Protective shutter assembly for electrical terminals and method of using same

The present invention provides a shutter assembly for covering an exposed electrical terminal located in a control center into which removably inserts an electrical control device connecting to the terminal. The assembly includes a shutter to cover the exposed terminal when superposed thereover. The shutter has a pivotal axis at one end, so that the opposite end of the shutter pivots away from the exposed terminal and swings clear of the control device to provide access to the terminal. The rotation of the shutter is automatically controlled to expose the terminal when the control device is inserted in the cell and reversibly pivots the shutter to cover the terminal upon removing the control device from the cell. The present invention also provides a method of safely protecting an exposed terminal mounted in a control center. A control center is provided with a partially enclosed framework for removably inserting a control device. Subsequently, a self-contained shutter assembly is installed for supporting a shutter in a superposed relation over the exposed terminals and for controlling the rotation of the shutter to expose the terminal when the control device is inserted in the cell and reversibly pivots the shutter to cover the terminal upon removing the control device from the cell.

FIELD OF THE INVENTION 
The present invention relates to control centers for distributing and 
controlling electrical service which have exposed electrical terminals 
and, more particularly, to a shutter assembly which protects the exposed 
terminals preventing accidental contact when an individual control device 
is removed therefrom. 
BACKGROUND OF THE INVENTION 
Motor control centers, as well as other electrical equipment like 
switchgear, are equipped with draw-out type protective control devices 
such as fusible disconnect switches or circuit breakers. These control 
devices are inserted into individual cells or compartments within the 
center to establish mechanical and electrical contact with bus bars, load 
and line stabs, or similar electrical terminals. Where there are several 
control devices stacked together or otherwise arranged, the terminals 
usually remain energized when any one of the individual control devices is 
removed. 
The exposed terminals pose a safety hazard. An operator could be severely 
burned or shocked if the terminals were accidentally touched while 
servicing the center or installing other components near the terminals. 
Therefore, when a control device is removed, it is desirable to close off 
access to the exposed terminals to prevent inadvertent contact with the 
energized terminals. 
There are several prior art shutter arrangements which are mounted to the 
rear portion of the individual cells in a control center. When the control 
device is inserted into the cell, shutters slide to different areas to 
expose the terminals for connection with the control device. The sliding 
mechanism supporting the shutters is complex and bulky, requiring an 
intricate interaction with the control device during the insertion 
procedure for the shutters to open properly. The sliding shutters and 
accompanying support mechanism occupy a substantial amount of space in the 
rear portion of the cell. Thus, other components and features of the 
center are prevented from using this area. 
There is a need for a space-saving shutter using an inexpensive, simple 
assembly which does not interfere with the other components or operation 
of the control center and the respective control devices. In view of 
increasing safety requirements for control centers already in operation 
that do not contain protective apparatus for exposed terminals, there is 
also a need for a field-installed protective shutter assembly that fits 
the control center designs of various manufacture. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a shutter assembly is provided 
for covering an exposed electrical terminal located in a control center 
having at least one cell which receives an electrical control device 
connecting to the terminal. The assembly includes a shutter having 
sufficient size to substantially cover the exposed terminal when 
superposed thereover. The shutter has a pivotal axis at one end, so that 
the opposite end of the shutter pivots away from the exposed terminal and 
swings clear of the control device to provide access to the terminal. The 
assembly includes means for controlling the rotation of the shutter on the 
pivotal axis so that the control means automatically pivots the shutter to 
expose the terminal when the control device is inserted in the cell and 
reversibly pivots the shutter to cover the terminal upon removing the 
control device from the cell. The control means is connected to the 
pivotal axis of the shutter. The assembly also includes means for 
supporting the shutter in a superposed relation to the terminal and 
fastening the control means to the center. 
The present invention also contemplates providing a center for controlling 
electrical service with at least one control device. The center includes a 
partially enclosed framework and at least one cell defined in the 
framework for receiving the control device. The center also includes a 
plurality of terminals extending from a rear portion of each cell for 
mating with a corresponding plurality of terminal receivers extending from 
a teat portion of the control device. The center further includes a 
shutter assembly as described above. 
The present invention also provides a method of safely protecting an 
exposed terminal mounted in a control center. A control center is provided 
with a partially enclosed framework and at least one cell defined in the 
framework for receiving a control device. The control center has a 
plurality of terminals extending from the portion of the framework in each 
cell for mating with a corresponding plurality of terminal receivers 
extending from a rear portion of the control device. Subsequently, a 
self-contained shutter assembly, as described above, is installed for 
supporting a shutter in a superposed relation over the exposed terminals 
and for controlling the rotation of the shutter to expose the terminal 
when the control device is inserted in the cell and reversibly pivots the 
shutter to cover the terminal upon removing the control device from the 
cell. 
Accordingly, an object of the present invention is to provide a shutter 
assembly which automatically protects exposed terminals in a control 
center when the individual control devices have been removed. 
Another object of the invention is to provide a shutter assembly which can 
be used with control centers which are already operating in the field. 
A further object of the present invention is to provide a shutter assembly 
which is self-contained, easily mounted and saves space in the protected 
area. 
Other and further advantages, embodiments, variations and the like will be 
apparent to those skilled in the art from the present specification taken 
with the accompanying drawings and appended claims.

DETAILED DESCRIPTION 
Referring now to the drawings there is illustrated a control center 
embodying the present invention. In FIG. 1 the control center 10 is 
defined with a plurality of individual cells occupied by different control 
devices shown typically by reference numerals 12 and 34. The control 
devices like 12 are removably accommodated in the respective individual 
cells. The control devices 12, 14 are typically similar in mechanical 
structure to one another although they may have different dimensions and 
include different electrical components. 
A covered framework, generally designated as 16, partially encloses each 
control device leaving the front 18 of the framework open to insert the 
control devices 12, 14 therethrough. If the control center 10 is to 
operate for a long time period without a control device mounted in a 
particular cell, a cover panel 20 is placed over the opening in the front 
18 of the framework while it is in operation. 
The control center 10 also illustrates using the present invention with a 
variety of cell arrangements. The stacked configuration of individual 
cells in a first column 22 can be repeated any number of times as 
exemplified with a second column 24 of stacked individual cells. 
Referring now to FIG. 2, there are a plurality of individual cells 26, 28 
in a stacked configuration. The cells 26, 28 are separated by a barrier 
like the horizontal shelf 30. Each cell 26 is defined by a rear portion 
32, a side portion 34, and a front portion 36 of the framework comprising 
the control center 10. 
Mounted to the rear portion 32 of the framework are electrical terminals 
38, in particular, bus bars, for the load and line connections of a 
multiphase circuit. The terminals 38 are accessible in each individual 
cell 26, 28. The terminals 38 are positioned to mechanically and 
electrically connect with corresponding terminals on the control device. 
The framework 16 typically provides the alignment necessary to complete 
the connection with the terminals 38 as the control device is inserted 
into the cell 26. 
When the control device is removed from the individual cell 26, the 
terminals 38 become exposed to inadvertent contact with an operator or 
their tools. To protect the exposed terminals 38, a preferred embodiment 
of the inventive shutter assembly 40 is mounted to the side portion 34 of 
the framework. A shutter 42 is provided in a superposed relation over the 
terminals 38. The shutter 42 has a generally planar shape and is of 
sufficient size to substantially cover the area of the otherwise exposed 
terminals 38. 
The shutter 42 has a pivotal axis 44 extending along its top end 46. The 
shutter 42 is supported in superposed position relative to the terminals 
38 by a housing generally designated as 48. The shutter 42 is rotatably 
mounted to the housing 48 so that the opposite or bottom end 50 of the 
shutter pivots in an upward direction along the pivotal axis 44. The 
housing 48 is attached to the side portion 34 of the framework with 
fasteners like screws 52. 
The housing 48 also supports a lever 54 which has one end 56 extending into 
the area of the cell 26. The lever 54 is rotatably mounted to the housing 
48 so that the lever end 56 rotates towards the housing 48. When the 
control device is inserted into the cell 26 at the front portion 36 of the 
framework, the rear corner of the control device engages the lever end 56. 
As the control device moves rearwardly, the lever end 56 abuts the side of 
the control device and eventually rotates flush with the side portion 34 
of the framework and the housing 48. 
The lever 54 is connected to the shutter 42 and the position of the lever 
end 56 controls the opening and closing of the shutter 42. As the lever 
end 56 moves toward the flush position, the shutter 42 rotates along the 
pivotal axis 44. The bottom end 50 of the shutter pivots away from the 
rear portion 32 of the framework to provide access to the terminals 38 and 
clear the approaching rear face of the control device. 
As the control device is removed from the cell 26, the lever end 56 returns 
to its original position, extending into the vacant area of the cell 26. 
As the lever end 56 moves to this position, the shutter 42 rotates along 
the pivotal axis 44 to pivot the bottom end 50 of the shutter downwardly 
and cover the exposed terminals 38. 
Referring now to FIG. 3, a preferred configuration for the housing 48 is 
illustrated. A U-shaped channel 58 is provided with a bight portion 60 
defined by two upstanding side walls 62, 64. One of the side walls 62 has 
a plurality of holes 66 to accommodate screws 52 and attach the channel 58 
to the side portion 34 of the framework as previously described. Other 
means for attaching the housing 48 to the framework 16 is contemplated by 
the present invention. Bolts, clips, other mechanical fasteners, 
adhesives, even wielding, are suitable for use in attaching the housing 48 
to the framework 16. 
The lever 54 is rotatably mounted to the top edge 68 of the channel side 
wall. A fastener, like screw 70, is provided through a hole 72 in the 
lever and into an accommodating hole 74 located in the top edge 68. The 
area surrounding the top edge hole 74 is reinforced to support the 
rotation of the lever 54 around this point. The lever end 56 extends into 
the area of the cell. The opposite end of the lever 54 provides a hole 76 
for connection with the shutter 42. 
A link 78 is provided for rotatably connecting one end 80 with the opposite 
lever end hole 76. The opposite end 82 of the link rotatably connects with 
a hole 84 in a cam 86. The link 78 is positioned within the bight portion 
60 of the channel. 
A rod 88 is affixed to the shutter 42 along the pivotal axis 44 at the top 
end 46 of the shutter. The rod 88 extends beyond the side edge 90 of the 
shutter to affix to end of the cam 86 opposite the cam hole 84. 
A second channel 92 is connected at one end of the channel side wall 62. 
The second channel 92 extends perpendicularly from the channel side wall 
62 into the area of the cell. The second channel 92 similarly includes a 
bight portion 94 defined by two upstanding side walls. The width of the 
bight portion 94 is sized rotatably mount the diameter of the rod 88. The 
second channel side walls defining the bight portion 94 resiliently 
separate to accommodate the snap insertion of the rod 88 therebetween. A 
section 96 of the rod between the cam 86 and the side edge 90 of the 
shutter is extended to rotatably mount within the length of the second 
channel 92. The end of the channel 58 is open to accommodate the insertion 
of the cam 86 as the rod 88 is mounted to the second channel 92. 
A spring 98 connected to the link 78 provides an energy means for returning 
the shutter 42 to the closed position when the control device is removed 
from the cell. The spring 98 is mounted to the link 78 between a crimp 100 
in the link, best illustrated in FIG. 5, and a retaining wall 102. 
FIG. 4 more clearly illustrates the retaining wall 102 extending 
perpendicularly across the bight portion 60 of the channel. The retaining 
wall 102 contains an aperture 104 therethrough which accommodates the link 
78. The end 105 of the spring 98 opposite the crimp 100 is fitted with a 
washer 108 which rests against one face of the retaining wall. Thus, the 
spring is held in position between the retaining wall 102 and the crimp 
100. 
In the operation of the shutter assembly 40, when the control device has 
been removed from the cell and it is empty, the lever end 56 extends into 
the area of the cell 26. In this lever end 56 position, the shutter 42 is 
in a superposed relation to the terminals 38. As the control device is 
inserted into the cell 26, the rear face or corner of the device contacts 
or engages the lever end 56 and pushes it rearwardly. The lever 54 pivots 
around the mounting screw 70 and pulls on the link 78. 
As the link 78 is being pulled by the lever hole 76, the crimp 100 in the 
link moves toward the retaining wall 102 and compresses the spring 98 
therebetween. Simultaneously, the opposite end 82 of the link pulls on the 
cam hole 84 to rotate the cam 86 clockwise as viewed in FIG. 3. Since the 
rod 88 is affixed to the cam 86, the rod 88 rotates in the second channel 
92. Consequently, the shutter 42 rotates about the pivotal axis 44 along 
the top end 46. The bottom end 50 of the shutter swings away from the 
terminals 38. The bottom end 50 of the shutter rotates sufficiently to 
clear the rear face of the control device as it connects mechanically and 
electrically with the terminals 38. 
When the control device is disconnected from the terminals 38 and removed 
from the cell 26, the opposite procedure described above occurs. The 
compressed spring 98 provides a force which pulls the link 78 rotatably 
mounted in the lever hole 72 to rotate the lever end 56 back into the area 
of the cell 26 vacated by the removal of the control device. As a 
consequence of the link 76 and lever 54 returning to their original 
position, the cam 86 rotates the rod 88 and swings the bottom end 50 of 
the shutter downwardly to cover the exposed terminals 38. 
The lever 54, link 78, rod 88 and spring 98 cooperate together to control 
the automatic opening and closing of the shutter over the terminals. Other 
means for controlling the position of the shutter is also contemplated by 
the invention. It is within the skill of those in the art to adjust the 
length and travel of the link 78 with the appropriate size of the other 
parts of the control means to provide the degree of rotation required for 
the shutter 42 to clear the rear face of an inserted control device. In 
fact, the present invention even contemplates rotating the bottom end 50 
of the shutter so that the shutter 42 is again parallel and flush with the 
rear portion 32 of the framework. 
The spring 98 can be positioned in many places along the assembly 40 and 
still provide the force necessary to return the control means to its 
original position. For example, one end of the spring 98 can be connected 
to the cam 86 and the other end of the spring to a hole in the channel 
side wall 62. Consequently, there would be no need for the retaining wall 
102 and crimp 100 in the link to hold the spring 98 therebetween. 
Other means of biasedly returning the control means to its original 
position are also contemplated by the present invention. For example, a 
torsion rod is a suitable to provide the biased force between the lever 54 
and the rod 88. 
In another embodiment of the present invention, the housing is eliminated 
and the various elements of the control means and the support for the 
shutter 42 is directly attached to the framework 16. Accordingly, the 
lever 54 and rod 88 are both directly mounted in a rotatable manner to the 
framework 16 itself. For example, holes are provided at the appropriate 
position in the side portion 34 of the framework. Although this embodiment 
does not have the attendant advantages of the self-contained assembly 40 
previously described, the particular design of a control center may 
necessitate this approach. 
Preferably, the shutter 42 and the housing 48 is made of an electrically 
insulating material. Although the shutter 42 does not have contact with 
the terminals 38 in the preferred embodiment, it is a safety precaution 
that the shutter 42 not be electrically conductive in case it touches a 
live terminal. A thermoplastic material is preferred although other 
plastics are suitable for use with the invention. For the housing 48, it 
is also suitable to use metal with an insulating coating or paint finish. 
The inventive shutter 42 can be made in various colors, although, safety 
related colors like red and yellow are preferred. Warning labels, symbols, 
or instructions can be readily attached to the face of the shutter. Such 
items can be integrally formed along with the shutter. 
The present invention is specifically disclosed for use with control 
centers manufactured by the Square D Company under the catalog designation 
OmegaPak (registered trademark of the Square D Company) and others. Motor 
controls like the Model 6 units and the Model 5 units (registered 
trademarks of the Square D Company) and other power output units are a 
type of the control devices referred to herein. In particular, the 
preferred embodiment is used as either an original equipment or 
aftermarket attachment with the Model 6 units. These control units are 
used in control centers which have been in the marketplace for years and 
have been continually updated. 
As described herein, the present invention provides a method of safely 
protecting an exposed terminal mounted in a control center. The control 
center 10 is provided with the partially enclosed framework 16 and at 
least one cell like 26 defined in the framework for receiving the control 
device like 12. The control center 10 has a plurality of terminals 38 
extending from the rear portion 32 of the framework in each cell for 
mating with a corresponding plurality of terminal receivers extending from 
a rear portion of the control device. 
Subsequently, the self-contained shutter assembly 40 is installed for 
supporting a shutter 42 in a superposed relation over the exposed 
terminals 38. The shutter assembly 40 also controls the rotation of the 
shutter 42 to expose the terminal 38 when the control device is inserted 
in the cell and reversibly pivots the shutter 42 to cover the terminal 38 
upon removing the control device from the cell. 
As those skilled in the art will appreciate, the inventive shutter assembly 
can be adapted and configured for usage with a wide variety of control 
centers. Adapting the shape of the housing and shutter to utilize features 
of a control center framework to attach the self-contained shutter 
assembly thereto allows upgrading the safety of control centers already in 
the marketplace. 
It will be further understood that whereas the term control centers is 
defined to include, but not be limited to, motor control centers and 
switchgear. Likewise, the term control devices is defined to include motor 
controls and other types of control units like circuit breakers, switches, 
fuses, and combinations thereof. 
While particular embodiments and applications of the present invention have 
been illustrated and described, it is to be understood that the invention 
is not limited to the precise construction and compositions disclosed 
herein and that various modifications, changes, and variations which will 
be apparent to those skilled in the art may be made in the arrangement, 
operation, and details of construction of the invention disclosed herein 
without departing from the spirit and scope of the invention as defined in 
the appended claims.