We all know that Type C miniature circuit breakers are used in ordinary circuits, such as lighting circuits; and Type D circuit breakers are used in motor circuits. So I would like to ask everyone, can Type C miniature circuit breakers be used in motor circuits?
Putting aside whether it's possible or not, let's first look at the differences between type C and type D microfractures:
Type C miniature circuit breaker: Includes overload protection and short circuit protection, with a short circuit protection tripping value of 5 to 10 times the rated current;
Type D miniature circuit breaker: Includes overload protection and short circuit protection, with short circuit protection tripping value of 10 to 20 times the rated current;
Both have the same overload protection; the only difference is the short-circuit protection tripping range.
Normally, ordinary loads have no starting current, meaning the starting current is the rated current; the starting current of a motor is about 7 to 10 times the rated current.
For example: a 4kW three-phase motor with a rated current of 9A, and a starting current calculated at 10 times that, 90A;
Typically, a type D 16A miniature circuit breaker is chosen as the protective device. Calculated at 10 times the operating current, the short-circuit protection operating current is 160A, which can avoid the motor starting current.
If a 16A type C miniature circuit breaker is chosen as the protective device, the short-circuit protection operating current is 80A based on a 5 times operating current, which cannot avoid the motor starting current. Does that mean that a type C circuit breaker should never be chosen?
Of course not. If a type C 25A miniature circuit breaker is chosen as the protective device, calculated at 5 times the operating current, the short-circuit protection operating current is 125A, which can avoid the motor starting current; technically, there is no problem.
Let's take a look at the economic aspect:
Taking Schneider C65 series micro-breaks as an example,
The C65N3PC25A is priced at 130.3 yuan.
The C65N3PD16A is priced at 158.9 yuan.
As can be seen, the C series is slightly cheaper.
Reflection: Generally, we select circuit breakers based on the principle that the rated current of the circuit breaker is greater than the load current, and then choose between type C and type D based on the load characteristics. Type D is specifically designed for motor loads, but this doesn't mean that type C circuit breakers cannot be used; it just requires adjusting the calculation method. Our learning still needs to explore the essence and apply knowledge flexibly.
