The most common load has three categories: electricity and home with similar household (lighting, household appliances, etc.). This corresponds to the distribution protection type, motor protection and home and similar home protection. The protection properties and protection characteristics of these three types of circuit breakers are different. For distribution type circuit breakers, it has Class A and Class B: A class is a non-selective, Class B is selected. The so-called selection type refers to the circuit breaker.
It has three-segment protection characteristics with overload length delay, short circuit short delay and short circuit instantaneous. Some specifications in the universal (also known as framework) circuit breaker are only a short-circuit instantaneous segment.
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When the F spot is short, only the circuit breaker movement near the F point, and the upper circuit breaker does not operate, which is selective protection (due to not action, the unable to hold the branch).
If it is a Class A circuit breaker, the F point is short-circuited, and the short-circuit current value is a certain value, and all the brackets under the circuit breaker will be powered down. It is not selective protection.
The reason for the ability to achieve selective protection is that the B circuit breaker has short-circuit short-term performance. When F is short-circuited, the short-circuit current flows through the branch, and it has flowed back and instantaneously moves the desertifier (usually it. The full break time is not more than 0.02s). When the short delay is short, it does not move in 0.02s (its short delay ≥ 0.44 or 0.2, 0.3, 0.4s). The entire system is restored to the normal when the fault line is turned off.
It can be seen that if you want to achieve selective protection, the previous level of circuit breakers should use a B-type circuit breaker with three-segment protected. For motor protected circuit breakers that directly protect the motor, it is enough as long as there is over-long delay and short-circuit instantaneous second-segment protection performance, that is, it can choose A class circuit breaker (including plastic shell and universal). In addition to the performance of power distribution protection, their 630A and the following specifications have the function of protecting the motor.
Protection of home and similar places (in the past, it is called wire protection or lighting protection), is also a small A-class circuit breaker
Distribution (line), motor and home, etc., due to protective objects (such as transformers, wire cables, electric machines, household appliances, etc.) to overload current (including motor start current and start-up time, etc.) There are differences, so the protection characteristics of the selected circuit breakers are also different.