US3602852A - Case assembly for circuit breakers - Google Patents

Abstract

Two half shells forming a complete circuit breaker case are constructed with a view to simplicity of configuration and assembly therein, of essential components of a trip free circuit breaker. The shells carry magnetic arc deflectors which clear the closed contacts. Venting apertures lead directly through the shells above and below the arc deflectors and have protective guards, one of them between the deflectors and a shelf for the fixed contact. The shells have bosses which secure the metallic frame of the breaker movement and limit axial displacement of smooth pins of the breaker mechanism, pivoted in the frame. The shells can be extended to accommodate an auxiliary switch structure operated from the circuit breaker by an actuator guided by wings in grooves of the shells. Ferrules threaded throughout their length are held in correspondingly opposite recesses of the respective shells, with rivets for holding the shells together being placed in the recesses to prevent injury to the shells by screws that might be accidentally dimensioned to reach beyond the ferrules.

Description

United States Patent [72] Inventors Lawrence W. Brackett, Sr.; Lawrence W. Brackett, Jr., both of Georgetown, Mass. [21] Appl. No. 43,826 [22] Filed June 5, 1970 [45] Patented Aug. 31, 1971 [731 Assignee Wood Electric Corporation Danvers, Mas.

[54] CASE ASSEMBLY FOR CIRCUIT BREAKERS 9 Claims, 18 Drawing Figs.

[5 2] US. Cl 335/202, 200/168 [51] lnt.Cl HOlh 45/04 [50] Field of Search 335/202, 132; 200/168 A, 168 B; 317/120 [56] References Cited UNITED STATES PATENTS 3,290,627 12/1966 Davis et a1. 335/9 3,329,793 7/1967 Camp 200/168 A 3,422,235 1/1969 Camp 200/168 A 3,506,799 2110/1685 4/ 1970 Ellsworth et al.

Primary Examiner-Harold Broome Attorney-Roberts, Cushman & Grover ABSTRACT: Two half shells forming a complete circuit breaker case are constructed with a view to simplicity of configuration and assembly therein, of essential components of a trip free circuit breaker. The shells carry magnetic arc deflectors which clear the closed contacts. Venting apertures lead directly through the shells above and below the arc deflectors and have protective guards, one of them between the deflectors and a shelf for the fixed contact. The shells have bosses which secure the metallic frame of the breaker movement and limit axial displacement of smooth pins of the breaker mechanism, pivoted in the frame. The shells can be extended to accommodate an auxiliary switch structure operated from the circuit breaker by an actuator guided by wings in grooves of the shells. Ferrules threaded throughout their length are held in correspondingly opposite recesses of the respective shells, with rivets for holding the shells together being placed in the recesses to prevent injury to the shells by screws that might be accidentally dimensioned to reach beyond the ferrules.

inserts.

CASE ASSEMBLY FOR CIRCUIT BREAKERS BACKGROUND or THE INVENTION 1. Field of the Invention The invention relates to electromagnetically actuated switches of the circuit protecting trip-free type with arc suppression means (Class 335-6, 24, 201

2. Description of the Prior Art .Circuit breakers of various types for similar purposes are well known but they often incorporate construction details which are for given purposes impractical, unnecessarily complex, or are based on 'misconceived theories of operation. Examples of such circuit breakers are for example US. Pat. Nos. 2,159,645, 2,320,437, 2,363,606, 2,467,937, 2,719,203, 2,764,315, 3,016,438, 3,412,351, 3,422,235 and 3,444,488 with regard to are blowout and venting structures, US. Pat. Nos. 3,290,627 and 3,329,913 with regard to association and assembly of the breaker mechanism with or without separate frame and the casing, US. Pat. Nos. 3,329,793 and 3,501,606 with regard to combinations of circuit breakers and auxiliary switches, and US. Pat. No. 3,329,793 with regard to mounting The present invention departs from the prior art by utilizing the complementary shells of a circuit breaker casing and the breaker components in direct contact therewith to avoid various defects of the prior art to promote simplicity and functional reliability of the circuit breaker as a whole.

SUMMARY OF THE INVENTION Objects illustrating the usefulness of improved circuit breakers according to the invention are, among others, to provide simplified and hence inexpensive, and yet fully secure mounting of the breaker mechanism within the casing, to provide arc extinction and venting in simple and inexpensive manner yetfully effective for severe requirements, to provide shell moldings capable of accommodating with but simple additions an auxiliary switch securely actuated from the circuit breaker, to provide convenient, uncomplicated and yet secure joining of half shells of a casing, and mounting of single as well .as multipole circuit breaker casings, and to provide for within and transverse of the casing in front of respective vents,

mechanism which include a rigid mounting frame with faces contacting corresponding faces of the frame plates for restraint against turning and shifting in and around the three axes. The pivot pins of the breaker mechanism extend through perforations of the frame plates towards respective shell walls wheretheir axial movement is restrained without restraining force exerted by the frame which is held in place solely by the bosses. In a preferred embodiment, is a web which connects the frame plates has a perforated bracket for the magnet structure which is thus held directly by the shells.

In another aspect of the invention, two magnetic deflectors with Ll-shaped inner edges extend from the casing between the closed and open positions of the moving contact accommodating the contact as it opens. A first vent leads through the casing essentially at right angles, formed by two matching cutouts in the fitting peripheries of the shells between the fixed contact and one deflector, and a second vent is similarlyformed such that the moving contact is when closed at the first vent between the fixed contact and the first guard and deflector, and when open directly at the second deflector and the second vent and guard. The two deflectors are placed betweenthe guards, well beyond the fixed contact which rests on a divided shelf in a comer of the split peripheral shell walls.

In a further aspect of the invention, if an auxiliary switch is to be provided, the shells have supporting extensions for the switch with a hole leading to the circuit breaker, for the shank of a T-shaped actuator whose leg contacts the circuit breaker mechanism, whereas the arm of the crossbar, extending trans versely of and contacting the auxiliary switchblade, is guided in grooves at opposite sides .of the shell extensions.

In still another aspect, a so-called mounting adapter is provided in polygonal recesses for confining inside threaded polygonal ferrules, the recesses extending into holes for shell joining rivets which serve as backstops for the mounting screws to be inserted in the ferrules.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of a circuit breaker according to the invention;

FIGS. 2 and 3 are side elevations of the breaker, with and without auxiliary switch, respectively;

FIG. 4 is a section on lines 4-4 of FIG. 1 with auxiliary switch, showing the breaker in closed position indicated by the position of the switch;

FIG. 5 is a side elevation with one shell removed to show the breaker in opening position with the armature still attracted;

FIG. 6 is a section on lines 66 of FIG. 4;

FIG. 7 is an isometric view of the frame for supporting to breaker movement;

FIGS. 8 and 9 are views of the interior sidewall faces of the two casing shells showing, in relation to FIG. 7, the frame positioning faces of the shell bosses;

FIGS. 10 and 11 are partial sections on lines 10-10 and 1 l--1l respectively, of FIG. 4;

FIGS. 12 and 13 are isometric view of the arc deflecting, venting, and mounting ferrule portions of the two shells, incorporating arc deflectors according to FIG. 14;

FIG. 14 is a section on lines 14-14 showing a preferred embodiment of the arc deflectors; and

FIG. 15 is a section similar to FIG. 14, showing another embodiment of the arc deflectors.

DESCRIPTION OF PREFERRED EMBODIMENTS The circuit breaker casing according to the invention is particularly suitable for confining and mounting circuit breaker mechanism of conventional construction of the general type such as described in US. Pat. No. 2,360,922 of Oct. 24, 1944, to K. W. Wilckens, although it will be understood that the present novel casing can easily be adapted to breaker movements of different types. It will also be understood that deviations from the above or other conventional constructions form part of the invention so far as they cooperate with the im proved casing construction.

As shown in FIGS. 1 to 3, and 7 and 8, the casing consists of two shells 11 and 12 which are held together by rivets I15, 116 as will be described hereinbelow. As indicated by way of FIGS. 2 and 3 the casing can be molded with an extension for an auxiliary switch as indicated at A of FIG. 2, or without such an extension as in FIG. 3. It will be appreciated on inspection of FIG. 4 that it is easy to modify a mold for that purpose by omitting the auxiliary housing, retaining a flat closed wall of the main casing.

For properly describing the casing according to the invention and the circuit breaker components in immediate association therewith, it has to be related to active components of a breaker mechanism and for that purpose a circuit breaker based, with certain improvements on the above US. Pat. No.

2,360,922 will first be described so far as necessary for an understanding of the invention.

Referring to FIGS. .4, 5, 6 and 7, the circuit breaker mechanism is mounted on a frame 31 with two parallel sideplates 32 and 33, a web 34 and a magnet support 35. The plates have holes for the pivot pins, and several projections with restraining faces which will be described in detail hereinbelow. The handle 41 is pivoted on pin 42 in the sideplates and fits semicircular recesses 41.1 (FIGS. 6, 8, 9) of respective shells. A toggle mechanism has an operator link 45 and a double walled contact link 46. The operator link 45 is pivoted on the handle at 47 and the contact link is pivoted to the movable contact 51 at 52. The movablecontact rotates on pin 53. The two links are joined by a pivot pin 48 and a toggle trigger catch pin 60 which includes a so-called half moon catch with a flat 65. This catch pin 60 is pivoted on the two walls of contact link 46 and associated with a crank 61 and a tripping pin 62, compare FIGS. 4 and 6. The operator link 45 has a latch tooth 67 between the two walls of the contact link 46 (FIGS. 5 and 6). Appropriate springs, described in the abovementioned patent 3,329,912, keep the several toggle and trigger elements with proper bias in the positions described and shown. With the switch in closed position and the movable contact 51 resting on the fixed contact 50 as shown in FIG. 4, the latch tooth 67 engages the convex region of the catch pin 60 at the edge 65.1 of the half moon catch. The toggle is then locked in the position of FIG. 4. When the actuator 71 of the armature 70 turns on its pivot 75 towards the solenoids, the armature leg 72 (FIGS. 4, 6) touches the pin 62, rotates the crank 61 and with it the catch pin 60 with its flat 65, releasing the tooth 67. The locking connection between the contact link 46 and the operator link 45 is now open and the toggle collapses as shown in FIG. 5, and the biasing springs quickly break contact at 50 and 51.

If it is attempted to close the circuit breaker by turning the handle after the toggle linkage is triggered by a persistent abnormal condition, and assuming the position of FIG. 5, the two links 45 and 46 will rotate relatively to each other but the contacts will remain open and the handle will move back into open position. This is commonly referred to as trip free operation. It should be noted that the armature actuator 71 remains in the position of FIG. 5 only so long as current is still flowing in the solenoid. Upon current interruption the armature returns to the position of FIG. 4.

For manually breaking contact the handle is rotated counterclockwise with reference to FIG. 4 and this moves the two links 45 and 46 while remaining rigidly joined at 60, towards the right of FIG. 4 thus moving the contact 51 into open position by rotation on its pivot 53.

THe mounting of the mechanism within the casing will now be described. For a better understanding of the interrelation of the shells and the frame it should be noted that, as indicated in FIGS. 7, 8 and 9, the frame plates have locking faces extending in all three dimensions, indicated at x, y and z with distinguishing numerals. These correspond to similarly identified faces u, v, w of the casing shells.

Referring now particularly to FIGS. 7, 8, 9, 10 and 11, the frame sideplates 31, 32 have several restraining faces indicated at x, y and z which correspond to holding faces 14, v and w ofthe shell bosses 11.1, 11.2, 11.3, 11.4,11.5 and 11.6 on shell 11 (FIG. 9) and 12.1, 12.2, 12.3, 12.4, 12.5 and 12.6 on shell 12. The restraining and holding faces of frame plates and shells, respectively, are indicated by numerical modifiers of the directional indicators x, y, z and u, v and w at one of shells (11) and at one of the frame plates (33) in FIGS. 7 to 11. These labels demonstrate without further explanation that the frame and the two shells are positively and firmly locked in all three dimensions. It will be noted that by appropriate selection and placing of the restraining and holding faces (not necessarily as described above by way of example) it is possible to provide a statically determined mounting system or, if desired, an overdetermined frame system.

The above-described mounting of the frame directly on the casing is more satisfactory as previously proposed mounting systems whereby the frame is held by movement pins which are associated with the frame by collars or similar devices and contact the shell walls.

Referring especially to FIGS. 6 and 7, it will be noted that the handle pin 42, the armature pin 75, and the contact pin 53 are pivoted in corresponding holes of the frame plates. These holes are indicated in FIG. 6 at 42.1, 75.1 and 53.1 of plate 32. These pins can freely move axially in their holes and are sufficiently long for restraint by casing walls, making provisions such as the above-mentioned pin collars unnecessary.

Referring to FIg. 4, the overload responsive magnet structure is supported on the frame 3 in the following manner. A metal tube 81 is inserted into a circular opening 82 of the frame bracket 35 (FIG. 7) and welded thereto where the tube is flush with the bracket. The coil form 85 of insulating material and cylindrical throughout, has an interior circular recess 86 fitting the tube 81. In this manner the coil form can be easily assembled by slipping it over the tube 81. A magnet terminal bus 86 is supported on the terminal 89 which is held by the shells in known manner, as indicated.

Referring to FIGS. 4, 5 and 12 to 15, the arc quenching arrangement according to the invention will now be described.

In one embodiment of the arc quenching construction, particularly shown in FIGS. 12 and 14, two solid plates of magnetic material 91, 92 with generally speaking U-shaped cutouts are molded into one of the shells such as 11 (FIG. 14), by means of dove tails 91.1 and tails 91.2. As shown in FIG. 4, the deflector 92 is appreciably above the movable contact 51 in closed position whereas, as shown in FIG. 5, the deflector 91 essentially clears the movable contact in open position. The deflectors are essentially parallel to the bar 50.1 with terminal 59, of the fixed contact 50, which is supported on a ledge 11.9, 12.9 of the two shells which have corresponding slits for the terminal 59, one slit in each shell. Each shell has two semicircular grooves 93, 94, one above the deflector 91 and one between the deflector 92 and the fixed contact 50. When the shells are joined, these grooves constitute vents leading directly through the peripheral wall of the casing, of-

fering minimum flow resistance. The vents are protected by guards 95, 96 each of which is formed in two halves, one end fastened to the respective shell and the other in closed contact with the free end of the guard half of the other shell, as clearly indicated in FIGS. 12 and 13.

A modification of the deflector construction is indicated in FIG. 15. In this embodiment, each deflector is divided to form halves 99.1 and 99.2, each of which is molded into a respective shell with dovetails and tails corresponding to the single dovetail and tail construction of the deflector according to FIG. 14.

The fixed contact 50 is applied to a terminal bar 50.1 which rests on the ledges 1 1.9, 12.9 of the shells (FIG. 4) and the terminal 59 held in appropriate slits of the shells. for further rigidity, the bar 50.1 is provided with lateral tabs 50.5 received in slots 50.7 and 50.8 (FIGS. 8 and 9) of the shells as shown in FIGS. 8 and 9. In addition, a longitudinal extension 50.6 can be provided for reception in slots of the peripheral rim portions of both shells (not shown).

Referring to FIGS. 2, 4, 5, 6, 8, 9, 17 and 18, an optional auxiliary switch will now be described. As indicated in FIGS. 2, 4, 6, 8 and 9, the casing shells are identical for circuit breakers with and without auxiliary switch excepting for the extension below line AA on FIGS. 4 and 6. It will be appreciated that the procurement of separate molds for the respective types is considerably less expensive than dual purpose shells that accommodate auxiliaries or substituted dummies, due to the essential identity of the circuit breaker portion of the two types.

Held by slots in the respective halves of the shells at the auxiliary switch portion thereof, are three auxiliary terminals, namely a common terminal 112, a normally closed terminal 113 and a normally open terminal 114. The terminal 112 which is also supported in aslot of the main housing at 112.1

carries riveted thereto a contact blade 116, an actuating breaker as follows.

A T-shaped pusher or actuator 121 (FIGS, 4, 5, and 18) reaches through a rectangular hole 122 into the main compartment for the circuit breaker, in the vicinity of the lower cam portion 123 of the movable contact member 51 of the circuit'breaker mechanism, being kept in contact therewith by the switch blade 116. The square shank 122.1 of the pusher reaches through the aforementioned guiding perforations 122. The crosspiece-122.2 of the pusher is guided in grooves 123, 124,"(FIG.'18) of the respective half shells. It will be evident that the auxiliary spring blade 116 connects terminal 112 with terminal 113 when the main circuit breaker is closed as indicated in FIG. 4 and that the blade 116 transfers contact to the terminal 114 when the circuit breaker contact 51 is open either by manual operations or by emergency tripping.

In FlGS. l, 4, 5, 8, 9, 12, 13 and 16 two circuit breaker mounting devices, sometimes referred to as adapter? are indicated; at 101 and 102 of FIG. 1. These adapters utilize threaded metal ferrules 105 (FIG. 16) which have polygonal heads 106 and inside threaded shanks 107. The ferrules are held in two pairs of corresponding recesses 101.1, 101.2 and 102.1, 102.2 of the shells (FIGS. 8 and 9), one pair on either side of the handle. As indicated in FIGS. 12 and 13, each pair of recesses has a polygonal portion 108 and a cylindrical portion 109. Mounting provisions of this type have been provided before but they have the disadvantage that screws which are accidentally too long, when inserted into the open shanks are apt to be forced against and to injure the shells. The ferrules could 'be closed but that makes their manufacture rather expensive. The shells are held together by rivets 115, 116, 117, 118 which pass through appropriate holes of the shells, as indicated in FIGS. 1 to 5. In accordance with the present invention, the rivets 115, 116 which hold the two shells together, (FIGS. '1, 4, 5, 8, 9. 16) are inserted through holes at the ends of the open ferrules as indicated at 117 in FIG. 4. As clearly shown in FIG. 16, these rivets serve as backstops for mounting screws inserted in the ferrules.

In this manner an inexpensive, yet very effective, expedient for protecting the shells from injury by inadvertence or improperly selected mounting screws is provided, at minimumexpense simply by correlatingtwo elements each of which also serves its own purpose.

It will be noted that the shells have six holes. As indicated in FIGS. 2 and 3, two of these, namely 115.1 and 116.1 receive the above-described backstop rivets 115 and 116. Two additional ones, 115.2 and 115.3 receive rivets corresponding to 115 and 116 on the handle side for joining the two shells. Two further sets of holes, M1 and M2 can be provided if it is intended to join two or more of the present circuit breaker units to form a multipole circuit breaker. For similar purposes, knockout portions M3, M4 can be provided in sidewalls of the shells, as shown in FIGS. 2, 3, 8 and 9. 1

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

1. Acasing for supporting circuit breaker mechanism which includes rotatable handle means rotatable armature means, rotatable contact means, pivot pins for said handle means armature means and contact means, and a rigid frame with parallel sideplates having surfaces extending in three dimensions and having pivot holes for said pins, said casing comprismg:

two shells each having a sidewall and projecting from the sidewall peripheral walls having matching rim means interengaging in a common plane, the shells being essentially symmetric to said plane asreflections of each other through the plane, the interengaged shells forming the casing; and

on each shell interior frame restraining faces extending in three dimensions corresponding to and contacting said plate surfaces;

said pivot pins extending through said pivot holes towards said sidewalls of the casing formed by the shells for restraint of their axial movement in the pivot holes and fixed with the frame relatively to the casing by said plate surfaces and said restraining faces.

2. A frame for mounting circuit breaker mechanism sup ported 1 in a casing according to claim 1, wherein said sideplates have sets of parallel edges and sets of stepped indentations, said edges and said indentations having surfaces extending in said three dimensions.

3. A pair of shells for mounting circuit breaker mechanism according to claim 2, wherein each shell has internal wall portions with opposite internal restraining faces fitting said parallel plate edges, and wherein each shell has internally projecting bosses with restraining faces fitting said indentations.

4. A frame according to claim 2 having a web connecting said plates and a bracket extending laterally from said web, said bracket having a hole for supporting an overload sensitive magnet.

5. A casing with two shells each having a sidewall surrounded by a rim which forms peripheral walls with the rim of the other shell for housing a circuit breaker mechanism mounted on a frame with sideplates one in each shell, with fixed contact means secured by both shells, and with movable contact means mounted on the frame for closing and opening circuit at said fixed contact means, in combination with:

magnetic deflector plate means mount'don and extending from the casing between the closed and open positions respectively of the moving contact means, the plate means being closed at the casing, open oppositely to the casing, and extending to accommodate the movable contact means;

a first vent transverse of the casing essentially at right angles therethrough and formed by two matching cutouts in said rims between the fixed contact means and the deflector means;

a second vent transverse of the casing essentially at right angles therethrough and formed by two matching cutouts in said rims beyond the deflector means; and

two split vent guards, one half of each guard fixed at one end to a respective rim and touching the other half at the other end, and each complete guard extending transversely of the casing interior in front of a respective vent, such that the moving contact means is in closed position at the first vent and guard between the fixed contact means and one side of the deflector means, and in open position directly at the second vent and guard at the other side of the deflector means.

6. Casing according to claim 5, wherein each of said arc deflector plate means includes a solid sheet with a U-shaped cutout for accommodating said movable contact means, and

with straight rectangular edges on the periphery having tail means extending into and held in one of said shells, the

remaining edge portion contacting the other shell.

7. Casing according to claim 5 wherein each of said arc deflector plate means includes two half sheets together forming a U-shaped cutout for accommodating said movable contact means, and having two straight edges inclined to each other, an edge of each half sheet having tail means extending into and held in a respective one of said shells.

8. A casing with two shells each having a sidewall suran auxiliary switch mounted in said auxiliary housing having movable spring contact means and fixed auxiliary contact means, said auxiliary housing being separated from said circuit breaker housing by a partition having a hole, the auxiliary housing having sidewalls on either side of said spring contact means with grooves in the direction of said partition hole; and

an actuator having a leg reaching through said hole to contact said contact arm and a crossbar extending within the auxiliary housing transversely of said spring contact means, guided in said grooves, and contacting said spring contact means, said actuator being made of insulating material.

In a circuit breaker, the combination of:

two essentially rectangular half shells forming a casing for the circuit breaker mechanism' each shell having a sidewall and projecting therefrom peripheral half-walls a ferrule having a polygonal head and a round shank fitting said polygonal and round cavities respectively, the ferrule being threaded throughout its length; and

means for holding the shells together having rod portions in said aligned holes, said rod portions forming backstops for mounting screws threaded into said ferrules.

Claims (9)

1. A casing for supporting circuit breaker mechanism which includes rotatable handle means, rotatable armature means, rotatable contact means, pivot pins for said handle means armature means and contact means, and a rigid frame with parallel sideplates having surfaces extending in three dimensions and having pivot holes for said pins, said casing comprising: two shells each having a sidewall and projecting from the sidewall peripheral walls having matching rim means interengaging in a common plane, the shells being essentially symmetric to said plane as reflections of each other through the plane, the interengaged shells forming the casing; and on each shell interior frame restraining faces extending in three dimensions corresponding to and contacting said plate surfaces; said pivot pins extending through said pivot holes towards said sidewalls of the casing formed by the shells for restraint of their axial movement in the pivot holes and fixed with the frame relatively to the casing by said plate surfaces and said restraining faces.

2. A frame for mounting circuit breaker mechanism supported in a casing according to claim 1, wherein said sideplates have sets of parallel edges and sets of stepped indentations, said edges and said indentations having surfaces extending in said three dimensions.

3. A pair of shells for mounting circuit breaker mechanism according to claim 2, wherein each shell has internal wall portions with opposite internal restraining faces fitting said parallel plate edges, and wherein each shell has internally projecting bosses with restraining faces fitting said indentations.

4. A frame according to claim 2 having a web connecting said plates and a bracket extending laterally from said web, said bracket having a hole for supporting an overload sensitive magnet.

5. A casing with two shells each having a sidewall surrounded by a rim Which forms peripheral walls with the rim of the other shell for housing a circuit breaker mechanism mounted on a frame with sideplates one in each shell, with fixed contact means secured by both shells, and with movable contact means mounted on the frame for closing and opening circuit at said fixed contact means, in combination with: magnetic deflector plate means mounted on and extending from the casing between the closed and open positions respectively of the moving contact means, the plate means being closed at the casing, open oppositely to the casing, and extending to accommodate the movable contact means; a first vent transverse of the casing essentially at right angles therethrough and formed by two matching cutouts in said rims between the fixed contact means and the deflector means; a second vent transverse of the casing essentially at right angles therethrough and formed by two matching cutouts in said rims beyond the deflector means; and two split vent guards, one half of each guard fixed at one end to a respective rim and touching the other half at the other end, and each complete guard extending transversely of the casing interior in front of a respective vent, such that the moving contact means is in closed position at the first vent and guard between the fixed contact means and one side of the deflector means, and in open position directly at the second vent and guard at the other side of the deflector means.

6. Casing according to claim 5, wherein each of said arc deflector plate means includes a solid sheet with a U-shaped cutout for accommodating said movable contact means, and with straight rectangular edges on the periphery having tail means extending into and held in one of said shells, the remaining edge portion contacting the other shell.

7. Casing according to claim 5 wherein each of said arc deflector plate means includes two half sheets together forming a U-shaped cutout for accommodating said movable contact means, and having two straight edges inclined to each other, an edge of each half sheet having tail means extending into and held in a respective one of said shells.

8. A casing with two shells each having a sidewall surrounded by a rim which forms peripheral walls with the rim of the other shell, said walls forming a housing for circuit breaker mechanism with fixed contact means secured by both shells, and with a movable contact arm for closing and opening circuit at the fixed contact means and said walls having extensions forming a housing and support for an auxiliary switch, in combination with: an auxiliary switch mounted in said auxiliary housing having movable spring contact means and fixed auxiliary contact means, said auxiliary housing being separated from said circuit breaker housing by a partition having a hole, the auxiliary housing having sidewalls on either side of said spring contact means with grooves in the direction of said partition hole; and an actuator having a leg reaching through said hole to contact said contact arm and a crossbar extending within the auxiliary housing transversely of said spring contact means, guided in said grooves, and contacting said spring contact means, said actuator being made of insulating material.

9. In a circuit breaker, the combination of: two essentially rectangular half shells forming a casing for the circuit breaker mechanism each shell having a sidewall and projecting therefrom peripheral half-walls having rims abutting with the rims of the other half-wall to complete the casing with at least two abutting half-walls forming a straight wall section with a flat near a corner, each shell having adjacent said corner an internal polygonal recess opening to the outside of the wall section with a round recess, the recesses of both half-walls forming complete polygonal and round cavities, respectively, and the shells having transversely aligned holes in respective sidewalls adjacent to and open towards said polygonal cavity; a ferrule haVing a polygonal head and a round shank fitting said polygonal and round cavities respectively, the ferrule being threaded throughout its length; and means for holding the shells together having rod portions in said aligned holes, said rod portions forming backstops for mounting screws threaded into said ferrules.

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