US2200509A - Disconnecting switch - Google Patents

Description

y 1940. w. H. LINDAE DISGONNECTING SWITCH 2 Sheets-Sheet 1 Filed March 30, 1936 May 14, 1940. w. H. LINDAE 2,200,509

DISCONNECTING SWiTCH Filed March 50, 1936 2 Sheets-Sheet 2 IN VENTOE Wf/flam L/ndae.

HTTOENEY I Patented May 14, 1940 UNITED STATES PATENT OFFICE 11 Claims.

This invention relates generally to electrical switching apparatus and has more particular referenceto disconnecting switches of the swingable blade type for engaging or disengaging fixed or stationary poles or contact-members for, respectively, making or breaking the electrical circuit. 4

It is known that contact resistance is a function of pressure and not of area; and that by decreasing the contact-area to a point or a line and increasing the pressure, greater contact efliciency is obtained. Nevertheless, high contact pressures produce difliculty in switch operation. Moreover, the limited contact surface which accompanies point contact area necessarily occasions relatively high temperature at the point of contact, which must, of course, be dissipated through the metal-work of the switch structure.

My present invention has for its prime object the provision of a disconnecting switch employing a point contact between the blade and the pole or poles of the switch and having superior current carrying characteristics obtained by employing low resistance contact elements of unique formation in conjunction with ample thermal radiating surface for dissipating heat from the switch structure.

My invention has for another object the provision, in a disconnecting switch of the type stated, of a novel structure for the connection of the switch elements to the bus or line, so that, contrary to present general practice, it is unnecessary to carefully prepare the contact surthe provision of a disconnecting switch of which both the moving and stationary operative parts may be readily disassembled from thebase or frame of the switch without necessitating the dismantling of the switch base from its support or from the associated busses and line structures, a feature found to be particularly useful and economical in the installation and maintenance of both indoor and outdoor disconnecting structures.

My invention has for a still further object to generally improve upon, and reduce the cost of manufacture, installation, and maintenance of, disconnecting switches of the type stated.

And with the above and other objects in view, my invention resides in the novel features of form, construction, arrangement, and combination of parts presently described and pointed out in the claims.

In the accompanying drawings (two sheets) Figure l is a top plan view of a single pole single throw disconnecting switch embodying one form of my invention, the insulation supports and the bus-bars or line terminal connections being shown by dot-dash lines;

Figure 2 is a side elevational view, partly, broken away and in section, of the switch of Figure 1;

Figure 3 is an enlarged fragmentary side elevational view of the latch end of the swingable blade and its associated stationary contact-post, other parts of the switch structure being omitted and the blade being shown in opened position, that is, disengaged from the contact-post;

Figure 4 is a fragmentary sectional view through the latch-structure, taken approximately along the line 4-4, Figure 2;

Figure 5 is a disassembled perspective broken view showing one of the blade-arms, the latch carrying bracket, and one of the filler-plates associated therewith; 4

Figures 6, 'I, and 8 are, respectively, enlarged fragmentary side elevational views of modified forms of the contact post constructions;

Figure 9 is an enlarged detail side view of one of the bell-crank latch members;

Figure 10 is a reduced side elevational view of a single pole double throw disconnecting switch embodying another form of my invention;

Figure 11 is a top-plan view of a single pole single throw multiple contact disconnecting switch also embodying my invention, this form of the switch being similar to that of Figure 1, the

supporting structure and terminal connecti'ons proved switch construction; and

Figure 13 represents a series of fragmentary sectional views of various modified forms for providing low resistance contact areas in the switch structure.

Referring now more in detail and by reference characters to the drawings, which illustrate practical embodiments of my invention, A, in Figures 1 and 2, designates a disconnecting switch of the front connected type especially, though not exclusively, adapted for indoor or switchboard mounting, I and 2 being the pair of spaced insulator stands or supports common in such constructions, as well known to those skilled in the art.

My new switch structure includes a pair of spaced base or terminal plates 3, 4, each, respectively, mounted on a corresponding insulator stand I, 2, by'suitable fastening means, as bolts 5, 5.

The plates 3, 4, which are each formed of a suitable conductive material, as copper or the like, are respectively provided with an extension 6, which projects rearwardly, as it may be said, in the case of the plate 3 and forwardly for the plate 4, from the corresponding insulator sup- D rt I, 2, each extension 6 being provided with an aperture 1 for receiving a suitable fastening element in the form preferably .of a bolt 8, by means of which there may be attached to the plate 3, or 4, the corresponding terminal of the circuit served by the switch, as, for example, the bus-bars 9, H1, or the like.

Disposed in each extension 6 around its aper-'- ture I, is a series of, in the present instance three, contact plugs I I of relatively small diameter or area and formed of a suitable highly conductive material whose oxide is preferably also conductive, as silver or the like.

The plugs II are welded or otherwise attached to, or inset into, one or both faces of the extension 6 and project outwardly therefrom a small distance, so that, when the particular bus-bar is mounted on the terminal-plate, the plugs H will be compressed therebetween for establishing a substantially small contact area under heavy pressure, a type of electrical joint construction having the characteristics of high current carrying capacity with low resistance losses.

In contrast to the usual and, so far as I am aware, heretofore necessary, laborious work and painstaking caretaken to insure perfectly flat contact surfaces between the conducting members to be connected, it will be seen that, in my construction, a highly efficient electrical joint connection may, with the greatest of ease and facility and with minimum expenditure of time and labor, be readily formed in the field during the installation of the switch or other structure.

Threaded or otherwise fixed at their respective lower ends into, and upstanding from, the respective plates 3, 4, are preferably cylindrical conducting posts l2, l2, each provided at its upper end with a switch-contact i3 having a balllike, spherical, or other suitable arcuate surface conformation. In practice, the contact-member I3 is mounted on a reduced upwardly presented section M of the particular post and secured, thereto for axial or rotatable shiftable movement by means preferably of a round-head machine screw I5, as shown.

The arcuate or spherical members I3 preferably form the stationary contacts of the switch A, as will presently more fully appear, and it is to be particularly here pointed out that the members iii are each provided with a silver surface coating or otherwise formed, as will presently'appear, for reducing their surface resistance losses.

Further upstanding from the plate 3 intermediate the posts I2, i2, and having foot-lugs i6 engaged by means of suitable fastening elements in the form of screws IT with the plate 3, is a hinge-post I8 carrying at its upper or free end a transverse pintle 0r fulcrum-pin l9.

Upstanding from the plate 4 adjacent to, but disposed outwardly from, the post I2, similarly having lugs 20 engaged by means of screws or other suitable fastening elements 2! with the plate 4, is a latch-post 22 carrying a forwardly and downwardly turned detent or bill 23 and having a pair of opposing lateral lugs or ears 24 disposed flush with its upper or free end.

The swingable contact-member of the switch A includes a pair of laterally spaced registering parallel members in the form preferably of bars 25 having plane surfaces and constructed of suitable conducting material, as copper or the like, the bars 25 being pivotally mounted, each intermediate its ends, on the respective opposite ends of the fulcrum-pin i9, which for such purpose, pro- .iects suitably from the respective opposite sides of the post l8.

The bars 25 are adapted at their relatively short rear end-portions for simultaneously embracing and fiatwise slidingly engaging and disengaging diametrically opposite points on the arcuate or spherical member [3 on the post l2 and at their relatively long front end-portions for simultaneously embracing and flatwise slidingly engaging and disengaging diametrically opposite points on the arcuate or spherical member 13 that is mounted on the post l2.

Since the contact-members II are of arcuate or spherical contour and the bars 25 have fiatwise engagement therewith, there ensues a substantially point contact between the members l3 and 25, which, as has been said, provides a highly efficient electrical joint connection.

For furthering or increasing the efficiency of the contact between the members 13 and 25, each of the members 25 is provided, at or adjacent its respective opposite ends, with a surface coating or with an insertedplug 26 of highly conductive material, as silver or the like, disposed in the path of contact of the bar 25 with the spherical mem- 'ber l3, and, since the latter. is likewise coated with a silver plating or the like, the contact resistance is, therefore, reduced to a minimum.

However, a point contact joint of this kind must be accompanied by pressure for realizing its best effects. Accordingly, at the hinged end of the pair of bars 25, there is provided on the respective opposite ends of the pintle IS a pair of spring-cup washers 21 for bearing on the respective flat outer faces of the bars 25, suitable nuts or similar screw members 28 being threaded on the respective outer ends of the pintle IQ for drawing the washers 21 into compressive bearing upon the bars 25, whereby, in turn, the latter may, with ease and facility, be tensionally biased or adjustably compressed upon the contact-memher I! on the post l2.

At the same time, the employment of a pair of the bars 25, each taking half the current from or to the respective members l3, provides twice the thermal radiating surface that would be provided by a single blade type of switch of the same current rating, whereby it readily becomes possible, as I have done, to employ a point contact under pressure without appreciable rise in temperature of the switch structure and makes it highly feasible and practicable to employ such a switch successfully in indoor service.

At the swingable end of the pair of bars 25, there is provided a transverse pin 29, likewise A, which includes a U-shaped bracket 30 disposed I in horizontal outwardly open position between the free ends of the bars 25. The bracket 30, at each of its legs or ears is registrably apertured to receive the pin 29 and is further provided with a pair of small apertures 3I for reception of corresponding positioning pins 32 projecting from the inner face of the abutting bar 25.

The bracket 30, at the upper marginof its bightor transverse portion is forwardly extended or flanged to provide a ledge or stop-member 33, between which and the adjacent legs of the bracket 30 are slots 34 for-the reception of respective bills 35 projecting rearwardly from the upper margin of filler-plates 35 disposed flatwise with respect to the legs of the'bracket and also apertured, as shown, for the-pin 29 and positioning pins 32.

The latch members proper comprise a pair of reversible companion bell-cranks '31, 33, each including a normally 1 forwardly.- extending: leg

equipped with abowed handle 39, 'and a more or less normally vertically disposed leg having a rearwardly extendingllugf or spring support 4 I,

the cranks 31; 38 being pivotallymounted on the pin29 in reversed, interflttin'g relationship after the manner, of a pairof scissors, that is to say, the cranks 31, 38', areof substantially similar contour and of fullwidth-throughout their extent, except at their hub, as at '31, and again at their respective free ends, as at 38', for permitting such nested or interfitting relationship, the handle-members 39 being adapted to overlap each other at all times, so that a well defined but expansible eye or aperture, as at 42, is formed therebetween for entry of a hook-stick (not shown), for operating the latch in the customary manner, the overlapping relationship of the members 39, however, acting to preserve the continuity of thewalls of the expansible eye 42 for preventing accidental dislodgement of the hook- 'also having a stop-shoulder 45, fora purpose shortly appearing.

Additionally, the leg 40 of the crank 31 is equipped with a depending latch-arm 46 having a rearwardly turned catch or bill 41, which, when 1 the bars 25 are engaged with the contact-members I3, is adapted, under bias of the spring 43, to snap under and latchlngly engage the detent or bill 23 of the latch-post 20 for releasably retaining the switch A in closed position, the

shoulder 45 on the lug M of the crank 38 meanwhile abutting the stop 33 of the mountingbracket 30. t

In use and operation, the switch being in closed position as in Figures 1 and 2, a hook-stick of the customary form is thrust into the latch handle opening 42, and a pull is exerted on the handle 33 of the latch-crank 31, causing the same to rotatively shift on the pin 29 until the crank 31 engagesthe stop 44 on the crank 38 for releasing the bill 41 from the latch-post 20, whereupon the members 25 may be swung upwardly and away, and for disengagement, from the contact-member I3 on the post I2, as shown in Figure 3, for rupturing or breaking the circuit with which the switch A is associated, the members 25 preferably being swung to a right angular position, as shown by dot-dash lines in Figure 2.

Not merely the latch mechanism, however, but

' also the switch-structure as a whole, is characterized by the ease and facility with which repairs may be made and the manner in which the maintenance of the switch maybe effected in a simple' and facile manner.

For example, those parts of the switch which are mounted on the plates 3, 4, mayreadily be removed therefrom without dismantling the supporting structure of the switch or disassembling the same from the bus-bars to which they are connected; even so, the plates 3, 4, may readily be removed and replaced without destroying the efficiency of the joint connection between the plates and the busses.

I Likewise, new bars 25 may be installed, and the balls ,or' members I3 may be removed and replaced, without impairing the current carrying capacities ofa'the switch,- and, in general, the entire switchistructurepossesses a high degree of accessibility and ease of replacement of its several parts greatly conducive. to the economical use.-

thereof.

For closing the switch A, the hook-stick is again insertedin the aperture 42'and engaged with the crank 33 for pushing the bars 25 until the members 25 rest on the lugs 24 of the latch- It will be seen that the latch mechanism of the switch comprises relatively few parts, the cranks 31, 38, being made or constructed from merely a single pattern, if desired, and therefore inexpensively produced. The simple and rugged construction favors a minimum maintenance attention and expense, and repairs, when necessary, may be effected with faciilty and dispatch.

As has been said, for aiding in reducing the resistance losses at the point contact between the arms 25 and the contact-members I3, the latter are preferably surface-plated with a silver coating. As an alternate, the contact-members I3 may be provided with a circumferential inserted collar 48, asshown in the contact-member I 3a of Figure 6; or with a circumferentially'spaced series of diametrically opposite pairs of silverplugs or the like 43, as in the contact-member I3b of Figure 7. l

Again, for increasing the amperage of the switch, the contact-supporting post, as 1211, may be modified to permit the mounting thereon of two or more segmental spherical members, as, for example, the members I3, I 30, of Figure 8, the swingable bars of the switch (not shown), then being suitably widened. and their cross sectional area correspondingly enlarged, for simultaneously engaging the pair of contactmembers I3, I30, when-the switch is in closed position.

As a result 'of repeated operations of the switch A wear will, of course, occur in the stationary contact-members through the sliding engagement therewith oi the bars 25. When wear.becomes excessive, the efliciency of the contact between the contact-members I3 and 25 may be readily restored by simply loosening the screws I5, which will permit rotative shifting of the stationary contact-members until an unworn surface is presented to the members 25, the stationary contact-members being then rigidly positioned on their respective supporting posts by a tightening of the screws I5. I :The same procedure may be easily followed in the case of the contact-members Ila and I30, while, in the ease of thecontact-member I3b, it will be obvious that, by 'sufliciently rotating the member, successive diametrical pairs of the inserts 49 may be selectively presented to the members 25 from time to time, as circumstances may require.

In the bar member 25, also, the silver inserts 26 may take various forms, more especially in the respect that such plugs 26 may be provided on both sides of the bar 25, as at 26a in Figure 13; again, instead of the plug form of insert, a silver disc 26b may be plated, welded, or otherwise fixed on one or both sides oi! the bar 25, or a silver rivet, having flattened heads, as at 260 in Figure 13, may be provided, as may best serve the intended purpose, all such several forms of silver contact-surfaces permitting the mere reversal of the bar 25 for restoring the efficiency of the contact surface when the same is impaired by wear.

In Figure 10 is illustrated a modified form of .double throw switch A. In its essential details,

posed oftwo of the cranks 31, so that, in either of the opposite positions of the swingable contact-member, a latch-arm 46 will be available for latching engagement with the corresponding latch-post. Though not specifically here shown, it will be understood that the stop 30 of the latchbrackets is eliminated to permit unlatching movement of either of the cranks 31 as occasion may require.

Also the bars 25' constituting the swingable contact-member are each provided with an additional silver contact 26', in order that the bars 25' may have engagement with the stationary contact-member I3 adjacent the hinge pin I9 '01 the switch in either of the alternate positions thereof.

- The use and operation of the switch A is, with obvious modifications, substantially similar to that of the switch A.

In Figure 11 is illustrated a so-called double switch, that is to say, a switch including duplicate pairs of switch elements or bars 25", each generally similar to the bars 25 of the switch A, the pairs of bars 25" being mounted side by side for parallel connection in an electrical circuit for affording a switch A" of twice the current carrying capacity of the switch A.

In this case, the switch construction is modified in an obvious manner to provide merely a single latch-post, not indicated, but similar to the latch post 20 of the switch A. Merely one bracket 30 and pair of fillers 36 are employed and are disposed intermediate the inner opposing bars of the respective pairs of bars 25" of the switch structure.

For such purpose, the pins 29 of the switch A are here replaced by an elongated pin 29', which extends through all four of the bars 25", and a filler block 50 is mounted on the pin 29' between each pair of the bars 25".- Spring washers 21 are mounted against the outer faces of the outer bars 25", as in the switch A, but the other washers 21 are disposed against the inside face of the inner bars 25", as will be readily seen by an in spection of Figure 10.

. The switch A" is, likewise, in use and operation, substantially similar to the switch A, hereinbefore described.

A so-called air-break horn-gap type of switch A, suitable for use as an outdoor disconnecting switch,-is shown in Figure 12. Switches of such typet'are commonly mounted in elevated positions and are operated from the ground for disconnecting the line while under potential, while indoor disconnecting switches, as on switchboards and the like, are commonly protected by oil-switches or similar devices and are not opened or closed when under line potential.

My new switch construction is particularly adapted for cutting out a line when under poten-,

tial, especially, as has been said, in outdoor service. As here shown, the switch A' comprises three spaced insulator-stands 52, 53, mounted on a suitable base, not shown, but as will be readily understood by those familiar with the art.

The insulator 5| is the rotor stand and carries the rotor bearing 54 in which turns the customary operator-shaft which is, as has been said, commonly operated from the ground and serves to rotate the operator crank 55, the latter, in turn, through a link 56, being connected to a bracket 51 mounted-between the bars 25' of the switch A', which bars 25" correspond in all essential details to the bars 25 of the :switch A.

The stand 52 carries the hinge structure of the switch. The terminal plate 3', in this instance, extends from the stand 52 to and over the stand 5|, and at its extreme end is formed with the terminal portion 8, as hereinbefore described. Similarly, the plate 3' carries the terminal post I2 with its ball-contact I3 and the hinge-post I5, with its pintle I9, on which the bars 25" are pivotally mounted, all, together' with their appurtenant members, being similar in form and function to the like elements or members of the switch A.

The stand 53 supports the plate 4', with its extension 5 and supported contact-post I 2, ball I3, and associate parts, but in place of the latchpost of the switch A, there is mounted on the plate 4 an upstanding stationary arcing horn 58.

On the swingable end of, and between, the bars 25', there is mounted a block 59 carrying a so-called movable arcing horn 60 adapted for co-operation with the born 58 for breaking the are when the switch is opened, as is usual in such installations.

In use and operation, the switch A' does not depart materially from that of the usual form of air break horn-gap switch. It is to be particularly pointed out, however, that my switch construction is highly advantageous in service, inasmuch as, firstly, the need of pigtails or flexible leads is entirely eliminated, and, secondly,

the wiping contacts between the ball I3 and the pair of bars 25" at both ends thereof serve to preserve and maintain the cleanliness and effectiveness of the electrical joints made thereby, thusavoiding, also, the need of sleet-hoods and the like.

It may be added that the respective bars 25 are preferably formed, as best seen in Figures 3 and 5, upon their inner face with oppositely disposed arcuate slots or ways, as at I5, opening upon a side edge of the blade and leading 'to the re spective inserts 2.6 for facilitating non-resistant electrical connection between the bars 25 and contact-members I3, and it will be understood that changes and modifications in the form, construction, arrangement, and combination of the several parts of my switch construction may be vmade and substituted for those herein shown and described without departing from the nature and principle of my invention.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In an electrical switch, in combination, a spherical contact-member having a low resistance conducting surface coating, a second contact-member comprising spaced rigid blades for embracing the spherical member, the blades being each provided with an inwardly presented ,arcuate recess open at its lower end, and low resistance conducting elements mounted on the blades at the upper end of the respective recesses for electrically engaging the surface coated spherical member.

7 2. In an electricalswitch, in combination, a pair of spaced upstanding posts, spherical contact-members mounted on the respective posts, a third contact-member comprising spaced rigid cross-pin connected blades for electrically connecting the spherical contact-members, one of said pins having engagement with one of said posts for pivotal movement of said blades, and means including spring-washers on the pins for adjustably efiecting pressure-engagement of the blades on the spherical contact-members.

3. An electrical switch comprising, in combination, a pair of spaced companion base-members, upstanding posts mounted on the respective base-members, contact-members mounted upon, and at the upper extremity of said posts, a

- third post mounted on one of said base-members intermediate the first posts and their said supported contact-members, and a co-operable third contact-member comprising a pair of spaced companion electrically conductive blades pivotally mounted .on the intermediate post each being provided at its opposite ends with contactplug members mounted therein and extending outwardly from the inwardly presented-faces thereof for at its respective opposite ends embracingly engaging the first contact-members in substantially point-wise tangential electrical contact.

4. In an electrical switch, in combination, a pair of spaced contact posts, an intermediate post, a pair of parallel laterally spaced contact blades pivotally mounted intermediate adjacent an end on the intermediate post, and at their other end being connected, said blades each being provided along their inwardly presented faces with respectively juxtaposed recesses opening at one end upon an outer longitudinal margin of the blade, contact plug members mounted rigidly on the respective blades in and extending outwardly from said recesses, a fixed contact post mounted in the path of movement of the blades, and a spherical contact member mounted on the post for projecting disposition between the blades into substantially point-wise tangential engagement pair of spaced contact posts, an intermediate post, a pair of parallel laterally spaced contact blades pivotally mounted intermediate adjacent an end on the intermediate post, and at their other end being connected, said blades each being provided along their inwardly presented faces with respectively juxtaposed recesses opening at one end upon an outer longitudinal margin of the blade, juxtaposed contact plug members mounted on the respective blades in and projecting outwardly from said recesses, a fixed contact post mounted in the path of movement of the blades, and a spherical contact member mounted on the post for projecting disposition between the blades into substantially point-wise tangential engagement with said contact plug members when the blades are .swung into contact forming position, said spherical member having a diametrical size greater than the distance between the opposed outwardly presented faces of the contact plugs whereby said contact plugs will be placed under substantially an axial pressure when in contact-forming position with the spherical member.

6. In an electrical switch, in combination, a pair of spaced contact posts, an intermediate post, a pair of parallel laterally spaced contact blades pivotally mounted adjacent an end on the intermediate post and at their other end being connected, and spherical contact members mounted on the contact posts for projecting disposition between the blades when the latter are swung into contact-forming position, said spherical contact members being sized for substantially point-wise tangential contact on their opposed faces with the respective adjacent faces of said switch blades.

7. In an electrical switch, in combination, a first stationary spherical contact, a second stationary spherical contact in spaced relation to the first contact, a hinge-post intermediate said contacts, a fulcrum-pin transversely disposed on the hinge-post, a movable contact member comprising spaced registering parallel-fiat blades pivotally mounted adjacent an end on the fulcrumpin and disposed upon opppsite sides of the hingepost, and a second transverse pin connecting the blades adjacent their opposite end, said blades being adapted for slidable make-and-break point-engagement with the first contact at a point located outwardly of both said pins and with the second contact at a point intermediate said pins.

8. In an electrical switch, in combination, a first stationary contact, a second stationary contact in spaced relation to the first contact, a hinge-post intermediate said contacts, a fulcrumpin transversely disposed on the hinge-post, a movable contact-member comprising spaced registering parallel blades pivotally mounted adjacent an end on the fulcrum-pin and disposed upon opposite sides of the hinge-post, and a second transverse pirr connecting the blades adjacent their opposite end, said blades being adapted for make-and-break engagement with the first contact at a point located outwardly of both said pins and with the second contact at a point intermediate said'pins.

9. In an electrical switch, incombination, a pair of spaced insulation supports, a first stationary spherical contact on the first support, a second stationary spherical contact on the second support, a hinge-post upstanding from the first support and disposed intermediate said contacts,

a fulcrum-pin transversely disposed on the hingepost, a movable contact member comprising spaced registering parallel fiat blades pivotally mounted adjacent an end on the fulcrum-pin and disposed upon opposite sides of the hingepost, and a second transverse pin connecting the blades adjacent their opposite end, said blades being adapted for slidable make-and-break pointengagement with the-first contact at a point located outwardly of both said pins and with the second contact at a point intermediate said pins.

10. In an electrical switch, in combination, spaced insulation supports, a first stationary spherical contact on the first support, a second stationary spherical contact on the second support, a hinge-post upstanding from the first support and disposed intermediate said contacts, a fulcrum-pin transversely disposed on the hingepost, a movable contact member comprising spaced registering parallel fiat blades pivotally mounted adjacent anend on the fulcrum-pin and disposed upon opposite sides of the hingepost, asecond transverse pin connecting the blades adjacent their opposite end, said blades being adapted for slidable make-and-break pointengagement with the first contact at a point located outwardly of both said pins and with the second contact at a point intermediate said pins, and co-operable latch-members on the movable contact-member and on the second support for releasably securing the contact member in circuit-c1osing engagement with said contacts.

11. In an electrical switch, in combination, spaced insulation supports, a first stationary spherical contact on the first support, a second stationary spherical contact on the second support, a hinge-post upstanding from the first support and disposed intermediate said contacts, a fulcrum-pin transversely disposed on the hingepost, a movable contact member comprising spaced registering parallel flat blades pivotally mounted adjacent an end on the fulcrum-pin and disposed upon opposite sides of the hinge-

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