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The circuit breaker's instantaneous tripping mechanism is designed to provide rapid protection when a large overload or short-circuit current occurs in the electrical system. In cases of a near-area short circuit—such as a direct metal-to-metal connection—the short-circuit current can surge to over 20 times the rated current (20In). However, in some situations, reduced insulation resistance due to aging, moisture, or conductive dust can lead to partial insulation breakdown. Even though the resulting overcurrent may be much smaller than a full short-circuit current, it can still cause damage to the power distribution system.
To ensure effective protection, the electromagnetic trip must respond quickly and accurately, allowing the circuit breaker to isolate the faulty circuit. At the same time, the instantaneous tripping current should not be set too low, as this could lead to unnecessary trips caused by normal load variations. Ideally, the setting should be based on the starting current of the connected load. According to GB14048.2, the adjustable range for instantaneous tripping current is typically set between 5–10In or 6–12In, depending on the application.
As a molded case circuit breaker, it is essential not only to rapidly disconnect the faulty line but also to coordinate with the overload capacity of the protected equipment. This prevents unwanted tripping that could result in unnecessary power interruptions. Additionally, the long-time delay function helps the circuit breaker adapt to changes in load conditions and characteristics. Users can adjust this setting within a wide range, usually from 0.4In to 1.0In, ensuring proper protection without causing false trips.
Compared to thermal-magnetic circuit breakers, electronic trip units offer a broader range of adjustable settings, making them more versatile for different applications. Their flexibility and reliability make them increasingly popular in modern power distribution systems, offering better performance and greater control for both engineers and end-users.