US3908108A

US3908108A - Slide button tool handle switch with interlock

Info

Publication number: US3908108A
Application number: US455382A
Authority: US
Inventors: Harold W Hults
Original assignee: Cutler Hammer Inc
Current assignee: Cutler Hammer Inc
Priority date: 1974-03-27
Filing date: 1974-03-27
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23

Abstract

A double-pole, reversing switch adapted to be mounted in the handle of a portable electric tool. The switch includes a trigger type pushbutton on-off switch and a slide button reversing switch electrically connectable for reversing shunt or series motors and mounted in a unitary housing, and having an external interlock preventing operation of the slide button while the trigger is depressed. The on-off switch is provided with double-pole butt contacts that have a controlled amount of wipe, very low bounce, are non-teasable, and have maximum contact pressure at the point of tripping open. The trigger has a considerable amount of movement between trip ''''on'''' and trip ''''off'''' positions. The slide button reversing switch is provided with spring biased ''''ball-bearing'''' movable contacts operating with snap-action to engage converging flat surfaces of pairs of stationary contacts.

Description

United States Patent H9] (H1 3,908,108 Hults Sept. 23, I975 SLIDE BUTTON TOOL HANDLE SWITCH Primary Examiner-Robert K. Schaefer WITH INTERLOCK Assistant Examiner-William J. Smith 75 lnventor: Harold w. Hults, Milwaukee, Wis gf u IO [73] Assignee: Cutler-Hammer, Inc., Milwaukee,

57 ABSTRACT [22] plied: 1974 A double-pole, reversing switch adapted to be 21 55 332 mounted in the handle ofa portable electric tool. The

[52] 200/153 LA; 200/67 A; 200/68; nectable for reversing shunt or series motors and 2 200/157 mounted in a unitary housing, and having an external 15/18; HOIH 5/10 interlock preventing operation of the slide button [58] Field of search'm' 200/77 67 while the trigger is depressed. The on-off switch is 200/68 provided with doublepole butt contacts that have a [56] References cued teasable, and have maximum contact pressure at the UNITED STATES PATENTS 2,633,5[0 3/1953 Schellman 200/68 positinns. The Slide button reversing switch is 2,743,330 4/i956 Ludwig i i i i i i i ..200/67A vided p g biased u gn movable 2,789,170 4/!957 Johnson... 4 200/l53GX 3,600,533 8/1971 English n 200/68 onary contacts.

8 Claims, 14 Drawing Figures I II 4 III.

US Patent Sept. 23,1975 Sheet 1 of3 3,908,108

| o I l I: 1H1

ill II 32 Z6 Z4 22 I8 185 US Patent Sept. 23,1975 Sheet 3 of 3 3,908,108

-' Hill fig.

jziq I3 SLIDE BUTTON TOOL HANDLE SWITCH WITH INTERLOCK BACKGROUND OF THE INVENTION Reversing tool handle switches with interlock have been known heretofore. However, these prior switches have been subject to one or more disadvantages that have limited their electrical capabilities such as sliding contacts subject to excessive wear that limits the life of the switch, contacts that close on corners or edges at reduced contact area inherently subject to deterio-- SUMMARY OF THE INVENTION This invention relates to tool handle switches with interlock between the on-off and reversing actuators and more particularly to switches of the-slide button actu-.

ated type.

An object of the invention is to provide an improved reversing switch.

A more specific object of the invention is to provide an improved reversing switch having larger area engagement between movable contacts bridging stationary contacts.

Another specific object of the invention is to provide an improved slide button switch mechanism.

Another specific object of the invention is to provide an economical and reliable contact mechanism for a tool handle switch.

Another specific object of the invention is to provide an improved interlock between the slide button ofa reversing switch and the pushbutton trigger of an on-off switch which interlock is external of the switch housing to avoid sealing problems.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an enlarged. vertical cross-sectional view of the reversing tool handle switch with interlock taken along line l-l of FIG. 2;

FIG. 2 is a horizontal cross-sectional view taken along line 22 of the switch of FIG. 1;

FIG. 3 is a vertical cross-sectional view taken along line 3-3 of the switch of FIG. 2;

FIG. 4 is a fragmentary, horizontal cross-sectional view taken along line 4-4 of the switch of FIG. 1;

FIG. 5 is a top view of the switch of FIGS. 1-4;

FIG. 6 is a vertical cross-sectional view taken along line 6-6 of the switch of FIG. 1;

FIG. 7 is a vertical cross-sectional view taken along line 7-7 of the switch of FIG. 1;

FIG. 8 is a front elevational view of one of the contacts of the reversing slide button switch of FIGS. 1 and 3;

FIG. 9 is a circuit diagram showing the switch of FIGS. I-S connecting an electrical power supply to a shunt motor for reversing;

FIG. 10 is a circuit diagram showing the modified switch of FIGS. 12-14 connecting an electrical power supply to a series motor for reversing;

FIG. 11 is a circuit diagram showing the modified switch of FIGS. 12-14 connecting an electrical power supply through a rectifying diode to a series motor for two-speed operation;

FIG. 12 is an enlarged fragmentary horizontal crosssectional view of a modified reversing tool handle switch;

FIG. 13 is a front elevational view of one of the contacts of the on-off switch of FIG. I2; and

FIG. I4 is a front elevational view of one of the contacts of the reversing slide button switch of FIGS. 12 and 13.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is shown a tool handle switch with interlock constructed in accordance with the invention.

As shown in the drawings, this switch is provided with an insulating base 2 generally rectangular in shape and open at the top for housing the double-pole contacts of both the trigger on-off switch and the slide button reversing switch. the former being shown at the left end in FIG. I and the latter being shown at the right end therein.

The top of this base is closed by an insulating cover 4 that is set into and secured within and generally flush with the top of the base by two or more rivets 6 or the like. This cover has a suitable oblong aperture at its right end beneath slide button 8 to provide clearance for reciprocal movement of the shank 10a of overcenter cam actuator 10 that extends up through the cover and is secured by a snap fit into bushing 8a of the slide button. This cover also has a round hole at its left end surrounded by a raised collar 4a beneath pushbutton trigger lever 12 for guiding shank N0 of plunger actuator 14 as shown in FIG. 1 that extends up through the cover and is secured by a snap fit into bushing 12a of trigger lever 12.

This cover is also provided with means for limiting reciprocal movement of and guiding slide button 8. This means comprises an upstanding lug 4b near the middle of the cover that projects into an elongated groove 8b on the underside of extension of the slide button. Opposite ends of this groove stop against this lug to limit movement of the slide button in opposite directions, and this lug guides extension 8c in its sliding movement.

The interlock between the trigger lever 12 and the slide button 8 comprises an upstanding lug 8d on the end of extension 8c of the slide button and a pair of notches in the underside of the trigger lever separated by a dividing wall 12h. As will be apparent, when the slide button is in the right-hand position shown in FIG. 1, lug 8d will enter the right-hand notch when the trigger lever is depressed and dividing wall 12b will prevent actuation of the slide button toward the left. On the other hand, when the slide button is moved to its lefthand position and the trigger lever is then depressed. lug 8d will enter the left-hand notch and dividing wall 1211 will prevent actuation of the slide button toward the right. This interlock prevents application of reverse power to the motor while it remains connected to the power supply, that is. it prevents *plugging" the tool motor. The motor must be disconnected from the power supply by restoring the trigger lever before the reversing switch can be operated. This gives the motor time to stop or slow down almost to a stop before reverse energy can be applied thereto.

The on-off switch is provided with snap-action double-pole butt contacts having a predetermined or controlled amount of wipe. For this purpose, there are provided a pair of

angular terminals

16 and 18 arranged vertically in retaining grooves in the base as shown in FIGS. 2 and 4. Each such terminal is bent at a right angle along its longitudinal center to provide a contacting portion, 16a and 18a, and a terminal portion, 16b and 18b, as shown in FIG. 4. As shown in FIG. 3, the opposite ends of terminal portion 18b are provided with connector lugs. While only the lower connector lug is used to connect to an external circuit, the connector portion is made symmetrical so that one design can be used for both connectors. The other connector is turned around and inserted in the base so that contacting

portions

16a and 18a are in a common plane as shown in FIG. 4 for sliding engagement by the movable contacts hereinafter described. As shown in FIG. 3, the lower lug of terminal portion 18b is exposed in an opening in the bottom corner of the base to provide a terminal T2 shown in FIG. 9 for engagement by a wire connector. Similar, the lower lug of terminal portion 16b of the other connector is exposed on the opposite bottom corner of the base as terminal Tl shown in FIG. 9.

A pair of U-shaped

movable contacts

20 and 22 shown in FIGS. 3, 4 and 6 are carried by opposite ends of a generally rectangular movable contact block 24. These U-shaped movable contacts embrace the ends of the movable contact block and are slid thereby along contacting portions 16a and 180, respectively, of the terminals and remain in constant contact with the latter.

The center portion of the movable contact block is provided with an over-center cam 240 shown in FIG. 1 and in dotted line profile in FIG. 3 whereby the movable contacts are given a snap-action movement. For this purpose, a plunger 26 is biased laterally against this over-center cam by a helical compression spring 28 retained in a lateral well 14b of plunger actuator 14 as shown in FIGS. 1 and 4. This plunger actuator 14 is slidably guided in the base and is biased upwardly by a pair of helical compression springs 30 and 32 that hear at their lower ends against the bottom of the base. As shown in FIG. 3, plunger actuator 14 is provided with recesses for the upper ends of these springs and the bottom of the base is provided with shallow recesses for the lower ends of these springs to hold them in place.

As shown in FIGS. 1-4, the movable contacts serve to connect

terminals

16 and 18 to respective

stationary contacts

34 and 36. Each such stationary contact is provided with a generally U-shaped connector portion 340, 360 as shown in FIG. 2 and an arm 34b, 36b extending therefrom up and toward the left to a point overlying the respective movable contact as shown in FIG. 3. The contacting end of each such arm 34b, 36b is biased down from a horizontal plane toward the movable contact and it is this bias that determines the amount of wipe when the contacts close and open. This wipe is set at an amount sufficient to keep the contacts clean for good conductivity but not so much as to cause excessive wear. As will be apparent in FIG. 1, arms 34b and 36b are biased down tight against the top of wall 2a in the base to fix the distance therefrom to the two movable contacts when open.

When the trigger lever is depressed, the tip of plunger 26 slides down along the upper incline of cam 24a of the movable contact block until it passes the center high point on this cam. During this time plunger actuator springs 30 and 32 are compressed and plunger spring 28 is also compressed. Upon passing the high point of the cam, plunger 26 causes the movable contact block to snap up while the plunger rides along the lower incline of the cam. The movable contact block carries the movable contacts with it so that the upper arms thereof engage

stationary contacts

34 and 36, respectively. The upward force on the movable contact block causes arms 34b and 36b to move up and straighten out against the lower surface of cover 4 cffecting wiping action between the movable and stationary contacts.

This trigger on-off switch may be locked in its on position. For this purpose, there is provided a horizontal bushing 2b molded integrally on the base as shown in FIGS. 2 and 5. This bushing retains a spring-biased lock pin 38. The adjacent end of the base is provided with a vertical slot 2c into which the inner end of the lock pin may be laterally depressed. Trigger lever 12 is provided with a downwardly extending tab 12c formed integrally therewith that fits into slot 2c. This tab has a hole 12d in it for receiving the lock pin after the trigger lever has been depressed thereby to hold the switch on after the trigger is released. A slight depression of the trigger lever allows the bias spring to snap the lock pin out of the way so that the trigger can return to its extended position.

Upon return of the trigger under spring force, the tip of plunger 26 slides up the lower incline of cam surface 24a while maintaining maximum contact pressure between the movable and stationary contacts. When it reaches the high point of the cam at maximum contact pressure, and passes thereover, the force of bias spring 28 causes the movable contacts to snap open while plunger 26 slides along the upper incline of cam surface 24a. Thus, teasing of the contacts is prevented because maximum contact pressure is maintained until the contacts are suddenly separated.

A small amount of contact wiping takes place on initial opening movement of the contacts. At this point, stationary contact arms 34b and 36b move down with and wipe the movable contacts a small amount until these arms abut dividing wall 2a of the base. This serves to keep the contacting surfaces clean of any dust, dirt or oxides for a good electrical connection whenever the contacts close.

The slide button reversing switch is provided with two pairs of stationary contacts with the inner contacts of the pairs being crossed at notch 2e in dividing wall 2f of the base so as to provide reversing double-pole connections from

stationary contacts

34 and 36 of the on-off switch to external terminals T5 and T6 shown in FIG. 9. For this purpose. there are provided a first pair of contacts including an outer contact 40 and an inner contact 42, and a second pair of contacts including an inner contact 44 and an outer contact 46 as shown in FIG. 2.

Outer contacts

40 and 46 are alike and each has a pair of slightly inwardly turned wings, inwardly referring to the interior of the switch housing as opposed to outwardly or the exterior of the housing.

Inner contacts

42 and 44 are alike and each is constructed as shown by stationary contact 42 in FIG. 8. As shown therein, the contact is provided with a terminal portion at its left end having symmetrically arranged upper and lower terminal lugs 42a and 42b and an angular contact portion at its right end having a notch 42c cut out to leave an upstanding leg 42d at the extreme right end thereof. As shown in FIG. 2, this angular portion extends inwardly at an obtuse angle with the terminal portion. This stationary contact is provided with two terminal lugs so that one such contact can be used for contact 42 and another such contact, turned over, can be used for contact 44 in FIG. 2. When so arranged, a connec tor lug of each such stationary contact will be exposed at the bottom corner of the base, as shown in FIG. 3 and terminals T3 and T4 in FIG. 9, to which a suitable wire connector may be attached if desired. Also, when so arranged, the portion below notch 42c in contact 42 will pass through the notch in contact 44 with clearance so that these inner contacts can be crossed but do not touch. In this manner, a first spherical ball bearing movable contact 48 when moved to the left will bridge the converging parts of

contacts

40 and 42 while at the same time a second spherical ball bearing movable contact 50 when simultaneously moved to the left will bridge the converging parts of

contacts

44 and 46. These converging parts are the inner flat surface of the left wing of outer contact 40 and the corresponding flat surface of inner contact 42, and the inner flat surface of the left wing of outer contact 46 and the corresponding flat surface of inner contact 44.

When the two ball bearing" movable contacts are snapped to the right, one of them will wedge between the inner flat surface of the right wing of outer contact 40 and the corresponding flat surface of inner contact 44, and the other one will wedge between the inner flat surface of the right wing of outer contact 46 and the corresponding flat surface of inner contact 42.

Movable contacts

48 and 50 are biased upwardly by a pair of helical compression springs 52 against like, spaced, respective over-center cams b and 10c of actuator l0. Conical projections 2d are molded in the bottom of the base and extend into the lower ends of springs 52 to hold them in place.

As shown in FIG. 7, actuator 10 is provided with a pair of earns 10!) and We having a groove therebetween into which dividing wall 2e of the base extends. These cams are alike and each is provided with a high point at its center as shown in FIG. 1. Thus, as the slide button is moved, this high point passes over the spherical movable contact, in the meantime compressing springs 52, and the movable contact then snaps along the opposite incline of the cam to reverse the connection. With the spherical movable contacts wedging between the vertical flat surfaces of the stationary contacts, a good contact of substantially contacting area is made, and the wedging action tends to keep the contact surfaces clean.

The terminal portions of

inner contacts

42 and 44 are retained in electrical connection with

U-shaped portions

34a and 36a of

stationary contacts

34 and 36, re spectively, of the on-off trigger switch. This is done by pressing these terminal portions into the narrow slots between

contacts

34 and 36 and the opposite walls of the base.

The parts are retained in place by suitable integrally molded portions on the lower surface of the cover. Thus, lugs 4c shown in FIG. 7 keep outer

stationary contacts

40 and 46 of the slide button switch up against the inner walls of the base and prevent them from falling into the interior cavity. Two downward projections 4d, one of which is shown in FIG. 3, press down on

stationary contacts

42 and 44 to retain them in place. U- shaped ridge 4e between projections 4d overlies U- shaped terminal portions 340 and 36a of

stationary contacts

34 and 36 of the on-off trigger switch to keep them in place in the base. Dividing wall 2fwithin the base has a suitable notch 2g for this ridge to pass across as shown in FIG. 2. A pair of very short lugs 4fon the lower surface of the cover press down on

terminals

16 and 18 to hold them in place, one of these lugs being shown in FIG. 3.

The switch provides three pairs of terminals for connections to external circuits as shown in FIG. 9. A first pair of connections can be made to the exposed lower lugs of

terminals

16 and 18, these lugs being marked as terminals T1 and T2 in FIG. 9. For example, these terminals T1 and T2 can be connected to AC. power supply lines L1 and L2.

A second pair of connections can be made to the exposed lower lugs of

stationary contacts

42 and 44, these lugs being marked as terminals T3 and T4 in FIG. 9. For example, the armature winding A1 of the shunt motor can be connected across terminals T3 and T4 as shown in FIG. 9.

A third pair of connections can be made to the exposed lower lugs of

stationary contacts

40 and 46, these lugs being marked as terminals T5 and T6 in FIG. 9. For example, the shunt field winding SF of the shunt motor can be connected across terminals T5 and T6.

With the above connections as shown in FIG. 9, the armature winding can be energized by the on-off switch and the shunt field winding can be reversely energized through the on-off and reversing switches to run the motor selectively in either the forward or reverse direction.

The openings in the bottom of the base through which the lugs are exposed for making wire connections are shown in FIG. 2 at 2h and 2], 2k and 21, and 2m and Zn.

A modification of the switch, enabling use thereof for reversing a series motor or for controlling a two-speed motor is shown in FIGS. 10-14. As will readily be apparent in FIG. 10, this modification involves disconnecting contact 44 in FIG. 3 from contact 36 and providing contact 36 with its own terminal.

The structure for accomplishing this is shown in FIGS. 12-14, wherein reference characters like those in FIG. 2 are used for like parts. As shown in FIG. 12, there is provided a modified base 54 having a first pair of holes 54a and 54b at its bottom corners for making connections to the lugs of

terminals

16 and 18, the same as in FIG. 2. These correspond to terminals T1 and T2 in FIGS. 10 and 11.

This base is also provided with another pair of holes 54c and 54d at its bottom corners for making connec tions to the lugs of

outer contacts

40 and 46, respectively, the same as in FIG. 2. These correspond to terminals T5 and T6 in FIGS. 10 and 11.

This base is also provided with another hole 54s at its bottom corner for making a connection to the lower lug of inner contact 42, the same as in FIG. 2. This corresponds to terminal T3 in FIGS. 10 and II.

This base is provided with a pair of relocated holes 54f and 54g for making connections to lugs on modified

stationary contacts

56 and 58, respectively. These correspond to terminals T4 and T7 in FIGS. and 11.

In order to disconnect one of the stationary contacts of the onoff switch from the corresponding contact of the reversing switch as aforesaid, one arm has been omitted from the U-shaped portion to provide a stationary contact 56 for the on-off switch as shown in FIG. 13. In addition, a connector lug has been provided at the lower edge of terminal portion 56a of this stationary contact. As a result, when this stationary contact is pressed into its slot in the base, this lug is exposed within hole 54ffor making a connection to an external circuit.

For this purpose also, inner contact 58 is shortened at its terminal portion 58a and is provided with a lug at its lower edge to be exposed within hole 543 in FIG. 12.

For uniformity of production, stationary contact 60 is made the same shape as stationary contact 56.

Otherwise, this modification of the switch is similar to that shown in FIGS. 1-9.

As shown in FIG. 10, this modified switch can be connected to an AC. power supply source at conduc tors L1 and L2 and to a series motor in a reversing relation. For this purpose, armature winding A2 is connected across terminals T4 and T7 and series field winding SF] is connected across terminals T5 and T6. Thus, when the slide button reversing switch is operated to shift the position of

movable contacts

48 and 50, the energization of the series field winding is reversed to reverse the direction of rotation of the motor.

As shown in FIG. 11, this modified switch can be used for controlling a two-speed motor. In this circuit, armature winding A3 is connected in series with field winding SF2 of the series motor across terminals T4 and T5, and a rectifying diode 62 is connected from terminal T5 to terminal T3. Thus, when the slide button switch is in its dotted line position as shown in FIG. 11, the current will flow through diode 62 for half-wave energization of the motor for slow speed operation. When the slide button switch is operated to its full line position, the diode is shunted for full'speed operation of the motor.

An alternative way of connecting the motor and diode in FIG. 11 would be to connect armature A3 and series field SP2 in series from terminal T4 to terminal T6, and to connect diode 62 from terminal T5 to terminal T6. Then, when the slide button switch is in its full line position, current will flow through the motor and the diode for slow speed operation. When the slide button switch is in its dotted line position, current will flow through the motor for full speed operation, and the diode will be disconnected. With this connection, terminal T3 is not required as it is not required in FIG. 10.

While the apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that this invention is not intended to be limited to the particular preferred embodiment of higher rated tool handle switch with interlock disclosed, inas much as it is susceptible of various modifications without departing from the scope of the appended claims.

I claim:

1. A double-pole tool handle switch comprising:

an insulating housing;

a slide button switch actuator mounted on said housing;

double-incline cam means secured to said slide button;

a pair of outer stationary contacts having slightly inwardly turned wings;

a pair of inner stationary contacts angularly crossing one another and arranged between said outer contacts; 4 said wings of each outer stationary contact and said inner stationary contacts having flat surfaces eonverging in opposite directions;

and a pair of movable contacts arranged for reciprocal actuation by said doubleincline cam to alternately bridge said opposite converging flat surfaces of said inner and outer stationary contacts to afford reversing switching.

2. The apparatus defined in claim 1, wherein:

said movable contacts are spherical;

and springs biasing said movable contacts against said double-incline cam means.

3. The apparatus defined in claim I, wherein:

said inner stationary contacts are each provided with a notch at their crossing point to prevent electrical contact therebetween.

4. The apparatus defined in claim 3, wherein:

said inner stationary contacts are identical and one of them is turned over relative to the other so that each passes through the notch of the other one at their crossing point. 5. The apparatus defined in claim I, together with: a double-pole on-off switch mounted in said housing having movable contacts and stationary contacts; and at least one of said stationary contacts of said onoff switch being connected to one of said inner contacts of said slide button switch.

6. The apparatus defined in claim 4, wherein said double-pole on-off switch comprises:

an actuator movable in a direction perpendicular to the direction of movement of said slide button;

and interlocking means comprising a lug on said slide button and notches in said actuator separated by a wall, said notches receiving said lug in alternate positions of said slide button and said wall preventing operation of said slide button when said actuator is in its on" position.

7. The apparatus defined in claim 1, wherein:

said inner stationary contacts are provided with exposed terminals for connection to an external circuit;

and said outer stationary contacts are provided with exposed terminals for connection to an external circuit.

8. The apparatus defined in claim 1, wherein:

said housing comprises a base and a cover;

and projections on said cover for retaining said contacts in place in said base.

Claims

1. A double-pole tool handle switch comprising: an insulating housing; a slide button switch actuator mounted on said housing; double-incline cam means secured to said slide button; a pair of outer stationary contacts having slightly inwardly turned wings; a pair of inner stationary contacts angularly crossing one another and arranged between said outer contacts; said wings of each outer stationary contact and said inner stationary contacts having flat surfaces converging in opposite directions; and a pair of movable contacts arranged for reciprocal actuation by said double-incline cam to alternately bridge said opposite converging flat surfaces of said inner and outer stationary contacts to afford reversing switching.

2. The apparatus defined in claim 1, wherein: said movable contacts are spherical; and springs biasing said movable contacts against said double-incline cam means.

3. The apparatus defined in claim 1, wherein: said inner stationary contacts are each provided with a notch at their crossing point to prevent electrical contact therebetween.

4. The apparatus defined in claim 3, wherein: said inner stationary contacts are identical and one of them is turned over relative to the other so that each passes through the notch of the other one at their crossing point.

5. The apparatus defined in claim 1, together with: a double-pole on-off switch mounted in said housing having movable contacts and stationary contacts; and at least one of said stationary contacts of said on-off switch being connected to one of said inner contacts of said slide button switch.

6. The apparatus defined in claim 4, wherein said double-pole on-off switch comprises: an actuator movable in a direction perpendicular to the direction of movement of said slide button; and interlocking means comprising a lug on said slide button and notches in said actuator separated by a wall, said notches receiving said lug in alternate positions of said slide button and said wall preventing operation of said slide button when said actuator is in its ''''on'''' position.

7. The apparatus defined in claim 1, wherein: said inner stationary contacts are provided with exposed terminals for connection to an external circuit; and said outer stationary contacts are provided with exposed terminals for connection to an external circuit.

8. The apparatus defined in claim 1, wherein: said housing comprises a base and a cover; and projections on saId cover for retaining said contacts in place in said base.