U.S. patent number 3,685,000 [Application Number 05/078,745] was granted by the patent office on 1972-08-15 for line plug with retractable grounding pin.
Invention is credited to Vernon L. Robbins.
United States Patent |
3,685,000 |
Robbins |
August 15, 1972 |
LINE PLUG WITH RETRACTABLE GROUNDING PIN
Abstract
A plug having a pair of fixed prongs, a retractable grounding
pin, and a grounding wire is provided for making an electrical
connection by insertion in a female receptacle. The fixed prongs
are connected to the line and load leads of a power cord and the
grounding wire is connected to the ground lead of the power cord.
The grounding wire is provided with a hook shaped terminal and the
retractable grounding pin is formed with an annular groove adapted
for locking engagement with the terminal. If the female receptacle
is of the type adapted to receive a three prong male plug, the
grounding wire is locked within the annular groove by means of the
terminal, whereby the grounding pin is secured in the extended
position. If the female receptacle is of the type adapted to
receive a two prong male plug, the grounding wire is attached to a
ground point on the box housing the receptacle by means of the
terminal, whereby the grounding pin is retracted as the plug is
inserted in the receptacle.
Inventors: |
Robbins; Vernon L. (Brockton,
MA) |
Family
ID: |
22145967 |
Appl.
No.: |
05/078,745 |
Filed: |
October 7, 1970 |
Current U.S.
Class: |
439/103 |
Current CPC
Class: |
H01R
27/00 (20130101) |
Current International
Class: |
H01R
27/00 (20060101); H01r 003/06 () |
Field of
Search: |
;339/14,31,32,33,45,62,63,157,195,196 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Champion; Marvin A.
Assistant Examiner: Hafer; Robert A.
Claims
What is claimed is:
1. A plug for use with two and three port female receptacles, power
being applied to at least two of the ports, said plug
comprising:
a. body means formed with a cavity;
b. at least two prong means operatively connected to said body and
projecting therefrom, said prong means in mating registration with
the ports having power applied thereto;
c. grounding pin means operatively connected to said body means and
adapted for extension from said body and retraction within said
cavity, said grounding pin means normally extending from said body
means in mating registration with the third port of the three port
female receptacle and in parallel space relationship with each said
prong means, said grounding pin means slidably retractable within
said cavity along a plane parallel to the longitudinal axis of each
said prong means, said grounding pin means having locking means;
and
d. grounding means operatively connected to said body means and
extending therefrom, said grounding means adapted for engagement
with said locking means, said grounding pin means being fixed
against retraction when said grounding means and locking means are
engaged.
2. The plug as claimed in claim 1 including power cord means
operatively connected to said body means, said power cord means
including at least first, second, and third lead means, said first
lead means connected to one of said prong means, said second lead
means connected to another of said prong means, and said third lead
means being an integral part of said grounding means.
3. The plug as claimed in claim 1 wherein said cavity is tubular,
one extremity of said cavity being closed and the other extremity
of said cavity being opened.
4. The plug as claimed in claim 3 including:
a. hub means operatively connected to said body at the closed
extremity of said cavity;
b. guide means operatively connected to said hub means;
c. bushing means operatively connected to said body means at the
opened extremity of said cavity, said bushing means formed with a
bore adapted to slidably receive said grounding pin means, said
guide means projecting from said hub means into said grounding pin
means; and
d. bias means enveloping said guide means, said grounding pin means
being held in the extended position by said bias means.
5. The plug as claimed in claim 4 wherein said grounding pin means
is formed with a bore, said bore being closed at one extremity of
said grounding means and opened at the other extremity of said
grounding pin means, said bore adapted to slidably receive said
guide and bias means.
6. The plug as claimed in claim 5 including stop means operatively
connected to said grounding pin means proximate to said opened
extremity of said grounding pin means, said stop means being larger
than said bushing bore.
7. The plug as claimed in claim 6 wherein said grounding means
includes terminal means, said terminal means adapted for engagement
with said locking means.
8. A plug for use with two and three port female receptacles, power
being applied to at least two of the ports, said plug
comprising:
a. body means formed with a cavity said cavity opened to one face
of said body means and closed to an opposite face of said body
means;
b. at least two prong means operatively connected to said body and
projecting therefrom, said prong means in mating registration with
the ports having power applied thereto;
c. grounding pin means operatively connected to said body means and
adapted for extension from said body and retraction within said
cavity, said grounding pin means normally extending from said body
means in mating registration with the third port of the three port
female receptacle and in parallel space relationship with each said
prong means, said grounding pin means slidably retractable within
said cavity along a plane parallel to the longitudinal axis of each
said prong means, said grounding pin means having locking
means;
d. grounding means operatively connected to said body means and
extending therefrom, said grounding means adapted for engagement
and disengagement with said locking means, said grounding pin means
being fixed against retraction when said grounding means and
locking means are engaged, said grounding pin means slidable in a
plane parallel to said prong means when said grounding means and
locking means are disengaged; and
e. power cord means operatively connected to said body means, said
power cord means including at least first, second, and third lead
means, said first lead means connected to one of said male prong
means, said second lead means connected to another of said male
prong means, and said third lead means being an integral part of
said grounding means.
9. The plug as claimed in claim 8 including:
a. hub means operatively connected to said body at the closed
extremity of said cavity;
b. guide means operatively connected to said hub means;
c. bushing means operatively connected to said body means at the
opened extremity of said cavity, said bushing means formed with a
bore adapted to slidably receive said grounding pin means, said
guide means projecting from said hub means into said grounding pin
means;
d. bias means enveloping said guide means, said grounding pin means
being held normally in the extended position by said bias means;
and
e. grounding pin means formed with a longitudinally extending bore
and a stop, said grounding pin means bore closed at one extremity
of said grounding pin means and opened at the other extremity of
said grounding pin means, said grounding pin means bore adapted to
slidably receive said guide and bias means, said stop being larger
than said bushing means bore, said stop engaging said bushing means
when said grounding pin means is extended and operating to retain a
portion of said grounding pin means within said cavity.
10. The plug as claimed in claim 8 wherein said grounding means
includes terminal means operatively connected to said third lead
means, said terminal means adapted for engagement and disengagement
with said locking means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrical plugs and more
particularly to electrical plugs adapted for use with two and three
port female receptacles.
2. Description of the Prior Art
Due to the potential hazards from electric shock, power tools are
provided with three prong plugs which allow the power tools to be
grounded. However, all female receptacles are not adapted to
receive three prong plugs. Accordingly, a separate adaptor is
provided as an interface between the three prong plug and the two
port receptacle. Often times, such adaptors are misplaced and the
grounding pin of the plug is removed in order to use the power
tool. After the grounding pin has been removed, the power tool can
no longer be grounded and the potential of electric shock is
presented whenever the tool is being used.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a line plug
adapted for use with two and three port female receptacles. The
plug is characterized by a body portion having extending therefrom
a pair of fixed prongs, a retractable grounding pin, and a
grounding wire. The fixed prongs are connected to the line and load
leads of a power cord and the grounding wire is connected to the
ground lead of the power cord. The body portion is formed with a
chamber adapted for slidable reception of the grounding pin. The
grounding pin is formed with a central bore adapted to slidably
receive a guide pin and spring which are axially mounted to the
body within the chamber. The spring is received within the central
bore, whereby the grounding pin is held normally in the extended
position. The ground pin is formed also with an annular groove and
the grounding wire is provided with a hook shaped terminal which is
adapted for locking engagement with the groove when the grounding
pin is in the extended position. If a three prong female receptacle
is provided, the terminal is latched within the groove and the
grounding pin is fixed against retraction. If a two port female
receptacle is provided the grounding wire is attached to a ground
point on the receptacle box housing by means of the terminal
whereby the grounding pin is retracted as the plug is inserted in
the receptacle. The combination of a pair of fixed prongs, a
retractable grounding pin, and a grounding wire is such as to
provide a power cord plug which is which is adapted for use with
two and three port female receptacles.
The invention accordingly comprises the device possessing the
construction, combination of elements and arrangement of parts that
are exemplified in the following detailed description, the scope of
which will be indicated in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the nature and objects of the present
invention, reference should be had to the following de-tailed
description taken in connection with the accompanying drawings,
wherein:
FIG. 1 is a perspective of a line plug made according to the
invention;
FIG. 2 is a front elevation of the plug; and
FIG. 3 is a side elevation, partly brokenaway, showing certain
details of the plug.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, reference character 10 denotes a
line plug embodying the invention and adapted for use with two and
three port female receptacles. Plug 10 comprises a body portion 12,
fixed prongs 14 and 16, a retractable grounding pin 18, and a
grounding wire 20. A power cord 22 having power line leads 24, 26
and ground lead 28 is operatively connected to body 12. Leads 24
and 26 are connected to fixed prongs 14 and 16, respectively, and
lead 28 is connected to grounding wire 20. Preferably, lead 28 and
grounding wire 20 are integral. Fixed prongs 14, 16 and grounding
pin 18 are oriented in mating registration with the correlative
ports of the female receptacle.
Body 12 is formed with a substantially tubular cavity 32 which is
closed at one extremity and opened at the other extremity and is
adapted to slidably receive grounding pin 18. Proximate to the
closed extremity of cavity 32, there is a rib 34 which is adapted
for locking engagement with a groove 35 of a hub 36.
A bias element 38, for example a helical compression spring,
envelops a rod 40 which extends from hub 36 into cavity 32.
Proximate to the opened extremity of cavity 32, there is a notch 42
which is adapted to lockingly engage a shoulder 44 of a bushing 46.
Body 12 is formed with an annular recess 48 which is adapted to
receive a shoulder 50 of bushing 46 in such a manner that exposed
face of bushing 46 is substantially flush with the face of body 12.
Bushing 42 is formed with an bore 52 which is adapted to slidably
receive grounding pin 18.
Grounding pin 18 is formed with a bore 54, an annular groove 56,
and a stop 58. Bore 54, closed at the one extremity and opened at
the other extremity, is adapted to receive rod 40 and spring 38,
the axis of bore 54 and rod 38 being in registration. Rod 40 is
positioned within bore 54 approximate to the outermost face of stop
58 and spring 38 abuts the closed extremity of grounding pin 18.
That is, rod 40 defines a guide for grounding pin 18 which is held
normally in an extended position by spring 38. Stop 58 is slightly
larger than bore 52, whereby grounding pin is prevented from being
pushed out of busiing 46 by spring 38. The innermost side of
annular groove 56 is substantially flush with the outermost face of
bushing 46.
Annular groove 56 is adapted for locking engagement with a terminal
60 which is attached to the free end of grounding wire 20 by means
such as crimping or soldering, for example. In the illustrated
embodiment, terminal 60 defines a hook shaped configuration having
a socket portion 62 which is adapted to receive grounding wire 20.
It is to be understood that, in alternative embodiments, terminal
60 defines other than a hook shaped configuration, for example a
snap-ring configuration. When terminal 60 engages annular groove
56, grounding pin 18 is fixed against retraction into cavity 32 of
body 12.
As previously indicated, plug 10 is adapted for use with two and
three port female receptacles. If the female receptacle is adapted
to receive a three prong plug, terminal 60 is locked within annular
groove 56, in consequence grounding pin is fixed against
retraction. If the female receptacle is of the two port type,
terminal 60 is attached to a ground point on the box housing the
receptacle, for example the screw holding the box plate, in
consequence grounding pin is retracted in cavity 32 of body 12 as
prongs 14, 16 are inserted into their respective ports of the
female receptacle. Accordingly, whether plug 10 is used with a two
or three port female receptacle, the power tool attached to the end
of power cord 22 is grounded.
For ease of manufacture, it is preferred that plug 10 is formed by
a molding technique such as injection molding, for example. In this
case, the outer covering of power cord 22 is cut back to expose
leads 24, 26, and 28. Leads 24 and 26 are cut and stripped so that
they are substantially equal in length and shorter than leas 28.
Leads 24 and 26 are connected to prongs 14 and 16, respectively.
Prongs 14 and 16, lead 28, cord 22, and hub 36 are position in
their respective locations in the molding fixture. Thereafter, body
12 is formed by injection molding. It is preferred that body 12 is
composed of an elastomer such as natural or synthetic rubber, for
example. Upon completion of the molding process, ground lead 28 is
stripped and terminal 60 is attached thereto. Spring 38 is
positioned about rod 40 and grounding pin 18 is inserted into
cavity 32, rod 40 and spring 38 being received within bore 54.
Thereafter, bushing 46 is urged into the opened extremity of cavity
32, bore 52 slidably receiving grounding pin 18, whereby shoulder
44 is locked into notch 42 and the fabrication of the plug is
completed.
Since certain changes may be made in the foregoing disclosure
without departing from the scope of the invention herein involved,
it is intended that all matter contained herein be construed in an
illustrative and not in a limiting sense.
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