Rated Current Of Residual Current Circuit Breaker

The correct and reasonable selection of the rated operating current of a residual current device (RCD) is crucial. Firstly, the RCD should selectively operate when an electric shock occurs or the leakage current exceeds the allowable value. Secondly, the RCD should not operate under normal leakage current to prevent power outages and unnecessary economic losses.

The rated operating current of an RCD should meet the following three conditions:

(1) To ensure personal safety, the rated operating current should not exceed the safe current value for the human body; internationally, 30 mA is recognized as the safe current value.

(2) To ensure reliable operation of the power grid, the rated operating current should avoid the normal leakage current of the low-voltage power grid.

(3) To ensure selectivity in multi-level protection, the rated operating current of the next level should be less than that of the previous level, and there should be a difference of 112 to 215 times between the rated operating currents of each level.

The first-level RCD is installed at the low-voltage side outlet of the distribution transformer. The first level of protection is for long lines with relatively large leakage currents. Its rated leakage current should not exceed 100mA in the absence of comprehensive multi-stage protection. With comprehensive multi-stage protection, the rated leakage current should be 75mA in non-rainy seasons and 200mA in rainy seasons for grids with smaller leakage currents; for grids with larger leakage currents, the rated leakage current should be 100mA in non-rainy seasons and 300mA in rainy seasons.

The second level of leakage current protection device is installed at the branch line outlet. The protected line is relatively short, with low power consumption and small leakage current. The rated leakage current of the leakage current protection device should be between the rated leakage currents of the upstream and downstream protection devices, generally between 30 and 75mA.

The third level of leakage current protection device is used to protect single or multiple electrical devices and is a direct protection device to prevent electric shock. The power consumption of the protected line and equipment is small, and the leakage current is small, generally not exceeding 10mA. A leakage current protection device with a rated operating current of 30mA and an operating time of less than 0.1s should be selected.