US2441465A - Switch and plug box - Google Patents

Description

1948. w. J. BAUROTH SWITCH AND PLUG BOX Filed May 1, 1943 3 Sheets-Sheet l w ON y k l/vvElvroei WALTER J. BAUEOTH, BY C W.

, May 1948- w. J. BAUROTH SWITCH AND PLUG BOX Filed May 1, 194:5

3 Sheets-Sheet 2 Rm Mr? K g E y 1, 1948. w. J. BAUROTH SWITCH AND PLUG BOX 5 Sheets-Sheet 3 Filed May 1, 1943 WALTER J. BAuEoTH,

BY MM QR S o mw Ynfirw T 8 N $1 .1 3 w 9. I s \\\\\A\k l m m I n m P. nw

I l I I I I I I I I I III IIIIIIII VIII-Mm In Q 3 X Q Patented May 11, 1948 UNITED STATES PATENT OFFICE SWITCH AND PLUG BOX Application May 1, 1943, Serial No. 485,291

1'7 Claims. 1

This invention relates to a switch or circuit breaker and plug box which is designed particularly for use in a gaseous mine such as a coal mine though it may have many other uses.

An object of the invention, therefore, is to provide an improved switch and plug box of the so-called permissible or flame or explosion-proof type.

A more specific object of the invention is to provide a device of the above-mentioned type in which the electrical disconnectible plug is in a permissible or flame or explosion-proof compartment of the box which is separated from another permissible or flame-proof compartment containing a control switch.

A further object of the invention is to provide apparatus of the'above-mentioned type in which a control switch is in one permanent flameproof compartment and is connected to a disconnectible plug in a compartment which may be selectively open or closed and when closed is of the flame-proof type and in which there is mechanism operable from the plug compartment to control the switch in the switch compartment.

Another object of the invention is to provide apparatus of the above-mentioned type in which a plug is locked in position in its flame-proof compartment and when so locked automatically closes the switch in the switch compartment, said switch being automatically open when the looking mechanism of the plug is adjusted to permit removal of said plug.

Another object of the invention is to provide an improved type of electrical plug having locking mechanism associated therewith as well as switch operating mechanism associated therewith.

A further object of the invention is to provide as an article of manufacture a plug sleeve having a lug including locking means and preferably an operating cam or key formed as an integral part thereof.

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 22 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;

Fig. 9 is a sectional view taken on the line 99 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 |n |n 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.

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 Ill which in cludes a relatively large switch compartment or enclosure II and an integral extension forming a plug compartment, housing or enclosure [2. The bottom, side and end walls of the explosion or flame-proof switch compartment l I 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 M. The rear wall of said compartment H is provided with a pair of stufiing boxes 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 10 are mounted upon a com mon base and are electricaly interconnected and to this end the rear of the compartment H is also preferably provided with openings [6 on opposite sides thereof which, when a single box is eniployed, is either filled by a removable plug or the Opening is not actually formed but is cast solidly close together with the sidewalls OI the box 13. The two cables received by the stuffing boxes [5 lead to a source of potential and consequently they are always energized or hot and these cables are connected within the compartment H to the receiving terminals of a combination switch and overload circuit breaker H.

The plug compartment l2 includes an integrally formed neck 18 which extends horizontally and forwardly from the front wall of the compartment H and this neck receives a sleeve lfi having a peripheral outer rim 20, the sleeve 19 being connected to the neck [8 by four spaced machine screws 2| (see Fig. 6). The inner end of the sleeve I3 includes ah integral wall 22 which wall acts as a partition to divide the plug compartment 52 into two parts and acts to support two separable parts of an electrical receptacle or socket 23 which is made of ir lli latiilg material arid which is connected to the paitition 22 by three bolts 22 (see Fig. 2). Said bolts 24 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 steam-g 26 formed in the partition 22, as illustrated in dotted lines in Figs. 2 and 6 of the drawings. Said central opening 26 provides for the eiite'ns'icn therethrcugh of bayonet type receiving coritacts which are provided in the receptacle 23, this type of electrical receptacle being well kncwn in the electrical art.

It may be mentioned that the plug or receptacle 23 includes an inner pcrtion 21 which has three terminals 28 which are connected to three electrical conductors renting part of a short cable 29 which extends through a smiling box 30 carried by a pair or arms 3|, said s'tuifiing box 30 having a fiarne-procf fitting betwe'e'h the outer cylindrical surface thereof and a cylindrical opening in the front w all of the switch compartment H, thus providing a permissible or flame-proof pasageway for the conductors of cable 29. In said compartment ll two of the conductcrs of cable 29 are connected to the output terminals of the switch I! and the third conductor thereof is the ground conductor which is grounded to the box l0 within 's aid compartment II, as is clearly illustrated in Fig. i or the drawings, by being connected to a p r dje ctiloh formed integrally with said box l0 and within the compartm'eht H.

The receptacle 23 also includes an outer portion 32 which is outside or to the left or the partition 22, the two "portions 21 and 32 of said receptacle 23 b ing held together and mounted on the partition 22 by the bolts 24, as above described. Said 'o'uter receptacle portion 32 carries three bayonet receiving contacts to receive the three bayonet prongs or a removable luses hereinafter described more completely, said plug and reeeptauejstrucmre being of a type Well known in the electrical art.

Mounted upon the end of a' three conductor am ss 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 34. It may be stated that the electrical apparatus 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 apparatu's' in which the cable 33 energizes 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 or 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 housing portion 31. Within the housing portion 31 is mounted an electrical insulated plug 33 provided with three bayonet type blades adapted to be projected into the aforementioned electrical contacts carried by the receptacle 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 31 is a generally cylindrical sleeve 40 which is provided with a plurality of radially extending lugs 4| (see Fig. 6) which are adapted to be gripped by an operator to rotate said sleeve 43 for the purpose of locking the complete plug 34 in place and simultaneously operating the switch I! to close its circuit, as hereinafter described more completely.

The sleeve 40" is also provided with a stop member 42 adapted to cooperate with a stationary stopmernber 43 carried by the rim 2'!) of sleeve 19 to limit rotary motion of said sleeve 40 in a counter-clockwise direction. The sleeve 40 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 plug 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 l 9.

These two relatively large bearing surfaces between the sleeve 4? 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 I2. 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 12 would not be capable of discharging a flame outside said compartment. This is because the hot expanded gases resulting from the explosion would have to travel over such elongated paths along the surface'spn both the outside and insideof the sleeve '48 as to 0001 said gases sufilciently to prevent the appearance of a flame outside said compartment l2. The sleeve "0 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 35 by virtue of the fact that the inner end of the cylindrical housing 3'! is. provided with a peripheral ledge 44 adjacent which the inner end of the cylindrical housing 31 abuts. The outer end of the sleeve 40 is held against longitudinal movement with respect to the plug holder 35 by a wire ring 45 which fits into a groove in said plug holder 35 and the ends of which are perfectly welded together after it is inserted in said groove.

It is an important feature of my invention that after the complete plug 34 is inserted in place to effect an electrical connection and with the parts in position as illustrated in Fig. 1 of the drawings it is possible by rotating the sleeve 48, by grasping the lugs 4 I, to lock the complete plug 34 in place, thus preventing its removal and simultaneously closing the switch I! by moving it to the on position. To this end the sleeve 40 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 40 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 I! (which switch I1 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 50 at the rear end of the switch compartment l I and sliding through a bore in a boss 5| (see Fig. 4) in the front wall of said compartment ll.

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 [3 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 50, 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 off 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 l1 opens in response to excessive current, this will take place only when the switch I! is closed and to reset the overload relay the operating member must be moved to the 01f position and then to the onpositlon which can be effected, of course, by operating the rod 48.

The left-hand end of the rod 48 extends into th plug compartment l2 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 40 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 40 extends through a very narrow arcuate elongated slot 58 (see Fig. 2) which is formed in the partition 22 and when 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 diflicult 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 difficu-lty is further increased by the fact that the end of the rod 48 is provided with an anti-friction roller 58 and if a tool such as a screw driver would project through the slot 58 it could not easily be caught on the rod 48 because the roller 58 would tend to cause it to roll off. The roller 59 provides an anti-friction bearing between the operating rod 48 and a cam surface 60 which is formed on the extension or key 46. Thus unauthorized closing of switch I! is prevented when plug 34 is removed. This precludes energization of the contacts in compartment l2 except when it is in a flame-proof condition.

It is obvious that when the sleeve 40 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 48 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 sufficiently to the right against the action of the spring 54 to operate the member 56 to move the switch I! to the circuit closing or on position. This on position of the rod 48 and roller 59 and the cam surface 68 is illustrated in Fig. 7 of thedrawings 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 48 and with respect to its position relative to extension or key 46. Thus with the sleeve 40 rotated in a clockwise direction with the parts all assembled the switch I! will be on and the completeplug 34 will be locked so as to provide the complete flame-proof character of the plug compartment l 2.

It may be noted that the cam surface 60 provides a hump on the extension or key 48 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 electrical drill which is provided with the electrical cable 33 and a complete plug 34 the complete plug 34 will be inserted by insorting the sleeve 48 into the sleeve l9. To insure the proper position of the parts, the top of 7 the handle is preferably provided witha; label, marked Top as illustrated in Fig. f oi the drawings;

It is, of'course, necessary thatthebayonet contacts oi the plug 38 be received properly bythe' receptacle 32 and to insure this alignment the plug has a fixed relation to the cylinder housing portion 31. of the plug holder v which isde't'ermined when the parts are rigidly assembled and this is determined by a small pin 6 I (see Rig-'79 whi'chprojects into a notclr 62 the pin at being carried by the cylinder housing portion fl 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 I 9 and this i'sefiected by virtueof a pin- 63- (see Fig. 2 which is carried by the partition 22 and= which-projects into a slotor groove 64: formed on the inner. end of the plug holder 35. These two cooperatingparts' 63 and 64, of course, prevent-rotation or the plug holder 35 when the sleeve 4!] is rotated t'o lock the complete plug 34 and to operate the switch: l-l.

Assuming, therefore, thatthe 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 I1 from the cable 33. The plug compartment I? will nowbe completelyclo'se'd provldi'ng a flame-proof or permissible compartment. The sleeve- 40 will then be rotated byan operator grasping the lugs 4 1, which are in the nature of anoperating handle for rotating said sleeve 40' in aclockwise direction. When this rotation is completed the complete plug 34 will be locked' in position by virtue of the slot receiving a portion of the partition 221 This, of course, will prevent removal of the complete plug 34 until sleeve 49- is rotated to a reverse position.

The condition of the parts with said complete piugil'locked is illustrated-in Fig. 'Tcf thed'ra-vw ings. This rotary motion in addition to locking thecomplete plug 34 will also close the switch I1- by'movin'g the operating rod 48 against the actionof the spring 54 or; in otherword's; move it to-lts=on-'position. This is effected bythe-cam surface 61F of the extension or key 46 pressing against the-anti-friction roller is and consequently-forcing the operating rod Ml-rearwardly, which movement operates the member 56 to close the switch H. The form of the cam'suriace' Bil with theflnal on position, will tend to'ho'l'd the'parts in the on or locked position, thesaid spring pressed roller 59 operating as a spring detent.

Afterthe drill has been used to-the extent desired; in case'it' isdesired to-disconnect the-cable so: as totake the drill to another part" of the mine,- the handleprovided by thelugs 41'" will be rotated in a counter-clockwise direction and-under the action of the spring 5 the-rod 48 will move to the left, or forwardly'to openthe switch ll, or move it to its oil position; and thecompl'ete-plug 34 will'b'e free so that it" can bepulled outby longitudinal pull on the h'andle'35:

It is to be particularly noted that the switch compartment II is a flame-proof compartment under all conditions. The plug compartment I2 is made flame-proof whenever the complete plug 33' is inserted 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-plugin position is a necessary incident to the operation of the control switch Hi It is also: evident that have. made it extremely dimcult, ii: not impossible, for any one to operate the switch- IT 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 impossibleto provide a voltage in the plug compartment I 2, by any manipulation of switch I-"I, except when the complete plug 35 is locked i'n-pla'ce and said plug compartment or housing I 2 is closed and flame-proof in character. In other words, when the plug 34is'removed, the receptacle 23' is dead.

In" Figsi- 8', 9' and 10 of the drawings I have shown a modified arrangement in which the structure is the'sa-me a-s that previously described unlessa contrary fact is indicated. In this'modlfled structure I have provided a toggle switch 65 which is placed inthe switch compartment ll alongside the switch IT. The toggle switch 65 controls a motor which drives the cutter chain 01" a mining machine and this switch 65 and switch I'l' are so interlocked that the former is in the oil 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'such as a hand-operated electric drill except when the cutting mechanism of the mining'machine'is shut off. To'provide this interlock, an operating arm 66 is carried by the 1 rod 68. and this arm 66 preferably is provided with spaced contact bearing'lugs' 61 which have sliding frictional contact with the cover plate I 3". The ar'nrGGTi's shown L-shaped and the outer end thereof is' provided with a U-shaped yoke 68 (see'Fi'g. 10') which straddles the operatingmember 69 or the. switch 65'. As illustrated in' Figs. 8,, 9 andlOof'the drawingsthe switch I1 is open or is in the ofl'position. When the rod 48 is moved'lto the right, as viewed in Fig. 8, by the operation. of the" cam surface 60, as previously describedi'n' connection with Figs; 1 to '7; inclusive; the rod 48 will be moved to the right and switch l1 will be closed while switch will be open.

The electrical circuit in which two switches I1 and as well as the complete plug 34" and assoelated. cable 33 are an. important part, is illustratedin'FigI 11 of the drawings; As here illustrated, the motor 10 is,.for example, the motor which" drives the cutter chain of a mining machine and purely" by' way or illustration it may be si'miiar'to the motor illustrated in detail in Fig: 37of the patent to R; K. Jeiirey'et all, 2,263,- 779; dat'edi November 25, 1941'. This electric motor is energizedfroma pair or mainline conductors H and is controlled by a magnetic contactor or switch 12, that is, the switch or contactor' l2 controls thei. energization of motor 10 from conducto'rs ll The contactor 12' is under the control of the toggle switch 65: and a starti'n'g" switch T4 over an obvious circuit so that whenever the toggle'switch 65 is closed or in its onp'ositlon' the c'ontactor'll maybe energized by closing". the switch 14 to drive the motor 10 andwlientoggle switch 65 is open or in its oii" position; contact'or' 12 cannot" be energized to start thefmotor' 101 Branch conductors lead ir'ommai'n' conductors ll directly to switch I] whichcontrolsthe conductorsofshort cable 29 andofr cable 33through the pl'ugi38an'd' receptacle 23. Cable 33' leads to an auxiliary motor" 13 which may be" the. motor of": any auxiliary apparatus; one illustration of whichmaybe the motor of a hand drill'such as illustratedinPatent'No. 2,159,087 to R. K. Jei- 9 trey, dated May 23, 1939, This hand drill is understood 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 connection with the devices of Figs. 1 to 7, it is evident that the devices of Figs. 8 to 11 provide a safety feature, in that the auxiliary device such as the hand drill, can only be operated when 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 cuting mechanism of the mining machine.- The features of invention herein described in connection with Figs. 8 through 11 are claimed in my copending application, Serial No. 13,648, filed March 8, 1948, for improvements in Electrical circuit including a switch and plug mechanism.

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. A device of the class described including an explosion-proof enclosure, a circuit controlling switch in said enclosure, a disconnectible electrical cable plug and receptacle carried outside said enclosure and connected to said switch, mechanism for operating said switch including operating means located entirely within said enclosure, means preventing operation of said operating means by an operator, and actuating means carried by said plug for .actuating said operating means when said plug is inserted in its receptacle.

2. A device of the class described including an enclosure, a circuit controlling switch in said enclosure, a disconnectible electrical cable plug and receptacle carried outside said enclosure and connected to said switch, mechanism for operating said switch including operating means located entirely within said enclosure, means preventing operation of said operating means by an operator, and actuating means carried by said plug for actuating said operating means when said plug is inserted in its receptacle.

3. In electrical circuit controlling apparatus, an explosion proof switch box, a connected explosion-proof plug and receptacle housing, a 7

switch in said switch box, a plug and receptacle in said connected housing connected with said switch, mechanism providing for closing said switch, means preventing operation of said switch closing'mechanism by an operator when said plug is removed from said receptacle, and means associated with said plug providing for operation of said switch closing mechanism when said plug is in the receptacle.

4. In electrical circuit controlling apparatus, an explosion-proof switch box, a connected explosion-proof plug and receptacle housing, a switch in said switch box, a plug and receptacle in said connected housing connected with said switch, mechanism providing for closing said switch, means preventing operation of said switch closing mechanism by an operator when said plug is removed from said receptacle, and mechanism for locking said plug in said receptacle and actuating said switch closing mechanism, said switch closing mechanism being operable only by said locking mechanism and requiring said switch to be opened before said plug can be removed.

5. In electrical circuit controlling apparatus, an explosion-proof switch box, a connected explosion-proof plug and receptacle housing, a switch in said switch box, a plug and receptacle in said connected housing connected with said switch, mechanism providing for closing said switch, means preventing operation of said switch closing mechanism by an operator when said plug is removed from said receptacle, and mechanism for locking said plug in said receptacle and actuating said switch closing mechanism, said switch closing mechanism being operable only by said lockin mechanism.

6. A combination switch and plug box including an explosion-proof switch compartment, a control switch in said compartment, an explosion-proof plug receptacle compartment, a plug receptacle in said receptacle compartment, an operating lever for said switch extending from said switch compartment into said plug receptacle compartment and operable in opposite di rections to operate said switch to off and on positions, respectively, conductors connecting said switch and plug receptacle, an electrical contacting plug having conducting means constructed for insertion into electrical contact with said receptacle and removal therefrom, means for simultaneously locking said plug in said receptacle when they are connected and operating said lever to move said switch to its on position, and means preventing operation of said lever except by said last-named means.

-7. In a switch and plug box, an explosion-proof compartment, a switch in said compartment, an operating lever for said switch, a, plug receptacle connected with said switch, a removable plug insertable in said receptacle, means preventing access to said operating lever by an operator, and mechanism carried by said plug for operating said lever to close said switch and lock said plug in said receptacle when said plug is in said receptacle.

8. In a switch and plug box, an explosion-proof compartment, a switch in said compartment, an operating lever for said switch, a plug receptacle connected with said switch, a removable plug insertable in said receptacle, means preventin access to said operating lever by an operator, and mechanism carried by said plug for operating said lever to close said switch when said plug is in said receptacle.

9. In a switch and plug box, an explosion-proof compartment, a switch in said compartment, an operating lever for said switch, a plug receptacle connected with said switch, a removable plug insertable in said receptacle, means preventing access to said operating lever by an operator, and mechanism carried by said plug for operating said lever to close said switch and lock said plug in said receptacle when said plug is in said receptacle, said mechanism including a rotary sleeve having a lever operating key and having a locking groove fitting over and interlocking with a member on said box when said sleeve is rotated to locking position.

10. In a switch and plug box, an explosionproof compartment, a switch in said compartment, an operating lever for said switch, a plug receptacle connected with said switch, a removable plug insertable in said receptacle, means preventing access to said operating lever by an

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