The Structure Of Miniature circuit breaker

Most people do know what miniature circuit breaker is,  but they may not know how miniature circuit breaker works, and how they protects from short circuit and overload, as they don’t know miniature circuit breaker construction, which is exactly  the basic for knowing more about miniature circuit breaker. Here we analyse the construction with example of mcb circuit breaker , which is mainly composed of parts as below:

(1) Operating handle: for circuit breaker’s switching, closing and resetting manually, also for locally instructing circuit breaker’s state of switching and closing

(2) Tripping mechanism (including lock catch, lever and tripping panel): for connecting and separating from contact

(3) Wiring terminals: for wiring at  top and bottom

(4) Device for contact (including moving and static contacts and joint plate): for current switched on and cut off

(5) Bimetal strips: bimetal strips bend as two bimetal strips have different coefficients of thermal expansion, the bending angle increases as overload current rises, which makes bimetal strips touch lever and then push tripping mechanism, thus making miniature circuit breaker play the role of overload protection

(6) Eletromagnetic solenoid (also called as instantaneous coil): when short-circuit happens, large current goes through induction coil, which will cause a strong suction and then push lever, making circuit breaker trips fast

(7) Adjusting screw: for factory workers to adjust tightness of bimetal strips, thus realizing adjustment of tripping current value of overload

(8) Arc-suppression device (including arc extinguish chamber and run-on plate): for arc suppressing

(9) Circuit breaker case, including base and cover

Items above are the main parts for a MCB. After you really know these main parts and their functions, you will naturally understand how a miniature circuit breaker works!