What is the derating of the circuit breaker

The manufacturer of the circuit breaker will prominently indicate the environment and conditions of use of the product in the installation and use instructions, two of which are: "Normal operating range -5℃~+40 ℃, the average temperature within 24 hours should not exceed +35℃", "The altitude of the installation site should not exceed 2000m, if it exceeds 2000m please reduce the capacity to use".

First of all, we need to understand that the so-called "capacity reduction" is not the reduction of the rated current of the circuit breaker, but the actual use of the circuit breaker capacity reduction, we often talk about the reduction factor should be the ratio of the current to the rated current.

The use of conditions we quantify the results of the temperature indicator, and the use of the environment we mainly from the dielectric properties to start to tell. The two indicators of temperature and dielectric almost contains a specific explanation of the circuit breaker capacity reduction.

First, the temperature as a variable, the need to analyze several cases of capacity reduction.

1, the circuit breaker itself is located in the surrounding environment temperature impact

Distribution cabinets are installed outdoors, the summer temperature is higher: when the ambient temperature exceeds 40 ℃, especially when the circuit breaker in a closed confined space (such as charging pile cabinet), when the ambient temperature is high, poor heat dissipation, the circuit breaker overload characteristics will change.

2、The protection level of the switch or equipment leads to

Installation experience of electricians should have such experience, the same environmental conditions, after running a period of cabinet door open state cabinet breaker temperature is significantly lower than the closed state. The same cabinet door closed, the cabinet has no ventilation conditions, will also lead to significant changes in temperature. When the ambient temperature remains unchanged, the higher the temperature of the circuit breaker, the higher the temperature rise.