1. Working Conditions of Molded Case Circuit Breakers

(1) The upper limit of ambient air temperature is + 40 C; the lower limit of ambient air temperature is - 5 C; and the average value of ambient air temperature for 24 hours is not more than + 35 C.

(2) Elevation: The installation site is not more than 2000m above sea level.

(3) Atmospheric conditions: atmospheric relative humidity does not exceed 50% at ambient air temperature of + 40 C; higher relative humidity can be obtained at lower temperatures; the maximum monthly average relative humidity of the wettest month is 90%, and the minimum monthly average temperature of that month is + 25 C, taking into account the condensation occurring on the surface of products due to temperature changes.

(4) Pollution grade: pollution grade is 3.

2. Working Principle of Molded Case Circuit Breaker

[1] The main contacts of low-voltage circuit breakers are operated manually or electrically. After the main contact is closed, the free release mechanism locks the main contact at the closing position. The coil of the overcurrent release and the thermal element of the thermal release are in series with the main circuit, and the coil and the power supply of the undervoltage release are in parallel.

[2] When the circuit is short-circuited or seriously overloaded, the armature of the over-current tripper is sucked, which makes the free tripping mechanism act and the main contact disconnects the main circuit

[3] When the circuit is overloaded, the heating element of the thermal release makes the bimetal sheet bend, pushes the free release mechanism to move, and the main contact disconnects the main circuit.

[4] When the circuit is under-voltage, the armature of the under-voltage tripper is released, which also makes the free tripping mechanism move and the main contact disconnects the main circuit.

[5] When the release button is pressed, the armature of the release device is sucked, so that the free release mechanism can move and the main contact can disconnect the main circuit.

Molded case circuit breakers are classified according to different quenching media. Air circuit breakers are called air circuit breakers (air switches), inert gas circuit breakers are called inert gas circuit breakers (inert gas switches) and oil circuit breakers are called oil circuit breakers. Circuit implement (oil switch).