper selection, installation, and ongoing maintenance of leakage protection switches are vital for ensuring electrical safety in both residential and industrial settings. By following these guidelines, the risk of electric shock and equipment damage can be significantly reduced.