Dead Front Fuse Door

The present invention relates to electrical equipment such as 25 Kv fuse and switch enclosures. More particularly the present invention relates to fuse mountings in such enclosures and specifically to what is known as a dead front fuse door for mounting a phase fuse such that it may be removed from electrical contact by pivoting an associated mounting door. In even greater particularity, the present invention relates to a fuse door configured to avoid high impact upon opening the circuit and to seal an associated fuse compartment against airborne contamination when closed.

It is current practice to mount power fuses used in conjunction with power distribution circuits within a metal enclosure having hinged access doors. In such structures, fuses and other live electrical components may be mounted behind a dead front wall which isolates the human operator from these components when they are energized. Such devices in the prior art are represented by the disclosure in U.S. Pat. No. 4,250,357 wherein a fuse isolating wall is provided inside a metal housing structure and is located immediately behind the housing doors. Fuse panels are hingedly mounted to the isolating wall and constitute parts thereof so that a fuse mounted or fuse mounting insulating structure secured to the interior of each fuse panel is isolated from access by an operator so long as the panel is in its normal position forming a part of the insulating wall. Conducting means preferably in the form of a bushing having a conventional bushing well extends through the fuse panel and is interconnected with one terminal of the fuse on the inside of the fuse panel while a part of the conducting structure extends outside the fuse panel and is arranged for disjointable engagement with connecting means such as a circuit elbow connector. The fuse panel is held in its normal position as a part of an isolating wall by latch means and such latch means is held in its latching position by an interlock movably mounted on the fuse panel. Portions of the interlock operating lever are interposed between the fuse panel and the disjointable connector. When it is desired to replace a fuse, the disjointable connecting means is removed from its associated conductor and the interlock operating lever is moved to its latch releasing position following which an operating rod is used to engage the latch and to rotate it to its unlatched condition. The fuse panel is then swung out of its position as a part of the isolating wall and may then be removed therefrom to a convenient location for the replacement of the fuse. Thereafter the procedure is reversed to reinsert the replacement fuse into the circuit.

One problem inherent with this type system is that the human operator may be required to use a 10 to 14 foot long "hook stick" to open or close the mounting assembly. A force of above 50 lbs. may be required to lift the assembly to begin movement thereof to a closed position, thus requiring considerable strength from an operator using a "hook stick". Conversely, when opening the assembly, if the "hook stick" slips for any reason the door and fuse can slam down to the open position causing severe damage or destruction to the mounting plate and high voltage fuse. This is particularly hazardous when glass tube current limiting fuses are used.

Another problem is isolation of the components within the fuse compartment when the fuse mounting door is open. Prior U.S. Pat. Nos. 4,827,374 and 4,463,227 have each dealt with the problem, however neither has provided a totally satisfactory solution. Consequently there remains a need for an assembly that controls the descent of a fuse mounting plate as it is opened and a mechanism for simultaneously isolating the fuse mounting assembly from the fuse compartment.

It is the principal object of the present invention to provide a mounting door for a dead front fuse panel which will reduce the likelihood of damage to the equipment or injury to personnel resulting from free fall of the panel.

Yet another object of the invention is to provide a means for sealing the fuse mounting opening to prevent airborne contamination in the fuse chamber.

Still another object of the invention is to make it easier for the human operator to properly close the fuse mounting plate when maintenance thereof is complete.

These and other objects and features of my invention are advantageously accomplished by my novel design which utilizes a damping mechanism to arrest the downward motion of the fuse mounting plate and urge the plate toward the closed position over at least a part of the range of motion of the plate. Secondly I use a camming door latch mechanism to urge the fuse mounting panel against the transverse wall to seal against airborne contamination. I also use a secondary door which isolates the fuse from the fuse compartment when the panel is in the open position and phase isolation in the panel closed position.

Apparatus embodying features of my invention are depicted in the accompanying drawings which form a portion of this disclosure and wherein:

FIG. 1 is a side sectional view taken along a vertical plane through the enclosure;

FIG. 2 is a front elevational view of the transverse wall and face mounting plates;

FIG. 3 is a partial sectional view taken along line 3--3 of FIG. 1 showing the fuse mounting panels;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3; and

FIG. 5 is a sectional view taken along line 5--5 of FIG. 4.

Referring to the Figures for a clearer understanding of my invention it may be seen in FIG. 1 that my invention is to be used in connection with a metal electrical enclosure 11 or cabinet having a set of hinge mounted doors 12 which allow access to the interior thereof. The interior is divided into a front compartment 13 and a fuse compartment 14 by a transverse wall 16. Wall 16 is inclined rearwardly from the front of the enclosure 11 and provides electrical isolation between the front and rear compartments 13 and 14. Access to the fuse compartment 14 is gained by opening one of the fuse mounting assemblies 17 shown in FIGS. 1 and 2.

Each fuse mounting assembly 17 includes a fuse mounting plate 18, pivotally mounted to wall 16 by a rigidly mounted hinge 19 which rotates on precision bearings, a latch assembly 21, and fuse mounting members 22 and 23. Each plate 18 has an electrical fitting 24 for receiving an elbow connector 26, with the fitting 24 and connector 26 forming part of an electrical circuit to one end of a fuse 27 secured in mounting members 22 and 23. Lower fuse mounting member 22 includes a contact arm 28 which engages a contact 29 in a switch assembly 31, also located in compartment 14. The switch assembly operates in a manner well known in the art to open the circuit between the fuse 27 and an electrical fitting 32 which connects to the remainder of the associated high voltage circuitry.

With reference to FIGS. 1 and 2, it may be seen that each fuse mounting panel 18 has a pair of shock absorber elements 33 mounted to the lower portion thereof. Each shock absorber element 33 includes a guide rod 34 pivotally mounted at its upper end to the panel 18 and extending downwardly below the hinge 19 to a resilient mount 36. Each resilient mount 36 is essentially a pivotally mounted guide sleeve 37 and a spring 38 mounted concentrically about the guide rod 34 such that downward movement of the guide rod 34 causes compression of the spring 38.

The latch assembly 21 includes a generally U-shaped handle 39 having a mounting leg 41 formed at each end thereof to extend outwardly from the plane of the handle 39 to pivotally engage associated mounting pins carried on each side of the panel 18. Each end of the handle 39 terminates in a curved camming member 42 having a cam surface 43 which engages a latch pin 44 mounted on the wall 16. The cam surfaces 43 are formed such that when the handle is lowered with the cam members between the wall 16 and the latch pins 44, the panel 18 is urged tightly against the wall at the periphery of the panel to prevent entry of dust or other airborne contaminants within compartment 14. It will be appreciated that with the handle 3 in the full down position the panel is locked to the wall and by virtue of the placement of fitting 24 and elbow 26 the handle cannot be raised to unlock or open the panel without first removing elbow 26 from the fitting 24. Accordingly the panel 18 cannot be pivoted on hinge 19 without first creating an open circuit condition.

Referring to FIGS. 1 and 3 it may be seen that a secondary insulating door 46 is pivotally mounted to the transverse wall 16 on a set of hinges 50 such that the door 46 moves orthogonally to the motion of the panel 18. The door 46 carries thereon a guide bracket 47 which slidably engages a guide rod 48 mounted on the panel 18 such that when the panel is in the closed position the door 46 is held open, spaced from the fuse mounting and thus acting as a partial partition intermediate fuses on adjacent phases. The guide bracket is a channel-like member mounted at an acute angle to the rod 48 when the panel 18 is closed. Thus the bracket 47 forms an internal slide surface 49 against which the rod 48 moves to open the door 46 and a latching flange 51 which, as may be seen in FIGS. 4 and 5, abuts against rod 48 to prevent inadvertent opening of the door when the panel is in the open position. It will be noted that a set of springs 52 urge the door toward a closed position. Thus the door is maintained in contact with the rod 48 through brackets 47 at all times.

From the above, the operation of my apparatus is readily understood. In normal use panel 18 is closed and urged tightly against wall 16 by the camming action of the latch mechanism 21. A high voltage circuit is completed through the associated switch assembly 31 and fuse 27 for each phase within the enclosure 11. With the panel 18 in the closed position the insulating door 46 is held in a partition position by the associated rod 48 extending from the door and engaging the bracket 47. To service them the operator would first disengage the elbow connector 26 and switch assembly 31. He may then view the interior of the compartment 14 through a pair of windows 53 in the plate 18. If it becomes necessary to access the fuse, handle 39 is raised to move the cam member 42 out of engagement with the locking pin 44. Note that the foregoing is accomplished using a hot stick, so the operator is at a distance of 8-12 feet from the plate as he opens it. As the mounting plate 18 pivots downwardly to the open position the springs of the shock absorber assembly 33 are compressed, thereby slowing the descent and lessening the impact of the fuse mounting assembly 17 against the enclosure 11 if the assembly 17 is allowed to free fall. When the assembly 17 abuts the enclosure 11 a spring loaded latch 54 engages a pin carried on the side of the mounting plate to secure the assembly in a down and locked position. Concomitant with the downward movement of the mounting plate 17, the spring loaded door 46 is urged by spring 52 to its closed position. As the mounting plate reaches its lowermost position the door completes its pivot of approximately 90 degrees such that rod 48 is positioned between flange 51 and the door, hence the door is held in its closed position. Upon inspection or replacement of the fuse 27 the latch 54 is released and the shock absorber springs assist in urging the mounting assembly toward its closed position. The precision bearings of hinge 19 assure that the contact arm 28 is received properly in the contact for the switch assembly.

Thus it may be seen that my device significantly reduces the possibility of injury to the equipment or the operator at all times by reducing the potential impact forces which can be generated in a free fall condition; latching the access door to prevent inadvertent entry of the operator or tools into the fuse compartment; and reducing the force and effect required to lift the mounting assembly in returning it to a closed position.

While I have shown my invention in one form, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit thereof.