US1832761A - Temperature sensitive electrical circuit closer - Google Patents

Description

G. H. BRADY Nov. 17, 1931.

TEMPERATURE SENSITIVE ELECTRICAL CIRCUIT CLOSER 2 Sheets-Shee l Filed Jan. 27, 1931 WA [i G. H. BRADY Nov. 17, 1931.

TEMPERATURE SENSITIVE ELECTRICAL CIRCUIT CLOSER FiledJan.

27, 1931 2 Shee'ts-Shee' lmllllllll-lflllllmnlfl llllllllllllllllillll" luci/mag Patented Nov. 17, 1931 UNITED STATES PATENT oFFic-E GEORGE H. BBADT', OF BALTIMORE, MARYLAND, ASSIGNOR T0 IHPBOVED FIRE l DETECTOR CORPORATION, OF BALTIMORE,

TEMPERATURE SENSITIVE ELECTRICAL ciacurr -cnosaa Applicatioii'led January 27, 1931. Serial No. 511,590.

This invention relates to certain new and useful improvements in temperature sensitive electrical circuit closers, and particularly circuit closers of that type in which -the circuit closing action is effected by the bowing move` ment of a bimetallic contact strip having a- 'contact portion movable into engagement with a pointed contact member.

In the use of such temperature sensitive circuit closers in a lire alarm system, it is the general practice to fix the circuit closing'de- I vice on the ceiling or a wall support adjacent to the ceiling', so that'the bimetallic circuit closin strip will be iniiuenc'ed by therising heate air when a fire breaks out in the guarded room or apartment inwhich the circuit l closer is arranged. The contact member and circuit closing `strip are commonly made of certain metals which are subject to surface oxidation or corrosion interfering with agood electrical contact, and to prevent" such` 4paints or other wall coatings dissipated into the atmosphere in paint spraying actions.

For these reasons, the Underwriters Laboratories standards require that the stationary' contact member andcontact portion of f 7 the contact strip. of the electric switch be so guarded or constructed as to protect the same from oxidation, corrosion or deposits of electric-insulating substances thereon, and/or j that the contact elements have such an action as to ensure a good physical contactfor a positive circuit closing operation when the thermostatic strip moves .into engagement.

with its coacting .contact member.

In my application for patent, led November 12, 1930, Serial No. 495,255, I have disclosed a temperature sensitiveelectrical circuit closer which is proof against oxidation and corrosion and which embodies novel and 50 improved means for securing a wiping en, gagement `of the circuit closing contacts, whereby any deposits thereon will be removed and a good electrical contact ensured. It is', however, desirable to provide a temperature 55 sensitive electrico-circuit closing or switch device which'will not only be proof a inst deleterious actionsof the character rerred to, but which may be employed in conjunction with a standard outlet box of wall or w ceiling type, so that its binding posts or terminals vma be connected to circuit conductors exten 'ng into the outlet box,'and thereby enabling the circuit closer to be connected up in a` circuit having concealed or surface 55 wiring. f

One object of my invention, therefore, is to rovideI a tem rature sensitive circuit closing switch which lis adapted for use in l conjunction with a standard outlet box and 70 which embodies a novel and improved construction of casing for this purpose.

'A furtherobject of the invention is' to provide a circuit closer having a casing comprising a back section and a body section 75 -which back section is adapted to be secu to the outlet box and to support the switch device so that'its contacts will be located in the body section and its binding posts or moved from the back of the casing, and to provide a construction of casing in which one and the same style of body section may be interchangeably applied to different styles of back plates or sections.

With these and other objects in view, the invention consists of the features of construction, combination and arrangement of parts, hereinafter fully described and claimed, reference being had to the accompanying drawings, in which :H-

Fig. 1 is a front view of a temperature sensitive'circuit closer embodying my invention.

Fig. 2 is a front view of the back plate thereof and the switch device applied thereto.

Fig. 3 is a sectional View on line 3-3 of Fig. 4 showing the circuit closer as applied for use in connection with a standard con cealed type of outlet box.

Fig. 4 is a section taken on line 4-4 of Fig. 3.

Fig. 5 is an inner or rear-,elevational View of the body section of the casing.

F ig. 6 is a view of a portion of the switch device, showing the contact elements in normal condition.

Fig. 7 is a similar view showing the contact elements in circuit closing contact.

Fig. 8 is a section on the line 8-8 of Fig. 10 showing the circuit closer as employed jn conjunction with a surface type of outlet Fig. 9 is a front View of the back plate of the casing shown in Fig. 8.

Fig. 10 is a sectional view on the line 10-10 of Fig. 3.

Referring now more particularly to Figs. 1 to 7, inclusive, of the drawings, 1 desig-n nates the enclosing casing of the circuit closer, which may be made of cast or stamped metal and which comprises a body section 2 and a base plate or back section 3. The casing 1 here shown is of circular form and comparatively shallow and is designed to be employed in connection with a standard concealed type of outlet box 4 which fits within a concavity or depression in the wall or ceiling 5 upon the surface of which the circuit closer is applied.

The body section 2 of the casing comprises a front or body plate 6 having a'rearwardly extending annular wall portion 7 normally open at its rear side, or that side opposite the plate 6, and adapted to fit within a receiving groove or recess S formed by an annular flange 9 projecting from the face of the plate 3. This plate 3 is formed With a front surface 10 extending rearwardly on an out-V ward and rearward bevel or slope toward the wall or ceiling 5, so as to give a desired kfinished or ornamental conformation thereto.

The plate 3 is of sufficiently greater diameter than the box 4 to cover the outer open side thereof and to lap over the adjacent wearer portions of the wall or ceiling 5. In the rear face of the plate 3 is a recess 11 to receive the edge of the box 4 at its open side, whereby the front of the outlet box is e'ectually closed and concealed by the circuit closer when the latter is applied for use. Any suitable means, such as(V screws 12, may be employed to detachably secure the casing members 2 and 3 to lugs 12 'on the box 4.

A casing structure is thus provided which i comprises a front wall 6, an 'intermediate wall 7, and a removable rear wall formed by the back plate 3, which serves as a cover.

The wall 7 of the body section 2 is formed with an annular series of rectangularlyshaped spaced slots or openings 13, preferably formed by making such wall of an annular series of rectangular or oblong rectangular bars 13', providing a grating-like forni of perforate wall. Two or more'of these bars may be of thickened cross section to provide portions of suliicient thickness for the forniation of openings 14 therein for the passage of the fastening screws or bolts 12 to secure the body section 2 and the plate 3 to the outlet box, as previously*described. The plate or wall 3 is also provided with openings 14EL for passage of screws 12a which enter threadedb openings 14b in the body plate 6 to hold the casing sections united to each other. The front or body plate or wall 6 is provided with a flattened rim portion 15 and an outwardly bulged, convex or dome portion 16 provided with a central circular opening 17and annular concentric rows of radially arranged elongated or oblong rectangular slots 13, the slots of the rows being disposed in staggered relation to each other. From the rim portion 15 projects a shallow annular flange 19 which lies in spaced relation to and parallel with the l an e 9 of the back plate 3, thereby providing etween said flanges an annular peripheral recess with which the slots 13 communicate. The ventilated casing as thus con- Structed lies close 'to the wall or ceiling 5 and operates to ensure a quick and elective flow of heated air to and its circulation within the casing so as to obtain a rapid circuit closing action as hereinafter described.

The back plate 3 of the casing is provided with a pair of spaced longitudinal slots 2O separated by an intermediate intact portion or bridge piece 21. On the rear side of the back plate is mounted an insulated carrier strip or support 22 for the switch proper and current carrying parts of the device. This carrier or support comprises an oblong rectangular block or strip of suitable electric insulating materia. On the outer face of this strip 22 are mounted terminal plates 23 and 24 of phosphor bronze or other suitable material, and on the inner face of the strip is arranged a'supporting block 25 arranged opposite the terminal plate 24.. The terminal plate 23 is .secured in position by screws 26V and 27, while the terminal plate l23 and the block 25 are secured in position by screws 28 and 29. The screws 27 and 28, the former of which passes through the stri 22 and the plate 23, land the latter of W ich passes through the strip-22, plate 24 and block 25, are rovided with binding washers 30 and binding nuts 31. 1

The screw 26 has a conical or pointed inner end 32 projecting beyond the stri 22 and through one of the slots 2O into t e casing chamber 33, said conical end of the screw providing a preliminarily adjustable but normally fixed circuit closing contact. Ar-

- ranged within the casing for coaction with contact 32-is a movable switch member comprising a bimetallic strip 34 ormed of two metals of different coefliciencies of expansion and contraction. These metal strip members are coextensive in length and welded together and are jointly secured at one end by the screws 28 and 29. This strip may be provided with a coating of a suitable material to protect the same'from oxidation and corrosion, such, for example, as a coating of chromium. rlhe screw 26 is provided with line or micrometer screw threads, the threaded portion of said screw engagmgv threaded openings in the strip 22 and plate 23. llnitially the outer end of the screw projects, as shown in Figs. 4 and l0, a suitable distance beyond the outer face of the plate 23 and is provided with a-nick or other means 35 whereby a screwdriver or other suitable tool may be engaged therewith to secure it in position. The screw body is preferably made of sottmetal so that after having once been set vor adjusted its outer end or projecting portion may be cut od hush with the outer tace of the plateA 23, as shown in Figs. 6 and 7 so as to prevent accidental displacenient or' said contact screw ,from its said po- -s1t1on or meddlesome persons turning it and changing its position.

The pointed end 32 of the screw 26 lies in the pathL of movement or the free end of the strip 34, whenV the latter is bowed or deflected in one direction by the action of heat at a certain predetermined tem erature,

sothat when the stri is thus bowe the tree end of the strip will e brought into engagement with 'theF pointed end of the screw for avcircuit closing' action.

The carrier or support22 is adapted to be detachablysecured in position to theback-3 bv fastening screws 36 and 37. lt will be bbserved' that the switch proper and all the current carrying connections are thus mount` ed upon the common insulated support or car rier strip 22, which is detachablysecured to the back3, and which provides for the .mount-- ing of all the current carrying connections vv"upon, or, the dismounting of said current carrying `connections from, the back-'section of the casing in a slmple and convenlent man.

ner, and so that when the parts are assembled 33 while the binding posts project at the rear of the back 3 and into the box 4 for the ready connection of the circuit conductors A, A therewith.' n the device as organized for use the contact pin 26 lies within one of the slots20, free from connection with the casing, while thev block 25 projects through the other slot 20. In applymg the unitary current carrying or switchl structure to the casing body, said current carrying structure is brought-into position on the exterior of the back 3 so that the free end of the strip 34 will be in alinement with the slot 20 to'be occu ied strip 34 is inserted through said slot andthe `current carrying unit then moved longitudinally in the direction toward the other slot 20 untilthe block 25 comes opposite the slot 20 through which the strip 34 has been introduced, after which the current carrying unit is simply moved inward to bring the parts thereof into working position and secured in place by means lof the screws 36 and 37. When it is desired to remove the current carrying unit, all that is necessary is to une fasten the screws 36 and 37 and to shift the unit longitudinally in the reverse direction to that in which it was introduced and then to withdraw it laterally, as will be readily understood.

lin accordance with my invention, the pointed. contact portion 32 of the contact screw or member 26 is made of an alloy;of gold and silver which will not oxidize or corrode under the action of corrosion inducing acids or gases of the character described. Also the strip 34 has vits ree end bent to form a contactportion 38 carrying a contact button' or member 39 iitted and secured in an o, ening therein, which contact member or utton may be made, like the point of the screw, of lan alloy of gold and silver for the pur ose described. The end 38 of the strip 34 isf ent at an oblique angle thereto and at such an angle that in the movement of the strip toward the contact point 32 from the open po- 'sition shown in Figs. 4 and 6 to the closed position shown in Fig.. 7, the contact member 34 and its contact lbutton 39 will be bowed, as

tween the fixed end of the strip and the con.

tact 39 .will be lshortened so that a wiping action of part 32 on contact 39 willzoccur.

Preferably this wiping action is increased by makina the range of circuit closing motion of the end 38 ofthe strp34 of a distance greater than the distance normally between such end of the strip in its open position and the contact 32, so that the bowing of the strip will continue for a certain time after contact is made, with the result that the face of the button 39 will be drawn across the eX- tremity of point 32 to obtain a strong rubbing or wiping contact. This rubbing or wiping contact will be of such character that, even in the event that there should be film or coating of an insulating material on the face of the button 39, said film or coating will be scratched Yoff, so that there will be an absolute metal to metal contact between the parts 32 and 39 to Vensure a certain and positive conducting engagement of the contacts and closing of the electric circuit.

The construction shown in Figs. 8, 9 and 10 is similar to that above described, except that the back rear wall or plate section 3a of the casin la is slightly modified in form to ada-pt it or cooperation with a standard surface outlet box 4a, as employed in the surface mounting of the elements of an electrical alarm system including the supply conductors A and A', said back plate having a iiat tened rear face for abutting contact with the rim edge of the outlet box or a gasket interposed therebetween. The box may be suitably constructed for attachment to a ceiling or other wall surface or support carried thereby. This construction of the casing with back plate 3a of small diameter and flat rear face is especially desirable for use in the application of the circuit closer to the surface mounted parts of a fire alarm system of a marine vessel. The boit 4a in this connection is here shown as adapted for attachment to the metallic ceiling 5 of the vessel, and in this use of the circuit closer a sealing washer or gasket 4b of rubber or other suitable waterproof and electric insulating material is preferably applied between the back 3a and bon 4 to prevent leakage of water into the loon, as well as to give protection against possible short circuiting of electric. currents. The body section of the box in this construction is the same as that shown in Figs. 1, 2, 3 and 4.

ln practice it is preferably intended to make all the body sections of the casing` alilre and interchangeable for use with back secn tions varying to certain degrees, as herein il lustrated, for example, for application to different types of concealed and surface outlet boxes, so that changes in the back plates only will be necessary to adapt the circuit closer for use in conjunction with outlet boxes of all types. llhile the construction of bon shown in Figs. 8, 9 and 10 is well adapted for marine service, as stated, it may also be used in all applications where a surface type of outlet box may be employed. The outlet box construction shown in llligs. 1, 2, 3 and 4 is adapted for use for flush mounting of the box and cables or conduits in marine, industrial, domestic and commercial work of all kinds, as will be readily understood. In practice, it is preferred to bend the contact portion 38 of the strip 34 at an angle of about 45 to the strip, so as to secure a positive scraping contact with the contact point 32, as a result of which construction, and by making the con tact members of an alloy of the character described, a type of temperature sensitive fire alarm switch employing a thermostatic contact strip is produced for efficient use in marine and commercial applications where corrosive influences have heretofore been an obstacle to the successful operation of contact making switches of this type.

By the provision of a casing of the construction described, material and important advantages are obtained. By casting or punching the casing of heavy sheet metal, preferably brass or bronze having corrosion resistance and providing a ventilated casing of this character full exposure of the temperature sensitive switch member 34 toheatwaves entering the casing from all sides through the slots 13 or from the bottom or front through the slots 18 is allowed, thereby causing the strip to be quickly influencedand to close the circuit before the heat is absorbed by the relatively greater mass of metal in the base', while the casing at the same time oiiers a great mechanical protection to the heat sensitive element arranged therein. The purpose of making the slots or openings 13 and 18 of rectangular or oblong rectangular shape, instead of circular shape, is to secure a freer passage of heat/ed air into and its circulation within the casing than can be obtained by the use of circular openings. This has been determined by test, asit is found that the tendency of air, water or other fluids passing through round holes is to cling to the edges of the holes and clog them, whereas sharp, straightedged openings do not have this objection, and elongated straight-edged openings in particular, allow extremely free circulation of the air without clogging tendencies. rllhus heated air rising in a room will be allowed to quickly enter the casing and displace the air contained therein, thus pre-venting banking or pocketing of air in the casing, which would. interfere with the perfect and rapid closing of the circuit and sounding of the alarm. The purpose of providing the front wall of the casing with a bulged portion is to dispose the slots or openings 18 'therein in such a manner as to catch and guide air coming in all directions into the lcasing. ln this connection, also, the flanges 9 and 19 act as air dctlectors or guiding surfaces to guide the air toward the slots or openings 13, while the surface of plate 3 and corresponding surface of the outside of flange 9 of plate 3a act as deectors to ward off any moisture which may accumulate on ping or being conducted down into the cas- 'ingchamben lThe slots 18 in the bulged portion of the casing, furthermore, operate, when the casing is mounted in a pendant position, to allow any dust or other substances falling into the casing to discharge under the action of vibration or air currents.

From thewforegoing description, taken in connection with'the drawings, the construction and mode of operation of my improved circuit closing device will be readily.v understood and it will be seen that the invention provides a means for securing a positive engagement between the circuit closing contacts even under conditions where'the contacts are coated with a ilm of dust, paint or other wall coating material, or are affected on the surface by oxidation or corrosion, so that all requirements in this connection may be effectually met for the provision of a circuit closing device which will be absolutely positive in action under the conditions mentioned. Also s mediate walls having it will be seen that my invention provides a circuit closing device which may be employed in connection with an outlet box of any of the standard types and used in alarm or other circuits employing commercial line voltages. Having thus fully described my invent-ion, I claim :-n

l. A. temperature sensitive electrical circuit closer comprising front and rear walls and an intermediate wall, the front and interperforations therein, and a temperature sensitive circuit closing device carried bythe rear wall and having circuit closing contacts disposed in advance of said wall and on the interior of the casing and having terminals for the connection of circuit conductors therewith disposed in rear of said rear wall.

2. A temperature sensitive electricalcircuit closer comprising a casing having front and rear walls and an intermediate wall, said front and intermediate walls being provided with elongated rectangularly-shaped perforations therein, and a temperature sensitive electrical switch carried by the rear wall and having circuit closing contacts disposed with'- lco in the casing and terminals for connection with electrical conductors disposed in rear of said rear wall. l f

3., A temperature sensitive electricalcircuit tiloser comprising a casing having iront and rear wallsv and an .intermediate wall, said front wall `being provided with annular series of radially arranged and staggered oblong rectangular openings, and said intermediate wall having an annular series of similarly shaped openings therein, and a temperature sensitive circuit closing switch carried by the rear wall and having circuit closing contacts disposed on the inner side of said rear wall within the casing and terminals for connection of electric conductors therewith disposed on the loutside of the casing and inv rear of walls and an intermediate wall of less diameter than said front and rear walls, said front wall and intermediate `wall being provided vwith elongated openings therein, a temperature sensitive switch carried by the rear wall of the casing, and annular flanges on the casing at the front and rear of the intermediate wall.

5. In atemperature sensitive electrical circuit closer, an outlet box, a casing closing the open front of and detachably connected-with said outlet box, said casinor comprising front and rear walls detachably connected with each other and an intermediate wall carried hy one of said walls, the front and interme-4 diate walls being provided with air passages, and a temperature sensitive circuit closing device carried by the rear wall.

6. ln a temperature sensitive electrical circuit closer, an outlet box, a casing closing the open front of and detachably connected with said outlet box, said casing comprisin front and rear' walls detachably connecte with each other and an intermediate wall carried by one of said walls, the front and intermediate walls being provided with air passages, and a temperature sensitive circuit` closing switch carried by the rear wall and having circuit closing contacts arranged in advance of said rear wall and within the casing and terminals for connection of circuit conductors therewith arranged in rear of the rear wall and within the outlet box.

7. A temperaturesensitive circuit closer comprising a hody section having perforate side and front walls, a back member having an outer face formed to close the open side of an outlet box and having an inner face 'formed 1to engage the said body section, and a switch carried by the back section and having terminals projectin at the rear of the loack section sofas to he isposed in the outlet Yoox and havin circuit closing contactsprojecting at the ront ofthe back section so as to be disposed in said body section.

8. A circuit closer of the character set 4forth in claim 7 wherein the switch device is of unitary type and detachably mounted on the back section.

9. A circuit closer of the character set forth in claim 7 wherein the body section comprises an annularbody wall provided with elongated air openings anda front wall provided 11. A circuit closer of the character set forth in claim 7 wherein the body section comprises an annular body wall provided with elongated air openings and a front wall proided with similar openings and with a rim ange.

12. A circuit closer of the character set forth in claim 1 wherein the fromJ Wall and the rear Wall are formed with flanges -ar ranged respectively in advance and in rear of the openings in the intermediate Wall.

In testimony whereof I affix my signature.

GEORGE H. BRADY.

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