The overload protection of the low-voltage circuit breaker is completed by a thermal tripper. Usually, the rated current of the thermal trip unit of the low-voltage circuit breaker is determined by the manufacturer according to the IEC898 standard at a reference temperature of 30 ° C (2 conditions. The thermal trip is Made of a set of bimetals, when the line is overloaded, the overload current flows through the heating resistor wire to cause the bimetal to heat and deform, and the hook is opened to open the low voltage circuit breaker contacts. The trip unit has a direct relationship with the ambient temperature. If the ambient temperature changes, the rated current value of the low-voltage circuit breaker will change. The low-voltage circuit breaker is generally fixedly arranged on the switchboard and then installed in the distribution box. The installation method of the distribution box is divided into two types: clear and concealed. The heat dissipation effect of the assembled electrical box is better than that of the dark assembled electric box. The air in the dark assembled electric box is not suitable for convection, and the heat dissipation effect is poor. As a result, the temperature rise of the low-voltage circuit breaker in the distribution box causes the ambient air temperature to rise.
Therefore, the actual operating temperature of the low-voltage circuit breaker is about 10 ° C - 15 ° C higher than the ambient temperature. Therefore, when the ambient temperature is greater or less than the calibration temperature, we must correct the rated current of the low-voltage circuit breaker according to the temperature and current-carrying capacity correction factor table provided by the manufacturer. Taking C65N/H as an example, if the low-voltage circuit breaker C65N/H is installed separately, its surrounding environment is 30°C, and the rated current of C65N/H is 20A, the actual working current is 20A; if the low-voltage circuit breaker C65N/H is installed separately, The surrounding environment is 40 ° C, the rated current of C65N / H is 20A, the actual working current is 18.97A; if multiple C65N / H are installed in the distribution box, the surrounding environment is 30 ° C, C65N / H rated If the current is 20A, the actual working current is 16A. If multiple C65N/H are installed in the distribution box, the surrounding environment is 40°C, and the rated current of C65N/H is 20A, the actual working current is 15.18A. From this we can see that different ambient temperatures and different installation methods have a certain impact on the actual operating current value of the low-voltage circuit breaker.
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