Differences between Type C circuit breakers and Type D circuit breakers

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1. **Definitions and Applications**

- **Type C circuit breakers**: Type C circuit breakers are generally used in situations where the load current has little variation and there is no significant inrush current, such as in lighting circuits. For example, in ordinary household lighting circuits, the current is relatively stable, and using Type C circuit breakers can effectively provide overload and short-circuit protection for the circuits.

- **Type D circuit breakers**: Type D circuit breakers are mainly suitable for power equipment with large starting currents, such as motors. For example, an electric motor in a factory will generate a relatively large starting current at the moment of starting, which is usually 4 to 7 times the rated current. Type D circuit breakers can withstand such large inrush currents without malfunctioning.

2. **Differences in Tripping Characteristic Curves**

- **Type C circuit breakers**: The tripping characteristic curve of Type C circuit breakers is a relatively gentle curve. Its instantaneous tripping current is generally 5 to 10 times the rated current. For example, for a Type C circuit breaker with a rated current of 10A, the range of its instantaneous tripping current is approximately 50 to 100A. This means that when the current in the circuit exceeds this range, the circuit breaker will trip quickly to cut off the circuit and protect the safety of the circuit.

- **Type D circuit breakers**: The tripping characteristic curve of Type D circuit breakers is different from that of Type C circuit breakers. Its instantaneous tripping current is generally 10 to 20 times the rated current. Taking a rated current of 10A as an example, the range of the instantaneous tripping current of a Type D circuit breaker is approximately 100 to 200A. This characteristic enables Type D circuit breakers to adapt to the large current impact during the startup of power equipment and avoid false tripping in situations such as motor startup.

3. **Differences in Protection Emphases**

- **Type C circuit breakers**: They focus on protecting against overload and general short-circuit conditions. In lighting circuits and the like, overload may be caused by an increase in the number of lamps, circuit aging, and other reasons. Type C circuit breakers can trip after a certain period of time according to the magnitude of the overload current. For example, when the overload current is 1.3 times the rated current, it may trip in about one hour, thus protecting the circuit from being damaged due to long-term overload.

- **Type D circuit breakers**: They are mainly designed to protect the safety of power equipment during startup and operation. Since the starting current of equipment such as motors is large, Type D circuit breakers are designed to allow such large currents to pass through, and at the same time, they can quickly cut off the circuit when the equipment has short-circuit or other faults. For example, when a motor has a phase-to-phase short circuit or other faults, the Type D circuit breaker can act quickly to protect the motor and the entire circuit system.