JPH033331B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a circuit breaker that can cut off a circuit when a short circuit occurs or when an excessive current exceeding the rating continues to flow. The present invention relates to a circuit breaker that can reliably protect circuits that include elements that are vulnerable to short-circuit currents.

This type of circuit breaker has a fixed contact having a fixed contact and a movable contact that can contact the fixed contact, as disclosed in US Pat. A manual opening/closing mechanism that normally operates to separate the movable contact from the fixed contact and includes a trip mechanism that forcibly separates the movable contact from the fixed contact, and It comprises an electromagnetic device that operates in response to an electric current and attracts an armature linked to the trip mechanism, and an arc extinguishing device disposed near the opening/closing position of the fixed contact and the movable contact.

Normally, the contacts are opened and closed by opening and closing the movable contact with respect to the fixed contact via a manual opening/closing mechanism.On the other hand, in the event of a short circuit or when an excessive current exceeding the rating continues to flow, an electromagnetic device is activated.
The contacts are opened and closed by attracting the armature and separating the movable contact from the fixed contact via a trip mechanism. The arc generated when this contact is opened is transferred to an arc extinguisher where it is split, cooled and extinguished.

However, in a well-known circuit breaker, the short circuit current activates the electromagnetic device and attracts the armature, and then the movable contact is separated from the fixed contact via a trip mechanism and the arc is completely extinguished. was relatively long. Therefore, when the circuit for realizing the interruption includes an element with low voltage resistance, such as a semiconductor element, there is a problem that the semiconductor element or the like is destroyed by the high voltage applied during a short circuit. Therefore, in this type of circuit breaker, especially when the electromagnetic device operates in response to a short circuit current, the movable contact is abruptly separated from the fixed contact to extinguish the arc, greatly improving the current limiting effect. It has been desired to be able to smoothly apply the method to circuits including elements with low voltage resistance.

However, the main purpose of the present invention is to
Significantly shortens the time from when the protective sensor detects a current exceeding a predetermined rated value is activated until the movable contact is separated from the fixed contact and the arc is extinguished, greatly increasing the current limiting effect. To provide improved circuit breakers.

Another object of the present invention is to provide a circuit breaker that minimizes the application of short-circuit voltage to a circuit that achieves interruption in the event of a short circuit, and that can sufficiently protect the circuit even if the circuit includes elements with low withstand voltage. It is on offer.

Other objects and advantages of the invention will become apparent from the following detailed description of the embodiments illustrated in the drawings.

It will be understood, however, that the invention is not limited to these examples only, but includes modifications within the scope of the appended claims.

Referring to the drawings, according to one salient feature of the present invention, the protection sensor has both the function of immediately responding to a short circuit current and the function of responding with a delayed action to a current exceeding a predetermined rated value. For this purpose, a pair of plungers are provided sandwiching a magnetic head disposed in the center of the cylinder. To explain this in more detail, the protective sensor 10 includes a magnetic yoke 1 having a substantially rectangular cross section.
1 as well as an elongated cylinder 12 are included.
The cylinder 12 is made of a non-magnetic material with an open upper end;
The lower cylinder body 13 is preferably made of brass, and the upper cylinder body 14 is made of a non-magnetic material, preferably plastic, and has a slightly larger diameter than the lower cylinder body. A magnetic head 15 is fitted into the opening of the upper cylinder body 14 and the opening of the upper cylinder body 14 so as to connect the two cylinder bodies 13 and 14 to each other. A viscous fluid, preferably silicone oil, is sealed inside the lower cylinder body 13, and a magnetic oil plunger 16 and a coil spring 17 that normally presses the oil plunger 16 toward the inner surface of the lower end of the lower cylinder body 13. is housed therein, passes through the center of the lower side 18 of the yoke 11, and is fixed to the lower side 18 with a portion protruding downward. Furthermore, an actuating plunger 19 made of a magnetic material is housed inside the upper cylinder body 14, and a rod portion 21 having a head portion 20 fixed thereon is integrally provided in the actuating plunger 19, and the rod portion 21 is connected to the upper cylinder. It is provided so as to be able to extend outward from the narrow upper end of the body 14. The tapered upper end of the upper cylinder body 14 is fitted into a circular hole having a lip 23 on the upper side 22 of the yoke 11;
Fixed.

Further, a detection coil 24 is wound around the cylinder 12 substantially over the entire longitudinal direction thereof, and the lead-out ends 25 and 26 of the detection coil 24
One side extends substantially horizontally through one side 27 of the yoke 11 and is connected to a sufficiently flexible lead wire 28, and the other side extends downward from the open side of the yoke 11. It is bent and fixed to the terminal fitting 29 of the circuit breaker. Furthermore, the spring force of a coil spring, which will be described later, is normally applied to the actuating plunger 19 so as to displace it upward, and the upper surface of the actuating plunger 19 is normally placed in contact with the inner surface of the upper end of the upper cylinder body 14. ing.

A frame 31 for supporting a manual opening/closing mechanism including a trip mechanism is integrally provided at the upper end of the side portion 27 of the yoke 11 and extends substantially in the direction in which the upper side portion 22 extends. The frame 31 includes a short frame portion 32 and a long frame portion 33 that extend vertically and parallel to each other. In the short frame portion 32, shaft holes 35 and 36 are formed in the most advanced ear portion 34 and in the upper corner near the rear edge, respectively, and a shaft hole 37 is formed in the vicinity of the rear edge below the shaft hole 36. It is perforated. On the other hand, the long frame part 33 has a shaft hole 39 in an enlarged part 38 provided at a position corresponding to the ear part 34 of the short frame part 32, and corresponds to the shaft holes 36 and 37 of the short frame part 32 near the rear edge. Shaft holes 40 and 41 are drilled at the positions shown in FIG. Further, an inverted L-shaped sliding window 42 is formed in the long frame portion 33 with an arcuate edge 43 on one side, and the tip portion is bent at a substantially right angle. Further, a locking portion 45 is provided on the upper edge of the bent portion 44, and a small disk-shaped arc running ear portion 46 extends horizontally on the lower edge.

Cylindrical lower part 4 of handle 47 of manual opening/closing mechanism
8 has a shaft hole 49 bored in its center, and an enlarged portion 51 having a through hole 50 protruding from a part of its circumferential surface. The handle 47 has short and long shafts 5 held in shaft holes 35 and 39 of the long frame parts 32 and 33.
2 into the shaft hole 49, the frame 31
is rotatably supported. Further, one leg portion 54 of a U-shaped link pin 53 is inserted into the through hole 50 of the enlarged portion 51, and the free end of the leg portion 54 is connected to an L-shaped sliding window of the long frame portion 33. 42 and is movable along the arcuate edge 43. The other leg side 55 of the link pin 53 is inserted into the shaft holes 61, 62 of the ears 57, 58 provided oppositely to the link arm 56, and its free end is loosely engaged with the sliding window 42, It is disposed movably within the other side.

The link arm 56 itself has an inverted U-shaped base 63 when viewed from the end surface, and the base 63 has an insertion window 64.
is formed. The ear portions 57 and 63 extend vertically and parallel to each other downward from the front end of the base portion 63.
Arm portions 65 and 66 with 58 projecting upward are integrally extended, and the arm portions 65 and 66
Shaft holes 67 and 68 are bored in the tip portions, respectively. Furthermore, a kicking tongue part 69 is bent in an L-shape and slightly inclined upward with respect to the vertical direction from the lower edge of one of the arm parts, and is bent in an L-shape from the upper edge so as to substantially A horizontally extending stop ear 70 is provided. A support shaft 71 is held in the shaft holes 67 and 68 at the tips of both the arm parts 65 and 66, and the support shaft 71 is connected to an angle-shaped movable contact 72 connected to one end of the detection coil 24 via a lead wire 28. Shaft hole 7
3 is inserted through the movable contact 72, thereby pivotally supporting the movable contact 72 with respect to the link arm 56. Above the shaft hole 73 of the movable contact 72, an enlarged portion 75 having a locking hole 74 is provided to protrude upward, and a movable contact 76 preferably made of a highly conductive contact material is provided at the lower edge of the tip. is permanently installed.

The movable contact 76 of the movable contact 72 is arranged so as to be able to come into contact with a fixed contact 78 attached to a fixed contact 77 disposed below the movable contact 72 and preferably made of a highly conductive material. The fixed contact 77 itself has an arc running portion 80 that extends downwardly from one leg of the U-shaped portion 79 on which the fixed contact 78 is fixed and faces the arc running ear portion 46 of the frame 31. L is extended from the other leg of the U-shaped portion 79.
A connecting portion 82 which is bent into a letter shape and is integrated with the terminal fitting 81 is extended.

To further explain the trip mechanism in detail, an interlocking arm 84 of the trip mechanism is pivotally supported on a support shaft 83 held in the shaft holes 36, 40 of the frame 31. The interlocking arm includes a base portion 86 having a notch 85 that engages the head portion 21 of the protection sensor 10, and a pair of arm portions 87 and 88 extend perpendicularly and parallel to each other from the front end of the base portion 86. Each arm part 87,
The support shaft 83 is inserted through the shaft holes 89 and 90 protruding from the shaft 88, and the interlocking arm 84 is pivotally supported on the frame 31 as described above. Further, one arm portion 87 is bent into an L shape and extends downward, and the interlocking arm 8
A kicking leg portion 91 that can strike the kicking tongue portion 69 of the link arm 56 when the link arm 4 rotates is provided in a protruding manner. Further, a latch fitting 92 which is L-shaped when viewed from the side and operates integrally with the interlocking arm 84 is pivotally supported on the support shaft 83 via shaft holes 93 and 94, and one side of the latch fitting 92 is attached to the interlocking arm. The arm part 95 is provided as an arm part 95 that can come into contact with the lower surface of the base part 86 of the link arm 56, and the other side part extends downward, and the insertion window 64 of the link arm 56
It is provided as a foot portion 97 having a hook portion 96 that protrudes into and locks on the edge thereof.

On the other hand, a coil spring 101 is wound around the support shaft 52 of the handle 47, and the coil spring 101 is guided by a semi-annular guide 47a at the lower part 48 of the handle 47, and one end of the coil spring 101 is connected to the sliding window 42. The other end is locked to the leg side 54 of a U-shaped link pin 53, and the contact is always opened in the direction of opening of the contact with respect to the handle 47, that is, clockwise in FIG. It provides the turning force. Further, one end of a return spring 102 is engaged with the engagement portion 45 at the tip of the long frame portion 33 of the frame 31, and the other end of the return spring 102 is engaged with the engagement hole 74 of the movable contact 72. A force is always applied to the movable contact 72 in the direction of separating it from the fixed contact 77. Further, an interlocking arm spring 103 and a latch spring 104 are wound around the support shaft 83 of the interlocking arm 84. One end of the interlocking arm spring 103 is attached to the lower surface of the base 86 of the interlocking arm 84, and the other end is attached to the shaft of the frame 31. It is locked by a locking shaft 105 held in the holes 37, 41, and always acts on the interlocking arm 84 in the counterclockwise direction in FIG. In addition, the latch spring 104
One end is attached to the locking shaft 105, and the other end is attached to the frame 3.
1 suitable place, for example, the round hole 106 of the long frame part 33
The latch fitting 94 always locks in the counterclockwise direction in FIG. 2, that is, with the link arm 56.

An arc extinguishing device 110 is provided between the arc running ear portion 46 of the frame 31 and the arc running portion 80 of the fixed contact 77.
is installed. The arc extinguisher 110 includes a recess 111 through which the tip of the movable contact 72 can pass, and a number of de-ion grids 112 spaced apart from each other with small gaps. The group of deion grids 112 is held by both side plates 113 and 114, and an end plate 115 fixed to the side plates 113 and 114 is provided at the edge thereof. An arc gas outflow window 116 is formed in the end plate 115, and a direct emission prevention plate portion 117 is provided at the center of the outflow window 116 at a location corresponding to the recess 111 of the deion grid 112.

Casing 120 housing all the components mentioned above
The casing halves 121 and 122 are divided into two parts.
When the casing halves 121 and 122 are combined, a rectangular long hole 123 is formed in one end surface on the side where the arc extinguishing device 110 is disposed. A notch is provided in the. The elongated hole 123 is located at the back of the direct discharge prevention plate 117 of the arc extinguisher 110. Further, a handle hole 124 is defined in the upper surface of the casing 120 so that the handle 47 can protrude therefrom and its rotation can be restricted within a predetermined rotation angle. A lower portion 48 of the handle 47 is rotatably seated. Also, casing 12
0 has a protrusion 125 swelled inside which abuts the stop ear 70 of the link arm 56 and restricts the range of rotation of the link arm 56, and is a prismatic column into which the U-shaped portion 79 of the movable contact 72 can be fitted. A portion 126 is provided in a protruding manner. Furthermore, a protection sensor 1 is provided inside the casing 120.
The pedestals 127 and 128 are expanded so that the arc extinguisher 110 and the arc extinguisher 110 can be seated securely.

Further, the operation of the present invention will be explained. When the handle 47 of the manual opening/closing mechanism is currently rotated clockwise in the position shown in FIG. 2, FIG. 4, or FIG. 14, one leg portion 54 of the link pin 53 is in the sliding window. 42, and the other leg side 55 is located above the other side of the sliding window 42, and the return spring
02 is also applied, and the link arm 56 and the movable contact 72 are moved upward. Therefore, the movable contact 76 of the movable contact 72 is separated from the fixed contact 78 of the fixed contact 77, that is, the contact is in an open state.
In this case, the link arm 56 is prevented from moving upward more than necessary by the protrusion 125 of the casing. On the other hand, from the position shown in Fig. 2, Fig. 4, or Fig. 14,
The coil spring 1 is in the position shown in the figure or FIG. 15, that is, the handle 47 is wound around the handle spindle 52.
01 and the spring force of the return spring 102, the enlarged portion 5 of the lower part of the handle 48
When the position of one leg side 54 of the link pin 53 inserted through the through hole 50 of 1 crosses the line connecting the support shaft 52 of the handle and the other leg side 55 of the link pin 53, the coil spring 101 In addition, the handle 47 overcomes the spring force of the return spring 102.
is stopped and held in the counterclockwise rotation position. As a result, one leg side 5 of the link pin 53
4 reaches the lower part of the arcuate edge of the sliding window 42, and the other leg part 55 reaches the lower part of the other side of the sliding window 42, that is, the link pin 53 is in a substantially vertical state, and the link arm Since the hook part 96 of the latch metal fitting 92 is locked to the edge of the insertion window 64 of 56, the link arm 56 and the movable contact 72 connected to the link arm 56 via the support shaft 71 are both moved downward. The movable contact 76 contacts the fixed contact 78, that is, the contact is in a closed state. In this case, the electrical circuit includes the terminal fitting 29, the detection coil 24, and the lead wire 2.
8, movable contact 72, movable contact 76, fixed contact 7
8, a fixed contact 77 and a terminal fitting 81.

Furthermore, if an excessive current, for example, a current 1.15 times the rated current, continues to flow when the contacts shown in FIGS. and the oil plunger 16 is connected to the coil spring 1.
7 and the magnetic head 15 relatively slowly while resisting the viscosity of the oil sealed in the lower cylinder body 13.
is adsorbed to. This provides a time delay effect and does not respond to an excessive current flowing for a relatively short period of time, such as a starting current, even if it is detected. magnetic head 15
When the oil plunger 16 is attracted to the position shown in FIG. It is attracted to the magnetic head 15 in this way. Accordingly, the interlocking arm 84 and the latch fitting 92 rotate around the support shaft 83, and the hook portion 96 of the latch fitting 92 comes off the edge of the locking window 64 of the link arm 56, and the interlocking arm 84 and the latch fitting 92 rotate as shown in FIG. The kicking leg 91 of the link arm 84 hits the kicking tongue 69 of the link arm 84. Therefore, this impact strongly applies a so-called starting force to the link arm 56, and the rotational force of the link arm 56 is rapidly increased. Together with the tensile forces 102, the movable contact 72 is rapidly separated from the fixed contact 77 as shown in FIG. At this time, the arc generated when the contact is opened is driven toward the arc extinguishing device 110 by the electromagnetic driving force generated by the current flowing through the fixed contact 77 or the movable contact 72, and is extinguished. In addition, when the movable contact 72 moves upward, the upper tip of the movable contact 72 is located very close to the frame 31, and after the contact is opened, the frame 31 having the arc traveling ear portion 46 and the yoke integrated with the frame 31 are disposed. An electrical path can be formed via 11. Further, the arc gas generated during arc extinguishing can be released from the discharge window 116 formed in the end plate 115 of the arc extinguishing device 110 to the outside through the elongated hole 123 of the casing 120.
Since the direct discharge prevention plate 117 is attached to the discharge window 116 so as to be aligned in the longitudinal direction of the casing 120, the arc gas bypasses the direct discharge prevention plate 117 without being directly discharged to the outside.

Furthermore, when the contacts shown in FIGS. 5 and 15 are opened, when a short-circuit current, for example, a current two or three times the rated current flows, the excitation force by the detection coil 24 is extremely large, so as shown in FIG. 12. Actuation plunger 19
The magnetic head 15 immediately begins to be attracted to the magnetic head 15. At this time, the interlocking arm 84 and the latch metal fitting 92 rotate around the support shaft 83, and the latch metal fitting 92 rotates around the support shaft 83.
When the hook part 96 of the link arm 56 comes off the edge of the locking window 64, the kicking leg part 91 of the interlocking arm 84 hits the kicking tongue part 69 of the link arm 84 as described above with reference to FIG. Therefore, as described above, this impact imparts a so-called strong starting force to the link arm 56, and the movable contact 72 is rapidly separated from the fixed contact 77 as shown in FIG. Other actions are the same as when excessive current is detected.

In the circuit breaker according to the above-described embodiment, the protective sensor 10 operates relatively slowly at an overcurrent of up to twice the rated current, as shown by curve X in FIG. It has been found that for currents that exceed the current range, the contact can be opened in 0.01 seconds or less, and that for large currents exceeding 10 times the rated current, the contacts can be opened in a time closer to 0.001 seconds than 0.01 seconds, that is, instantaneously. are doing. On the other hand, with conventional protective sensors that have a time-delaying effect, it usually takes more than one second for the contact to open even when a short-circuit current of about three times the rated current flows, as shown by curve A, and, for example, due to magnetic characteristics etc. Even with a conventional protective sensor that has a time-delaying effect that improves the speed and speeds up the contact, it takes nearly one second to open the contact at a short-circuit current that is more than three times the rated current, as shown by curve B. Therefore, it cannot be applied when the circuit for realizing the interruption includes an element with low voltage resistance such as a semiconductor element. On the other hand, conventional protection sensors that focus only on immediate action do not have a time delay effect, so they operate even if a current of 1.25 times the rated current or less flows for about 0.1 seconds as shown in curve C. For example, even with starting power, In addition to being sensitive and lacking in versatility, it still required about 0.01 seconds to operate even at a current exceeding 10 times the rated current, and was still inferior in terms of quick action.

In addition, in the circuit breaker according to the above-described embodiment, the responsiveness is greatly improved by further striking the link arm when the effective protection sensor is activated, and the peak value of the arc voltage can be reduced even in a very short time. This greatly improves the current limiting effect. Therefore, the arc extinguishing time when the arc extinguishing device is not provided is substantially 10 seconds as shown in curve a shown in FIG. 19, and the arc extinguishing time when the arc extinguishing device is provided is as shown in curve b. It has been found that when the present invention is applied to a conventional circuit breaker, which takes approximately 6 seconds, extinguishing can be achieved in approximately 4 seconds.

According to the circuit breaker of the present invention configured as described above, the protective sensor has a time-delaying effect and a sufficient immediate action function, and the opening operation time of the movable contact with respect to the fixed contact is significantly reduced. Since it can be shortened to
Since it can be applied to a wide variety of circuits and generally achieves a high degree of current limiting effect, it can also be applied to circuits that include elements with low withstand voltage, providing extremely high versatility.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a circuit breaker according to the present invention, Fig. 2 is a side view of the circuit breaker of Fig. 1 with half of the casing made up of two parts removed, and Fig. 3 is a circuit breaker of the same type. Figure 4 is an exploded perspective view showing the components of the device excluding the casing, and Figure 4 is the same as Figure 1.
5 is a sectional view showing only the main components of FIG. 4 when the contacts are closed. FIG. 6 is a sectional view taken along the - line in FIG. 2. The figure is a sectional view taken along the - line in Fig. 2, Fig. 8 is a sectional view taken along the - line in Fig. 3, Fig. 9 is an end view of the same circuit breaker, and Fig. 10. is a cross-sectional view similar to Fig. 5, when an excessive current flows through the detection coil of the same circuit breaker, and Fig. 1.
Figure 1 is a cross-sectional view similar to Figure 5 when the protective sensor of the above circuit breaker is fully activated due to excessive current, and Figure 12 is a cross-sectional view when a short circuit current flows through the detection coil of the above circuit breaker. Fig. 13 is a sectional view similar to Fig. 5 showing a process of operation of the protective sensor and manual opening/closing mechanism of the above circuit breaker, and Fig. 13 is a cross-sectional view of the circuit breaker shown in Fig.
14 is a sectional view similar to that shown in the figure, and FIG. 14 is a diagram in the same state as FIG.
Fig. 15 is a diagram similar to Fig. 14 in the same state as Fig. 5, and Fig. 16 is a diagram showing a process of operation when an excessive current flows through the detection coil of the circuit breaker as described above. Fig. 17 is a diagram similar to Fig. 14 in the same state as Fig. 11, and Fig. 18 is a diagram showing the relationship between current flowing to the protection sensor and operating time in the same circuit breaker as before. Figure 19 in comparison with the product
The figure is a diagram showing the arc-extinguishing characteristics of the circuit breaker same as the above. 10...Protection sensor, 11...Yoke, 12...
...Cylinder, 13...Lower cylinder body, 14...
Upper cylinder body, 15... Magnetic head, 16...
Oil plunger, 17...Coil spring,
18... Lower side part, 19... Operating plunger, 20
...head part, 21 ... rod part, 22 ... upper side part, 23 ... lip part, 24 ... detection coil, 2
5, 26... Pull-out end, 27... Side part, 28...
Lead wire, 29...Terminal fitting, 31...Frame, 32...Short frame part, 33...Long frame part, 34...Ear part, 35, 36, 37...Shaft hole,
38... Ampulla, 39, 40, 41... Shaft hole, 4
2... Sliding window, 43... Arc-shaped edge, 44... Bent part, 45... Locking part, 46... Arc traveling ear part,
47... Handle, 48... Lower part, 49... Shaft hole, 50... Through hole, 51... Ampulla, 52... Support shaft, 53... Link pin, 54, 55... Leg side part, 56 ... Link arm, 57, 58 ... Ear part, 61, 62 ... Shaft hole, 63 ... Base, 64 ...
...Intrusion window, 65, 66...Arm part, 67, 68
...Shaft hole, 69...Kicking tongue, 70...Stop ear, 71...Spindle, 72...Movable contact, 73...
...Shaft hole, 74...Latching hole, 75...Ampulla, 76
... Movable contact, 77 ... Fixed contact, 78 ... Fixed contact, 79 ... U-shaped part, 80 ... Arc traveling plate, 81 ... Terminal fitting, 82 ... Connection part, 83 ...
... Support shaft, 84 ... Interlocking arm, 85 ... Notch, 8
6... Base, 87, 88... Arm part, 89, 9
0...Shaft hole, 91...Kicking foot part, 92...Latch fitting, 93, 94...Shaft hole, 95...Arm part,
96... Hook portion, 97... Leg portion, 101... Coil spring, 102... Return spring, 10
3... Interlocking arm spring, 104... Latch spring, 105... Locking shaft, 106... Round hole, 110... Arc extinguishing device, 111... Recess, 11
2...Daiongrid, 113,114...
Side plate, 115...End plate, 116...Outflow window, 11
7... Direct release suppression plate, 120... Casing, 1
21, 122...Casing half body, 123...Elongated hole, 124...Handle hole, 125...Protrusion, 1
26...Prismatic section, 127, 128...Pedestal section.

Claims (1)

[Claims] 1 includes a casing, a handle that partially protrudes from the casing and is rotatably held by the casing, a link member linked to the handle, and a trip mechanism that can be engaged and detached from the link member, and is operated via the handle. a movable contact that can be swung by the manual opening and closing mechanism, a movable contact that has a movable contact, a fixed contact that has a fixed contact that connects and separates the movable contact of the movable contact, and a movable contact. A return spring that acts to separate the child from the fixed contact, an arc extinguishing device disposed near the contact point between the fixed contact and the movable contact, and a detection coil that detects overcurrent. and a protective sensor that moves the trip mechanism in a direction to separate it from the link member. A first plunger is filled with a viscous fluid, and a spring force is applied in a direction to separate the plunger from the magnetic head, and the first plunger is capable of being attracted to the magnetic head in response to an excessive current, and the other cylinder body includes a first plunger that can be attracted to the magnetic head in response to an excessive current. It has a head part that protrudes from the cylinder body of the trip mechanism and engages with the interlocking arm of the trip mechanism, and is provided so that it can be independently attracted to the magnetic head when a spring force is applied in the direction away from the magnetic head and a short circuit current is detected. A circuit breaker characterized in that the second plunger is enclosed.