US3710294A

US3710294A - Convertible thermal safety cut-out switch

Info

Publication number: US3710294A
Application number: US00233072A
Authority: US
Inventors: J Dries
Original assignee: DOERR ELECTRIC CORP
Current assignee: DOERR ELECTRIC CORP
Priority date: 1972-03-09
Filing date: 1972-03-09
Publication date: 1973-01-09
Anticipated expiration: 1990-01-09
Also published as: CA972016A

Abstract

A frangible hold-down member is applied to the manual button for resetting a cut-out switch, thereby conditioning the switch for automatic reset when the member is in place and for only manual reset when the member is removed.

Description

United StatesPatent 191 Dries 22 Filed:

54] CONVERTIBLE THERMAL SAFETY CUT-OUT SWITCH [75] Inventor: James P. Dries, Milwaukee, Wis.

[73] Assignee: D oerr Electric Corporation, Cedarburg, Wis.

March 9, 1972 [211 App]. No.: 233,072

[:56] Y References Cited UNITED STATES PATENTS 3,413,583 11/1968 Clark et a]. ..337/66 X 1 1 Jan. 9, 1973 3,321,597 5/1967 Meijer ..337/66 x 2,611,052 9/1952 mm et al. ..337/68 )1 2,318,076 5/1943 Johns 337/68 x Primary Examiner-Bernard A. Gilheany Assistant Examiner-A. T. Grimley Attorney-Andrus, Sceales, Starke & S awall Q ABSTRACT A frangible hold-down member is applied to the manual button for resetting a cut-out switch, thereby conditioning the switch for automatic reset when the member is in place and for only manual reset when the member is removed.

7 Claims, 13 Drawing Figures PATENTEDJM @1975 SHEET 2 0F 2 CONVERTIBLE THERMAL SAFETY CUT-OUT SWITCH BACKGROUND OF THE INVENTION This invention relates to a convertible thermal safety cut-out switch and particularly to one that is selectively adaptable for either automatic or manual resetting de pending upon the requirement of the intended installation.

When electric motors, for instance, are shipped from the factory with a thermal safety cut-out switch thereon, it is generally not known whether the motor will be installed under conditions permitting automatic restarting of the motor after a thermal cut-out has occurred or under conditions requiring that the motor not be restarted except by manual resetting of the switch after such a cut-out.

Because of this, sales outlets have heretofore been required to stock motors having automatic reset cutout switches and motors having manual reset cut-out switches.

Cut-out switches convertible from manual to automatic reset have been proposed but are objectionable in the market because the user can too readily convert a manual reset installation which for safety reasons should require a manual reset into an automatic reset condition which then may become dangerous for the particular service.

SUMMARY OF THE INVENTION The present invention utilizes a thermal safety cutout switch which automatically resets unless the manual reset button has tripped to the open circuit position in which latter case only a manual reset is possible and is required.

A frangible hold-down member is applied to the button at the factory so that all motors shipped to the sales outlet are in immediate condition for automatic reset of the thermal safety cut-out' switches.

When each motor is installed, if the service is such as to permit automatic restarting of the motor following cooling down, the hold-down member is left in place. If the service is such as to require a manual restarting of the motor after a cooling down, the installer merely breaks and removes the hold-down member thereby freeing the manual button for operation.

The hold-down member is generally in the form of a cover plate extending across the button and holding it in, and which is frangible with respect to its mounting so that it is first broken and then removed to convert the resetting of the switch to a manual actuation of the button.

The construction .is such that even though a user removes the original plate mounting tabs and attempts to secure a flat plate across the button, the unit will not be thus re-converted to an automatic reset condition. Instead, he will have to go to the sales outlet for a new hold-down member and will then be subject to questioning so that safety requirements will be main tained on the installation and the sales outlet will not permit him to so re-convert the installation.

BRIEF DESCRIPTION OF THE DRAWING The best mode presently contemplated for carrying out the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a longitudinal central section through the mounting for the cut-out switch;

FIG. 2 is a diagrammatic showing of the cut-out switch in condition for automatic reset;

FIG. 3 is a view similar to FIG. 2 having the cut-out switch open and in condition for manual reset;

FIG. 4 is a view similar to FIGS. 2 and 3 showing an inoperable attempt by a user to re-convert from manual to automatic reset;

FIG. 5 is an end elevation of the switch of FIG. I attached to a motor;

FIG. 6 is a view similar to FIG. 5 showing the holddown member broken away to condition the switch for manual reset;

. FIG. 7 is a detail view of a portion of FIG. 1 showing the hold-down member broken away to condition the switch for manual reset as in FIG. 6 and showing the cover for the switch removed;

FIG. 8 is a front elevation of the hold-down member;

FIG. 9 is an edge elevation of the member of FIG. 8;

FIG. 10 is a plan view of the clip for mounting the switch; 7

FIG. I 1 is a side elevation of the clip of FIG. 10

FIG. 12 is a front view of the block for securing the assembly of the switch with the clip of FIGS. 10 and 11; and

FIG. 13 is a side elevation of the block of FIG. 12, with a portion thereof sectioned.

With reference to the drawings, the cut-out switch 1 is mounted in a connector box 2 on the side of the motor 3 in a position where thermal conditions arising from motor operation will actuate the switch to open the same and cut out the motor for safety reasons.

The switch 1 is shown in principal detail in FIGS. 2 and 3 wherein a manual reset button 4 is biased outwardly of insulating casing 5 by a suitable spring means 6. The bimetallic strip 7 constitutes a thermal element which snaps its contact 8 away from fixed contact 9 upon an unsafe thermal condition and returns to engage

contacts

8 and 9 when that condition subsides.

The inner end of button 4 has a lateral projection 10 which engages the side of contact 8 and prevents button 4 from being biased outwardly when the contacts are closed.

When

contacts

8 and 9 are opened (separated) reengagement of the contacts will occur automatically upon restoration of normal operating temperatures, assuming that button 4 is held inwardly to prevent projection 10 from entering the space between the contacts. If, however, button 4 is permitted to move outwardly causing projection 10 to move into the space between

contacts

8 and 9, the latter will remain separated even though normal operating temperature conditions have been restored, and until manual pressing of button 4 inwardly to reset position. a

The switch 1 is mounted to one end of box 2 by means of an insulating generally U-shaped block 11 and a pair of spaced screws 12 which pass through the end of the box and into the base of the legs 13 of the block.

A clip 14 of sheet metal has prongs 15 adapted to engage the ends and sides of easing 5 and hold switch '1 in the recess of block 11 between the legs 13. For this purpose, the ends of clip 14 are flanged to enter corresponding longitudinal bores 16 in the legs 13, with a reverse bend 17 on each flange to retain the same after assembly.

After assembly of switch 1, block 11 and clip 14, the assembly is mounted in box 2 with a portion adjacent button 4 in the form of a circular flange 18 on block 11 extending through an opening in the end of the box.

The button 4 being retracted and contacts 8 and 9 closed with projection 10 abutting contact 8, the outer end face of button 4 will be recessed slightly below the outer place of the face of the encircling flange 18.

In carrying out the present invention, a hold-down member 19 comprising a plate 20 with attachment ears .21. extending beneath the heads of screws 12 and with a central button projection 22 engaging reset button 4, prevents the latter from interference with the automatic resetting of

contacts

8 and 9 when the motor is installed for uses permitting automatic cut-out resetting.

Should the installation require amanual resetting for safety reasons, the service man making the installation can remove the member 19 and throw it away, thus releasing button 4 for biasing outwardly in the event of a thermal cut out whereby projection 10 enters the space between

contacts

8 and 9 and prevents closing of the contacts upon restoration .of safe thermal conditions until the button 4 is manually pressed inwardly beyond the outer plane of flange 18. I

r In order to make sure that the discarded hold-down member 19 is not retrieved by the user and later restored to the unit to save necessity for manual reset, the present invention contemplates that the juncture between ears 21 and plate 20 will be frangible as by providing the transverse groove 23 therein to weaken thickness of cars 21 in place thereof with the expectation that the switch will thereby be restored to automatic reset condition. 1 I

However, as shown in FIG. 4, such a plate 25 will not depress button 4 sufficiently to clear projection 22 from the space between

contacts

8 and 9. In order to maintain the switch in automatic reset condition it is necessary that the face 'of button 4 be held inwardly a slight distance from the plane of the face of flange 18. Thus, the projection 22 on the original plate 20 is needed.

If, after such an unsuccessfulattempt by an operator to re-convert the unit to an automatic reset condition, he goes to the dealer or supplier for a new hold-down member 19, he can be questioned as to his purpose and there educated to the danger of such a re-conversion for his installation.

Thus, the safetyrequirements of all installations can be established and maintained as dictated by the original installation.

At the same time, the dealer or supplier needs keep in stock motors with only one type of cut-out switch. This can substantially reduce his inventory as against prior practice in which he had to keep motors with automatic reset cu'tout switches and motors with manual reset cut-out switches.

' The operating instructions may be applied as decals to the outer face of plate 20, as shown in FIG. 5, and to the end face of box 2 beneath the plate, as shown in FIG. 6, the latter being exposed for use by the operator only in those installations in which plate 20 is broken away. 7 I

Various modes of carrying out the invention'are contemplated within the scope of the following claims which particularly point out and distinctly claim the subject matter that is regarded as the invention.

I claim:

1. In combination, a safety thermal cut-out switch capable of automatic resetting upon restoration of safe thermal conditions and having a manual reset means capable of interfering with said automatic resetting until manually released, means mounting said switch in an environment requiring safety thermal cut-out of an electric circuit controlled by said switch, and removable means to prevent interference with said automatic resetting by said manual reset means.

2. The combination of claim 1, in which said manual reset means comprises a button spring biased outwardly of said switch and having'a portion disposed to enter the space between the operative switch contacts to preventsaid contacts from closing while said button is in an outward position.

3. The combination of claim 2, in which said removable means comprises a hold-down member engaging the face of said button and retaining the latter depressed to a" position where said portion does not at any time interfere ,with the automatic closing of said switch contacts. I

4. The combination of claim 2, and fixed means comprising a portion adjacent said button and extending outwardly beyond the face thereof when the button is in its depressed state with the switch contacts closed and providing for interference with resetting of the contacts to closed position upon opening of the con,- tacts and movement of the button outwardly to a position wherein the face of the button has at least reached the general plane of the face of said adjacent portion.

5. The combination of claim 3, in which said holddown means comprises a plate extending across the face of said button, and frangible means securing said the face of said button and holding the same in a posi tion freeing automatic resetting of said switch contacts.

7. The combination of claim 6, and frangible means securing said plate in place whereby upon breaking of said plate away from said securing means said button is freed for actuation in response to cut-out of said switch thereby requiring manual resetting of the switch.

Claims

2. The combination of claim 1, in which said manual reset means comprises a button spring biased outwardly of said switch and having a portion disposed to enter the space between the operative switch contacts to prevent said contacts from closing while said button is in an outward position.

3. The combination of claim 2, in which said removable means comprises a hold-down member engaging the face of said button and retaining the latter depressed to a position where said portion does not at any time interfere with the automatic closing of said switch contacts.

4. The combination of claim 2, and fixed means comprising a portion adjacent said button and extending outwardly beyond the face thereof when the button is in its depressed state with the switch contacts closed and providing for interference with resetting of the contacts to closed position upon opening of the contacts and movement of the button outwardly to a position wherein the face of the button has at least reached the general plane of the face of said adjacent portion.

5. The combination of claim 3, in which said hold-down means comprises a plate extending across the face of said button, and frangible means securing said plate in place whereby upon breaking of said plate away from said securing means said button is freed for actuation in response to cut-out of said switch thereby requiring manual resetting of the switch.

6. The combination of claim 4, in which said hold-down means comprises a plate removably secured across the face of said encircling portion of said mounting means and having a projection thereon engaging the face of said button and holding the same in a position freeing automatic resetting of said switch contacts.