US3743800A

US3743800A - Mechanical safety interlock for covers of explosionproof electrical housing

Info

Publication number: US3743800A
Application number: US00258983A
Authority: US
Inventors: A Appleton; R Pastorel
Original assignee: Appleton Electric LLC
Current assignee: Appleton Electric LLC
Priority date: 1972-06-02
Filing date: 1972-06-02
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03
Also published as: CA946887A

Abstract

An explosionproof electrical enclosure has a body with two caps threaded on opposite ends of the body. Within the body is an electrical switch operable by a handle positioned outside the body. The caps are held against rotation by pins which extend through the body and are resiliently urged into recesses in the caps. These pins are accessible from outside the body so that they can be moved out of the recesses thereby allowing the caps to be rotated and unthreaded. A second set of pins adjacent and parallel to the first are moved longitudinally by the caps when the caps are removed or replaced. A safety interlocking mechanism includes plates positioned adjacent the inner ends of the pins and movable coincident with the turning of the handle between the switch-open and the switch-closed position. This interlocking mechanism prevents the first pins from being unseated from the cap recesses so long as the electrical switch is closed and prevents the handle from being turned from the switch-open to the switch-closed position so long as one or both of the second pins detects the absence of a cap.

Description

United States Patent [191 Appleton et a1.

MECHANICAL SAFETY INTERLOCK FOR COVERS 0F EXPLOSIONPROOF ELECTRICAL HOUSING Filed:

Appl. No.: 258,983

Inventors: Arthur L. Appleton,Northbrook;

Robert Pastorelt @5959: eihe lll.

Assignee: Appleton Electric Company,

Chicago. 111.

June 2, 1972 July 3, 1973 l 5 7 1 ABSTRACT An explosionproof electrical enclosure has a body with two caps threaded on opposite ends of the body. Within the body is an electrical switch operable by a handle positioned outside the body. The caps are held against rotation by pins which extend through the body and are resiliently urged into recesses in the caps. These pins are accessible from outside the body so that they 'can be moved out of the recesses thereby allowing the caps to be rotated and unthreaded. A second set of pins adjacent and parallel to the first are moved longitudinally by the caps when the caps are removed or replaced. A safety interlocking mechanism includes plates positioned adjacent the inner ends of the pins and movable coincident with the turning of the handle between the switch-open and the switch-closed position. This interlocking mechanism prevents the first pins from being unseated from the cap recesses so long as the electrical switch is closed and prevents the handle from being turned from the switch-open to the switch-closed position so long as one or both of the second pins detects the absence of a cap.

5 Claims, 7 Drawing Figures Patented July 3, 1973 3,743,00

2 Sheets-Sheet 8 WITH ' ununun 1 nnnnzn III II ELECTRIC SWITCH A: v q. '1

MECHANICAL SAFETY INTERLOCK FOR COVERS OF EXPLOSIONPROOF ELECTRICAL HOUSING BACKGROUND AND SUMMARY OF THE INVENTION The present invention is an improvement on the apparatus of U. S. Pat. No. 3,582,535. In the apparatus of that patent there is an electrical housing having caps which are threaded over openings on opposite sides of the housing. These caps have pins which seat in recesses in the housing to locate the caps in a proper rotational position on the housing. The pins are moved longitudinally to withdraw them from the recesses and thereby permit the caps to be unthreaded for removal from the housing body.

The present invention is an improvement on that apparatus. In the first place it prevents the pins from being unseated from the recesses unless the electrical switch within the housing has been moved to the switch-open position so that the electrical circuits accessible when the cap is removed will be deenergized. Secondly, the safety interlock of the present invention prevents the electrical switch from being closed so long as the caps have not been put fully into place to make the housing explosionproof. A further feature of the invention is that the pins that must be unseated to permit the unthreading of the caps are concealed and access thereto is not readily apparent. This prevents tampering by someone who is not fully familiar with the apparatus.

The present invention relates to a safety interlock for caps threadedly mounted on an explosionproof housing body, which interlock is simple yet effective to guard against the dangers present with electrical devices installed in a flammable atmosphere.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an embodiment of the invention;

FIG. 2 is an enlarged partial side view showing portions broken away as seen at line 2--2 of FIG. 1;

FIG. 3 is a fragmentary view illustrating the operation of the safety interlock and showing the parts as positioned when the covers are in place and the electrical switch closed;

FIG. 4 is a fragmentary view corresponding to FIG. 3 but showing the position of the parts with a cover removed and the switch in the open circuit position;

FIG. 5 is a sectional view of the housing body and interlocking apparatus as seen at line 5-5 of FIG. 2;

FIG. 6 is a section as seen at line 6-6 of FIG. 5; and

FIG. 7 is an enlarged sectional view as seen at line 7-7 of FIG. 6.

DESCRIPTION OF SPECIFIC EMBODIMENT The following disclosure is offered for public dissemination in return for the grant of a patent. Although it is detailed to ensure adequacy and aid understanding, this is not intended to prejudice that purpose of a patent which is to cover each new inventive concept the body. About these openings are

collars

13 and 13. The exteriors of the collars are in the form of truncated cones and have threads 14 and 14' thereon. The bottom portions of the

caps

11, 11 are of a corresponding configuration and have threads 15, 15' which mate with and engage threads 14, 14'. Around the bottoms of the caps are peripheral flanges l6, 16. At the front, the body 10 has a rectangular projection 17.

There are

recesses

20, 20 in the end faces of the flanges l6, 16'. At each of these recesses a small opening 21, 21' extends through the flange. These recesses cooperate with pins 22, 22' to properly position the caps in an explosionproof, but not jamming, position on the body. This is explained more fully in US. Pat. No. 3,582,535.

As best seen in FIG. 7, the pins have a shoulder 23. A spring 24 bears against this shoulder and against the end of a plug 25 of a mounting 26. The pin 22 is movable longitudinally thereof within the openings in mounting 26 and plug 25. It is urged outwardly by the spring 24. In the outward position it will seat in the recesses 20, 20' of the caps.

Within the housing is an electric switch 28. It is operatively connected to a crank 29 secured to the end of a shaft 30. The shaft 30 is journaled in the projection 17 of the body 10. At the outside end of the shaft a handle 31 is secured thereto. A movement of the shaft in the clockwise direction, as viewed in FIGS. 1 and 5, turns the switch 28 to a position such that the electrical circuits within the housing are hot, that is, energized. A rotation of the handle 31 in the counterclockwise direction actuates switch 28 so that the accessible electric circuits within the housing are dead, that is, deenergized.

There is a second pair of

pins

33, 33 which serve as sensors for the presence or absence of the caps on the body. These pins are journaled in mountings 34, 34' and plugs 35, 35'. At the inner ends these pins have

heads

36, 36 forming abutments. They also have shoulders 37. A spring 38 is in compression between shoulder 37 and the end of plug 35 (FIG. 7).

U-shaped brackets 40, 40' are held by the

mountings

26, 26', 34, 34 and the

plugs

25, 25, 35, 35. Adjacent the distal ends of the brackets 40, 40' are

slots

41, 41 through which plates 42, 42' slide. One end of each plate is formed into a hook and these have

openings

43, 43 therethrough. A link 44 has two arms 45 and 45'. The arm 45 extends upwardly through openings 43 in plate 42 and the arm 45' extends downwardly through the openings 43 in plate 42'. A pin 46 pivotally connects link 44 to a crank 47 on shaft 30.

The distal ends of plates 42, 42' are bifurcated. Adjacent the ends they have relatively wide slots 49, 49'. Near the centers of the plates are comparatively narrow slots 50, 50'. The relatively wide slots are slightly wider than the diameters of the heads 36, 36' of the pins 33, 33'. The relatively

narrow slots

50, 50 are just slightly wider than the diameters of pins 22, 22', but smaller than the diameters of the heads 36, 36'. From the slots toward the other end there are third areas 51, 51' which are completely closed. These serve as a stop or an abutment to block movement of pins 22, 22', as hereinafter described.

OPERATION Assume that the housing is closed, as illustrated in FIG. 1, and that the handle 31 is positioned so that the electric switch 28 is closed, energizing the accessible electrical components within the housing. The housing is explosion-proof; that is, should flammable vapors obtain access to the interior of the housing and be ignited therein, the resultant flame will not propagate outside of the housing. The pins 22, 22' are extended into the recesses 20, in the caps, thus restraining the caps against rotation. The

closed areas

51, 51 are aligned with the pins 22, 22 (as illustrated in FIG. 3) so that the pins may not be moved inwardly to unseat the pins from the recesses 20, 20' of the caps 11, 11'. Thus, it is not possible to remove the caps. The flanges 16, 16' are pressing against the adjacent ends of

pins

33, 33 and have moved the pins toward each other against the urging of springs 38, 38'. Thus, the heads 36, 36' of the pins 33, 33' are clear of

plates

42, 42, as seen in FIG. 2 and as illustrated in dotted lines in FIG. 7. Therefore, neither pins 22, 22' nor pins 33, 33' are interfering with the movement of plates 42, 42'. Handle 31 is free to rotate shaft between the switch-on position and the switch-off position.

Now if it is desired to remove one or both of

caps

11, 11, the handle 31 is turned counterclockwise to rotate shaft 30 to the switch-off position. This moves the

plates

42, 42 from the position illustrated in FIG. 3 to the position illustrated in FIGS. 4-7. Here the relatively

narrow slots

50, 50 are aligned with

pins

22, 22. It is now possible for the workman to insert a narrow object (e.g. asmall screwdriver, a nail, etc.) through opening 21 in flange 16 and push pin 22 downwardly out of recess 20. At the same time cap 11 can be rotated to disengage the threads and remove the cap. Similarly, the narrow object can then be inserted through the small inconspicuous opening 21' of cap 11 to push pin 22' inwardly and release cap 11 for rotation in a thread disengaging direction. The removal of cap 11 allows spring 38 to move pin 33 outwardly. At the same time, the head 36 on the pin 33 moves into the relatively large slot 49 of the plate 42. Also, the removal of cap 11' frees pin 33 so that head 36 thereof moves into slot 49' ofplate 42. Thus, with either of the caps 11, 11' removed, the

respective pin

33, 33 moves into a position at which the

head

36, 36 thereof blocks the return movement of plate 42, 42'. For example, referring to FIGS. 4 and 7, the plates 42, 42' cannot be moved to the right. Thus, shaft 30 cannot now be rotated from the switch-off to the switch-on position.

With the covers off, it would be possible to manually depress both of pins 33, 33', thereby permitting movement of the handle 31 toward the position at which the switch 28 is closed. However, it is exceedingly awkward for this operation to be performed. It could not be done accidentally, but only when a knowledgeable individual was working about the apparatus and was satisfied that it was safe to close switch 28.

With the caps removed and the interlocking device in the position illustrated in FIGS. 4-7, the return of the caps push the pins 33, 33' inwardly so that the

heads

36, 36 thereof are clear of the plates 42, 42'. When, during the same act of returning the caps onto the body, the proper degree of thread engagement is achieved, the

pins

22, 22 snap outwardly into the recesses 20, 20' of the caps. This then locks the caps in that proper position of engagement. Prior to this time, either or both of

pins

22, 22' or 33, 33 are positioned in the paths of movements of the plates 42, 42' so that the handle 31 cannot be moved in the direction of rotation towards the switch-on position. Thus, for example,

with the cap 11 almost in place so that it is depressing pin 33, but not sufficiently in place so that pin 22 is in recess 20, the flange 16 will have depressed pin 22 to the same extent that it depressed pin 33. This will have caused pin 22 to move into the dotted line position illustrated in FIG. 7 at which position it is blocking the movement of plate 42, even though the head 36 of pin 33 may have cleared the plate 42 for movement. With both of the covers fully in place, the plates 42, 42' are free to slide to the right from the positions illustrated in FIGS. 4-7. This permits the handle 31 to be rotated to the switch-on position. In this latter position the slides are now in the FIG. 3 position. Again, the covers are locked against removal since pins 22, 22' cannot be moved inwardly to release the covers.

We claim:

1. In an explosionproof electrical enclosure apparatus comprising a housing having a body with an opening with threads therearound and a cap threaded onto said threads and covering said opening, an electrical switch within said housing and operable between a switchopen position and a switch-closed position, said switch having a member within said housing for moving the switch between said positions which member is operable from outside said housing, a locking device interengaging said cap of said housing and movable between a first position at which said cap is locked at a desired location against rotation and a second position at which said cap is free to be rotated to unthread the cap for removal to expose said opening, said locking device being operable from outside said housing, the improvement comprising:

interlocking means operatively interconnecting the switch operating member and said cap locking device for retaining said locking device in said first position so long as the member is in the switchclosed position while freeing the locking device for movement to the second position so long as the member is in the switch-open position, and for normally blocking the member for movement from switch-open to switch-closed position so long as the cap is off the body, said interlocking means including a sensor positioned to be contacted by said cover and in a first position when said cover is in place and to be moved to a second position when said cover is off the body;

said locking device including a first pin in said body and movable in a direction generally parallel to the axis of the threads between a blocking position and an unblocking position, said cap having abutment means positioned adjacent the pin when the cap is in place and said pin is in the blocking position to prevent rotation of the cap to unthread the cap from the body, resilient means bearing on the pin to urge the pin to said blocking position, said pin being movable against said resilient means to said unblocking position at which said cap may be rotated;

said sensor including a second pin on said body, movable in a direction generally parallel to the axis of the threads and positioned so that one end of the second pin will contact said cap when said cap is in place, resilient means bearing against the second pin and urging it in the direction of said one end, whereby said second pin is held in a first position by the pressure of said cap when the cap is in place and is moved to a second position by the lastmentioned resilient means when the cap is removed; and

said interlocking means including a plate movable in said housing and having portions adjacent said pins, said plate being connected to said member. 2. In an apparatus as set forth in claim 1, wherein said pins each have a longitudinal axis, said plate being movable in a plane intersecting said axes between a first position at which the member is in the switchclosed position and a second position at which the member is in the switch-open position, said plate having a closed area aligned with the axis of the first pin when the member is in the switch-closed position with said closed area being positioned to block movement of the first pin from the blocking to the unblocking position, said plate having an open area aligned with the axis of the first pin when the member is in the switchopen position with said open area unblocking said first pin so that it may be moved to the unblocking position, said second pin having an abutment thereon which abutment is moved with the second pin, said abutment being positioned to block the movement of the plate from the switch-open to the switch-closed position when the second pin is in its second position, said abutment being moved to an unblocking position when the second pin is moved to the first position.

3.1m an apparatus as set forth in claim 2, wherein said cap has a flange thereon, said abutment means being in the side of said flange adjacent said body, said flange having a small opening extending from said abutment means to the other side of the flange, whereby a small object may be inserted through said small opening to move the first pin from the blocking to the unblocking position.

4. In an apparatus as set forth in claim 2, wherein as said cap is moved toward said desired location by the rotation of said cap and said second pin is being moved from said second position toward said first position to release said plate, said first pin is simultaneously being moved by the cap into a position at which it blocks the movement of the plate until the cap reaches said desired location and the first pin engages said abutment means thereby moving the first pin out of blocking position to free said plate.

5. In an apparatus as set forth in claim 1, wherein said cap has a flange thereon, said flange having a recess in the side of said flange adjacent said body and defining said abutment means, said flange having a small opening extending from said recess to the other side of the flange, whereby a small object may be inserted through said small opening to move the first pin from the blocking to the unblocking position.

Claims

1. In an explosionproof electrical enclosure apparatus comprising a housing having a body with an opening with threads therearound and a cap threaded onto said threads and covering said opening, an electrical switch within said housing and operable between a switch-open position and a switch-closed position, said switch having a member within said housing for moving the switch between said positions which member is operable from outside said housing, a locking device interengaging said cap of said housing and movable between a first position at which said cap is locked at a desired location against rotation and a second position at which said cap is free to be rotated to unthread the cap for removal to expose said opening, said locking device being operable from outside said housing, the improvement comprising: interlocking means operatively interconnecting the switch operating member and said cap locking device for retaining said locking device in said first position so long as the member is in the switch-closed position while freeing the locking device for movement to the second position so long as the member is in the switch-open position, and for normally blocking the member for movement from switch-open to switch-closed position so long as the cap is off the body, said interlocking means including a sensor positioned to be contacted by said cover and in a first position when said cover is in place and to be moved to a second position when said cover is off the body; said locking device including a first pin in said body and movable in a direction generally parallel to the axis of the threads between a blocking position and an unblocking position, said cap having abutment means positioned adjacent the pin when the cap is in place and said pin is in the blocking position to prevent rotation of the cap to unthread the cap from the body, resilient means bearing on the pin to urge the pin to said blocking position, said pin being movable against said resilient means to said unblocking position at which said cap may be rotated; said sensor including a second pin on said body, movable in a direction generally parallel to the axis of the threads and positioned so that one end of the second pin will contact said cap when said cap is in place, resilient means bearing against the second pin and urging it in the direction of said one end, whereby said second pin is held in a first position by the pressure of said cap when the cap is in place and is moved to a second position by the last-mentioned resilient means when the cap is removed; and said interlocking means including a plate movable in said housing and having portions adjacent said pins, said plate being connected to said member.

2. In an apparatus as set forth in claim 1, wherein said pins each have a longitudinal axis, said plate bEing movable in a plane intersecting said axes between a first position at which the member is in the switch-closed position and a second position at which the member is in the switch-open position, said plate having a closed area aligned with the axis of the first pin when the member is in the switch-closed position with said closed area being positioned to block movement of the first pin from the blocking to the unblocking position, said plate having an open area aligned with the axis of the first pin when the member is in the switch-open position with said open area unblocking said first pin so that it may be moved to the unblocking position, said second pin having an abutment thereon which abutment is moved with the second pin, said abutment being positioned to block the movement of the plate from the switch-open to the switch-closed position when the second pin is in its second position, said abutment being moved to an unblocking position when the second pin is moved to the first position.

3. In an apparatus as set forth in claim 2, wherein said cap has a flange thereon, said abutment means being in the side of said flange adjacent said body, said flange having a small opening extending from said abutment means to the other side of the flange, whereby a small object may be inserted through said small opening to move the first pin from the blocking to the unblocking position.