Note: Descriptions are shown in the official language in which they were submitted.
4~
Backqround of the_Invention
The present invention comprises a quickly assembled
electrical plug of dead front design.
While many electrical wiring devices still are of
the so-called live front variety, in which the conductive
terminals are connected to the cord conductors through the
face of the device, the trend in industry is toward the
safer, dead front design. In ~ead front plugs, the terminals
are wired from the back of the device, and the non-conductive
face contains slots or the like through which the terminal
prongs protrude. Several dead front plug designs have been
proposed, bu~ these generally have been complex and expensive--
to produce, or must be molded with the line cord in place.
Summary of the Invention
The present invention concerns a dead front
electrical plug comprising a cover, a composite, integrally
molded assembly and contact terminals. The molded composite
member includes the terminal block, a irst semi-cylindrical
housing portion connected to the terminal block by a molded
hinge, a second ~emi-cylindrical housing portion connected to
the first housing portion by a second molded hinge, and two
cord gripping fingers integrally connected to the hou~ing
portions by further molded hinges. ~he terminal block of
this composite member is designed so that all terminal wiring
screws are accessible from the same direction. Therefore~
3~
,
3~
they May be connected during assembly wi~hout the need to
rotate the devi~e. Peatures ~ontained in the housing
portion~, the terminal blo~k and ~he cover shell cooperRte
once the plug has been ~ ~embled and the ~hell added to
provi~e resistan~e to longitudin~l 3nd ~ransverse ~tresses
that occur during use of the plug. In a preferred embodiment,
there is, also molded into the housing portions, a ratchet pa~l
which cooperates with ratchetramp surfaces on the interior of
the cover shell. The ratchet action allows the shell to be
screwed on, but prevents inadvertant loosening of the shell.
These and other features of the inven~ion will be
~ore fully described in connection with the following
detailed description of a preferred embodiment.
Description of the Drawings
Figure 1 is a side view of an assemble~ 3-wire plug
~ccording to the present invention.
Figure 2 is an exploded view in per~pe~tive of the
3-wire plug shown in Figure 1.
Figure 3 i5 a plan view of the composite member of
the pre~ent invention, shown in its unassembled configur~tion
with the ter~inal prongs installed.
Figure 4 is a side view o the composite member of
the present invention, ~hown in its unassembled ~onfiguration
with the terminals prongs installed.
Figure 5 is a front view o the line terminal
prong~ u~ed in the plug of the present invention.
--3--
~,
Figure 6 is a side view of the line terminal prongs
used in the plug of the precent inventions.
Figure 7 is a front view of the ground terminal
prong used in the plug of the present invention.
Figure 8 is a side view of the ground terminal
prong used in ~he plug of the present invention.
Figure 9 is a front view of the composite member in
its partially assembled state, with the terminal prongs
installed.
Figure lO is an end view of the assembled plug of
the present invention.
Detailed Description
The Figures show the preferred embodiment of the
present invention. Referring first to Figure l, the
invention as there pictured comprises a terminal block lO
with line terminal prongs 2 and 3 and ground terminal prong 4
extending from the front thereof, housing portions 20 and 40
interconnected by hinge 7, and a cover or shell 60 which has
been ccrewed onto the assembly over the housing. Cover 60
has a rear end 61 with an opening therethrough for the line
cord~ a tapered portion 62 with a frusto-conical interior
surface and a generally cylindrical portion 63 haviny grooved
areas 64 to provide a be~ter grip. Finally, Figure l sho~s
ratchet pawl 42 molded into housing portion 40. Its
interaction with cover 60 will be clarified in the discussion
of subsequent figures.
-4-
.. . . . . .. . .. .. . . . .
Figure 2 shows how cover 60 mates with the
assembled composite member 5. Cover 60, at it~ front end,
has molded onto its interior surface eight convoluted ratchet
ramp ~urfaces 65 which interact with ratchet pawl 42 on
housing portion 40 in a manner described below to prevent
backing off of cover 60 after wiring and assembly. The
middle interior segment of cover 60 is threaded, as shown at
66, and the rear end of cover 60 has a frusto-conical shaped
interior which terminates in opening 61 through which the
line cord freely passes.
~ During assembly, cover 60 first encloses cord grip
fingers 21 and 41 which are integrally molded respectively
onto the rear of housing portions 20 and 40, as described in
more detail below~ Then the threaded interior segment 66 of
cover 60 engages the threaded exterior segment 50 of member
5. As the cover 60 is screwed home, the angle of the cord
grip fingers 21 and 41 is forced to assume that of the
frusto-conical interior of the coverO The fingers are thus
caused to move inwardly towards each other and thereby to
grip the cord which lies between them. During the last
stages of tightening of cover 60 on member 5, ratchet pawl 42
will engage the convoluted ramp surfaces 65. When the
tightening is complete, ratchet paw~ 42 will be engaged as
shown in Figure 1, with a portion exposed where it can be
reached for radially inward depression to release the ratchet
action to facilitate intentional disassembly of the plug.
Figure 10 shows the mating of ratchet pawl 42 wi~h one of
ramp sur f aces 6 5 .
To facilitate the manual gripping cf member 5 as
~over 60 is tightened down onto that member~ grooved areas
~uch as 222 are provided around the lower end of the ex~erior
surface of housing portions 20 and 40.
~ he detailed structure of the member 5 is best seen
in Figures 3 and 4. The fiYe main elements of member 5 are
terminal block 10, housing portions 20 and 40, and cord grip
fingers 21 and 41. Terminal block 10 is connected to housing
portion 4D ~y integrally molded hinge 6. ~ousing portions 20
and 40 are joined by a similar hinge 7. Cord grip fingers 21
and 41 are joined respectively to housing portions 20 and 40
by hinges 8 and 9.
Terminal block 10 comprises a flat front face 11
containing openings for line terminal prongs 2 and 3 and
ground terminal prong 4. Immediately behind front face 11 is
a disk 12 of slightly greater diameter than face 11. The
periTneter of this disk seats in grooves 23 and 43 in housing
portions 20 and 40 when the plug is assembled. This
interlock provides resistance to longitudinal stress on the
plug such as occurs when the plug is disconnected from a
socket. It will be noted that disk 12 ha~ flattened sections
13 and 14 at opposite positions around its perimeter 90~ away
from hinge 6. These flattened sections facilitate insertion
of terminal block 10 into housing portion 40 in view o the
-6- -
relative stiffness of the preferrecl thermoplastics ~aterials:
polypropylene or, for high temperature environments, nylon.
Formed on the rear face of disk 12 are three upstanding
insulated chambers which contain the rear portions of line
terminal prongs 2 and 3 and ground terminal prong 4. As is
best seen in Figures 3, 4 and 9, the rear portion OI each of
terminal prongs 2 and 3 i5 seated in a chamber ormed by
front wall 15, outside wall 16, rear wall 17 and middle wall
18. Wall 15 has two arcuate cut-out portions thrvugh which
protrude the wiring screws of terminal prongs 2 and 3. The
chamber for the reae portion of ground terminal prong 4 is
bounded by front wall 19, side walls 191 and 192 and as i~s
rear wall, the walls 15 that form the front walls of the
chambers for the line terminals. Wall 19 has an arcuate
cut-out portion through which protrudes the wiring ~crew of
terminal prong 4. As appears most clearly in Figures 4 and
9, the chamber for ground terminal prong 4 is shallower than
the chambers for line terminal prongs 2 and 3, so that all
three wiring screws are accessible for wiring in the same
direction, a featuEe of the present invention which
facilitates its assembly as compared to prior art devices.
Housing portion 20 contains two generally
semi-circular internally mounted shelves 24 and 25 and r along
its side wall remote from hinge 70 a rectangular latch 26.
Shelves 24 and 25 respectively have slots 27 and 28
therethrough. Housing portion 40 contains ratchet pa~l 42
and also semi-circular internally mounted shel~ 44, contoured
,
~ C~
to fit around wall 18 of terminal block 10 and having sl~ts
45 and 441 therethrough. Housing portion 40 further
includes, along i~s side wall remote from hinge 7, a
rectangular seat 46 adapted to receive la~ch 26 of housing
20. Latch 26 snaps into engagement with seat 46 at the end
of the assembly operation. When, near the end of the plug
assembly operation, housing portions 20 and 40 are brought
together around terminal block 10, the lower edge of shelf 2S
rests on a shoulder formed in wall 15 and shelves 24 and 44
meet The end of the line cord abuts wall 18 which, as best
shown in Figure 9, extends upward through slot 45 above
shelves 24 and 44O The ground and line conductors reach the
ground and line terminal screws through slots 27, 28 and 441.
In addition, as seen in ~igures 3 and 4, housing
portion 40 includes two tabs 47 and 48 along its side wall
remote from hinge 7, which tabs interlock during assembly
respectively with slots 29 and 291 alony the side wall of
housing portion 20 remote from hinge 7. These interlocks
provide additional resistance to longitudinal stress on the
assembled plug. Further, housing portion 40 has molded on
its inner surface blocks 49 and 491. These blocks abut the
rear wall 17 of terminal block 10 when the terminal block has
been rotated about hinge 6 into position within housing
portion 40 during assembly, and the abutment of the blocks
against wall 17 provides resistance to tr2nsverse stress
arising during use of the plug.
Cord grip fingers 21 and 41 contain serrated
gripping surfaces 210 and 410 and rounded shoulders on their
outer surfaces, such as shoulder 411 seen on finger 41 in
~igure 4. These shoulders are contacted by the
frusto-conical inner surface of cover 60 as cover 60 is
screwed down onto the housing during assembly thereby causing
the cord gripping action described above.
Figures 5 and 6 show the unique line terminal prong
design utilized in the present invention to place all wiring
screws in a common orientation for wiring. The terminal
includes a blade 71 and a head 72 containing the wiring screw
73. Though formed from an initially flat metal blank, the
plane of the head of ~he terminal is rotated 90 from the
plane of the blade. By contrast, as seen in Figures 7 and 8,
the ground terminal 4 has a contact element 81 formed in the
standard configuration and a head B2 containing screw 83 and
lying in a plane parallel to the plane of the original blank.
It will be apparent to persons skilled in the art that
various other terminal and blade configurations, required for
other amperage and voltage applications, may be substituted
for those shown in Figures 5-8 without departing from the
spirit and scope of the present invention.
_g_
