Leakage protector rated leakage current selection - Database & Sql Blog Articles

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Choosing the correct and appropriate rated leakage current for a residual current device (RCD) is crucial for both safety and system reliability. On one hand, it ensures that the RCD will selectively trip when an electric shock or excessive leakage current occurs. On the other hand, it should not activate under normal conditions to avoid unnecessary power interruptions and energy loss.

The rated leakage current of an RCD must meet three key requirements:

1. To ensure personal safety, the rated leakage current should not exceed the safe current level for the human body. Internationally, 30 mA is widely recognized as the threshold for safe current.
2. To ensure reliable operation of the electrical grid, the rated leakage current should be higher than the normal leakage current of the low-voltage network to prevent false tripping.
3. To maintain selectivity in multi-stage protection systems, the rated leakage current of the next stage should be lower than the previous stage, with a step difference of 1.12 to 2.15 times between each level.

The first-level RCD is typically installed at the low-voltage side of the distribution transformer. The protected line is long, and the leakage current can be significant. Without a complete multi-level protection system, the rated leakage current should not exceed 100 mA. In a well-designed multi-stage system, it may be reduced to 75 mA during dry seasons and up to 200 mA during rainy periods. For grids with high leakage currents, it should be set to 100 mA in dry weather and 300 mA during rain.

The second-level RCD is placed at the branch line exit. Since the line is shorter and the load is smaller, the leakage current is also lower. The rated leakage current here should fall between the upper and lower levels, usually ranging from 30 to 75 mA.

The third-level RCD is used to protect individual or multiple powered devices directly, offering the highest level of personal protection. These devices typically have low power consumption and minimal leakage current, generally not exceeding 10 mA. It is recommended to use an RCD with a rated operating current of 30 mA and an operating time of less than 0.1 seconds for optimal safety and performance.