US3286071A

US3286071A - Circuit interrupter with improved operating means

Info

Publication number: US3286071A
Application number: US470274A
Authority: US
Inventors: Francis L Gelzheiser
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1960-08-25
Filing date: 1965-04-12
Publication date: 1966-11-15
Anticipated expiration: 1983-11-15
Also published as: GB926076A; US3283102A; US3254176A

Description

Nov. 15, 1966 F. L. GELZHEISER 3,286,071

CIRCUIT INTERRUPTER WITH IMPROVED OPERATING MEANS Original Filed Aug. 25, 1960 4 Sheets-Sheet l Nov. 15, 1966 F. L. GELZHEISER 3,

CIRCUIT INTERRUPTER WITH IMPROVED OPERATING MEANS 4 Sheets-Sheet 2 Original Filed Aug. 25, 1960 Nov. 15, 1966 F. L. GELZHEISER 3,286,071

CIRCUIT INTERRUPTER WITH IMPROVED OPERATING MEANS Original Filed Aug. 25, 1960 4 Sheets-Sheet a Nov. 15, 1966 F. L. GELZHEISER CIRCUIT INTERRUPTER WITH IMPROVED OPERATING MEANS Original Filed Aug. 25, 1960 4 Sheets-Sheet 4 Fig. 7

Fig. 6

Fig. 5

Fig. I0 I83 IBI Fig. 9

Fig. 8

off

[Ev fl E5 off United States Patent 3,286,071 CIRCUIT INTERRUPTER WITH IMPROVED OPERATING MEANS Francis L. Gelzheiser, Fairfield, Conn., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application Aug. 25, 1960, Ser. No. 51,963, now Patent No. 3,240,902, dated Mar. 15, 1966. Divided and this application Apr. 12, 1965, Ser. No. 470,274

6 Claims. (Cl. 200-172) This application is a division of the copending application Serial No. 51,963, filed August 25, 1960.

This invention relates to electric circuit breakers and more particularly to manually and automatically operable circuit breakers for controlling small and moderate power electric circuits.

An object of this invention is to provide a circuit breaker embodying improved means for manually operating the movable contact arm to the open and the closed positions.

Another object is to provide an improved dependable duplex circuit breaker which is relatively inexpensive and easy to manufacture and assemble.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional objects and advantages thereof, will 'be best understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of one of the interrupting units of a circuit breaker embodying the principal features of the invention. The interrupting unit is shown in the closed position;

FIG. 2 is a view similar to FIG. 1 except that the parts are shown in the open positions;

FIG. 3 is a side elevational view of the other interrupting unit of the duplexcircuit breaker, the parts being shown in the tripped position;

FIG. 4 is an exploded perspective view, on an enlarged scale, of some of the mechanism of the interrupting unit shown in FIGS. 1 and 2;-

FIG. 5 is an end view, on a smaller scale, of the assembled duplex circuit breaker;

FIG. 6 is an elevational view, on an enlarged scale, of one of the operating members, showing the other side of the member from that shown in FIGS. 14;

FIG. 7 is a view taken along line VII-VII of FIG. 6;

FIG. 8 is an elevational view of part of the cover of a load center or panelboard having adjoining circuit breakers mounted thereon with adjacent handles connected by a handle tie;

FIG. 9 is a view similar to FIG. 8 showing the operating handle for one of the circuit interrupting units in the tripped position; the operating handle of an adjacent interrupting unit being shown in the open or off position; and

FIG. 10 is an elevational view of the handle-tie seen in FIGS. 8 and 9.

Certain features of the circuit breakers of this invention are described and claimed in the patents to Francis L. Gelzheiser, Patent No. 3,088,008 and Patent No. 3,110,786.

Referring to FIG. 5 of the drawings, a duplex circuit breaker indicated generally at 9 includes an insulating housing which is composed of two parts, 11 and 13, forming two compartment. Each of the

parts

11 and 13 is composed of a back portion molded integral with four sides forming an open front. The open front of the part 11 is covered by the back portion of the part 13, and the open front of the part 13 is covered by a cover 15.

3,286,071 Patented Nov. 15, 1966 ice The three

housing parts

11, 13 and 15 are held rigidly together by three rivets 17 (FIGS. 13).

The

housing parts

11 and 13 form two independent compartments housing two circuit interrupting units which, except for a line terminal structure that will be described later, are of substantially identical construction and operation, each, for most applications, operating independently of the other. FIGS. 1 and 2 illustrate the closed and open positions respectively of the circuit interrupting unit housed in compartment 13 (FIG. 5). The tripped position of the interrupting unit of the compartment 11 is shown in FIG. 3. The interrupting units illustrated in FIGS. 1-3 are different units in order to more clearly illustrate front mounting means which will be hereinafter described. Since the operation of the interrupting units and all of the parts except those that are specifically mentioned to be otherwise are alike, like parts are shown with like reference characters, and the description of the operation of the mechanism of only one of the interrupting units can be applied, unless otherwise mentioned, to both of the units of the duplex circuit breaker.

Referring to FIG. 1 of the drawings, the circuit interrupting unit shown therein comprises a stationary contact 21, a cooperating movable contact 23, a supporting metal frame indicated generally at 25, an operating mechanism indicated generally at 27 and a trip device indicated generally at 29.

The stationary contact 21 is welded, or otherwise attached, to a line terminal 31 which has a flange upper portion 32 (FIG. 4) that fits into a slot in the housing part 13. The line terminal 31 is held firmly in place by a stamped-out portion 33 that biases against a projection 34 that is molded integral with the housing part 13. A portion of the line terminal 31 protrudes through an opening 35 (FIG. 5) in the housing part 13. A similar portion of a symmetrically constructed line terminal 37 protrudes through an opening 39 in the housing part 11. Each of the

line terminals

31 and 37 is a part of a separate independently functioning circuit interrupting unit. These terminals are resiliently biased to engage opposite sides of a contact member in a load center when the duplex circuit breaker is mounted in operating position.

The stationary contact 21 cooperates with a movable contact 23 that is welded or otherwise attached to a small flange 40 of a generally C-shaped contact or switch arm 41. Means for operating the switch arm 41 to the open and closed positions comprises an operating member indicated generally at 43 having a V-shaped opening 45 therein, which opening receives a projection 47 of the metallic frame 25. The operating member 4-3 is biased outwardly or upward as seen in FIGS. 1-3, by means to be hereinafter described, to a position wherein the lower edges of the projection 47 pivotally engage the lower side walls of the V-shaped opening 45. As can be best seen in FIG. 4, the switch arm 41 is bent over at its upper end at 48 and an opening 49 is stamped in the part 48. Depress-ions 51 are formed in the part 48 on opposite sides of the slot 49. When the parts are in operating position, a projection 53 (FIGS. 4, 6 and 7), molded integral with the operating member 43, extends into the slot 49 of the switch arm 41 to position the operating member 43 relative to the switch arm 41, and pivoting portions 55 on opposite sides of the projection 53 of the operating member 43 pivotally engage in the depressions 51 in the switch arm 41. The operating member 43 has a handle portion 57 molded integral therewith which extends through an opening 61 (FIGS. 1 3) in the housing whereby the mechanism may be manually operated to open and close the breaker. Arcuate surfaces 63 on op posite sides of the handle 57 substantially close the opening 61 in all positions of the operating member 43. Mo-

tion is transmitted from the operating member 43 to the switch arm 41 when the breaker is manually operated, and, from the switch arm 41 to the operating member 43 when the breaker is automatically tripped open.

The frame 25 supports an insulating pivot 65 (FIG. 4) having shoulders 67 at opposite ends thereof, which shoulders rest within a slot 69 in the frame 25 and a slot 71 in a projection 73 of the frame 25. A trip member 79 is pivotally supported at one end 77 by means of a bight portion 75 which is pivotally supported in a slot 81 in the insulating pivot 65. The other end 82 of the trip member 79 has a latch point 83 which rests on a ledge 85 on an armature 86 to support the trip member in latched position. The armature 86 is part of the trip device 29 which will be described later.

As best illustrated in FIG. 4, the ends 77 and 82 of the trip member 79 are offset, and disposed in a plane which is parallel to a plane in which the main body portion of the trip member 79 is disposed. A spring 88 (FIGS. 1-3) is connected, under tension, at one end in a slot 89 in the contact arm 41, and at the other end in a slot 91 (FIG. 4) in a projection 93 extending from the trip member 79.

The movable switch arm 41 is connected by means of a flexible shunt 95 (FIG. 1) to the free end of a bimetal 97 which is attached, near its other or upper end, to a projection 101 extending out from the supporting frame 25. A terminal conductor 103 is welded or otherwise attached to the upper end of the bimetal 97 to electrically connect the bimetal to a load terminal structure that is indicated generally at 104. The closed circuit through the breaker extends from the line terminal 31 through the stationary and

movable contacts

21, 23, the switch arm 41, the flexible shunt conductor 95, the bimetal element 97, the load terminal conduct-or 103 to the load terminal structure 104. Since the movable switch arm 41 extends downwardly from its pivot, the arc is established adjacent the bottom of the housing in an arc chamber 111, one end of which is connected by a vent passage 113 to an opening in the end of the housing beneath the load terminal structure 104.

The circuit interrupting unit may be manually operated to open and close the contacts by operation of the insulating handle 57. Movement of the handle 57 clockwise, from the :position shown in FIG. 1 to the position shown in FIG. 2, carries the upper end of the switch arm 41 to the left of the line of action of the spring 88 whereupon the spring acts to move the contact arm 41 with a snap action to the open position shown in FIG. 2. A projection 109 molded integral with the housing acts as a limit stop for the movable contact arm during an opening operation. Movement of the operating handle 57 in a counterclockwise direction, from the position in which it is shown in FIG. 2, to the position in which it is shown in FIG. 1 moves the upper end of the switch arm to the right to move the parts to the closed position shown in FIG. 1. Movement of the handle 57 in either direction is limited by the surfaces 115 which strike the housing at either extreme position. The modified knife edge bearings of the projection 47 of the frame 25 within the opening 45 of the operating member 43, and of the pivoting portions 55 of the operating member 43 with the depressions 51 of the switch arm 41, encounter little friction and they, therefore, provide for a smooth operating type of mechanism.

The trip device 29 includes the bimetal 97, a U-shaped magnet 117, the armature 86 which is pivotally supported on the bimetal 97, and a spring 119 which biases the armature in a counterclockwise direction about its pivot. Upon the occurrence of an overload current below a predetermined value, I the bimetal element 97 becomes heated, and when it is heated a predetermined amount it deflects to the right as seen in FIG. 1. Due to the engagement of a tail portion 121 of the armature 86 with the bimetal 97, the armature is carried to the right with the bimetal to release the trip member 79.

When the trip member 79 is released, the spring 88 acts to rotate it clockwise about its pivot 65 until it is arrested when a stop portion133 thereon strikes the projection 109 of the housing. During this movement, the line of action of the spring 88 moves to the right of the

pivot

55, 51, of the switch arm 41, whereupon the spring biases the switch arm in opening direction and moves the switch arm so that the line of action of the force exerted by it on the operating member 43 shifts across the

pivot

45, 47 and actuates the operating member 43 to the tripped position shown in FIG. 3. In order to provide a visual indication that the breaker has been automatically tripped open, movement of the operating member 43 is stopped in an intermediate position (FIG. 3) when a projection 135, molded integral with the operating member 43, strikes the projection 93 which extends from the trip member 7 9.

Positive separation of the contacts is assured during a tripping operation by the provision of a projection 137 extending from the trip member 79. If the contacts are slow in opening due to sticking, drag or other reasons, the projection 137 engages the inner edge of the switch arm 41, with a swiping action, to start the switch arm in opening direction.

The interrupting unit is trip-free in that it will automatically trip open even though the handle 57 is held in the closed position.

Before the contacts can be closed following an automatic opening operation, it is necessary to reset and relatch the mechanism. This is accomplished by moving the operating handle 57 clockwise from the tripped position (FIG. 3), slightly beyond the full open position (FIG. 2). During this movement, the projection of the operating member 43 engages with the projection 93 of the trip member 79, and the trip member is moved counterclockwise until the latch point 83 thereon is again supported in the latched position on the ledge 85 (FIG. 4) of the armature 86, which position is shown in FIG. 2.

The circuit interrupting unit is tripped automatically and instantaneously by the

electromagnet

97, 117, 86 in response to overload currents above the predetermined value. Upon the flow of current through the bimetal 97, a magnetic flux, which is induced around the bimetal, takes the path of least reluctance through the magnet 117, across an air gap 139, and through the armature 86. When an overload current above the predetermined value occurs, the pull of the magnetic fiux is of such strength that the armature 86 is attracted to the magnet 17 and pivots in a clockwise direction about the bimetal 97. This movement releases the trip member 79, and the contacts are opened in the same manner previously described in connection with the thermal tripping operation. The features of the trip device 29 are specifically described and claimed in the aforementioned patents of Francis L. Gelzheiser, Patent Nos. 3,088,008 and 3,110; 786. For this reason, only a brief description of the trip device is given herein.

As best seen in FIG. 4-, the conducting strip 103 is shaped in such a manner that it will readily deform when a stress is applied at either end. The conducting strip 103 is provided with a number of slots opening on opposite lateral edges of the strip. When the circuit breaker is connected for operation, a load line is inserted into the load terminal structure 104 (FIGS. 1-3) whereupon a screw 161 is turned so that a tapped plate 162 will ride up the screw and apply pressure to the conducting member and to the load conductor in a manner well known in the art.

It is desirable to prevent any unusual stress, which may be applied to the outer end of the conducting strip 103 during a connecting operation, from being transmitted to the bimetal 97 at the inner end of the conducting strip, so that there will be no interference with the calibration of the trip device 29. For this reason, the slots 160 are provided presenting a tortuous path for the body of the conducting strip 103 to permit the strip to readily deform if for some reason an unusual force is applied to the load or outer end thereof.

When the line terminals 31, 37 (FIG. 5) are clipped onto a bus bar they serve not only to electrically connect the breaker to the bus bar, but to also physically support the line-terminal end of the breaker on the panelboard. The other or load-terminal end of the breaker is supported by means of a clip (not shown) that is mounted on the panelboard and that clips over a ledge 163 (FIGS. 1-3). For some applications, it is desirable to mount the breaker, near its front or outer side, to a panel, in which case the ledge 163 and the clip-on

type line terminals

31, 37 cannot be used for support.

Means are provided for simultaneously operating two circuit interrupting units. In normal operation, the duplex circuit breaker 9 (FIG. 5) is plugged onto a bus bar which is at a potential of 120 volts above ground. For servicing certain heavy appliances or loads, 240 volts are supplied by connecting the load to two leads connected in series each of which leads is brought from one interrupting unit of a separate circuit breaker 9, each of which circuit breakers is plugged onto a bus bar which is at 120 volts above ground so that the two bus bars and the two circuit breakers are at 240 volt potential to each other. In this manner, 240 volt service can be provided when desired. When such service is provided, both of the interrupting units must be simultaneously manually operated to their open and closed positions. For this purpose, a handle tie 181 (FIG. is provided. As can be seen in FIG. 8, two adjacent interrupting units of two adjacent circuit breakers 9 are connected by means of the handle tie 181. Each of the two openings 183 (FIG. 10) in the handle tie 181, receives one operating handle 57, and is so shaped as to permit some play and pivotal movement of the handle tie relative to the handles. Thus, a lost motion connection is provided between the two handles 57 of the two adjacent circuit interrupting units.

In the past, circuit interrupting units have been provided with a handle tie in order to effect simultaneous manual operation of the units. Moreover, lost motion connections are used that permit the handle of only one of the connected interrupting units to go to the tripped or intermediate position without interference from the handle of the other interrupting unit. My invention, however, provides two circuit interrupting units which are connected in such a manner that movement of one of the handles to the tripped or intermediate position upon the automatic opening of its interrupting unit, will effect movement of the other handle to its open position to thereby open the other interrupting unit which is associated with the said other handle.

As is well known in the art and a was hcreinbefore described, when one of the two circuit interrupting units of the circuit breaker 9 is automatically tripped, the handle 57 is carried to the tripped or intermediate position shown in FIG. 3 by the tension in the spring 88 and the movement of the moving switch arm 41. When one of the connected interrupting units shown in FIG. 8 is tripped, the handle 57 of the tripped interrupting unit is moved to its intermediate position. During the start of this movement, a certain amount of free play in the handle tie is first taken up. Once this free play is taken up, the inertia of the moving handle of the tripped unit, plus the tension in the operating spring 88 act, through the handle tie 181, on the handle 57 of the adjacent connected interrupting unit tending to pull that handle to its open or off position. This movement begins under somewhat of a shock condition since it begins abruptly as soon as the free play in the handle tie 181 is taken up. This initial shock plus the remainder of the force which is applied through the handle tie when the handle of the tripped unit moves to its intermediate position, is enough to throw the handle 57 of the adjacent interrupting unit far enough towards its open or off position to a point where the spring 88, of the adjacent interrupting unit, will operate to move the mechanism of that unit to its open position.

This dual operation is possible because the handle 57 need only be thrown a relatively short distance before the spring 88 takes over, collapsing to move its associated mechanism to the open position; and because, when the parts are in the closed position, the spring is stretched as much as it is ever stretched during the operation of the interrupting unit, so that the moving forces need not effect a stretching of the spring when they operate to throw the handle 57 this relatively short distance. This dual operation is possible also because the modified knifeedge-type pivots which are provided between the moving parts, provide that very little physical resistance is encountered during operation of the interrupting units.

One of the interrupting units is shown in the closed position in FIG. 1. As the handle 57 is moved in a clockwise direction, it moves the upper end of the switch arm 41 to the left moving the lower end to the right. Only a relatively slight movement of the operating handle 57 will move the parts to a position where the

pivot

55, 51 is to the left of a line drawn between the lower spring support 89 and the pivot 47. Once the parts have reached this position, the spring 88 will take over retracting to move the parts to the open position shown in FIG. 2.

Since, when the parts of either of the interrupting units are in the closed position, the spring 88 is stretched as much as it will ever be stretched during the operation of the interrupting unit, there is no overcenter peak which the spring must approach and pass during an opening operation. During movement of the parts from the on or closed position (FIG. 1) to the off or open position (FIG. 2), the spring 88 is never stretched, so that the opening forces need not overcome any increase in resistance of spring tension in moving the parts to the open position.

The parts are shown in FIG. 8 with both of the connected interrupting units in the on or closed positions. The parts are shown in FIG. 9 after one of the interrupting units has automatically tripped moving its handle 57 to the intermediate or tripped position, which movement brings the previously mentioned forces into play to effect, through the handle tie 181, movement of the handle 57 of the other connected interrupting unit to the point where the operating spring of the said other unit operates to ef-.

fect movement of the parts of the other unit to the off or open position shown in FIGS. 9 and 2.

Since numerous changes may be made in the abovedescribed construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A circuit interrupter comprising a stationary contact, a movable contact arm, a movable contact on said movable contact arm, said movable contact arm being movable to move said movable contact into and out of engagement with said stationary contact, an operating member operable to move said movable contact arm, said movable contact arm having a fiat portion with a slot therein, a part of said operating member extending into said slot, and pivot parts of said operating member pivotally engaging said flat portion of said movable contact arm on opposite sides of said slot 2. A circuit interrupter comprising a stationary contact, a movable contact arm, a movable contact supported on the rearward end of the movable contact arm and movable 'with the contact arm to open and close a circuit, an operating member manually operable from the front of the interrupter, means biasing the movable contact arm toward the front of the interrupter forcing the movable contact arm into pivotal engagement with the operating member, said operating member having an opening therein, a stationary supporting projection extending into said opening, and said biasing means forcing said operating member toward the front of the interrupter whereby said operating member pivotally engages said stationary supporting projection at the rearward end of said opening.

3. A circuit interrupter having a front and a rear and comprising a stationary contact, a contact arm, a movable contact disposed at the rearward end of said contact arm and movable with said contact arm to open and close the interrupter, an operating member manually operable from the front of the interrupter and having an opening therein, a stationary supporting member extending into said opening, said contact arm having a flat portion with a slot therein, a part of said operating member extending into said slot, pivot parts of said operating member pivotally engaging said flat portion of said contact arm on opposite sides of said slot, means biasing said contact arm toward the front of said interrupter forcing said contact arm into pivotal engagement with said operating member and forcing said operating member to pivotally engage said stationary supporting member at the rearward end of said opening.

4. A circuit interrupter comprising an insulating housing having an opening at the front thereof, a circuit interrupter structure disposed within said housing, said circuit interrupter structure comprising a stationary contact, a movable contact arm, a movable contact on said movable contact arm, an operating member comprising a handle part extending through said opening for manual operation, pivot support means supporting said operating member for pivotal movement about a fixed pivot, an operating "spring biasing said movable contact arm toward the front of said housing and into engagement with said operating member, said movable contact arm comprising a front part having a contact-arm opening therein and spaced pivot supports on opposite sides of said contactarm opening, said operating member comprising a pair of spaced pivot parts and a projection between said spaced pivot parts, said projection positioned in said contact-arm opening and said spaced pivot parts engaging said spaced pivot supports, said operating member movable about said fixed pivot between operating positions during which movement said spaced pivot parts engage said pivot supports to move said contact arm to thereby move said movable contact between opened and closed positions relative to said stationary contact.

5. A circuit interrupter comprising an insulating housing having an opening at the front thereof, a circuit interrupter structure disposed within said housing, said circuit interrupter structure comprising a stationary contact, a movable contact arm, a movable contact on said movable contact arm, a mechanism for operating said movable contact arm to open and close said contacts, an operating member comprising a handle part extending through said opening for manual operation, said operating member having an opening therein, a stationary support pin extending into said opening, an operating spring biasing said movable contact arm toward the front of said housing into pivotal engagement with said operating member to bais said operating member toward the front of said housing such that said operating member engages said stationary support pin at the rearward part of said opening whereby said operating member is pivotally supported to pivot about said stationary support pin, and said operating member pivotally movable to move said movable contact arm to open and close said contacts.

6. A circuit interrupter comprising an insulating housing having a housing opening at the front thereof, a circuit interrupter structure disposed within said housing, said circuit interrupter structure comprising a stationary contact, a movable contact arm, a movable contact on said movable contact arm, said movable contact arm comprising a generally flat main body part moving endwise during operation of said movable contact arm and a bent-over front part bent over to provide a fiat surf-ace that extends generally normal to the plane of said generally flat main body part, a unitary molded insulating operating member comprising an integral handle part extending through said housing opening for manual operation, said operating member having an operating member opening therein, a stationary support pin extending into said operating member opening, a trip member pivotally supported at one end thereof and latched in a latched position at the other end thereof, trip means latching said other end of said trip member, a tension-type operating spring supported at one end thereof on said trip member and at the other end thereof on said movable contact arm to bias said movable contact arm toward the front of said housing into engagement with said operating member to thereby bias said opcrating member toward the front of said housing such that said operating member engages said stationary support pin at the rearward part of said opening whereby said operating member is pivotally supported to pivot about said stationary support pin, said movable contact arm at the front part thereof having a contact-arm opening therein and spaced pivot support depressions on opposite sides of said contact-arm opening, said molded insulating operating member comprising a pair of spaced pivot parts and a projection between said spaced pivot parts, said projection being positioned in said contact-arm opening and said spaced pivot parts engaging said spaced pivot support depressions, and upon pivotal movement of said operating member about said stationary support pin, said spaced pivot parts operating against said spaced pivot support depressions to move said movable contact arm to open and close said contacts.

References Cited by the Examiner UNITED STATES PATENTS 2,150,013 3/1939 Von Hoorn 200172 X ROBERT K. SCI-IAEFER, Primary Examiner.

KATHLEEN H. CLAFFY, Examiner.

H. O, JONES, Assistant Examiner.

Claims

1. A CIRCUIT INTERRUPTER COMPRISING A STATIONARY CONTACT, A MOVABLE CONTACT ARM, A MOVABLE CONTACT ON SAID MOVABLE CONTACT ARM, SAID MOVABLE CONTACT ARM BEING MOVABLE TO MOVE SAID MOVABLE CONTACT INTO AND OUT OF ENGAGEMENT WITH SAID STATIONARY CONTACT, AN OPERATING MEMBER OPERABLE TO MOVE SAID MOVABLE CONTACT ARM, SAID MOVABLE CONTACT ARM HAVING A FLAT PORTION WITH A SLOT THEREIN, A PART OF SAID OPERATING MEMBER EXTENDING INTO SAID SLOT, AND PIVOT PARTS OF SAID OPERATING MEMBER PIVOTALLY ENGAGING SAID FLAT PORTION OF SAID MOVABLE CONTACT ARM ON OPPOSITE SIDES OF SAID SLOT.