High-reliability magnetic latching relay

Abstract

The utility model discloses a high-reliability magnetic latching relay, which comprises a shell, an electromagnetic assembly, a movable spring assembly, a static reed and the like, and is mainly characterized in that an armature assembly which swings in a reciprocating manner and a push plate which moves in a seesaw manner are additionally arranged in the shell, and two ends of the push plate are respectively connected with the armature assembly and the movable spring assembly. And the push plate is driven to move in a wane manner, so that the movable spring assembly can be driven to contact a pair of static reeds to switch on a load circuit or be separated from the pair of static reeds to switch off the load circuit. Meanwhile, a structural mode that a short-circuit-resistant armature and a short-circuit-resistant piece are in contact fit, a steel ball is matched with a movable groove and a convex rib in the movable groove is additionally arranged between the movable spring assembly and the shell, and a pressure spring piece is arranged in the movable spring assembly to reduce the rebound time during contact of contacts, and a microswitch additionally arranged in the shell is in linkage with the movable spring assembly. Therefore, the improved magnetic latching relay has the advantages of high power, low temperature rise, high short circuit resistance, more reliable structure and the like.

Description

Technical Field

[0001] The utility model relates to a magnetic latching relay, in particular to a high-reliability magnetic latching relay. Background Art

[0002] Smart meters are smart terminals of smart grids. In addition to the basic electricity consumption metering function of traditional electricity meters, in order to adapt to the use of smart grids and new energy, smart meters also have intelligent functions such as two-way multi-rate metering function, user-side control function, two-way data communication function with multiple data transmission modes, and anti-electricity theft function. The magnetic latching relay used with the built-in switch of the smart meter is an important guarantee for ensuring the safety of electricity use. In order to improve the safety of smart meters, the State Grid has recently put forward the following new improvement requirements for the performance of the magnetic latching relay with built-in switch, namely, carrying the rated safe short-time withstand current capability, connecting the rated short-circuit current capability, maintaining low terminal temperature rise, load switching capability and air gap between contacts, etc. According to the above-mentioned usage requirements, the structure of a traditional magnetic latching relay is usually composed of a housing, an electromagnetic assembly and a moving spring assembly in the housing, and a pair of static spring pieces on the housing. The moving spring assembly is directly driven by the electromagnetic assembly to contact or disengage from a pair of static spring pieces, and the anti-short circuit structure design on the moving spring assembly cannot meet the new usage requirements. Therefore, in actual use, it is impossible to achieve the purposes of high power, low temperature rise and anti-short circuit. In particular, the contact between the moving spring assembly and the pair of static spring pieces to connect the load circuit or the separation to disconnect the load circuit cannot be directly perceived. Therefore, the structural reliability of the traditional magnetic latching relay has been difficult to adapt to the new usage needs, and thus cannot meet the new usage requirements of smart meters. Utility Model Content

[0003] The technical problem to be solved by the utility model is to overcome the defects of the prior art and provide a high-reliability magnetic latching relay with high power, low temperature rise, strong short-circuit resistance and more reliable use structure.

[0004] The technical problem of the utility model is achieved through the following technical solutions:

[0005] A high-reliability magnetic latching relay comprises a housing, an electromagnetic assembly and a moving spring assembly in the housing, and a pair of static spring pieces on the housing, an armature assembly and a push plate are arranged between the electromagnetic assembly and the moving spring assembly, the middle part of the armature assembly is hinged in the housing to form a reciprocating swing, the middle part of the push plate is hinged in the housing to form a seesaw motion, and the two ends of the push plate are respectively connected with the armature assembly and the moving spring assembly; the electromagnetic assembly drives the armature assembly to swing back and forth, and drives the push plate to seesaw motion, thereby driving the moving spring assembly to contact a pair of static spring pieces to connect a load circuit or to disengage from a pair of static spring pieces to cut off the load circuit.

[0006] A micro switch is arranged in the shell; the dynamic spring assembly contacts a pair of static spring pieces to connect the load circuit, and the push plate seesaws to open the micro switch; the dynamic spring assembly separates from a pair of static spring pieces to cut off the load circuit, and the push plate seesaws to close the micro switch.

[0007] The push plate is embedded with a support sheet, and both sides of the middle of the push plate are respectively provided with rotating shafts for constituting a seesaw motion of the push plate, and both ends of the push plate are respectively provided with transverse shafts for connection.

[0008] The dynamic spring assembly includes a dynamic spring plate, a fixing frame arranged above the dynamic spring plate, and a U-shaped frame arranged below the dynamic spring plate. The U-shaped legs of the U-shaped frame clamp the dynamic spring plate upward and are fixed on the fixing frame. A compression spring sheet is provided between the dynamic spring plate and the fixing frame, and the compression spring sheet is respectively connected to the dynamic spring plate and the fixing frame, and forms an elastic compression and fixation on the dynamic spring plate.

[0009] An anti-short-circuit armature is provided on the U-shaped frame, and an anti-short-circuit piece is correspondingly provided in the shell. The movable spring assembly contacts a pair of static spring pieces to connect the load circuit, and synchronously drives the anti-short-circuit armature to contact the anti-short-circuit piece. The movable spring assembly disengages from a pair of static spring pieces to cut off the load circuit, and synchronously drives the anti-short-circuit armature to disengage from the anti-short-circuit piece.

[0010] A steel ball is embedded in the fixing frame, and a corresponding movable groove for accommodating the steel ball is provided in the shell. The movable spring assembly contacts or separates from a pair of static spring sheets and drives the steel ball to move back and forth along the movable groove, and a convex rib is also provided in the movable groove.

[0011] A guide frame is provided between the movable spring plate and the fixed frame, and guide holes are respectively provided at both ends of the guide frame. Correspondingly, two positioning columns are respectively mounted in the guide holes at both ends in the shell. The movable spring assembly contacts or disengages from a pair of static spring sheets, and the positioning columns are reciprocated along the guide holes to form a motion guide for the movable spring assembly.

[0012] The movable spring plates are provided with two pieces arranged side by side, and positioning grooves are respectively provided on both sides of each movable spring plate, and the positioning grooves between the two movable spring plates arranged side by side are mutually surrounded to form a positioning hole.

[0013] The U-shaped legs of the U-shaped frame clamp two movable spring plates upward and are fixed on the fixed frame, and the U-shaped legs are positioned and fitted in the positioning grooves of the movable spring plates. Rivets are provided on the U-shaped frame, and the rivets pass through the positioning holes to rivet the fixed guide frame.

[0014] Both ends of each movable spring plate are provided with movable contacts, and each stationary spring plate is provided with two stationary contacts.

[0015] Compared with the prior art, the utility model mainly adds an armature assembly and a push plate between the electromagnetic assembly and the movable spring assembly, the middle part of the armature assembly is hinged in the housing and forms a reciprocating swing, the middle part of the push plate is hinged in the housing and forms a seesaw motion, and the two ends of the push plate are respectively connected with the armature assembly and the movable spring assembly; in this way, the electromagnetic assembly drives the armature assembly to swing back and forth, and drives the push plate to seesaw motion, so that the movable spring assembly can be driven to contact a pair of static spring pieces to connect the load circuit or to disengage from a pair of static spring pieces to cut off the load circuit; at the same time, the structure of the movable spring assembly is also improved, specifically, an anti-short-circuit armature and an anti-short-circuit piece are added between the movable spring assembly and the housing for contact cooperation, and a steel ball cooperates with an active groove and The structural mode of the convex rib in the movable groove and the arrangement of the compression spring sheet in the movable spring assembly can reduce the rebound time when the contacts are in contact; obviously, this seesaw-type movable spring assembly driving structure and the improved structure of the movable spring assembly can help to enhance the short-circuit resistance of the magnetic latching relay, and the bridge contact structure is also adopted between the movable spring assembly and a pair of static spring sheets, which can also reduce the contact voltage drop of the contacts and enable the magnetic latching relay to have the advantages of high power and low temperature rise; in addition, the micro switch added in the housing is linked with the movable spring assembly to better sense the contact between the movable spring assembly and a pair of static spring sheets to connect the load circuit or disconnect and cut off the load circuit. These designs can improve the reliability of the use structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural schematic diagram of the utility model.

[0017] Figure 2 for Figure 1 3D exploded view of .

[0018] Figure 3 for Figure 1 Schematic diagram of the structure with the cover removed.

[0019] Figure 4 for Figure 3 Front view of the structure with the protective plate and magnetic shield removed (the dynamic spring assembly is separated from a pair of static spring leaves).

[0020] Figure 5 for Figure 4 Stereoscopic diagram.

[0021] Figure 6 for Figure 5 3D exploded view of .

[0022] Figure 7 This is a first perspective view of the dynamic spring assembly.

[0023] Figure 8 This is a second perspective view of the dynamic spring assembly.

[0024] Fig. 9 for Figure 8A three-dimensional exploded view of the device with the fixing frame, compression spring and anti-short-circuit yoke removed.

[0025] Fig.10 It is a schematic diagram of the position structure between the U-shaped frame with the anti-short-circuit armature and the anti-short-circuit plate.

[0026] Fig.11 It is a structural diagram of the push plate.

[0027] Fig.12 for Fig.11 A-A section enlarged view.

[0028] Fig.13 It is a schematic diagram of the structure inside the shell. DETAILED DESCRIPTION

[0029] The embodiments of the present invention will be described in detail below according to the above-mentioned drawings.

[0030] like Figure 1 to Figure 13 As shown, 1. housing, 11. base, 111. movable groove, 112. convex rib, 12. cover plate, 13. protective plate, 2. static spring sheet, 21. static contact, 3. electromagnetic assembly, 31. coil assembly, 32. iron core, 33. upper yoke, 34. lower yoke, 35. magnetic shield, 4. armature assembly, 41. upper suction block, 42. lower suction block, 43. transverse groove, 5. push plate, 51. rotating shaft, 52. transverse Shaft, 53. Support sheet, 6. Dynamic spring assembly, 61. Dynamic spring plate, 611. Positioning groove, 612. Positioning hole, 62. U-shaped frame, 621. Mounting groove, 63. Fixed frame, 631. Embedded hole, 64. Guide frame, 641. Guide hole, 65. Compression spring sheet, 66. Anti-short-circuit armature, 67. Moving contact, 68. Rivet, 69. Positioning column, 7. Micro switch, 8. Steel ball, 9. Anti-short-circuit sheet.

[0031] A high-reliability magnetic latching relay is mainly used for the built-in switch of a smart meter. Its structure includes a housing 1, an electromagnetic assembly 3 in the housing, an armature assembly 4, a push plate 5, a micro switch 7 and a dynamic spring assembly 6, and a pair of static spring pieces 2 on the housing.

[0032] The shell 1 is composed of a box-shaped base 11 and a cover 12 detachably covered on the base, so that a hollow chamber for installing other components is formed in the shell 1 through the base 11 and the cover 12; the electromagnetic component 3 usually includes a coil group 31, an iron core 32 in the coil group and a magnetic shield 35 covering the outside of the coil group, and the two ends of the iron core 32 extend out of the coil group 31 and are respectively installed with an upper yoke 33 and a lower yoke 34, so when the coil group 31 is energized, magnetic attraction will be generated on the upper and lower yokes.

[0033] The armature assembly 4 is arranged on one side of the electromagnetic assembly 3, and Figure 3As shown, the armature assembly 4 is covered by the protective plate 13, and is hinged in the housing 1 through the middle rotating shaft. The upper end of the armature assembly 4 is provided with two upper suction blocks 41, and the lower end is provided with two lower suction blocks 42, and the upper yoke 33 of the electromagnetic assembly 3 is just located between the two upper suction blocks 41, and the lower yoke 34 is just located between the two lower suction blocks 42; in this way, when the coil group 31 is energized and positively excited, the upper yoke 33 absorbs the upper suction block 41 on the right and the lower yoke 34 absorbs the lower suction block 42 on the left; when the coil group 31 is energized and reversely excited, the upper yoke 33 absorbs the upper suction block 41 on the left and the lower yoke 34 absorbs the lower suction block 42 on the right, so the armature assembly 4 is subjected to the positive and reverse excitation of the coil group 31, and will form a reciprocating swing around the middle rotating shaft.

[0034] The push plate 5 is a flat rectangular plastic plate, which is embedded with a thin metal support sheet 53 with a certain elastic thickness. This structure of the insert injection molding can enhance the high temperature deformation resistance of the push plate 5 and increase the pushing rigidity, thereby ensuring the stability and accuracy of the push plate movement process.

[0035] The push plate 5 is provided with rotating shafts 51 on both sides of the middle part, and the push plate 5 is hinged in the housing 1 through the rotating shafts 51 on both sides of the middle part to form a seesaw motion, that is, Figure 4 The push plate 5 shown rotates around the central rotating shaft 51, so that the two ends of the push plate can form an up and down seesaw motion, and the two ends of the push plate 5 are also provided with a horizontal axis 52, which can be used to connect the armature assembly 4 and the movable spring assembly 6 respectively. Therefore, a horizontal groove 43 that cooperates with the horizontal axis 52 for connection is required on the armature assembly 4 and the movable spring assembly 6.

[0036] Therefore, by driving the armature assembly 4 to swing back and forth through the electromagnetic assembly 3, the push plate 5 can be driven to move in a seesaw manner, thereby driving the dynamic spring assembly 6 to contact a pair of static spring pieces 2 to connect the load circuit or to disengage from a pair of static spring pieces 2 to cut off the load circuit.

[0037] The dynamic spring assembly 6 is as follows Figure 7~Figure 8 As shown, it includes two movable spring plates 61 arranged side by side, a fixing frame 63 arranged above the movable spring plates, a U-shaped frame 62 arranged below the movable spring plates, and a compression spring sheet 65 and a guide frame 64 arranged between the movable spring plates 61 and the fixing frame 63. Positioning grooves 611 are respectively provided on both sides of each movable spring plate 61, so the positioning grooves between the two movable spring plates 61 arranged side by side are surrounded by each other to form a positioning hole 612, and moving contacts 67 are respectively provided at both ends of each movable spring plate 61.

[0038] The U-shaped legs of the U-shaped frame 62 clamp the two movable spring plates 61 upwards and are fixed on the fixing frame 63, and the U-shaped legs are positioned and fitted in the positioning grooves 611 of the two movable spring plates 61. Rivets 68 are provided on the U-shaped frame 62, specifically, two rivets 68 are provided on the U-shaped bottom surface of the U-shaped frame, and the two rivets pass through the positioning holes 612 to rivet and fix the guide frame 64, and guide holes 641 are respectively provided at both ends of the guide frame.

[0039] Each of the movable spring plates 61 is provided with a compression spring sheet 65, which is a rectangular metal sheet continuously bent into a hat shape. The metal material is usually stainless steel or beryllium copper. The two ends of the compression spring sheet 65 are fixed together through the movable contacts 67 at the two ends of the movable spring plate 61. The middle part of the compression spring sheet 65 is fixed to the fixing frame 63 by riveting. Therefore, the movable spring plate 61 and the fixing frame 63 are respectively connected by the compression spring sheet 65, and the movable spring plate 61 is elastically compressed and fixed. On the one hand, the rebound time when the contact is in contact can be reduced, and on the other hand, the short-circuit resistance can be enhanced when the contact is energized.

[0040] The U-shaped frame 62 is provided with an anti-short-circuit armature 66. Usually, a mounting groove 621 is provided on each of the two U-shaped legs of the U-shaped frame 62. An anti-short-circuit armature 66 is embedded and fixed in the mounting groove 621 of each U-shaped leg, and the end of the anti-short-circuit armature needs to extend out of the U-shaped bottom surface of the U-shaped leg 62. Correspondingly, an anti-short-circuit sheet 9 is provided in the housing 1, that is, in the base 11. Its position is as shown in FIG. Figure 3 , Figure 5 As shown, it is located exactly between a pair of static spring pieces 2, so that when the two movable spring plates 61 contact the pair of static spring pieces 2, they can synchronously drive the anti-short-circuit armature 66 to contact the anti-short-circuit piece 9 to form an anti-short-circuit structure, that is, the movable spring assembly 6 contacts the pair of static spring pieces 2 to connect the load circuit, and can synchronously drive the anti-short-circuit armature 66 to contact the anti-short-circuit piece 9. The movable spring assembly 6 detaches from the pair of static spring pieces 2 to cut off the load circuit, and can synchronously drive the anti-short-circuit armature 66 to detach from the anti-short-circuit piece 9.

[0041] The anti-short-circuit armature 66 and the anti-short-circuit piece 9 are both made of electrical pure iron. The purpose of designing this anti-short-circuit structure is that when a large current passes through the contact part, a large electric repulsion force will be generated between the moving spring plate 61 and the static spring piece 2, which will push the contact between the moving and static contacts apart, causing the contacts to be disconnected and causing product failure.

[0042] The contact between the anti-short-circuit armature 66 and the anti-short-circuit piece 9 will generate a large magnetic field when a large current passes through the moving spring plate 61. The magnetic field will magnetize the anti-short-circuit armature 66, and enable the magnetized anti-short-circuit armature 66 to generate a magnetic field attraction with the anti-short-circuit piece 9 installed in the housing 1, thereby resisting the electric repulsion generated between the moving and static contacts and avoiding accidental disconnection between the contacts.

[0043] The shell 1, that is, the base 11, is provided with two positioning columns 69 respectively mounted in the guide holes 641 at both ends of the guide frame 64. When the movable spring assembly 6 contacts a pair of static spring leaves 2 or detaches from a pair of static spring leaves 2, the positioning columns 69 can move back and forth along the guide holes 641 to form a motion guide for the movable spring assembly 6.

[0044] The fixing frame 63 is provided with a steel ball 8. Figure 7 As shown, a fixed steel ball 8 is embedded in the embedding hole 631 on one side of the fixing frame 63, and a movable groove 111 for fitting the steel ball 8 is correspondingly provided in the shell 1, that is, in the base 11. When the dynamic spring assembly 6 contacts a pair of static spring leaves 2 or separates from a pair of static spring leaves 2, it can drive the steel ball 8 to move back and forth along the movable groove 111, thereby ensuring that the movement process of the dynamic spring assembly 6 is smoother.

[0045] At the same time, a convex rib 112 is provided in the movable groove 111. When electricity is passed between the moving and static contacts to generate electric repulsion, the convex rib 112 can be used to block the steel ball 8 to increase the resistance of the movable spring assembly 6 when it moves upward and disconnects, thereby further improving the short-circuit resistance.

[0046] In the pair of static spring pieces 2, each static spring piece is provided with two static contacts 21, so the moving contacts 67 at one end of the two moving spring plates 61 can form contact conduction with the two static contacts 21 at one end of one static spring piece 2, that is, a bridge contact structure is designed between the moving and static contacts, which can increase the contact gap and reduce the terminal temperature rise by connecting the contact groups in series and in parallel.

[0047] Obviously, this seesaw-type dynamic spring assembly 6 driving structure and the improved structure of the dynamic spring assembly are helpful to enhance the short-circuit resistance of the magnetic holding relay, and the bridge contact structure adopted between the dynamic spring assembly 6 and a pair of static spring pieces 2 can also reduce the contact voltage drop and enable the magnetic holding relay to have the advantages of high power and low temperature rise.

[0048] In addition, a micro switch 7 is provided in the housing 1, that is, in the base 11. The micro switch is located above the push plate 5, and a normally closed micro switch is selected as the auxiliary contact part of the magnetic holding contactor. When the moving spring assembly 6 contacts a pair of static spring pieces 2 to connect the load circuit, that is, the main contact is connected, the push plate 5 will seesaw and open the micro switch 7. When the moving spring assembly 6 is separated from the pair of static spring pieces 2 to cut off the load circuit, that is, the main contact is closed, the push plate 5 will seesaw and close the micro switch 7.

[0049] In this way, the micro switch 7 and the dynamic spring assembly 6 are linked to each other, so that the contact between the dynamic spring assembly 6 and a pair of static spring pieces 2 can be better sensed to connect or disconnect the load circuit, thereby improving the reliability of the use structure.

[0050] The above description is only a specific embodiment of the present invention. Those skilled in the art should understand that any structural design equivalent to this embodiment should be included in the protection scope of the present invention.

Claims

1. A high-reliability magnetic latching relay, comprising a housing (1), an electromagnetic assembly (3) and a dynamic spring assembly (6) in the housing, and a pair of static springs (2) on the housing, characterized in that: An armature assembly (4) and a push plate (5) are provided between the electromagnetic assembly (3) and the movable spring assembly (6); the middle portion of the armature assembly (4) is hinged in the housing (1) to form a reciprocating swing; the middle portion of the push plate (5) is hinged in the housing (1) to form a seesaw motion; and the two ends of the push plate (5) are respectively connected to the armature assembly (4) and the movable spring assembly (6); The electromagnetic assembly (3) drives the armature assembly (4) to swing back and forth, and drives the push plate (5) to move in a seesaw-like manner, thereby driving the movable spring assembly (6) to contact a pair of static spring pieces (2) to connect the load circuit or to disengage from the pair of static spring pieces (2) to disconnect the load circuit.

2. A high reliability magnetic latching relay according to claim 1, characterized in that A micro switch (7) is provided in the housing (1); the movable spring assembly (6) contacts a pair of stationary spring pieces (2) to connect the load circuit, and the push plate (5) moves in a seesaw-like manner to open the micro switch (7); the movable spring assembly (6) separates from the pair of stationary spring pieces (2) to cut off the load circuit, and the push plate (5) moves in a seesaw-like manner to close the micro switch (7).

3. A high reliability magnetic latching relay according to claim 1, characterized in that The push plate (5) is embedded with a support sheet (53), and both sides of the middle of the push plate (5) are respectively provided with rotation axes that enable the push plate (51) to seesaw-like motion, and both ends of the push plate (5) are respectively provided with transverse axes (52) for connection.

4. A high reliability magnetic latching relay according to claim 1, characterized in that The dynamic spring assembly (6) comprises a dynamic spring plate (61), a fixing frame (63) arranged above the dynamic spring plate, and a U-shaped frame (62) arranged below the dynamic spring plate. The U-shaped legs of the U-shaped frame clamp the dynamic spring plate (61) upward and are then fixed on the fixing frame (63). A compression spring sheet (65) is provided between the dynamic spring plate (61) and the fixing frame (63). The compression spring sheet is respectively connected to the dynamic spring plate (61) and the fixing frame (63) and elastically compresses and fixes the dynamic spring plate (61).

5. A high reliability magnetic latching relay according to claim 4, characterized in that An anti-short-circuit armature (66) is provided on the U-shaped frame (62), and an anti-short-circuit piece (9) is correspondingly provided in the housing (1); the movable spring assembly (6) contacts a pair of stationary spring pieces (2) to connect the load circuit, and simultaneously drives the anti-short-circuit armature (66) to contact the anti-short-circuit piece (9); the movable spring assembly (6) disengages from the pair of stationary spring pieces (2) to cut off the load circuit, and simultaneously drives the anti-short-circuit armature (66) to disengage from the anti-short-circuit piece (9).

6. A high reliability magnetic latching relay according to claim 4, characterized in that A steel ball (8) is embedded in the fixing frame (63), and a movable groove (111) for receiving the steel ball (8) is correspondingly provided in the housing (1). The movable spring assembly (6) contacts a pair of static spring sheets (2) or detaches from the pair of static spring sheets (2), and drives the steel ball (8) to move back and forth along the movable groove (111). A convex rib (112) is also provided in the movable groove.

7. A high reliability magnetic latching relay according to claim 4, characterized in that A guide frame (64) is provided between the movable spring plate (61) and the fixed frame (63), and guide holes (641) are provided at both ends of the guide frame. Correspondingly, two positioning columns (69) are provided in the housing (1) and are respectively mounted in the guide holes (641) at both ends. The movable spring assembly (6) contacts a pair of stationary spring plates (2) or is separated from the pair of stationary spring plates (2), and the positioning columns (69) are reciprocated along the guide holes (641) to form a motion guide for the movable spring assembly (6).

8. A high reliability magnetic latching relay according to claim 4, characterized in that The movable spring plates (61) are provided with two pieces arranged side by side, and positioning grooves (611) are respectively provided on both sides of each movable spring plate (61), and the positioning grooves (611) between the two movable spring plates (61) arranged side by side are mutually surrounded to form a positioning hole (612).

9. A high reliability magnetic latching relay according to claim 8, characterized in that The U-shaped legs of the U-shaped frame (62) clamp the two movable spring plates (61) upwards and are then fixed on the fixing frame (63), and the U-shaped legs are positioned and mounted in the positioning grooves (611) of the movable spring plates (61). The U-shaped frame (62) is provided with rivets (68) which pass through the positioning holes (612) and are riveted to the fixing guide frame (64).

10. A high reliability magnetic latching relay according to claim 8, characterized in that Each of the movable spring plates (61) is provided with movable contacts (67) at both ends, and each of the stationary spring plates (2) is provided with two stationary contacts (21).

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