US2388784A - Switch assemblage - Google Patents

Description

Nov. 13, 1945. w. c. FURNAS ET AL SWITCH ASSEMBLAGE Filed Oct. 14, 1943 5 Sheets-Sheet 1 IN V EN TORS Nov. 13, 1945., w. c. FURNAS ET AL 2,388,784

SWITCH ASSEMBLAGE Filed Oct. 14, 1943 5 Sheets-Sheet 2 36 y INJl/AHT/ON vl 1W Nov. 13, 1945. w c. FURNAS ET AL 2,388,784

SWITCH ASSEMBLAGE Fiied Oct. 14, 1943 3 Sheets-Sheet 3 Patented Nov. 13, 1945 SWITCH ASSEMBLAGE William C. Furnas, Batavia, Edwin B. Schumacher, Aurora,

and Roy S. Kercher, Naperville,

111., assignors to Furnas Electric Company, 'Batavia, 111., a partnership composed of Leto M. Furnas, William C. Furnas, Gilbert H. Hansen,

and Helen R. Hansen Application October 14, 1943, Serial No. 506,150

20 Claims.

The present invention relates in general to improvements in the art of electric current control and distribution, and relates more specifically to various improvements in the construction and operation of electric switch or controller assemblages.

The primary object of our invention is to provide a new and useful electric switch assembly which is simple in construction and efi'icient in operation.

Some of the more important specific objects of the present invention are as follows:

To provide an improved electrical control assemblage which is compact and durable in structure, and which is also relatively shock-proof in construction against high impact and accelerations of great magnitude.

To provide a sturdy electric switch mechanism all parts of which are amply protected against dangerous operating conditions such as shock and overloads, and which is adapted to effectively protect electric motors and other equipment controlled by the mechanism.

To provide an improved combined electric controller and thermal oyerload device, all elements of which are readily accessible for inspection or replacement, which is conveniently operable during normal use and to reset the overload device, and which is also adapted with minor alterations for either alternating or direct current usage.

To provide a shock and vibration resistant electric switch assembly which is not materially affected by variations in ambient temperatures, and wherein all relatively intricate parts are protectively confined within a moisture-proof enclosure.

To provide an improved manual motor controller having automatic acceleration operative upon restarting of the electrical system, either by resetting of a tripped overload device or during normal starting.

To provide an improved electric switch having simple and efficient overload tripping mechanism incorporated directly therein, which overload mechanism may be promptly reset by simple apparatus functioning independently of the main switch operating elements, and which apparatus is operable from the exterior of the switch enclosure.

To provide a simple and compact compensated thermal overload unit which can be manipulated so as to produce emergency operation of equipment controlled thereby, and which may be quickly adjusted to vary its operating characteristics and can also be rapidly reset after normalfunctioning thereof.

To provide an improved electric controller assemblage all elements of which can be readily manufactured, promptly and conveniently assembled or dismantled with ordinary tools, and which is safely operable and flexible in its adaptations.

To provide a unique combination of a rotary electric circuit controller, thermal overload device, and compensating relays, various improved features of which are applicable to either direct or alternating electric circuits so as to provide a relatively small, durable and inexpensive but extremely reliable circuit controlling assemblage.

To providea neat appearing electric controller assembly of maximum capacity but having small size and light weight, and which is especially adapted for efficient use under adverse conditions such as extreme shock, vibration, moisture, and temperature changes.

To provide an improved motor control switch mechanism adapted for most efficient variable speed operation of a motor or the like, and which automatically protects the motor against dangerous overloading.

To provide an improved thermal overload device which controls the main line contacts, and does not involve as great a change in ultimate tripping current as the ordinary solder pot unit, and which is therefore thoroughly compensated and more sensitive but rugged in structure.

These and other specific objects and advantages of our invention will be apparent from the following detailed description.

A clear conception of the several improved features constituting our invention, and of the mode of constructing and of manipulating a switch assemblage built'in accordance with the improvement may be had by referring to the accompanying drawings wherein like reference characters designate the same or similar parts in the various views.

Fig. l is a perspective view of one of the improved switch assemblages With one side cover removed so as to reveal the thermal overload device;

Fig. 2 is a similar perspective view of the same assemblage with the opposite side cover removed so as to reveal the accelerating contactor;

Fig. 3 is a part sectional somewhat enlarged view of the assemblage showing some of the normally concealed mechanism, the irregular section having been taken transversely through the main casing, controller shaft, and a portion of the switch contact housing;

Fig. 4 is a further enlarged bottom view of the switch contact housing with the end closure plate removed;

Fig. 5 is a likewise enlarged side view of the switch contact housing with the side closure plate removed;

Fig. 6 is an enlarged part sectional View of a solder pot type thermal overload unit, showing the solder pot disposed within a ceramic bobbin embraced by the heater coil;

Fig. 7 is a side elevation of the switch assembly with a portion of the cover broken away so as to reveal internal mechanism;

Fig. 8 is a plan view of the controller lever positioning mechanism; and

Fig. 9 is a Wiring diagram showing the improved switch and overload assemblage disposed within a two speed motor control circuit.

While our invention has been shown and described herein as being specifically embodied in a two speed switch comprising primarily a drum controller combined with a single thermal overload heating unit and an accelerating contactor and being especially adapted for direct current electric circuits, it is not our desire or intent to unnecessarily restrict the scope of the improvement or the application of the improved features to other types of electrical systems, since the invention has in fact been successfully embodied in both direct and alternating current assemblages.

Referring to the drawings, the improved electric switch assemblage shown therein by way of illustration, comprises in general a main rectangular casing I2 having removable opposite side covers I3 and a rigid supporting bracket I4; a switch contact board unit or housing I 5 suspended medially within the casing I2 and forming an enclosure for four sets of cooperating fixed and movable contacts A, B, C, D; a controller assembly consisting of a shaft I6 journalled for oscillation relative to the casing I2 and having rigid projections II, I8 cooperative respectively with parallel rods I9, 20 carried by the stems of the movable contacts of said sets; a thermal overload device confined within the casing I2 and comprising a movable slide or plunger 2I having an abutment 22 cooperative with the longer rod I9 to simultaneously open the movable contacts A, B under overload conditions, and being provided with a heating coil 23 coacting with a solder pot 24 having a ratchet wheel 25 coacting with pawl 26 carried by the plunger 2I; a push button 21 and bridge 28 cooperating with a lever 29 to close the contacts A, B and to reset the thermal overload device for emergency run purposes independently of the normal controller operating devices; and a compensating accelerating contactor 36 also confined within the casing I2 on the side of the housing I5 remote from the overload device.

The main casing I2 is preferably formed of Welded sheet-metal or other suitable material, and the covers I3 are attached to the casing I2 by cap-screws 3I having shake-proof lock washers, and coact with gaskets so as to provide moisture-proof seals; and the supporting bracket I4 may be welded or otherwise rigidly attached to the rear casing wall so as not to interfere with free application or removal of the side covers. The points of penetration of the casing I2 by the controller shaft I6 and push button 27, are also provided with moisture- proof seals 32, 33 respectively, thus positively preventing ingress of moisture even if the assemblage is submerged. The switch contact housing I5 may be su p nded within the normally sealed casing I2 in any suitable manner as by studs 34; and the controller shaft I6 besides being journalled for rotation or oscillation within the upper seal 32, has its lower extremity journalled in a thrust bearing 35 mounted on the casing bottom, see Figs. 1 and 7.

The switch contact board unit or housing I5 is-built up of rigid plates of fabric base laminated phenolic or similar insulating material adapted to withstand extreme shock and vibration, and the contact carrier rods or bars 36 are formed of special laminated arc-resistant insulating material, while the contacts A, B, C, D are preferably coated with silver. This built-up construction of the housing I5 from plate stock makes it possible to readily replace any of the housing plates of available sheet stock in cases of emergency, and the several plates are normally firmly interconnected by means of cap screws 31 and shake-proof lock washers so as to thoroughly confine and conceal all of the fixed and movable contacts A, B, C, D. The interior of the housing I5 is divided by arc-resistant insulating partitions 38 into several segregated compartments within which the several sets of fixed and movable contacts A, B, C, D are confined; and the movable contacts A, B have their carrier barss'ifi connected to the longer rod I9' for simultaneous actuation and are constantly urged toward closed position by coil springs 39, while the carrier bars 36 of the other movable contacts C, D are connected to separate or independent shorter rods 26 for independent actuationQand the movable contacts D are constantly urged toward closed position by another coil spring 39 but the movable contacts C are constantly urged toward open position by a similar spring 46 coacting with a cushioning spring 4| which provides contact pressure and floating action when 40 the contacts C are closed, see Fig, 4. The fixed 7 spring 49.

contacts of the several sets are all firmly secured to the adjacent plates of the housing I5 and are provided with terminal connectors 42.

As previously indicated, the controller assembly comprises an oscillatory upright shaft I6 having rigid fingers or projections II, I8 which are cooperable respectively with the parallel rods I9, 26 carried by the movable switch contact stems 36; and the outer end of the shaft I6 is provided with an actuating lever 43 having a manipulating knob 44 at one end and ,a counterbalancing weight 45 at its opposite end for preventing the handle from changing position due to shock. The upper portion of the controller shaft I6 directly beneath the moisture-proof journal seal 32, is also provided with indexing or positioning mechanism such as shown in Figs. 1, 7 and 8, and this mechanism is confined within the casing I2 and consists of a notched cam 45 secured to the shaft I6 and the several notches of which are cooperable with a roller 46 carried by'the medial portion of a retaining lever 41 one end of which is fulcrumed on a pivot pin 48 secured to the casing I2, and the opposite end of which is constantly urged toward the shaft l6 by a tension The cam notches and spring biased lever 41 of this indexing mechanism are adapted to hold the shaft I6 in either high or low speed, or in off position, and the several fingers or projections l1, l6 are formed of durable fabric base laminated phenolic insulating stock and have square holes snugly embracing the square medial portion 56 of the shaft I6, the plates being properly positioned along this shaft by laminated phenolic spacing collars and a clamping nut 52, see Figs. 1, 3 and 7.

The thermal overload unit or device which is mounted on one of the side plates of the contact housing I5, is shown in Figs. 1, 3, 6 and 7, and comprises a reciprocable slide or plunger 2| having two spaced abutment plates 22 secured thereto and cooperable with the longer rod L! to simultaneously open the sets of movable contacts A, B when excessive overloading occurs. The reset slide 2| and the abutments 22 are formed of durable shock-proof and temperature resistant insulating material, and the slide 2| is guided in a block 53 and has a lateral arm 54 which coacts with a compression spring 55 constantly tending to push the slide 2| toward the right as viewed in Figs. 3 and 7. The heating coil 23 of the improved thermal overload device is interposed in the line between the contacts B and C and embraces a heat-conducting bobbin 56 formed of ceramic material which is resistant to heat changes and mechanical shock, and this bobbin 56 loosely surrounds the solder pct 24 with minimum air gap, and is suspended from a wire yoke 51 carried by a heat resistant insulating plate 58 formed of mica or the like. The supporting plate 58 is slidably adjustable along the block 53 so as to shift the bobbin 56 along the solder pot 24, by means of a clamping bolt 59 coacting with an elongated hole in the plate 58, see Fig. 6. The ratchet wheel 25 which normally coacts with the pawl 26 carried by the slide 2|, is formed integral with the solder pot 24, and snugly embraces a fixed stub pin 60 which is rigidly secured to a supporting block 6| and is provided with several grooves 62 containing high melting eutectic solder fused to the pct 24 which also coats the pin, and the solder pot 24, and ratchet wheel 25 are fixed against axial movement by a retainer 63, while the coil ends are connected to the line by flexible pig tails 64. v

The overload assemblage is obviously such that when the slide 2| is set and normal operating conditions prevail, the solder pot 24 will be fused or soldered to the fixed stub pin 60 thus holding the ratchet wheel 25 fixed, and the pawl 26 engages the wheel 25 and thus holds the slide 2| so as to compress the spring 55; but when the coil 23 is heated by an overload, sufficiently to melt the solder in the grooves 62, then the solder pct 24 becomes freely rotatable upon the pin 60 and the spring 55 quickly becomes effective to move the slide 2| and the abutment 22 so as to open the movable switch contacts A, B. When the overload condition subsides and the coil 23 cools, the solder again quickly solidifies and firmly units the solder pot 24 and pin 65, whereupon return of the slide 2| to set position will again cause the resilient pawl 26 to engage the teeth of the ratchet wheel 25 and placing the spring 55 under compression preparatory to subsequent automatic release by overloading.

The slide 2| and abutments 22 may be quickly returned to set condition by means of the push button 21 coacting with the lever 29 and bridge 28. As previously indicated, the push button 21 is slidable in the moisture-proof seal 33 and coacts with the mid-portion of the lever 29, and the bridge 28 coacts with the lever 29 in line with the button 21 and reacts at its opposite ends against compression springs 65, see Figs. 3 and 7. When only one thermal overload unit and slide 2| is employed, one end of the lever 29 may be fulcrumed beneath a strap 66 secured within the casing 2, thus causing the opposite end to move toward the adjacent end of the slide 2| when the button 21 is pressed. The springs will urge the button 21 outwardly when released. In cases where the overload conditions are of short duration and the solder pot 24 is quickly re-connected to the stub pin 66, mere pressing and release of the button 21 will restor the switch assembly to normal condition; but if the overload condition continues for some time, the button 21 may be pressed and held down to provide for emergency operation of the motor. After the overload has ceased and the solder has resolidified, the overload device can again be reset or restored to normal position. After the overload device has been reset, the movable switch contacts are all free to be actuated by the shaft l6 and actuating lever 43, and it is to be noted that the button 21 functions independently of the controller and its projections |1, |8 to close the contacts A and B when the controller handle is in either low or high speed position. The accelerating contactor 30 is mounted on the side of the switch contact housing, remote from the thermal overload device, and comprises an electromagnet coil 61 and a flapper armature 68. The construction and operation of thes relays is well known to those skilled in the art, and when the improved switch assembly is utilized to control the operation of a two speed direct current motor 69 having a series field 10 and a shunt field 1|, and which is normally supplied with current from a main supply line 12, the circuit should be provided with suitable resistors 13 as shown in the wiring diagram of Fig. 9.

During normal operation of the improved electrical system and switch, in order to start the motor 69 themain operating handle 44 and lever 43 may be turned from ofif position to either high or low speed position, thus closing the movable contacts A, B, C. When the switch is set for low speed motor operation, the shunt field resistor 13 is shorted out by the contacts D; but when set for high speed operation of the motor 69, the movable contacts D are opened to provide a i weakened motor field. The contactor 30 with its coil 61 and flapper armature 68, provides automatic acceleration, and this contactor 30 closes to short out the starting resistor and automatically places the motor 69 directly across the line,

after the voltage across the armature has reached a predetermined value. The motor 69 will stop either when the handle 44 and lever 43 are returned to off position, or if the thermal overload unit trips, or if the power fails. When the thermal overload unit trips, the reset emergency button 21 may be pressed to restart the motor 69, and in case of continued overload, the reset emergency-run button 21 may be held depressed as long as emergency running of the motor is necessary. When voltage fails, the motor 69 will restart immediately upon rc-establishment of the power, and in all cases the acceleration is en tirely automatic. As previously indicated, the improved switch can be produced for either direct 0r alternating current operation, the primary difference being the provision of two double thermal overload devices when used for alternating current. The accelerating contactor is also omitted when operating with alternating current and a greater number of main contacts are provided.

From the foregoing detailed description of the construction and operation of our improved switch assembly, it will be apparent that our invention provides improved electric switch mechoverloading, and moisture? and all elements of the structure while being normally thus protected, are still readily accessible for inspection, renewal, and adjustment. As a protection against shock and vibration, the various parts are specially mounted, connected with shake-proof fasteners, and properly counter-balanced, as well a being formed of stock-resistant materials, As a further protection all elements are amply insulated; and while the improved overload device will normally trip and stop the motor under overload conditions, this overload unit is constructed to withstand severe overloading and to permit emergency operation of the motor 69 with the aid of the push button 21. As a protection against excessive moisture, the contacts and other relatively intricate mechanism are effectively housed and concealed within a water-tight enclosure and the improved switch is adapted to actually be operated without danger while submerged. The improved structure i also adapted to automatically compensate for variations in the ambient temperature, and the overload unit is compensated so that it does not require much change in tripping current due to ambient temperature changes, this compensation being efiected by the use of high melting alloy; and by adjusting the heating coil 23 alon the solder pct 24, the operating characteristics of the overload unit may be quickly varied. It is to be noted that the thermal overload device will operate to open the movable contacts A, B regardless of the previous setting of the controller shaft I6, and this controller shaft may be'retained in running position when it is desired to effect emergency operation of the motor while under overload conditions. The pawl 26 may also be positioned so as to insure proper cooperation with the ratchet wheel 25, and these adjustments may be efiected and the mechanism may be quickly assembled or dismantled with ordinary tools such as a screw driver or pliers. Most of the elements of the assemblage may also be produced from relatively standard materials and with relatively few special tools, and the invention has proven highly satisfactory and successful in actual use.

It should be understood that it is not desired to limit this invention to the exact details of construction, or to the precise mode of operation and use, herein shown and described, for various modifications within the scope of the appended claims may occur to persons skilled in th art.

We claim:

1. In combination, a casing, a controller shaft journalled for oscillation within said casing and having local outwardly projecting fingers, a contact housing disposed within said casing and having therein movable contacts normally operable by said fingers, a thermal overload device disposed within said casing and having a slide for opening some of said movable contacts under overload conditions, and means for resetting said slide independently of said controller shaft to release said movable contacts for free closing. I

2. In combination, a casing, a controller shaft journalled in said casing and having a counterbalanced actuating handle and outwardly projecting fingers, a switch contact housin suspended within said casing and having therein movable contacts provided with rods with which said fingers are normally cooperable to open said contacts, and a thermal overload device mounted upon said housing within said casing and having a slide cooperable with one of said rods to automatically open the corresponding movable contacts.

3. In combination, a casing, a controller shaft journalled in said casin and having a counterbalanced actuating handle and outwardly projecting fingers, a switch contact housing removably suspended within said casing and having therein movable contacts provided with rods with which said fingers are normally cooperable to open said contacts, a thermal overload device mounted upon said housing within said casing and having a slide cooperable with one of said rods to automatically open the corresponding movable contacts, and means for resettin said slide and for effecting closing of said movable contacts independently of said controller shaft.

4. In combination, a continuous rectangular casing having opposite side openings, an upright oscillatory controller shaft journalled in the top and bottom of said casing and having outwardly projecting fingers oscillatable within the casing, a switch contact housing confined within said casing laterally of said shaft and between said openings and having therein movable contacts cooperable with said fingers to move the contacts, an overload tripping device mounted upon said housing adjacent to one of said side openings, and an accelerating contactor mounted upon said housing adjacent to the Other of said side openings, said device and said contactor being connected in the electric circuit controlled by said contacts.

5. In combination, a continuous rectangular casing having opposite side openings, an upright oscillatory controller shaft journalled in the top and bottom of said casing and havin outwardly projecting fingers oscillatable within the casing, a switch contact housing confined within said casing laterally of said shaft and between said openings and having therein movable contacts cooperable with said fingers to move the contacts. an overload tripping device mounted upon said housing adjacent to one of said side openings, an accelerating contactor mounted upon said housing adjacent to the other of said side openings, said device and said contactor being connected in the electric circuit controlled by said contacts, and means for resetting said device after tripping thereof independently of said shaft.

6. In combination, a shaft mounted for oscillation about a fixed axis and having outwardly projecting fingers, a switch contact housing disposed laterally adjacent to said shaft and having therein movable contacts provided with supporting stems slidable toward and away from said shaft, parallel contact actuating rods carried by said stems and coacting with said fingers to permit normal movement of said contacts by oscillation of said shaft, anda thermal overload device having a slide cooperable with one of said rods to automatically open the correspondin movable contacts under abnormal conditions.

7, In combination, a shaft mounted for oscillation about a fixed axis and having outwardly projecting fingers, a switch contact housing disposed laterally adjacent to said shaft and hav ing therein movable contacts provided with supporting stems slidable toward and away from said shaft, parallel contact actuating rods carried 2,388,784 by said stems and coacting with said fingers to permit normal movement of said contacts by oscillation of said shaft, 9, thermal overload device having a slide cooperable with one of said rods to automatically open the corresponding movable contacts under abnormal conditions, and means operable independently of said shaft and fingers for effecting resetting of said slide after actuation of said device and while the circuit is still overloaded.

8. In combination, an oscillatory shaft having counter-balanced actuating means and fingers radiating from the shaft axis on opposite sides of-a plane containing said axis, parallel rods disposed on the opposite sides of said plane and with which said fingers are cooperable when said shaft is oscillated, sets of switch contacts movable by said rods, and a thermal overload device cooperable with one of said rods to open the corresponding switch contacts under abnormal conditions.

9. In combination, an oscillatory shaft having counter-balanced actuatin means and fingers radiating from the shaft axis on opposite sides of a plane containing said axis, parallel rods disposed on the opposite sides of said plane and with which said fingers are cooperable when said shaft is oscillated, sets of switch contacts movable by said rods,'a thermal overload device cooperable with one of said rods to open the corresponding switch contacts under abnormal conditions, and means operable independently of said shaft and fingers for effecting emergency closing of said contacts after said device has operated to open the same.

10. In combination, an oscillatory shaft having fingers projecting therefrom on opposite sides of a plane containing the longitudinal shaft axis, parallel rods disposed on opposite sides of said plane and parallel to said axis and with which said fingers are alternately cooperable when said shaft is oscillated in opposite directions, sets of switch contacts disposed on opposite sides of said plane and having slidable stems connected to and movably by said rods, and a thermal overload unit having a slide releasable under abnormal conditions to coact with one of said rods and to open the corresponding movable contacts.

11. In combination, an oscillatory shaft having fingers projecting therefrom on opposite sides of a plane containing the longitudinal shaft ax s, parallel rods disposed on opposite sides of sa d plane and parallel to said axis and with which said fingers are alternately cooperable when said shaft is oscillated in opposite directions, sets of switch contacts disposed on opposite sides of said plane and having slidable stems connected to and movable by said rods, a thermal overload unit having a slide releasable under abnormal conditions to coact with one of said rods and to open the corresponding movable contacts, and means operable independently of said shaft and fingers for moving said slide to close said contacts after operation of said overload device.

12. In combination, an oscillatory shaft having oppositely extending outwardly directed fingers, rods disposed parallel to the shaft axis and being movable by said fingers, movable switch contacts having reciprocable stems secured to said rods, and an overload device cooperable with one of said rods to open the corresponding contacts independently of said shaft and fingers.

13. In combination, an oscillatory shaft having oppositely extending outwardly directed fingers,

rods disposed parallel to the shaft axis and being movable by said fingers, movable switch contacts having reciprocable stems secured to said rods, an

overload device cooperable with one of said rods to open the corresponding contacts independently of said shaft and fingers, and means for closing said corresponding contacts independently of said shaft and fingers and while the overload condition still prevails.

14. In combination, several sets of movable switch contacts resiliently biased toward closed position, actuating means for normally opening said contacts, a slide resiliently biased to open said contacts under overload conditions, a solder pot having a toothed wheel disposed near said slide, a pawl carried by said slide and being cooperable with said wheel to normally retain said slide in inactive position, a heating coil coacting wtih said solder pot to release said pawl from said wheel, and means for effecting adjustment of said coil relative to said pot to vary the operating characteristic of the latter.

15. In combination, several sets of movable switch contacts resiliently biased toward closed position, actuating means for normally opening said contacts, a slide resiliently biased to open said contacts under overload conditions, a solder pot having a toothed wheel disposed near said slide, a pawl carried by said slide and being cooperable with said wheel to normally retain said slide in inactive position, a heating coil coacting with said solder pot to release said pawl from said wheel, means for effecting adjustment of said coil relative to said pot to vary the operating characteristics of the latter, and means for resetting said slide and pawl into inactive position independently of said actuating means.

16. In combination, several sets of movable switch contacts spring biased toward closed position, manually operable means for normally opening said contacts, a reciprocable slide spring biased to open said contacts under overload conditions, a fixed stub shaft, a solder pot embracing and normally fixed to said shaft and having a toothed wheel disposed adjacent to said slide, a pawl carried by said slide and normally engaging said wheel to hold the slide in inactive position, a helical heating coil mounted upon a bobbin slidably embracing said pot, and means for effecting adjustment of said bobbin along said pot to vary the heating effect of said coil.

17. In combination, several sets of movable switch contacts spring biased toward closed position, manually operable means for normally opening said contacts, a reciprocable slide spring biased to open said contacts under overload conditions, a fixed stub shaft, a solder pot embracing and normally fixed to said shaft and having a toothed wheel disposed adjacent to said slide, a pawl carried by said slide and normally engaging said wheel to hold the slide in inactive position, a helical heating coil mounted upon a bobbin slidably embracing said pot, means for effecting adjustment of said bobbin along said pot to vary the heating effect of said coil, and means operable independently of said manually operable means for closing said contacts after release of said slide.

18. In combination, movable switch contacts biased toward closed position, means for normally manually opening said contacts, a reciprocable slide biased to open said contacts under overload conditions, a fixed stub shaft, a solder pot embracing and normally fixed to said shaft and having a toothed wheel, a pawl carried by said slide and normally engagingvsaid 'wheel to hold the slide in inactive position,a helical heating coil surrounding and spaced from said pot, anda ceramic heat-resistant bobbin substantially filling the space between said coil and said pot.

19. In combination, movable switchcontacts, a

slide biased to open said contacts only under ,overload conditions, a solder pot normally fixed against rotation and having atoothed wheel, a pawl carried bysaid slide and normally coacting with said wheel to hold the slide in inactive position, a helical heating coil surrounding said pot and being separated therefrom by an annular space, and a ceramic heat-resistant bobbin substantially filling said space.

20. In combination, movable switch contacts, a

slide biased to open said contacts only under over-

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