US2376793A - Switch construction - Google Patents

Description

May 22, 1945. |NK 2,376,793

SWITCH CONSTRUCTION Filed May 26, 1943 5 Sheets-Sheet 1 5 E INVENTOR.

May 22, 1945. A I K 2,37 ,793

SWITCH CONSTRUCTION Filed May 26, 1943 5 Sheets-Sheet 2 2'2 fig 4 f5 May 22, 1945; E A, UNK 2,376,793

SWITCH CONSTRUCTION Filed May 26, 1943 5 Sheets-Sheet 3 Qfflii r I w INVENTOR. [am/v A. [//1//( ATTORNEY May 22, 1945.

E. A. LINK SWITGH CONSTRUCTION Filed May 26, 1943 5 Sheets-Sheet 4 w M1 11 mm 1 a w a a a W O K III \A\\ v Hm 1Q R. m w W. Z l

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May 22, 1945. 'E. A. LINK 2,376,793

swmcn coNs'rRuc TI0N Filed May 26, 1943 5 Sheets-Sheet 5 INVENTOR. [pM/vAJ/M Patented May 22, 1945 UNITED STATES PATENT orslca SWITCH CONSTRUCTION Edwin A. Link, South Milwaukee, Wis., assignor to Line Material Company, South Milwaukee, Win, a corporation of Delaware Application May 26, 1943, Serial No. 488,487

, 17 Claims.

This invention relates to a, switch construction.

In greater detail, this invention relates primarily to a switch construction of the circuit breaker type.

Objects of this invention are to provide a circuit breaker which has'a quick make and a quick break, which has condition responsive means of the trip type, which is so constructed that it releases the circuit breaker so that the circuit breaker will open under predetermined conditlons, and which is provided with a, handle or other operating means for normally opening and closing the circuit breaker and for resetting the trip means, the trip means and the operating means being so related that the trip means will operate to release the circuit breaker irrespective oi the position of the operating means and irrespective 01' any motion that the operating means may be executing at the time the trip means operates so that the trip means is trip free and will operate no matter whether the operating means is forcibly held in closed position or is being moved from one position to another.

Further objects are to provide a circuit breaker which is so constructed that the circuit breaker cannot be closed until the trip means has moved back to normal Position, and in which the resetting oi the trip means is accomplished by moving the operating means towards open position, such motion being followed by movement to closed position after the resetting of the trip means when it is desired-to again close the circuit breaker after the occurrence of the predetermined condition.

Further objects are to provide a construction in which the trip means may be either thermostatically or magnetically or otherwise operated and which has either a quick action or a delayed action and which is adjustable so that the condition to which it will respond may be predeter mined.

Further objects are to provide a circuit breaker which has a heavy contact pressure when it is closed, in which this heavy contact pressure is maintained during the operation of the circuit breaker until the instant at which the contacts are suddenly separated, thereby avoiding burning of the contacts under overload conditions.

Further objects are to provide a circuit breaker in which the mechanism is so arranged that it is easy to operate in opening and closing the circuit breaker and in resetting the trip means, and which is so made that there is no great wear on the parts during the opening and closing of the circuit breaker or during the resetting of the trip means as the mechanism is so arranged that during resetting, for example, relatively small forces or pressures are exerted between the coo erating parts, thereby minimizing wear.

Further objects are to provide a circuit breaker which has a double switch construction, the switch means being operated'by toggle link mechanism which in turn is operated by means 01' a switch operating member or lever, and to provide an automatic mechanism responsive to overload conditions'ior tripping a trip lever, the trip lever in turn acquiring momentum and striking the switch operating means to open the switch means with a quick motion, thereby maintaining heavy contact pressure up to the instant that the switch means is suddenly opened, thus avoiding burning of the contacts.

Further objects are to provide a circuit breaker in which main operating means are employed and are effective to open or close the switch means with a quick stroke, the circuit breaker being so made that although heavy contact pressure is obtained, very little eil'ort is required to operate the circuit breaker and to so relate the trip lever and the main operating means that when the main operating means is moved towards and beyond switch open position, it will reset the trip lever, the main operating means also being arranged to move to an indicating position when the trip lever has acted to open the circuit breaker, thus indicating that automatic action has occurred. I

Further objects are to provide a circuit breaker in which the trip means is required to exert only a very small force in order to cause automatic operation, the construction being such that the spring means acting on the trip lever has a reduced effective lever arm when the trip lever is in latched position.

Further objects are to provide a circuit breaker construction which is sturdy and is reliable in operation, which may be installed in a transformer case and submerged in the oil in the transformer case if desired, andwhich ii a thermo-v static trip means is employed, may be arranged to have the thermostatic means respond solely to the heat generated by current passing through the thermostatic means or to the combined action of the heat in the oil from the transformer or other device as well as from the heat due to the current passing through the thermostatic means, or may be arranged to respond solely to the heat of the oil.

Embodiments oi the invention are shown in the accompanying drawings, in which:

Figure 1 is an end view of the circuit breaker with part of the links sectioned oil.

Figure 2 is a sectional view approximately on Figure 'I is a side view of the circuit breaker showing it in closed position.

Figure 8 is a plan view of the circuit breaker showing it in closed position. I

Figure 9 is a view partly in section and partly broken away showing the circuit breaker mounted within a transformer casing.

Figure 10 is a sectional view-on the line iii-l of Figure 9.

Figure 11 is a view showing a further form of mounting for the circuit breaker.

Figure 12 is a wiring diagram. Figure 13 is a view showing a of condition responsive means.

Referring to the drawings, it will be seen that the circuit breaker comprises an insulating base portion I which is provided with an insulating block like member 2 either integral with or secured to the base member in any suitable manner not shown. The block like insulating member 2 is provided with. a longitudinally extending guide slot 3 for a purpose hereinafter to appear.

The switch means consists of a pair oi stationary contacts E which may be carried by relatively stifl conducting spring like members connected to terminals t. Movable contacts 8 are arranged to engage the stationary contacts d. The movable contacts 8 are carried by insulating switch members I which are pivoted on the pins I and which are connected on their inner sides to a pair of toggle links 9. The movable confurther form tacts 8 are connected by means of flexible coriductors iii to a pair of thermostatic bi-metallic members ii. Each conductor i0 is connected to one of the legs of the U-shaped, inverted, bimetallic, thermostatic members Ii and the other leg is connected to a terminal i2. The bi-metallic members H each carry insulating pads i3 at their upper ends through which adjusting screws H are threaded.

A body portion I5 is provided and consists of two metal walls joined by transverse portions it which are secured to the insulating block 2.

A switch operating member in the form of a lever I1 is positioned between the walls of the body portion 15 and is pivotaliy carried by the pivot pin i8. It is provided with a rounded lower ringer it which loosely passes through an eyelet which constitutes the central pivot joining the toggle links 3. The finger l9 also rides within the guide slot 3 of the block .2, see Figure 6. It is to be noted from Figure 6 that the lever i1 is provided with a pair of outwardly projecting lugs 2i and also it will be noted that the upper end of the lever is bifurcated to provide a pair of spaced arms. Between the spaced arms of the lever I! a trip lever 22 is mounted and is pivoted on the pin l3. This trip lever is provided with a lug 23 which is connected to one end of a relatively heavy spring 24, the other end of the spring being anchored on the pin carried by the body portion It, as shown in Figures 2, 3 and 4.

The trip lever 22 is provided with projecting.

lugs 23 which are adapted to strike the lever I! when the trip lever 22 is released. Normally the trip lever is held against motion by means of a latch 21 pivoted on the pivot pin 23 and urged in a counterclockwise direction by means of the spring 23. The latch is provided with a pair oi outwardly projecting arms 30 which are adapted to be engaged by the ends of the adjustins screws ll so that the latch'will be released when either or both of the bimetallic members I l warp inwardly on overload. a

It is to be noted that the latch 21 is provided with a cam face 3| and that the trip lever 22 is also provided with a cam face 32 so that when the lever is forced back to latching position, these cam faces will ride one upon the other until the latch snaps into latched position.

Main operating means in the form of a pair or levers 33 are pivotally mounted on the pivot pins 34 carried by the block 2. These levers 33, which constitute the main operating means, are joined by means of a transverse pin 33 which is provided with a roller 33 for a purpose hereinafter to appear. Spring means indicated at M extend between the pin 33 of the main operating means 33 and the lugs H of the switch operating means or lever l1 and thus operatively connect the main operating means and the switch operating means ill.

The spring means 31 constitute an over center spring means in the manual operation or the circuit breaker for it is apparent t at when it is desired to close the circuit breaker, the main operating means 33 is rocked from the position shown in Figure 3 to the position shown in Figure 2 and when the line oi puii oi the spring means 31 passes to the left or the pivot pin it, as viewed in Figure 3, the lever ill will suddenly rock to the left, thus straightening out the toggle links 9 and simultaneously forcing both of the switch means outwardly from the position shown in Figure 5 to the position shown in Figure 8, thus closing the switch with a snap action. It is to be noted upon reierenw to Figures 5 and 8 that posts 38 extend upwardly from the base i and support the switch member i. These posts may be termed integrally with the base if so desired. The flexible conductors it, it will be noted from Figure 5, are positioned on the outer side of these posts.

Opening motion of the switch is obtained by rocking the main operating means 33 from the position shown in Figure 2 to the position shown in Figure 3. The line of pull 0! the spring means 31 will now pass to the right of the pivot pin i8 and consequently the switch operating lever I! will be quickly rocked to theright to the position shown in Figure 3, thus opening the switch means with a quick stroke.

It is to be noted from an examination of Figures 2 and 3 that upstanding portions of the block 2 constitute stops for limiting the motion of the toggle link mechanism at the two extreme ends of its stroke.

The toggle links 3 may be formed or metal. the members I being of insulating material. The body portion IS, the switch operating lever II, the trip lever 22, and the main operating levers 33 and the catch 21 are all formed of metal as none of these parts is alive.

The automatic action of the circuit breaker is as follows: When an overload occurs in either one or both of the circuits, one or both of the thermal members ii bows in a counterclockwise direction and its adjusting screw l4 bearing against the portion 34 of the latch trips the latch and releases the trip lever 22. This trip lever makes a very quick stroke from the position shown in Figure 2 to the position shown in Figure 4 and the pins 28 strike a hammer blow against the switch operating lever l1 and drive the lever I! to the position shown in Figure 4 with a quick motion, thus suddenly 'opening the circuit breaker. T

It is to be noted that the spring 24 has to be sufliciently powerful to impart enough momentum to the trip lever 22 to overcome the'action of the spring means 31.

From a comparison of Figures 2 and 4 it will' be seen that upon automatic operation when the trip lever 22 drives the switch operating lever l1 to the position shown in Figure 4, the center line of the spring means 31 is moved to the right of the pivotal axis 34 of the main operating means 33 and consequently such main operating means is moved to the right to the position shown in Figure 4 and is arrested in this position by engagement of the roller 36 with the trip lever 22. This is an indicating position for the main operating means and indicates that the circuit breaker has been opened due to automatic action.

When it is desired to reset the circuit breaker, the main operating means 33 is rocked in a clock wise direction from the position shown in Figure 4 and the roller 36 rides along the cam surface of the trip lever 22 and forces the trip lever downwardly until it is relatched 'bv the latch means 21. Obviously even if the thermostatic means had not cooled sufilciently, no jamming of any of the parts could occur. On the other hand, if the thermostatic means has cooled sufficiently, the latch 21 will latch the lever 22 in its reset position.

It is to'be noted from a comparison of Figures 2 and 4 that when the trip lever 22 is latched, the effective lever arm through which the spring 24 acts is materially less than the effective lever arm of the spring means 24 at the instant that th legs 26 of the trip lever strike the switch operating lever l1. Consequently by reducing the effective lever arm through which the spring 24 acts while the trip lever is latched, a relatively small pressure is exerted between the end of the trip lever and the latch 21, thus minimizing friction for the latch means. nism, therefore, is required to exert only a very small force in order to cause automatic operation.

It is to be noted upon an examination of F gure 4 that if an attempt is made to close the switch without resetting the tripping mechanism. the switch will not close though the main operating means 33 may be moved to switch closed position. The reason for this is that although the line of pull of the spring means 31 does cross the pivot l8 of the switch operating lever l1, nevertheless the force exerted by such spring means 31 is not suflicient to overcome the force exerted by the spring means 24, the spring means 24 act-- ing through the trip lever 22 and the projections 28 and holding the switch operating lever l1 against motion. I

It is to be noted that in both manual and automatic operation the samelever or switch operating member I1 is employed to actuate the toggle links and consequently to actuate the switch means.

It is to be noted also that the thrust from the toggle links 8 is symmetrically applied and balanced. Ii desired the toggle links when the switch is closed may be opened with their axes directly in line with each other as shown in Figure 8 or may slightly pass dead center. In either case the toggle links actually look the switch closed. It will be seen that although a relatively small force is required to actuate the toggle link mechanism, nevertheless high contact pressure for the switch means is obtained.

Any suitable means may be provided for rocking the main operating means 33. For example, the circuit breaker may be mounted directly on a transformer 39 and within the transformer housing 40 and the main operating means 33 may be connected by means of links' It with rock arms 42 carried by a rock shaft 43. This rock shaft 43 may extend outwardly at one end r through the casing of the transformer and may be provided with an operating handle 44. A stop tion.

The tripping mecha- If the circuit breaker is mounted within the transformer casing as shown in Figure 9, it may be mounted below the oil level indicated at 48 so that the switch is operated in oil and so that the thermostatic elements may be heated not only by the current passing therethrough but by the general temperature of the oil. The purpose oi this is to 'allow the thermostatic elements to respond not only to a. relatively sudden overload but to allow such elements to respond to the gradual rise of temperature of the oil which would result from a small and prolonged overload due to the heating of the transformer itself. Thus there may be afforded the double protection of opening the circuit breaker under the influence of an overload of reasonable magnitude or the opening of the circuit breaker from a prolonged small overload due to the heating of the transformer. It is obvious also that if desired the main current need not pass through the thermal members and the thermal members could then respond merely to the heat of the oil or the oil level could be so regulated that it is below the thermal members and then the thermal members would respond merely to the heat of the current passing therethrough.

The circuit breaker is also adapted for wall mounting. For instance as shown in Figure 11, it may be mounted in a housing 41 provided with a slotted. curved, outer wall 48 through which an insulatin operating handle 33' projects, such handle being directly attached to the main op-- erating means 33. The wiring diagram is shown in Figure 12 and it will be seen that the secondary 49 of the transformer 39 is connected to the stationary contacts 4 and through the movable contacts 6 to the thermal members I l.

Any desired form of condition responsive means may be employed for tripping the circuit breaker. For instance as shown in Figure 13 a solenoid type of condition responsive means maybe employed and may consist of a solenoid 50 adapted exactly the same manner to trip the latch as the adjusting screw ll hereinbeiore described. Obviously a pair of these condition responsive means are employed.

If desired any suitable time delay means may be employed such as the cylinder 54 within which the piston 55 operates, such piston being attached to the plunger SI, and a suitable spring 56 being employed to return the piston to its lowest position. The cylinder 5. is provided with suitable apertures above and below the plunger to allow fluid to escape. Obviously the size of the openings relative to the size of the cylinder will determine the time delay desired.

By adjusting the screws 53 or I4 the value of the condition for which the circuit breaker will open may be determined.

The purpose of having time delay is to prevent the circuit breaker from opening for any sudden or extremely transitory overload for instance, and to allow the circuit breaker to open as promptly as desired for an overload tor a longer period than that tor which the time delay has been designed. it is to be understood that the circuit breaker could be made to respond to over or under voltage, overload, phase reversal, or any other desired condition.

' By employing the double switch construction of opposed switch members and the toggle link connection therewith it is apparent that balanced thrusts are produced, the guiding slot 3 coasting with the pin iii and merely acting as an additional precaution against an unsymmetrical operation oi the toggle links if such unsymmetrical action should occur from any cause whatsoever.

it is to be noted that the switch operating means and the associated mechanism, such as the main operating means, all swing in planes at right angles to the plane in which the toggle link mechanism operates. This makes the circuit breaker very compact.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

l. A circuit breaker comprising a pair of opposed switch means, toggle link mechanism having its outer ends connected to said switch means, switch operating means joined to the center portion of said toggle link mechanism for extending and collapsing said toggle link mechanism to simultaneously operate said switch means, said switch operating means being arranged to movev in a plane at right angles to the plane in which said toggle link mechanism operates, movable main operating means operatively coupled to said switch operating means, tripping means biased for tripping motion and adapted to move said switch operating means to switch open position, and condition responsive means normally restraining said tripping means against motion and releasing said tripping means'upon the occurrence of a predetermined condition.

2. A switch construction comprising a pair of opposed switch means, toggle link mechanism having its outer ends connected to said switch means, pivoted switch operating means directly joined to the center portion of said toggle link mechanism for extending and collapsing said toggle link mechanism to simultaneously operate said switch means, said switch operating means being arranged to swing in a plane at right angles to the plane in which said toggle link mechanism operates, movable main operating means operatively coupled to said switch operating means, tripping means biased tor tripping motion and adapted to move said switch operating means to switch open position, and releasable means normally restraining said tripping means.

3. A switch construction comprising switch means, switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively connecting said main operating means and said switch means for imparting a quick motion to said switch operating means when said main operating means is moved, tripping means adapted to strike a blow against said switch operating means to open said switch means with a quick motion, biasmg means biasing said tripping means towards motion, and releasable means normally restraining said tripping means.

4. A switch construction comprising switch means, switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively connecting said main operating means and said switch means for imparting a quick motion to said switch operating means when said main operating means is moved, tripping means adapted to strike a blow against said switch operating means to shift said switch operating means to open said switch means with a quick motion, one end of said over center spring means being moved by the shifting of said switch operating means to aposition to move said main operating means to an indicating position to show that automatic op eration has occurred, biasing means biasing said tripping means towards motion, and releasable means normally restraining said tripping means.

5. A switch construction comprising switch means, switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively connecting said main operating means and saidswitch means for imparting a quick motion to said switch operating. means when said main operating means is moved, tripping means adapted to strike a blow against said switch operating means to open said switch means with a quick motion, biasing means biasing said tripping means towards motion, and releasable means normally restraining said tripping means, said main operating means and said tripping means having portions adapted to coact to reset said tripping means when said main operating means is moved to a predetermined position.

6. A switch construction comprising a pair of opposed switch means, toggle link mechanism having its outer ends connected to said switch means, pivoted switch operating means directly joined to the center portion 0f said toggle link mechanism for extending and collapsing said toggle link mechanism to simultaneously operate said switch means, movable main operating means operatively coupled to said switch operating means, tripping meansbiased for tripping motion and adapted to move said switch operating means to switch open position, and releasable means normally restraining said tripping means.

7. A circuit breaker comprising a pair of opposed switch means movable inwardly and outwardly to switch open and switch closed positions respectively, mechanism for simultaneous- 1y moving said switch means and transmitting balanced thrusts to said switch means, main op erating means operatively connected to said in! a quick opening and quick closing oi said switchmeans, a biased hammer like tripping means for imparting a blow to said mechanism to cause quick opening or said switch means. and

condition responsive means normally restraining said tripping means and releasing said trip- Ding means upon the occurrence oi a predetermined condition.

8. A vcircuit breaker comprising a pair oi opposed switch means movable inwardly and outwardly to switch open and switch closed positions respectively, mechanism for simultaneously moving said switch means and transmitting balanced thrusts to said switch means. main operating means operatively connected to said mechanism by over center spring means for causing a quick opening and quick closing of said switch means, a biased hammer like tripping means for imparting a blow to said mechanism to cause quick opening or said switch means independently of said main operating means, and condition responsive means normally restraining said tripping means and releasing said tripping means upon the occurrence of a predetermined condition.

9. A circuit breaker comprising a pair of opposed switch means movable inwardly andoutwardly to switch open and switch closed positions respectively, mechanism for simultaneously moving said switch means and transmitting balanced thrusts to said switch means, main operating means operatively connected to said mechanism by over center spring means for causing a quick opening and quick closing of said switch means, a biased hammer like tripping means for imparting a blow to said mechanism to cause quick opening of said switch means, said moves said main operating means to an indicating position to show that automatic operation has occurred, and condition responsive means normally restraining said tripping means and releasing said tripp ng means upon the occurrence of a predetermined condition.

10. A circuit breaker comprising switch means, switch operating means for opening and closing said switch means, movable main operatin means, over center spring means operatively con--' necting said main operating means and said switch operating means for imparting a quick motion to said switch operating means when said main operating means is moved, tripping means adapted to strike a blow against said switch operating means to open said switch means with a quick motion, biasing means biasing said tripping means towards motion, and condition responsive means normally restraining said tripping means against motion and releasing said tripping means upon the occurrence of a predetermined condition.

11. A circuit breaker comprising switch means, switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively connecting said main operating means and said switch operating means for imparting a quick motion to said switch operating means when said main operating means is moved, tripping means adapted to strike a blow against said switch operating means to open said switch means with a quick motion, biasing means biasing said tripping means towards motion, and condition responsive means normally restraining said t ping 75 means operatively connected to means against motion and releasing said tripping means upon the occurrence of a predetermined condition, the biasing means for said tripping means being of sumcient strength to overpower said over center spring means after said tripping means has operated, whereby said main operating means is ineflective to close said switch means while said tripping means remains in its released position.

12. A circuit breaker comprising switch means, switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively connecting said main operating means and said switch operating means for imparting a quick motion to said switch operating means when said main operating means is moved, tripping means adapted to strike a blow against said switch operatlng means to shift said switch operating means to open said switch means with a quick motion, one end of said over center spring means being moved by the shifting of said switch operating means to a position to move said main operating means to an indicating position to show that automatic operation has occurred, biasing means biasing said tripping means towards motion, and condition responsive means normally restraining said tripping means against motion and releasing said tripping means upon the-occurrence of a predetermined condition.

13. A circuit breaker comprising a pair of opposed switch means, toggle link mechanism having its outer ends connected to said switch means,

pivoted switch operating means directly joined to the center portion of said toggle link mechanism for extending and collapsing said toggle link mechanism to simultaneously operate said switch means, movable main operating means operatively coupled to said switch operating means, tripping means biased for tripping motion and adapted to move said switch operating means to switch open position, and condition responsive means normally restraining said tripping means against motion and releasing said tripping means upon the occurrence oi a predetermined condition, said main operating means and said tripping means having portions adapted to coactto reset said tripping means when said main' operating means is moved to a predetermined position.

14. A circuit breaker comprising a pair of opposed switch means movable inwardly and outwardly to switch open and switch closed positions respectively, mechanism for simultaneously moving said switch means and transmitting balanced thrusts to said switch means, main operating means operatively connected to said mechanism by over center spring means for causing a quick opening and quick closing of said switch means, a biased hammer like tripping means for imparting a blow directly to said mechanism to cause quick opening of said switch means, condition responsive means normally restraining said tripping means and releasing said tripping means upon the occurrence of a predetermined condition, and means operatively connected to said main operating means for engaging and resetting said tripping means when said main operating means is moved to a predetermined position.

15. A circuit breaker comprising a pair of opposed switch means movable inwardly and outwardly to switch open and switch closed positions said mechainsm by over center spring means for causing a quick opening and quick closing of said switch means, a biased and pivoted hammer like tripping means for imparting a. blow to said mechanism to cause quick opening of said switch means independently of said main operating means, condition responsive means normally restraining said tripping means and releasing said tripping means upon the occurrence oi. a predetermined condition, and

means operatively connected to said main operating means for engaging and resetting said tripping means when said main operating means is moved to a predetermined position.

16. A circuit breaker comprising switch means, a ivoted switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively conecting said main operating means and said switch operating means for imparting a quick motion to said switch operating means when said main operating means is moved, tripping means pivoted i'zoairialh; with said switch operating means, said tripping means being adapted to strike a blow against said switch operating means to open said switch operating means with a quick motion, biasing means hiadng said tripping means towards motion, and condition responsive means normally restrainin said tripping means against motion and releasing said tripping means uipon the occurrence of a predetermined condit on.

17. A circuit breaker comprising switch means, switch operating means for opening and closing said switch means, movable main operating means, over center spring means operatively connecting said main, operating means and said switch operating means for imparting a quick motion to said switch operating means when said operating means is moved, pivoted tripping means adapted to strike a blow against said switch operating means to open said switch operating means with a quick motion, latch means nor mally engaging and holding said tripping means against motion, condition responsive means adapted to operate said latch means and release said tripping means, and spring means biasing said tripping means towards motion, said spring means being connected at a point to said tripping means so that said spring means has less leverage when said tripping means is latched than when said tripping means released.

EDWIN A. LINK.

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