Electrical terminal lug

An electrical connector for use with a stranded conductor cable includes a metallic terminal lug body having a longitudinally extending conductor bore hole extending from end to end thereof and having an attachment tang extending from one end of the body and parallel to the axis of the bore. The body includes a threaded bore extending from the upper surface, perpendicular to and into the conductor bore hole. The bottom of the threaded bore is coterminous with an undercut relief portion extending further into the conductor bore hole in the body of the terminal lug. A setscrew which includes a conically shaped conductor interface area and which is of the same alloy and material as the terminal body is received within the threaded bore for engaging the conductor strands in high contact pressure relationship therewith. The contact pressure results in moving and wiping of the conductor strands against each other, and against the conductor bore hole and the setscrew which removes oxidation from the strand surfaces. The contact pressure also results in a cold flow and deformation of a portion of the cable strands into the undercut relief which further locks the cable into the terminal body and provides a lower resistance electrical connection.

BACKGROUND OF THE INVENTION 
This invention relates to electrical connectors and, more particularly, to 
such connectors for terminating the exposed end of a stranded cable 
conductor into the body of the connector by means of a threaded fastener 
such as a setscrew. 
Electrical terminal lug connectors for providing electrical and mechanical 
termination of a stripped stranded wire cable conductor are known and have 
been widely used in the art. These devices generally comprise a terminal 
lug body having a longitudinally extending conductor receiving bore 
therein and a threaded setscrew receiving bore therein which is 
perpendicular to the longitudinal axis of the conductor bore. The setscrew 
compressively engages the stranded wire bundle to complete the mechanical 
and electrical connection. Although these electrical connectors have been 
widely used in the art, they fail to consistently achieve good conductor 
holding ability and low resistance electrical connection characteristics 
particularly in environments having wide ambient temperature variations. 
For example, the industry has proposed a standard known in the art as the 
U/L 486B connector test which requires that the connection attain given 
mechanical and electrical specifications including specified performance 
in an elevated temperature heat cycle test. It has been found that many of 
these prior art electrical connectors fail to consistently attain such 
rigorous electrical and mechanical specifications. It has also been found 
that some of these devices tend to mechanically fail as the required 
torque specification is applied to the threaded fastener or setscrew. 
Improvements in electrical connectors of the above-mentioned type are also 
known and have been widely used in the art. The improved devices are 
exemplified and discussed in U.S. Pat. No. 4,146,290 which discloses such 
an electrical terminal lug connector wherein an additional set of 
apertures or windows are provided along the side walls of the connector 
and extend inwardly into the body of the connector in a direction which is 
transverse to the axis of both the conductor receiving bore hole and the 
threaded setscrew receiving bore hole. These apertures or windows function 
to provide improved mechanical and electrical connections in that as the 
setscrew is torqued to the recommended setting, the wire strands are 
slightly bulged into the apertures or windows creating a relatively firm, 
low resistance connection. The present invention provides a further 
improvement in electrical terminal lugs and which has been found to attain 
the specifications mandated by the abovementioned industry standard. 
SUMMARY OF THE INVENTION 
Briefly, an electrical terminal lug connector for use with a given diameter 
stranded cable conductor having a generally round cross section is 
provided. The connector includes a terminal lug body having a conductor 
receiving bore hole extending therethrough from end to end thereof. A 
threaded bore extends from an upper surface of the body which is parallel 
to the axis of the conductor bore hole, through the axis of the conductor 
bore hole and terminates into the lower portion of the conductor bore 
hole. A setscrew is threadedly received in the threaded bore for 
engagement with the stranded conductor. The lower portion of the conductor 
bore hole includes an undercut relief portion adjacent to and coaxial with 
the threaded bore for receiving deformed portions of the cable which 
extend radially outwardly of the normal circumference of the cable 
conductor.

DETAILED DESCRIPTION 
Referring now to FIGS. 1 and 2 there is shown generally at 10 plan and top 
views respectively of the terminal lug connector in accordance with the 
present invention. Connector 10 includes a metallic terminal lug body 12 
having an attachment tang 14 extending from one end of the body 12 for 
attachment to external means (not shown) as by way of a fastener inserted 
through bore hole 14a. Connector 10 further includes a setscrew 16 which 
is received within a threaded bore of connector 10 as described more fully 
hereinafter. Setscrew 16 may comprise a headless setscrew having a 
hexagon-shaped recess 16a which forms a socket for receiving an external 
torque tool. In accordance with a feature of the present invention, body 
12 and setscrew 16 comprise the same alloy of the same material. This 
relationship has the advantage that all of the characteristics of the 
components are essentially identical and, therefore, respond to 
temperature changes as a unit and not as independent components. 
Referring now to FIGS. 3a-3c there are shown cross-sectional, top and end 
views, respectively, of connector 10 of the previous drawing figures. It 
can be seen that body 12 further includes a longitudinally extending 
conductor bore hole 18 extending from opposite ends of body 12 and 
generally parallel to tang portion 14. Body 12 further includes a threaded 
bore hole 20 extending from the upper surface of body 12 into the lower 
portion of body 12 and perpendicular to conductor bore hole 18. It can be 
seen that threaded bore hole 20 extends into body 12, through the axis of 
conductor bore hole 18 and terminates into the lower portion of conductor 
bore hole 18 beween its axis and the round bottom portion thereof. The 
lower portion of threaded bore hole 20 is coterminous with, and coaxially 
disposed with relation to, an undercut relief portion 22 which extends a 
given distance into conductor hole 18 of body 12 and is formed such as by 
drilling the subsequently tapped hole a given distance past the intended 
threaded portion of threaded bore hole 20. This operation may necessitate 
end milling to achieve the desired depth without scarring or penetrating 
the round bottom segment of the conductor receiving bore 18. 
Referring now to FIG. 4 there is shown an end view similar to FIG. 3c but 
which further illustrates connector 10 in conjunction with setscrew 16 and 
the strands of the stripped end of a cable conductor C after 
installation--i.e., once the setscrew 16 is advanced into compressive 
engagement with cable C. It can be seen that undercut relief portion 22, 
in cooperation with the associated structure of the terminal lug, permits 
the conductor strands to cold flow, or to be deformed into, this area 
under high contact pressure as provided by setscrew 16. This action not 
only facilitates locking of the conductor into body 12 of connector 10 
under setscrew 16, but also permits the conductor strands to move and wipe 
against each other under the high contact pressure applied by operation of 
setscrew 16. 
The function provided by the structure of undercut relief portion 22 
wherein the strands of the cable are moved and wiped against each other, 
the conductor hole, and the setscrew 16, functions to remove oxidation on 
the surface of the strands and results in a low resistance electrical 
connection not only between the individual strands but the wall of 
conductor hole 18, the undercut relief area 22 and setscrew 16 as well. 
Further, the cold flow or deformation of a portion of the normally 
circular cross section of conductor C into relief area 22, in conjunction 
with the conical shape of setscrew 16 under high contact pressure, results 
in a low resistance connection and which also locks the conductor to meet 
conductor secureness and pullout requirements. 
In currently preferred practice, the cross-sectional area of conductor hole 
18 is selected to be in a range of 1.6 to 2.0 times the total area of the 
maximum conductor size for which the terminal is adapted. It has been 
found that this range of value with respect to the maximum size conductor 
provides optimum performance with respect to low resistance and a 
mechanically secure connection. In currently preferred practice, the 
common material of setscrew 16 and connector body 12 comprises a 
conductive aluminum material such as 6061-T6 aluminum. It will now be 
appreciated by those skilled in the art, that the enlarged conductor hole 
size and undercut relief portion area in conjunction with the operation of 
the conical shaped conductor interface area of the setscrew permits the 
strands of the conductor to move and wipe against each other under high 
contact pressure to remove oxidation from the surfaces of the strands. 
This structure further functions to cold flow or deform the normal cross 
section of the conductor into the undercut relief area under the setscrew 
which thereby serves to mechanically lock the cable conductor and provide 
a low resistance electrical terminal lug connection. Finally, the 
structural relationship which follows from the use of the same alloy in 
both the terminal lug body and the setscrew results in optimum performance 
of the connector, in accordance with the present invention, during heat 
cycle testing and wide ambient temperature variation applications. 
What has been taught, then, is an electrical terminal lug connector for 
locking and making a low resistance electrical connection to a cable 
conductor and facilitating, notably, a moving and wiping action of the 
individual strands of the cable so as to remove oxidation from the 
individual cable strands. The form of the invention illustrated and 
described herein is but a preferred embodiment of these teachings, in the 
form currently preferred for manufacture. It is shown as an ilustration of 
the inventive concepts, however, rather than by way of limitation and it 
is pointed out that various modifications and alterations may be indulged 
in within the scope of the appended claims.