US2467458A - Electrical circuit, including a switch and plug mechanism - Google Patents

Description

3 Sheets-Sheet l AA Z m p W. J. BAUROTH I ELECTRICAL CIRCUIT, INCLUDING A SWITCH AND PLUG MECHANISM April 19, 1949.

Original Filed May 1, 1945 April 19, 1949. w. J. BAUROTH ELECTRICAL CIRCUIT, INCLUDING A SWITCH AND PLUG MECHANISM Original Filed May 1, 1943 3 Sheets-Sheet 2 April 19, 1949. w. J. BAUROTH ELECTRICAL CIRCUIT, INCLUDING A SWITCH AND PLUG MECHANISM Original Filed May 1, 1943 3 Sheets-Sheet 3 BWALTER JBAURO g) wa flm,

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Patented Apr. 19, 1949 ELECTRICAL CIRCUIT, INCLUDING A SWITCH AND PLUG MECHANISM Walter J. Bauroth, Columbus, Ohio, assignor to The Jeifrey Manufacturing Company, a corporation of Ohio Original application May 1, 1943, Serial No. 485,291. Divided and this application March 8, 1948, Serial No. 13,648

11 Claims. 1

This invention relates to electrical circuits including at least two switches operated by a common operating means which is moved to operate the switches by a connector plug in one of the circuits.

One object of my invention therefore is to provide an improved mechanism for providing improved circuits of the type above set forth.

Another object of my invention is to provide improved electrical apparatus for a mining machine in which a pair of switches are contained preferably, but not necessarily, in a permissible, explosion or flame-proof box and are controlled by mechanism requiring one of the switches to be opened when one is closed and vice versa, one of said switches controlling the cutting motor for the mining machine and the other an auxiliary device that is to be operated such, for example, as a motor of a drill or water pump.

Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims.

In the accompanying drawings,

Fig. 1 is a sectional elevational view of the device of my invention, certain parts not being shown entirely in section in the interest of clearness;

Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1, looking in the direction of the arrows;

Fig. 3 is a sectional view taken on the line 33 of Fig. 1, looking in the direction of the arrows;

Fig. 4 is an enlarged plan view of a portion of the box and plug with the operating sleeve of the plug shown in developed relation;

Fig. 5 is a plan view of the device of my invention with parts broken away and in section and with certain parts omitted in the interest of clearness;

Fig. 6 is a front elevational view of the device;

Fig. 7 is a view of a portion of the plug compartment with the operating sleeve moved to the switch closing and plug locking position;

Fig. 8 is a view similar to Fig. 5 of a modified form of my invention in which two switches are housed within a flame-proof compartment and are controlled by common operating mechanism;

Fi 9 is a sectional view taken on the line 9-9 of Fig. 8, looking in the direction of the arrows, showing particularly the operating mechanism for one of the switches;

Fig. 10 is a sectional view taken on the line |0-l0 of Fig. 8, showing the operating mechanism for the other switch; and

Fig. 11 is a wiring diagram showing the connections to the mining machine motor and the auxiliary motor.

This application is a division of my co-pending parent application, Serial No. 485,291, filed May 1, 1943, for a Switch and plug box, now Patent No. 2,441,465, dated May 11, 1948.

In gaseous mines such as gaseous coal mines it is necessary in order to meet the requirements of the Bureau of Mines to provide what is known as permissible or explosion or flame-proof equipment and to this end it is necessary to prevent the exposing of any electrical conductors, plugs or the like, in which it is possible to have the exposed conductors or plugs energized even though current may not be flowing in them. In other words, a voltage must not be present on any exposed electrical conductors or plugs.

In the apparatus which I have provided, a disconnectible plug is provided and mechanism which forms a permanent part of the complete plug is provided to control a switch which disconnects the plug from the source of voltage before the plug can be exposed, the plug itself being contained in an explosion, or flame-proof compartment when it is in an electrical conducting condition.

Referring to the drawings it will be seen that I have provided a permissible, explosion or flameproof box, housing, or enclosure in which includes a relatively large switch compartment or enclosure II and an integral extension formin a plug compartment, housing or enclosure 12. The bottom, side and end Walls of the explosion or flame-proof switch compartment 1 l are integrally formed of such material as cast iron and the top is formed by a removable top plate l3, removably attached by a plurality of machine screws Hi. The rear wall of said compartment H is provided with a pair of stuffing boxes I5 each adapted to receive a single conductor cable and provide a flame-proof connection therewith.

In some arrangements which I have provided, a plurality of boxes iii are mounted upon a common base and are electrically interconnected and to this end the rear of the compartment l l is also preferably provided with openings IS on opposite sides thereof which, when a single box is employed, is either filled by a removable plug or the opening is not actually formed but is cast solidly close together with the side walls of the box Ill. The two cables received by the stuffing boxes l5 lead to a source of potential and consequently they "are always energized or hot" and these cables are connected within the compartment l I to the receiving terminals of a combination switch and overload circuit breaker H.

The plug compartment l2 includes an integrally formed neck I8 which extends horizontally and forwardly from the front wall of the compartment H and this neck receives a sleeve I9 having a peripheral outer rim 29, the sleeve 19 being connected to the neck It by four spaced machine screws 2! (see Fig. 6). The inner end of the sleeve l9 includes an integralwall' 22 which wall acts as a partition to divide the plug compartment i2 into two parts and acts to support two separable parts of an electrical receptacle or socket 23 which is made of insulating material and which is connected to the partition 22 by three bolts 25 (see Fig. 2). Said bolts 2t extend through three openings which can be seen at 25, particularly in Fig. 6 of the drawings, said openings 25 being formed in integral wings of the partition 22 that extend into a central opening 26 formed in the partition 22, as illustrated in dotted lines in Figs. 2 and 6 of the drawings. Said central opening 25 provides for the extension therethrough of bayonet type receiving contacts which are provided in the receptacle 23, this type of electrical receptacle being well known in the electrical art.

It may be mentioned that the plug or receptacle 23, includes an inner portion 21 which has three terminals 28 which are connected to three electrical conductors forming part of a short cable 23 which extends through a stuffing box 33 carried by a pair of arms 3!, said stuffing box having a flame-proof fitting between the outer cylindrical surface thereof and a cylindrical opening in the front wall of the switch compartment 1 l, thus providing a permissible r flame-proof passageway for the conductors of cable 29. In. said compartment Ii two of the conductors of cable 29 are connected to the output terminals of the switch H and the third conductor thereof is the ground conductor which is. grounded to the box it within said compartment 1 I, as. is clearly illustrated in Fig. l of the drawings, by being connected to a projection formed integrally with said box it and within the compartmentv H The receptacle 23 also includes an outer portion 32 which is outside or to the leftv of the partition 22, the two portions 21 and 32 of said receptacle 23 being held together and mounted on the partition 22 by the bolts 24, as above described. Said outer receptacle portion 32 carries three bayonet.

receiving contacts to receive the three bayonet prongs of a removable plug, as hereinafter described more completely, said plug andreceptacle structure being of a type well known, inthe electrical art.

Mounted upon the end of a three conductor electrical cable 33, which electrical cable may be the source of power for any desired piece of apparatus, I provide what I shall designate as a complete plug 3%. It may be stated that the electrical apparatus or device to be operated and. to which energy is supplied by the cable 33 may be of any type. By way of illustration it may be stated that the apparatus of my invention has been employed in coal mining apparatus in which the cable 33 energized electrical drills for drilling the mine face in a coal mine and electrical water wagons which provide water to spray the mine face while a cutting machine is cutting a kerf. These are only two illustrations of which many might be given of the type of apparatus in which my device may be employed.

Referring particularly to the structure of the complete plug 34, attention is directed particularly to Figs. 1, 5 and 7 of the drawings. Said complete plug 34 includes a plug holder or main body 35 which includes a handle 36 by which the plug may be connected or disconnected and also includes a cylindrical housingportion 31. Within the housing portion 3'? is mounted an electrical insulated plug 38 provided with three bayonet type blades adapted to be projected into the aforementioned electrical contacts carried by the reoeptacle 23. The electrical plug 38 is attached by three spaced screws 39 to integrally formed ears provided within the hollow interior of the plug holder 35. Rotatably mounted on the outer cylindrical surface of the housing portion 37 is a generally cylindrical sleeve ill which is provided with a plurality of radially extending lugs ll (see Fig. 6) which are adapted to be gripped by an operator to rotate said sleeve 4-9 for the purpose of locking the complete plug 3:3 in place and simultaneously operating the switch ll to close its circuit, as hereinafter described more completely.

The sleeve M is also provided with a stop member 42 adapted to co-operate with, a stationary stop member 43 carried by the rim 2B. of sleeve [9 to limit rotary motion of said. sleeve 40 in a counter-clockwise direction. The sleeve 4'0 is preferably made as a brass casting and, of course, the interior surface thereof is cylindrical and of appreciable longitudinal length so as to have contact over a, large bearing area with the outer cylindrical surface of the housing portion of plugv holder 35. Also the, outer surface of the. sleeve 40 is cylindrical and has an appreciable bearing area with the inner cylindrical surface of, the sleeve I9.

These two relatively large. bearing surfaces between the. sleeve 4'0. and the housing portion 31. in one instance and the sleeve IS in the other instance are for the purpose of insuring a permissible, explosion or flame-proof construction for the plug compartment. l2. In other Words, should. an explosion take place-within said compartment I2, due to it becoming filled with explosive gas in a gaseous mine, which gas was ignited by an electric spark, the explosion in the compartment I2 would not. be capable of discharging a flame outsidesaid compartment. This is because the hot expanded gases resulting from the explosion would have to travel over such elongated paths along the surfaces on both the Outside and inside of the sleeve lflas to cool saidgases sufficiently to prevent the appearance of a flame outside said compartment l2 The sleeve 40 is mounted for rotary movement with respect to the plug holder 35- as previously described but after being once assembled it becomes a permanent part of the complete plug 34 and is held against longitudinal movement with respect to said plug holder 3.5- by virtue of the fact that, the inner end of the cylindrical housing 3.1 is provided with a peripheral ledge 44. adjacent which the inner end of the cylindrical housing, 31 abuts. The outer endof the sleeve 40 is held againstv longitudinal movement with respect to the plug holder 35 by a wire ring t5 which fits into. a groove in said plug holder 35- and' the ends of which are perfectly welded together after it isinserted in said groove.

It is an important feature of my invention that after the complete plug 34 is inserted in place to eifect an electrical connection and with the parts in position as illustrated in Fig. 1' of the drawings itis possible by rotating the sleeve 48, by grasping the lugs 4|, to lock the complete plug 34 in place, thus preventing its removal and simultaneously closing the switch l1 by moving it to the on position. To this end the sleeve 48 is provided with a lug or actuator in the form of an integral extension or key 46 which is formed as a segment of a cylinder and which is provided with an arcuate slot or groove 41 (see particularly Fig. 4) which groove upon rotation of the sleeve 48 in a clockwise direction from the position illustrated in Fig. 1 to the position illustrated in Fig. '7 receives a portion of the partition 22 and as a consequence will prevent removal of the complete plug 34 and thus will prevent breaking of the electric circuit by the electrical plug 38 and receptacle 23.

At the same time that the complete plug 34 is thus locked in position it simultaneously is effective to close the switch H (which switch l1 otherwise cannot be closed) by moving the switch operating mechanism hereinafter described. To this end there is provided within the switch compartment II a longitudinally extending operating rod 48 slidably mounted in a bore 49 formed in a boss 58 at the rear end of the switch compartment H and sliding through a bore in a boss 5| (see Fig. 4) in the front wall of said compartment H.

The rod 48 of the switch operating mechanism is provided with a yoke 52 (see Fig. 3) which has sliding contact with the top plate l3 and which is removably attached to the rod 48 by a screw 53. The yoke 52 acts as one abutment for a coil spring 54 which is coiled about the rear end of the rod 48 with the opposite end abutting the boss 58. As a consequence of this structure the rod 48 is held against rotation and is mounted for longitudinally sliding movement and is resiliently urged or held in one position, that is, to the left as viewed in Figs. 1 and 5 of the drawings.

Intermediate its ends the rod 48 is provided with a transverse groove 55 which receives an operating member 56 of the switch l1, said groove 55 being provided on opposite sides of said member 56 with removable leather blocks 51 to provide cushion means for the operating member 56.

With the members in the positions illustrated in Fig. 1 of the drawings, the switch I1 is in the oif or open circuit position and to move it to the on or closed circuit position the rod 48 is shifted to the right carrying with it the operating member 56.

It may be stated that if the overload relay of the combined switch and relay I1 opens in response to excessive current, this will take place only when the switch [1 is closed and to reset the overload relay the operating member must be moved to the off position and then to the on" position which can be efiected, of course, by operating the rod 48.

The left-hand end of the rod 48 extends into the plug compartment 12 and as particularly illustrated in Fig. 4 of the drawings it is to be noted that the extreme left-hand end of said rod 48 is positioned adjacent and behind a portion of the partition 22. As a consequence, it is practically impossible for anybody to manipulate the rod 48 except by inserting the complete plug 34 and rotating the sleeve 48 to effect its operation in a manner now to be described.

It may be pointed out that the lug, extension or key 46 of the sleeve 48 extends through a very narrow arcuate elongated slot 58 (see Fig. 2) which is formed in the partition 22 and when v the parts are assembled as illustrated in Fig. 1

of the drawings this elongated slot 58 is the only effective opening in the partition 22 since all other openings have been closed by the receptacle 23.

It is to be noted that due to the small width of the slot 58 it would be extremely difficult for any person to extend a tool into it and get a working contact with the rod 48 to move it, particularly in view of the fact that the left-hand end of the rod 48 is behind a wall of the partition 22. This diificulty is further increased by the fact that the end of the rod 48 is provided with an anti-friction roller 59 and if a tool such as a screw driver would project through the slot 53 it could not easily be caught on the rod 48 because the roller 59 would tend to cause it to roll oif. The roller 59 provides an anti-friction bearing between the operating rod 48 and a cam surface 68 which is formed on the extension or key 46. Thus unauthorized closing of switch [1 is prevented when plug 34 is removed. This precludes energization of the contacts in compartment 12 except when it is in a flame-proof condition.

It is obvious that when the sleeve 48 is rotated in a clockwise direction from the position illustrated in Fig. 1, the cam surface 68 (see Fig. 4) will contact with the roller 59 forcing the rod 46 to the right, as viewed in Figs. 1, 4 and 5, and continued rotation of said sleeve 48 and extension 46 will move the rod 48 sufiiciently to the right against the action of the spring 54 to operate the member 56 to move the switch l1 to the circuit closing or on position. This on position of the rod 48 and roller 59 and the cam surface 88 is illustrated in Fig. '7 of the drawings and the position of the roller 59 is indicated in the on position in dotted lines in Fig. 4 of the drawings, both with respect to its position on the rod 46 and with respect to its position relative to extension or key 46. Thus with the sleeve 48 rotated in a clockwise direction with the parts all assembled the switch I1 will be on and the complete plug 34 will be locked so as to provide the complete flame-proof character of the plug compartment 12.

It may be noted that the cam surface 68 provides a hump on the extension or key 46 which will frictionally hold the parts in the on or circuit closing position as illustrated particularly in Fig. 7 of the drawings.

The operation of the device is believed clear from the above description but to review it briefly it will be assumed that if an operator desires to connect an auxiliary device that is to be operated, such, for example, as the motor of an electrical drill which is provided with the electrical cable 33 and a complete plug 34, the complete plug 34 will be inserted by inserting the sleeve 48 into the sleeve l9. To insure the proper position of the parts, the top of the handle 36 is preferably provided witha label, marked Top as illustrated in Fig. 5 of the drawings.

It is, of course, necessary that the bayonet contacts of the plug 38 be received properly by the receptacle 32 and to insure this alignment the plug has a fixed relation to the cylinder housing portion 31 of the plug holder 35 which is determined When the parts are rigidly assembled and this is determined by a small pin 6| (see Fig. '7) which projects into a notch 62, the pin 6i being carried by the cylinder housing portion 31 and the notch 62 being formed in the electrical plug 38. The plug holder 35 can have only one position with respect to the sleeve [9 and this is effected by virtue. of a pin 63. (see. Fig. 2.) which is carried by the partition. 22 and which projects into a slot or groove 6 3 formed on. the inner end:

of the plug holder These two co-operating parts 63 and 6 3, of course, prevent rotation of the plug holder 35 when the sleeve 4c is rotated to lock the complete plug 3 and to operate the switch ll.

Assuming, therefore, that the parts have been inserted as above described, the electric contact will be made between the electrical plug 38 and receptacle 23 to complete the electric circuit to the switch ill from the cable 33. The plug compartment 152 will, now be completely closed providing a fiame-proof or permissible compartment. The sleeve 58 will then be rotated by an operator grasping the lugs (ll, which are in the nature of an operating handle for rotating said sleeve if) in a clockwise direction. When this rotation is completed the complete plug 3 5 will be locked in position by virtue of the slot 47 receiving a portion of the partition 22. This, of course, will prevent removal of the complete plug 34 until sleeve M3 is rotated to a reverse position.

The condition of the parts with said complete plug 3c locked is illustrated in Fig. 7 of the drawings. This rotary motion in addition to locking the complete plug 34 will also close the switch ll by moving the operating rod d8 against the action of the spring 54 or, in other words, move it to its on position. This is effected by the cam surface til of the extension or key t3 pressing against the anti-friction roller 59 and consequently forcing the operating rod 33 rearwardly, which movement operates the member 56 to close the switch ll. The form of the cam surface til with the final on position, will tend to hold the parts in the on or locked position, the said spring pressed roller 59 operating as a spring detent.

After the drill has been used to the extent desired, in case it is desired to disconnect the cable 33 so as to take the drill to another part of the mine, the handle provided by the lugs 415 will be rotated in a counter-clockwise direction and under the action of the spring 54 the rod 48 will move to the left, or forwardly to open the switch H, or move it to its old position, and the complete plug 34 will be free so that it can be pulled out by longitudinal pull on the handle 3%.

It is to be particularly noted that the switch compartment H is a fiame proof compartment under all conditions- The plug compartment [2 is made flame-proof whenever the complete plug. 34 is'insertcd and it is impossible to energize any of the electrical connectors in the plug compartment [2 until the complete plug 34 has been locked in position because the locking of said complete plug in position is a necessary incident to the operation of the control switch I]. It is also evident that I have made it extremely difiicult, if not impossible, for any one to operate. the switch H to its on or closed position; except by inserting the complete plug 34 and adjusting it to its locked position. As a consequence, it is practically impossible to provide a voltage in the plug compartment i2, by any manipulation of switch ll, except when the complete plug 34" is locked in place and said plug compartment or housing I 2 is closed and flame-proof in character. In other words, when the plug 3 5 is removed, the receptacle-23 is dead.

Features of the invention herein described in connection with Figs. 1 through 7' are claimed in my parent application, Serial No. 485,291, hereinbefore identified.

In Figs. 8, 9 and 10 of the drawings I have shown a modified arrangement in which the structure is the sameas that previously described unless a contrary fact is indicated. In this modifieclstructure I. have providedv a. toggle switch which is placed in the flame-proof switch compartment H alongside the switch I' l. The toggle switch. t5 controls a device to be operated such as the motor which drives the cutter chain of a mining machine and this switch 65 and switch I! are so interlocked that the former is in. the off position while the latter is in the on position and. vice versa. This is an important safety feature and precludes operation of an auxiliary motor or device such as a hand-operated electric d-ril-l except when. the cutting mechanism of the mining machine is shut off. To provide this interloclc, an operating arm 66 is carried by the rod 38 and this arm 66 preferably is provided with. spaced. contact bearing lugs 67- which have sliding frictional contact with the cover plate H3. The arm 6G- is shown L-sha-ped and the outer end thereof is provided with a U-shaped yoke fit (see Fig. 10) which. straddles the operating member 5'9 of the switch 65. As illustrated in Figs. 8, 9 and 10 of the drawings, the switch l? is open or is in the off position. When the rod 42 is moved tothe right, as viewed in Fig. 8, by the operation of the cam surface 65-, as previously described in connection with Figs. 1 to 7, inclusive, the rod. 43: will be moved to the right and: switch l lwill: be closed while switch 65 will 7 beopen.

The electrical circuit in which two switches El and" t5 as well. as the complete plug a l and associated cable 33 are: an: important part, is illustrated in Fig. ll of the. drawings. As here illustrated, the motor 78' is, for example, the motor which drives the cutter chain of a mining machine and. purely by Way of illustration it may besimilar to the motor illustrated in detail in Fig. 3-7 of the patent: to R. K. Jeffrey et al., 2,263,779; dated Novemb'er'2'5, 1941. This electric motor. is energized from a pair of main line conductors ll: and. is; controlled by a magnetic conta'ctor or switch. 12, that is, the switch or contactor 72 controls the energization of motor ill from conductors H- The contactor 72 is under the control of the toggle switch 55 and a starting switch M over an obvious circuit so that wherever the toggle switch 65 is closed or in its on r position the conta'ctor 12 may be energized by closing the switch T4 to drive the motor iii and when: toggle switch 65 1s open or in its oif'position, contactor T 2 cannot be energized to start the motor 70;

Branch conductors lead from main conductors H directly to switch H which controls the conductors of short cable 29 and of cable 33* through the plug 38- and receptacle 23'. Cable 33 leads toan auxiliary motor T3 which may be the motor of any auxiliary apparatus, oneillustration of which maybe the motor of a hand drill such as illustrated in Patent'No. 2,159,087 to R. K. Jeffrey, dated May 23, 1939; This hand drill is UIZCIET- stood to be-only one'illustration' of various types of equipment which may be attached to cable 33.

In addition to the features above described in connectionwith' the devices of Figs. 1 to 7, it is evident that the devices of Figs. 8 to 11 provide a safety featiu'e; in that the auxiliary device such as-the-hand drill; can onlybe operatedwh'en the circuit to the cutting motor of the mining machine is open. As a consequence, an operator working at the face of a mine room is protected against the extreme hazard which might otherwise be occasioned by the operation of the cutting mechanism of the mining machine.

Obviously those skilled in the art may make various changes in the details and arrangement of parts without departing from the spirit and scope of my invention as defined by the claims hereto appended, and I therefore wish not to be restricted to the precise construction herein disclosed.

Having thus described and shown an embodiment of my invention, what I desire to secure by Letters Patent of the United States is:

1. In electrical apparatus, the combination with a flame-proof box, of a pair of switches in said box, a pair of electrical motors, electrical circuits for said motors including said switches, one for each circuit, common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a flame-proof plug and receptacle compartment therefor carried by said flame-proof box, said common switch operating mechanism extending from said flame-proof box into said flame-proof plug and receptacle compartment, means resiliently holding said switch operating mechanism in one position, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid.

2. In electrical apparatus, the combination with a flame-proof box, of a pair of switches in said box, a pair of electrical motors, electrical circuits for said motors including said switches, one for each circuit, common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a flame-proof plug and receptacle compartment therefor, said common switch operating mechanism extending from said flame-proof box into said flame-proof plug and receptacle compartment, means resiliently holding said switch operating mechanism in one position, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid.

3. In electrical apparatus, the combination with a flame-proof box, of a pair of switches in said box, a pair of electricalmotors, electrical circuits for said motors including said switches, one for each circuit, common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, and a flame-proof plug and receptacle compartment therefor carried by said box.

4. In electrical apparatus, the combination with a box, of a pair of switches in said box, a pair of electrical motors, electrical circuits for said motors including said switches, one for each circuit, common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a plug and receptacle compartment therefor, said common switch operating mechanism extending from said box into said plug and receptacle compartment, means resiliently holding said switch operating mechanism in one position, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid,

5. In electrical apparatus, the combination with a box, of a pair of switches in said box, a pair of electrical motors, electrical circuits for said motors including said switches, one for each circuit, common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a plug and receptacle compartment therefor, said common switch operating mechanism extending from said box into said plug and receptacle compartment, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid.

6. In electrical apparatus, the combination with a flame-proof box, of a pair of switches in said box, a pair of electrical motors, electrical circuits for said motors including said switches, one for each circuit, and common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed.

7. In electrical apparatus, a combination including a pair of switches, a pair of electrical devices to be operated, electrical circuits for said devices including said switches, one for each circuit, a common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a plug receptacle therefor, said common switch operating mechanism extending into said plug receptacle, means resiliently holding said switch operating mechanism in one position, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid.

8. In electrical apparatus, a combination including a pair of switches, a pair of electrical devices to be operated, electrical circuits for said devices including said switches, one for each circuit, a common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a plug receptacle therefor, said common switch operating mechanism extending into said plug receptacle, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid.

9. In electrical apparatus, a combination including a pair of switches, a pair of electrical devices to be operated, electrical circuits for said devices including said switch, one for each circuit, a common operating mechanism for said switches constructed and arranged to insure opening of one of said switches when the other is closed, one of said circuits including an electrical cable having a plug, a plug receptacle therefor, and means on said plug for moving said switch operating mechanism to operate both of said switches as aforesaid.

10. In mining apparatus, the combination with a mining machine motor, of an auxiliary motor, circuits for said motors including an individual switch for each, an electrical cable forming at least part of one of said circuits and having a removable plug, a flame-proof box within which both of said switches are housed, a plug compartment on said box having an electrical recepcal device to be operated, circuits for said motor 10 and auxiliary device including an individual switch for each, an electrical cable forming at least part of the circuit for said auxiliary device and having a removable plug, a flame-proof box within which both of said switches are housed, a plug compartment on said box having an electrical receptacle therein, co-operating means on said plug and compartment to provide a flameproof enclosure when said plug is inserted in said receptacle, and means for simultaneously opera-ting both of said switches to move one to open position and the other to closed position whereby said auxiliary device can be operated and said motor cannot be operated and vice versa.

WALTER J. BAUROTI-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 15 Number Name Date 1,811,090 Livingston June 23, 1931 2,159,087 Jeflrey May 23, 1939

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