Thermal electromagnetic and electronic differences - MCCB

Update date:2018-07-07 Source:MAXGE

The molded case circuit breaker is divided into structures, and has a thermal electromagnetic structure and an electronic structure.

Thermal electromagnetic MCCB

Thermal electromagnetic type, most of the previous circuit breakers are of such a structure, that is, the thermal effect of electricity and the magnetic effect of electricity are utilized. The thermal effect is implemented by using a bimetal structure. After the switching current is large, the bimetal is bent and deformed to After a certain degree, the trip device of the switch is pushed, the switch is tripped, and the thermal overload current of the switch is adjusted by mechanical adjustment screw. The adjustment precision is not high, and it belongs to the inverse time action, that is, the larger the current, the shorter the action time.


Some large switches, such as electric circuit breakers, do not directly use a bimetal structure, but use a current transformer to convert the primary current into a secondary current, which is connected to the thermal relay, through the normally open of the thermal relay or Normally closed contact, control trip coil, make the switch open, instantaneous large current trip is to use the magnetic effect, there is an electromagnetic coil structure at the lower end of the switch, when there is a large current or short circuit current (larger than the overload current of the switch) The increase in the suction force of the electromagnetic coil directly drives the switch release device, and the instantaneous trip current of the switch is adjusted by mechanical adjustment screws.

Because electromagnetic parts are few, the number of nodes is small, the probability of failure; plus its performance is not affected by voltage shock, and it is good against strong electromagnetic interference, so its comprehensive performance is better, more reliable and safer.

Thermal electromagnetic

The electronic structure is to check the switch current through the current transformer circuit, the current value to control the output, the output control trip coil, and let the switch trip. The advantage is high precision, easy adjustment, directly set the value or use the potentiometer to adjust.

Disadvantages: the need to use the trip coil, the need for power, electronic circuit problems are more difficult to deal with, anti-interference ability is a little worse. 

According to the use of the site to choose MCCB, as in those occasions where there are more temporary cables, it is safer to install electromagnetic leakage circuits, especially at construction sites.

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