Bus duct joint employing lightly-loaded multiple-point electrical connector

A single-bolt joint having louvered contact strips interposed the bus bars and conductor splice plates for improved electrical connection under low insertion forces is tightened to become a solid connector assembly prior to attachment to the bus bars of a first bus duct and requires no additional tightening after insertion of the bus bars of the second bus duct. Expansion of the bus bars is accommodated at each joint without special apparatus.

BACKGROUND OF THE INVENTION 
This invention relates to joint assemblies for electrical busway apparatus. 
Electrical busway is utilized to conduct low voltage, high current power 
between a source and the controls for the ultimate load apparatus. A 
typical busway system includes a number of lengths of bus duct connected 
together end-to-end, each bus duct comprising a housing containing a 
plurality of bus bars and a connection joint at one end. 
In present day busway systems, considerable emphasis has been placed on 
joint design to facilitate mechanical connection and provide good 
electrical connection. An exemplary busway joint is disclosed in U.S. Pat. 
No. 3,786,394, issued on Jan. 15, 1974 to Martin F. Koenig et al and 
assigned to the assignee of this application. As shown therein, a joint 
comprising a stacked assembly of insulators and electrical splice plates 
is disposed on the end of one length of bus duct such that pairs of splice 
plates are positioned on opposite surfaces of the respective bus bars and 
insulator plates are provided on the outer side of the assembly and 
between adjacent splice plates associated with different bus bars. A 
single, insulated bolt extends through the entire assembly, and loosely 
secures the joint to said one bus duct. Interfitting hook means are 
provided between the bus bars and splice plates to retain the joint to the 
bus duct even when loosely assembled. In installation, a second bus duct 
is inserted into the other side of the loose joint assembly such that the 
bus bars thereof are disposed between the respective pairs of splice 
plates. The connection is completed by tightening the bolt to compress all 
of the elements of the joint together, particularly the splice plates upon 
the opposite surfaces of the bus bars. To obtain the desired electrical 
conduction properties, such joints require compressive pressures which in 
turn require a torque to be applied to the bolt on the order of 75 foot 
pounds. 
The present invention relates to an improvement in the above described 
busway joint. It provides a joint which is rigidly secured to the first 
bus duct at the point of manufacture to provide a rigid receptacle into 
which the second bus duct may be plugged-in during installation. This 
construction requires no subsequent tightening of the bolt by the 
installer. In addition, an enhanced electrical connection is provided. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide a joint assembly for an 
electrical bus duct, which joint assembly is securely clamped to one end 
of the bus duct during the manufacture thereof to provide a rigid plug-in 
receptacle for receiving a second bus duct upon installation. 
It is a further object of this invention to provide a joint assembly of the 
aforementioned type which requires no compressive adjustment after 
installation with a second bus duct. 
It is still a further object of this invention to provide a joint assembly 
of the aforementioned type which provides enhanced electrical conduction 
with only a fraction of the compressive force required in present day 
joint assemblies. 
These and other objects and advantages of this invention will become 
apparent in the following specification and claims when read in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings and particularly to FIGS. 1 and 2 thereof, 
the joint assembly 10 of this invention is shown assembled between two bus 
duct sections 12. Bus duct sections 12 are identically constructed, each 
comprising a plurality of flat, elongated bus bars, A, B, C and N disposed 
within a sheet metal housing comprising top and bottom members 14 and 16, 
respectively, and side members 18 and 20. The latter are identical 
members, but are staggered with respect to each other in assembly of the 
bus duct such that member 18 extends beyond the ends of the members 14 and 
16 at the right-hand end of the bus duct while the member 20 similarly 
extends beyond the ends of members 14 and 16 at the left-hand end of the 
bus duct. The bus bars A, B, C and N also project beyond the opposite ends 
of members 14 and 16, but do not project beyond the extended end of the 
respective side member 18 or 20. 
Joint assembly 10 electrically connects bus duct sections 12 together, 
joining corresponding bus bars of one section to the other; i.e., A to A, 
B to B, etc. The joint assembly 10 comprises a plurality of electrically 
conductive splice plates 22, intermediate and outer insulator plates 24 
and 26, respectively, pressure distributing plates 28, and end plates 30, 
all arranged in a stack and held together by a bolt 32 which passes 
through aligned central apertures in each member and receives a lock 
washer 34 and hex nut 36 at its opposite end. Additionally, an insulating 
sleeve 38 is positioned over the shank of bolt 32 within the joint between 
the plates 28. 
In prior art busway joints, such as that disclosed in the aforementioned 
U.S. Pat. No. 3,786,394, the loosely assembled joint as described to this 
point would be assembled at the manufacturing plant to the end of a bus 
duct section. The cooperating pairs of splice plates 22 require careful 
initial alignment and spacing to position them on the opposite surfaces of 
their respective bus bars. As best seen in FIG. 3, the right-hand end of 
each bus bar is provided with a dog-leg slot 40 which receives 
cooperatively aligned raised bosses 22a formed on each splice plate 22 to 
mechanically interlock the splice plates to the bus bars. As a result, the 
entire joint assembly 10 is interlocked to the bus bars. The end plates 30 
of joint 10 are secured to top and bottom housing members 14 and 16 by 
screws 42. 
Having been assembled to the bus duct section as described above, the prior 
art joint is tightened to only finger-pressure compression until final 
installation. While this is a presently acceptable design, it does provide 
some dissadvantages with allignment in the initial assembly of the joint 
to the bus duct at the factory and in the installation of the section in 
the field. In the latter instance, the stack of splice plates and 
insulators must be checked to insure that they are sufficiently loose to 
enable the adjacent bus bars to be inserted, but are not so loose as to 
move out of position and block entry of the bus bars or become out of 
position in final assembly. A further dissadvantage is the requirement for 
tightening the joint bolt subsequent to insertion of the second bus duct. 
In order to obtain the desired electrical conduction properties between 
flat-surfaced bus bars and splice plates it is necessary to provide 
substantially high compressive forces. Thus the installer must tighten the 
bolt to the recommended torque, customarily 75 foot-pounds, when the two 
bus duct sections are installed in their final location. Apart from 
requiring special tools, the nature of such final location often renders 
this step difficult to accomplish. 
The joint assembly 10 of this invention eliminates each of the 
aforementioned disadvantages in that it provides a joint which may be 
tightened to a final torque before attaching it to either bus duct. In so 
doing, all of the splice plates, insulators and other elements of the 
joint assembly are secured firmly together and in position, thereby 
requiring no separate individual spacing to align with the bus bars and 
housing during assembly. The slots 40 cooperate with bosses 22a and screws 
42 secure the end plates 30 to the bus duct housing as before to 
mechanically secure the joint 10 on the bus duct. A second duct is 
electrically connected to the joint 10 solely by insertion thereinto, 
final mechanical connection being accomplished by the normal housing cover 
plates for the joint as will be described in detail hereinafter. 
To overcome the aforementioned disadvantages, the splice plates 22 of the 
improved joint assembly 10 are provided with inset louvered contact strips 
44 such as that shown and described in U.S. Pat. No. 3,453,587 issued on 
July 1, 1969 to R. Neidecker. These strips 44 are formed from a material 
having good electrical conductive and mechanical spring qualitites and a 
relatively thin cross-sectional thickness. The strips 44 are formed to 
have a multiplicity of curved louvers bent obliquely to the plane of the 
strip and extending transversely thereof. By example, strips 44 may 
preferrably be formed of 0.008 inch beryllium brass. 
As seen most clearly in FIG. 4, splice plates 22 are provided with dovetail 
grooves 22b in the front face 22c at each end thereof. Louvered contact 
strips 44 are inserted into grooves 22b, the strips 44 having downwardly 
offset tabs formed along the edges thereof for retention within the 
grooves 22b. The corners of grooves 22b may be upset with a hand punch or 
by a similar staking operation at the opposite edges of the plate 22 to 
prevent the strips 44 from being removed or falling out. It should also be 
noted that the presence of the raised boss 22a within one of the grooves 
22b requires two separate strips 44 to be inserted in that groove, one 
from each side of the plate. 
Splice plates 22 further have a raised rib portion 22d surrounding the 
central aperture. The height of rib 22d is tolerance controlled with 
respect to the front face 22c. As seen in FIGS. 2 and 5, the splice plates 
22 are arranged in mirror image relationship to each other in cooperative 
pairs for each bus bar, with the outer surfaces of ribs 22d in mating 
engagement. Accordingly a space is provided between the cooperating faces 
22c of adjacent splice plates which is twice the height of the rib 22d 
above the face 22c and which is dimensionally stable within controlled 
tolerances. 
The louvers of contact strips 44 project beyond the respective faces 22c of 
the splice plates 22 to extend into the space between cooperating pairs of 
said plates. The bus bar thickness and overall dimension of the 
aforementioned space as determined by the height of ribs 22d are selected 
to provide a predetermined deflection of the louvers upon insertion of a 
bus bar thereinto. When a bus bar is received in the space between 
cooperating splice plates, each louver engages the surface of the bus bar 
along one edge and the bottom surface of the groove 22b of the respective 
splice plate 22 along the other edge thereof, thereby providing individual 
electrical connections between the bus bar and splice plates at each 
louver. The spring pressure required for each such connection is extremely 
light, particularly as compared to the compressive force required in flat 
surface connections, and is provided by the deflection of the individual 
louvers. 
In assembly of the joint 10, the bolt 32 and hex nut 36 are firmly 
tightened to the final torque on the order of 15 foot-pounds, to compress 
the stack of splice plates 22, insulator plates 24 and 26, pressure plates 
28 and end plates 30 solidly together, such that none of the individual 
members are free to move in any direction. The solid joint assembly 10 is 
thereafter plugged onto the end of an assembled bus duct section 12 by a 
sequential longitudinal and transverse movement in order to engage the 
dog-leg slots 40 with bosses 22a. End plates 30 are secured to the top and 
bottom members 14 and 16 with screws 42. 
In installation, the bus duct section 12 with joint assembly 10 affixed 
thereto is normally secured in position and a second section 12 is then 
brought into position in alignment therewith. This condition is depicted 
in FIG. 5. The second section 12, shown on the right in the drawings, is 
then completely electrically connected to the first bus duct section and 
joint 10 solely by inserting the bus bars into the spaces between the 
cooperating splice plates 22. This is accomplished with very light force 
since the only forces necessary to be overcome are the deflective 
resistance of the individual louvers on contact strips 44. The depth of 
insertion is controlled by the engagement of the leading edges of the bus 
bars with the upstanding ribs 22d. When inserted, the connection comprises 
a multiplicity of individual electrical connections, one for each louver. 
After electrically connecting the two bus duct sections 12 together with 
the joint assembly 10, a mechanical connection between the members is 
effected through the attachment of sheet metal cover plates 46 to the 
sides 18 and 20 of the bus duct housing. Cover plates 46 overlap the gap 
between the ends of the side members of the respective sections 12 and are 
secured by bolts 48. This mechanical connection prohibits the sections 
from being pulled apart. 
The ability of joint assembly 10 to maintain electrical connection without 
rigidly clamping the bus bars and splice plates together affords another 
advantage, that of permitting expansion and contraction of the bus bars at 
each joint assembly. The heat generated by current passing through the bus 
bars causes such expansion. The exact amount of expansive movement is not 
large per section, but in systems employing rigidly clamped joints, the 
lineal expansion components become accummulative, often resulting in a 
tearing of the bus bar surfaces. In the joint assembly of this invention, 
each joint affords lineal expansive movement of the bus bars, thereby 
eliminating any damage due to the accumulative effect over several 
sections. Moreover, it is envisaged that expansion designs could be 
provided that would permit several inches of movement between adjacent bus 
bars utilizing the similar construction technology employed in the joint 
assembly 10. 
While the apparatus hereinbefore described is effectively adapted to 
fulfill the objects stated, it is to be understood that the invention is 
not intended to be confined to the particular embodiment of bus duct joint 
assembly disclosed, inasmuch as it is susceptible of various modifications 
without departing from the scope of the appended claims.