How Circuit Breakers Keep Us Safe

A miniature circuit breaker is an overcurrent protection circuit breaker suitable for use in households or similar places. It was formerly known as a wire protection switch (circuit breaker). Its main purpose is to protect the wires (or cables) and electrical equipment at the end of the line, which is different from the industrial distribution circuit breakers and motor protection circuit breakers used in trunk lines and main branches.

What are circuit breaker protections?

Overload protection

The realization of the overload protection function of the circuit breaker is based on the principle that the bimetal bends directionally and regularly as the temperature rises. After the miniature circuit breaker is closed, it is in normal working state. The internal bimetal is heated by a certain current passing through it. The two pieces of metal have different thermal expansion coefficients and cause bending. The normal current (1.13In) has a small bending angle, so the thrust is not enough to trip the tripping mechanism. When the line is generally overloaded, when the overload current (1.45In) is reached, The bimetallic sheet has a large bending angle and touches the lever in the tripping mechanism, and the thrust is enough to push the tripping mechanism, so that the small circuit breaker trips and plays the role of overload protection.

The magnitude of the current flowing through the miniature circuit breaker is different, and the degree of bending of the bimetal is also different. In the general overload of the line, because the overload current is not too large, the tripping time of the circuit breaker is generally longer. In the current time-current characteristics of GB10963.1-2005 standard, it is stipulated that the overcurrent tripping current is 1.45 times the rated current. The tripping time should be within 1 hour.​​

Short circuit protection

The short-circuit protection function of the circuit breaker is realized by the instantaneous release. According to the analysis of F=IN (the suction force is proportional to the product of the current and the number of turns), due to the small number of turns of the instantaneous release coil (generally less than 10 turns), although the instantaneous release is connected in series in the circuit, when the circuit is working normally, Due to the small number of turns, the suction force generated by the normal working current is not enough to overcome the reaction force of the spring, so the line can work normally.

When the line is short-circuited or severely overloaded, a very high current flows through the induction coil to generate a strong magnetic field. Since the generated current is several times or even dozens of times larger than the normal working current, the number of turns of the coil does not change. , but the current increases several times or even dozens of times, so the suction force also increases several times or even dozens of times. Pushing the lever makes the circuit breaker trip quickly. Due to the large current, the tripping time of the circuit breaker is generally within 0.1s. And as long as the reaction force spring is selected reasonably, it can meet the set requirements of B-type, C-type and D-type instantaneous release.

Some Notes on Circuit Breaker Installation

• When the circuit breaker is used, it must be installed correctly in the early stage. Before installation, check whether its data and usage requirements are in compliance, and it should not be too close to the AC contactor.
• We also need to pay attention to whether this circuit breaker has the function of short circuit protection, and must have enough arcing distance. At the same time, special copper wires should be configured, and the cross-sectional area should not be less than 1.5 square millimeters.
• When installing circuit breakers, some original grounding protection devices cannot be removed. It is necessary to strictly distinguish between the neutral wire and the ground wire, because the protective ground wire can cause the danger of electric shock when the electrical enclosure is electrified, so it needs to be reserved. That is to say, it is necessary to install a leakage protector and connect it to the ground wire.
• When wiring, it should be connected according to its load mark, and must not be reversed. And in single-phase lighting circuits, including three-phase circuits, the neutral line must exceed the current transformer. Electrical equipment can only be connected to the load side of the leakage protector.

Conclusion

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