US2266663A

US2266663A - Explosionproof plug receptacle

Info

Publication number: US2266663A
Authority: US
Publication date: 1941-12-16
Anticipated expiration: 1958-12-16

Description

Dec. 16, 1941. SPRAGUE 2,266,663

EXPLOSIONPROOF PLUG RECEPTACLE Filed April 6, 1958 3 Sheets-Sheet l ENOCH K. SPRAGUE ATTORNEYS Dec. 16, 1941. E. K. SPRAGUE EXPLOSIONPROOF PLUG RECEPTACLE Filed April 6, 1938 5 Sheets-Sheet 2 gnuc'nl'o'n ENOCH K. SPRAGUE Dec. 16, 1941. 1-:. K. SPRAGUE EXPLOSIONPROOF PLUG RECEPTACLE Filed April 6, 1938 3 Sheets-Sheet 3 NmVunH oo L anon MM ENOCH K. SPRAGUE ATTORNEYS Patented Dec. 16, 1941 UNITED STATES PATENT OFFICE 10 Claims.

This invention relates to explosion-proof plug receptacles of the type wherein a plug-in connection may be made without the danger of the parts being blown apart by an explosion which may take place.

Under certain circumstances the insertion of a plug in a receptacle when making an electrical connection presents very serious hazards. For example, in grain elevators, or in other places where dust is likely to accumulate, or in 'factories where an accumulation of gases is possible, the making of an electrical connection is extremely hazardous because ofthe fact that the are caused by the electrical contact will ignite the dust or gases with an explosive violence. While this explosion may be local in character and confined to the receptacle, it has been at times violent enough to blow the plug from the receptacle so that the plug has seriously injured the worker inserting the plug therein.

It is an object of this invention to make a plug receptacle in which the danger of creating an electrical are on insertion of the plug is substantially eliminated.

Another object of this invention is to make a plug receptacle so that at the time when an arc could be created, the plug is locked against outward movement and thus the danger of flying parts is avoided.

A further object of the invention is to make a plug receptacle in which the plug must be in serted and locked against outward movement before a switch is actuated to effect an electrical contact. H

lhe objects of the invention are in general obtained by forming a receptacle enclosing a mercury switch, and supplying means to lock the plug to the receptacle before the mercury switch can be closed. This is done by attaching the switch to an auxiliary plug body, which body has spring contact blades engaging the plug proper. The arrangement is such that the plug must be inserted simultaneously into the auxiliary plug and locked to the-base receptacle before'the switch is turned to create an electrical circuit between the plug and the auxiliary plug. In this way, should an arc be caused, the plug cannot be blown outwardly, because it has first been locked to the receptacle. Furthermore, the chances of an are forming are substantially eliminated as contact is made between metal blade parts before the fluid mercury in its sealed vessel flows to establish the electrical circuit.

The m ans by which these and other objects of my invention are obtained are more fully set forth in the following description of the invention taken in connection with the accompanying drawings, in which:

Fig. 1 is a side view partially in elevation, of the invention with all parts assembled, and the mercury switch in closed position.

Fig. 2 is a front View of the receptacle with the plug removed.

Fig. 3 is a cross-sectional view of the plug member on the line 3--3 of Fig. 1.

Fig. 4 is an end View of the receptacle box shown in Fig. l with a portion of the bottom plate removed to show the switch mechanism.

Fig. 5 is an enlarged detailed view of the plug locking mechanism of'the receptacle.

Fig. 6 is a side view of the plug member locked to the receptacle portion of Fig. 5.

Figs. 7, 8, and 9 are side views, partially in section, of the plug, the top of the receptacle, and the auxiliary plug member, respectively, shown in exploded relation.

In Fig. 1, the device is shown generally at A secured to a vertical wall B through any convenient means, such as a bolt C. The device is shown connected to a conduit D, and may be supported entirely thereby in lieu of the fastening means C. The device is formed of three units, which are the plug member 2, the auxiliary plug member 4, and the base receptacle 6.

The plug, note particularly Figs. 6 and '7, is constructed of a strong material such as cast metal, or it may be of any sufficiently strong material as will resist explosive stresses, and has a body portion 8 extended on one end into an annular portion l0. On the end opposite the portion I0 is an opening adapted to receive conductors [2 which are held by a jam nut l4, preferably formed of brass. The conductors are passed through an insulating plate l5 inset into the body 8, said conductors being fastened to the bases of contact prongs l3. Insulating plate l6 may be conveniently secured to the body portion 8 by bolts 20, and the contact prongs I3 are secured to the insulating piece l6 by screws 22. Projecting inwardly of the annular member ID on opposite sides thereof are hardened steel pins 24 which have a locking function as will later be described.

The base receptacle 6 is in the form of a box having integral bottoms and sides and preferably being constructed of a strong ferrous material. The top of the box has inwardly extending flanges 36 to which is secured a cover member 32 by means of screws 34. The contacting surfaces of the flanges 30 and the cover 32 are ground, or machined, to make a very close, gastight joint, and thus to prevent the spread of fire, or chance of a secondary explosion being caused by gas or flame leakage, in the event of explosion within the receptacle 6. Likewise, the joint between the annular portion !6 and the cover 32 is formed of contacting ground faces. One end of the box is provided with a threaded opening 35 for the securing of the box to a pipe line or conduit D, and through which electrical conductors are lead into the box.

Disposed on the cap member 32 and rigidly secured thereto is an annular member 36 which is of such a size as will enable it to engage telescopically the annular member [6 on the plug 2. Bayonet slots are cut in the walls of annular member 36 to provide longitudinally extending portions 38 and horizontally extending portions 46, these bayonet slots being in size and number so as tobe engaged by the pins 24 in the annular member ID. At this point it is noted that the plug 2 can telescopically engage the annular member 36 only by sliding the pins 24 through the openings 38, and said plug is locked to the annular member 36 by rotating the plug so that the pins are locked in the horizontally extended portions 46 of the bayonet slots A close joint is obtained between plug 2 and cover 32 by reason of the ground surfaces on the part l6 and the cover 32. On the side of cap piece 32 opposite that upon which the annular member 36 is mounted, are projecting

lugs

42 and 44, the lug 42 being a straight piece and the lug 44 being a Z-shaped member to form an opening 46 wider than the opening 48 for a purpose later described.

Telescopically fitting within the annular member 36 is the auxiliary plug member 4. This auxiliary plug member is formed of molded insulating material and carries therein spring contact blades 56 which are adapted to be engaged by the blades I6 located in the plug piece 2 so as to establish an electrical contact between these two plug members. One of these blades is connected to a lead 52, which lead extends to the supply line connected with the base box 6. The other lead 54 is connected to the mercury switch.

The end of the auxiliary plug facing the cap member 2 has eccentrically inset therein a pilot pin 56, which pilot pin telescopically engages a complementary recess 56 in the plug 2, when the parts are assembled, so that a rotation of the plug member 2 wil1 cause a like rotation of the auxiliary plug member. To the opposite end of the auxiliary plug 4 is secured, as by being molded therewith, a base 59 from which projects an arm 66 sufficiently beyond the body portion of the auxiliary plug so as to be adapted to engage the spaces 4-6 and 48 lying between the

projections

42 and 44. The same end of the auxiliary plug 4 has a longitudinal projection 62, which projection in assembled relation may at some times bear against the base of the box 6 and therefore has a rounded end 64 to minimize friction. As shown in Fig. 1, a spring 66 surrounds the projection 62 and presses the auxiliary plug 2 outwardly of the receptacle toward the plug 2.

Mercury switch 16 is of conventional type and includes a body of mercury within a closed and sealed vessel and is secured to arm 66 by a bracket 72, which is adjustably secured to the arm 66 at 76 by means of a bolt and slot construction. As previously stated, lead wire 52 has been connected with one of the spring contact blades 56. The

other spring contact blade is connected through lead 54 to the mercury switch.

The assembly and operation of the device are as follows: Base member 2, auxiliary plug'4, and cap piece 32 are assembled as a unit by placing the spring 66 over the projection 62, attaching the mercury switch by means of the bracket 12 to the arm 66, and placing them in the box. Cap piece 32 is bolted down to the side of the box, with the annular member 36 surrounding the auxiliary plug 4, and the arm 66 extending between the

projections

42 and 44 into the space 48, it being noted that the spring 66 presses the auxiliary plug against the cap piece 32 so that the end of the arm lies in the space 46. In this position, when the mercury switch is mounted on a wall and the plug 2 not yet inserted, the switch is open and no electrical contacts are established so that current can flow through the device.

The plug 2 is inserted over the annular member 36 with the pins 24 engaging the slots 38 and the blades 16 engaging the blades 56, and as the plug becomes completely telescopically engaged, the pilot pin 56 on auxiliary plug 4 enters into its corresponding hole 58. It is to be noted at this time that normally the end of the auxiliary plug 4 projects beyond the annular member 36 so that the auxiliary plug is pressed further within the base receptacle against the spring 66 as the plug 2 is being engaged thereby. Likewise, it is noted that although the

contact blades

16 and 56 are brought into engagement with each other, no current flows through these contacts as the mercury switch is still in open position.

When the plug has been inserted to its fullest extent over the annular member 36, it is rotated to make the pins 24 engage in the horizontally extending portions of the bayonet slots. As soon as this rotation is started, the pins 24 hold the plug 2 against any disengaging or outwardly moving movement. At the same time, this movement, by virtue of the engagement of the pin 56 in hole 56, rotates the arm 66 carrying the mercury switch 4'6, the inward movement of the auxiliary plug 4 having caused the end of the arm 66 to leave the space 48 and enter into the space 46 between the

projections

42 and 44, respectively. Thereupon, the arm 66 is angularly turned until it engages the free end of the projection 44. The mercury switch is tilted by this rotation and thereby forms an electrical circuit. This circuit is not formed until the pins 24 have locked the plug 2 with the horizontal portions 46 of the bayonet slot. Therefore, it is seen that should any arc be caused by the creation of the electrical circuit through the action of the mercury switch and an explosion created thereby, all the movable parts are firmly interlocked with each other so that they cannot be separated. It is by reason of having the plug 2 locked with the annular member 36 that any explosion will not cause an outward movement of the plug 2, and consequently, the danger of having a flying part moved by an explosive force is avoided. Likewise, it is insured that the switch cannot be closed until the parts have been interlocked with one another and. therefore danger of faulty or careless operation is avoided.

On withdrawal of the plug 2, the same must first be rotated to bring the pins 24 into the slots 36. This rotation again causes a rotation of the arm 66 and opens the mercury switch before the pins 24 reach the slots 38. Consequently, should an explosion occur, the plug 2 is still held interlocked with the annular member 36. As the plug 2 is removed and the contact between the contact prongs I B and 50 broken, no arc will occur, as the current has been previously cut off through the action of the mercury switch. When the plug 2 is entirely removed, the spring 66 forces the auxiliary plug outward and causes the arm 68 to be re-engaged by the space 48 so that the auxiliary plug and the mercury switch cannot be again operated until the plug 2 is again properly used.

Should the mercury switch become out of alignment, the position of the same can be easily adjusted by means of the adjustable clamp '12.

Having now described the structure with which the objects and advantages of the invention are obtained, what is claimed is:

1. A plug receptacle comprising a removable plug, an auxiliary plug, and a base member, means to lock said removable plug to said base member, means to form metallic contacts between said removable plug and said auxiliary plug, switch means carried by said auxiliary plug, means connecting said switch means with said metallic contacts, and means independent of said removable plug locking means for preventing the closing of said switch means until after said removable plug has been locked to said base member.

2. A plug receptacle comprising a removable plug, a base, and an auxiliary rotatable plug, switch means mounted upon and movable with said auxiliary plug, means for looking said removable plug to said base member, means for engaging said removable plug with said auxiliary plug, means for locking said switch means against rotation with respect to said base member, and means for rotating said switch means while said removable plug is locked to said base.

3. In a plug receptacle, a removable plug having an annular flange on one end thereof, first contact blades projecting into the space bounded by said flange, and leads connected to said blades; a base receptacle having a cover plate, an annular member joined to said cover plate and adapted to engage telescopically within said annular flange on said plug; an auxiliary plug telescopically engaged with said annular member and extending into said receptacle, resilient means for urging said auxiliary plug toward said cover plate, an arm secured to said auxiliary plug, a switch fastened to said arm, second contact blades within said auxiliary plug adapted to engage said first contact blades, conductor mean connecting said second blades and said switch in series; means for locking said plug to said annular member, means for rotating said auxiliary plug while looking said plug to said annular member, and means for establishing an electrical circuit through said switch after said plug has been locked to said member.

1. In a plug receptacle as in claim 3, said means for locking said plug to said. annular member comprising pins extending from said annular flange and corresponding bayonet slots in said annular member.

5. In a plug receptacle as in claim 3, a first lug connected to said cover plate, a Z-shaped lug spaced from said first lug and connected to said cover plate, said auxiliary plug being movable against said resilient means to allow said arm to move from a stop position between one portion of each of said lugs to a stop position between another portion of said lugs.

6. In a plug receptacle as in claim 3, a pilot pin in one plug and a complementary recess in the other plug, said pin being engageable with said recess upon engagement of said blades.

7. In a plug receptacle as in claim 3, stop means engaging said arm, and means for moving said arm from said stop means on locking said removable plug to said annular member.

8. In the combination of a base receptacle, an auxiliary plug in said receptacle, a switch operable upon turning of said auxiliary plug, and a removable plug adapted to be connected to said auxiliary plug, the improvement comprising means mounting said auxiliary plug in said receptacle both for rotation and for movement in the direction of the movement of connection of said auxiliary plug with said removable plug, and means for locking said auxiliary plug against rotation until after said auxiliary plug has been moved in said direction to complete contact between said auxiliary plug and said removable plug.

9. In the combination of claim 8, means for locking said removable plug to said receptacle upon rotation of said removable plug to rotate said auxiliary plug.

10. In the combination of claim 8, said switch comprising a mercury switch mounted upon said auxiliary plug for turning movement therewith.

ENOCH K. SPRAGUE.