Dead front fuse door

A dead front fuse mounting assembly for use in high voltage enclosures, utilizes a shock absorber assisted door design to reduce impact forces which occur when such assemblies are improperly opened. Secondly the interior of the fuse compartment is closed to entry by foreign objects by an insulating door which moves concomitantly with the fuse mounting assembly and is locked in a closed position when the assembly is in its open position.

FIELD OF THE INVENTION 
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. 
BACKGROUND OF THE INVENTION 
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. 
SUMMARY OF THE INVENTION 
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.

DESCRIPTION OF A PREFERRED EMBODIMENT 
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.