Note: Descriptions are shown in the official language in which they were submitted.
2061195
TITLE
FEMALE ELECI RICAL PLUG ~ITH OVERLOAD PROTECTION
BACKGROUND OF THE INVENTION
The present invention relates generally to an electric plug for an
5 extension cord and, in particular, to a circuit breaker protected female
electrical plug molded onto the end of a power cord.
Generally, when electrical appliances are connected to a typical wall
receptacle, there is no overload protection in the power line against surges of
electric current which might seriously damage the electrical appliances.
10 Typically, the only safety devices provided are circuit interrupters which are
adapted to either open or burn out when a current overload is present for a
predetermined time.
Conventionally, the circuit interrupters are located centrally,
particularly in a domestic establishment, with at least one circuit interrupter
15 having a capacity of approxim~tely 15 or 20 amperes governing each circuit.
The amperage capacity of the circuit interrupter may be excessive and afford
little protection for an individual electrical device. For example, a load with
a critical power rating below such a capacity may be damaged or may create
damage if its rating is exceeded for an appreciable length of time. The
20 circuit interrupters fail to adequately protect appliances because a current
overload which might be less than that required to open or burn out the
interrupter, and still great enough to cause damage, can flow through the
circuit interrupter unimpeded. Typically such current overloads result from
voltage surges caused by lightning striking the structure in which these
25 appliances are housed, or by striking an exposed power line. For such loads
which are not individually fused, adequate protection may be obtained by the
use of an electric cord equipped, as contemplated by the present invention,
with its own individual circuit interrupter.
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It should be understood that the term "circuit interrupter" is used to
designate any device which provides a conductive link in an electrical circuit
designed to "open" under overload thus interrupting the circuit. While
various types of circuit interrupters are available, the type used in the
5 present invention is restorable (or resettable) to the "closed" position thus
reconstituting the circuit when the overload has been removed or cured.
This type of circuit interrupter is generally identified as a circuit-breaker
whereas the common non-resettable type is known as a fuse which burns out
or "blows" under overload.
The use of power cables which are "fused" as distinguished from those
equipped with circuit breakers is not new; there being much prior art
relating thereto. These suffer, however, from one major disadvantage,
amongst others, in that the lack of a replacement fuse or the proper repair
materials in an emergency may prompt someone to resort to evasive means
for restoring a power cable to functionality, thereby, depriving its associated
load of essential protection more or less permanently. This is because it is a
common human tendency to leave an emergency repair as a permanent
repair, thereby, totally defeating the intent and primary function of the fused
power cable.
A variety of devices are known for isolating electrical appliances and
the like from electrical currents in excess of a predetermined value. U.S.
Patent No. 4,307,925 discloses a male plug connector encapsulating a circuit
breaker. In one embodiment, the reset button for the circuit breaker is
located in the same surface as the terminals of the plug. In another
embodiment, Fig. 5, the terminals extend radially outwardly from the
longitudinal axis of the plug and the circuit breaker reset button is located inthe surface from which the terminals would normally extend
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U.S. Patent No. 3,539,961 discloses an isolator having a male plug and
a female receptacle connected together by a fusible link for insertion
between an electrical appliance power line and a wall receptacle.
SUMMARY OF THE INVENTION
The present invention concerns a female electric plug typically
attached to one end of an electrical cord assembly having a male electrical
plug attached to the opposite end for engagement with an electrical outlet.
The female plug is selectively engagable with a male electrical plug
connected to an electrical device for supplying electrical current from the
outlet to the electrical device. The plug includes a pair of female terminals
and a female ground terminal for eng~ging the prongs of the male electrical
plug, a circuit breaker providing a path for electrical current and being
responsive to electrical current flow in excess of a predetermined amount for
opening the path and preventing the current flow, the circuit breaker having
a reset button m~ml~lly actuatable for closing the path, a first conductor
connected in series with the circuit breaker to one of the female termin~l~, a
second conductor connected to another one of the female terminals, and a
third conductor connected to the female ground terminal.
A body formed of an electrical insulating material encapsulates the
female terminals, the female ground terminal, the first, second and third
conductors and the circuit breaker. The body has a generally planar front
surface with a pair of prong shaped apertures formed therein providing
access to the female terminals, a ground prong shaped aperture formed in
the front surface providing access to the female ground terminal and another
aperture formed in a side surface of the body through which the reset button
extends. A pair of guard walls are formed on the side surface of the body,
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8378-20
the walls extending outwardly from the side surface on opposite sides of the
reset button for protecting the reset button from damage during normal use.
In an alternate embodiment, two additional sets of a pair of female
electrical terminals and a female ground terminal are encapsulated in the
body on opposite sides of the first two female terminals. Corresponding
terminals of each set are connected in parallel and additional prong shaped
- apertures are formed in the front surface of the body providing access to the
terminals for eng~ging up to three male plugs.
BRIEF DESCRIPTION OF THE DRAWINGS
The above, as well as other advantages of the present invention, will
become readily apparent to those skilled in the art from the following
detailed description of a preferred embodiment when considered in the light
of the accompanying drawings in which:
Fig. 1 is a perspective view of an electrical cord assembly having a
female electrical plug embodying the features of the present invention;
Fig. 2 is front elevational view of the plug shown in the Fig. 1;
Fig. 3 is a top plan view of the plug shown in the Fig. 2;
Fig. 4 is a left side elevational view of the plug shown in the Fig. 2;
Fig. 5 is a sectional view of the plug shown in the Fig. 2 taken along
the line 5-5;
Fig. 6 is front elevational view of an alternate embodiment of the
electrical plug in accordance with the present invention;
Fig. 7 is a top plan view of the plug shown in the Fig. 6; and
Fig. 8 is an electrical schematic of the plug shown in the Fig. 6.
DESCRIPTION OF THE PREFERRED EMBODIMENT
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Referring to the Fig. 1, there is illustrated an electric cord assembly
10 formed from a three conductor cable 11 having a three prong male plug
12 attached at one end for insertion into an electrical outlet 13 of a
conventional grounded wall socket 14 mounted in a wall 16. At an opposite
5 end of the cable 11 is attached a female plug 18 in accordance with the
present invention.
The plug 18 has a body 20 extending along a longitudinal axis 21 (Fig.
3) and formed of an electrically insulative material. The body 20 has a
generally rectangular cross section with rounded edges. As illustrated in
greater detail in the Figs. 3-5, the body 20 of the plug 18 has an enlarged
central portion 22 connected between a first or rear end portion 24 and a
second or front end portion 26. The first end portion 24 has a generally
cylindrical cross-section and is adapted to receive and encapsulate the
adjacent end portion of the electrical cable 11. The cable 11 extends in the
direction of the longitudinal axis 21 of the body 20 and exits a rear surface
25 of the end portion 24.
The second end portion 26 is generally square in cross section and has
a generally planar front surface 27. The surface 27 has three apertures
formed therein for receiving the prongs of a typical male electrical plug. An
aperture 28 and an aperture 30 are formed as horizontally spaced, vertically
extending slots with the aperture 28 at the left being longer as is typical of apolarized plug. An aperture 32 is semi-circular and positioned between and
below the apertures 28 and 30 for receiving a ground prong of the male plug.
An upper surface 33 of the end portion 26 has a projection 34 formed
thereon. The projection 34 is centered between the apertures 28 and 30 and
is generally semi-circular in cross section with a planar front surface 35
coextensive with the front surface 27.
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A reset button 36 extends outwardly from a left side surface 37 of the
central portion 22. The reset button 36 is positioned between a pair of
upstanding guard walls 38 and 40 which extend outwardly from the surface
37 in parallel planes perpendicular to the longitudinal axis 21 of the body 20.
S As shown in the Fig. 5, the reset button 36 is connected to a circuit breaker
42 encapsulated within the central portion 22. The guard walls 38 and 40
shield the button 36 to prevent accidental actuation of the button and the
circuit breaker 42.
Referring to the Fig. 5, the circuit breaker 42 is connected in series in
10 a conductor 44 electrically connected to a female terminal 45. The terminal
45 engages a male terminal or prong (not shown) of the circuit breaker 44
for current flow into the circuit breaker. A similar male terminal or prong
(not shown) on the circuit breaker 42 is engaged by another female terminal
46 for current flow from the circuit breaker. The electrical circuit of the
conductor 44 is extended to the aperture 28 by a conductor 47 connected
between the terminal 46 and a female terminal 48 positioned in the aperture
28 and adapted to receive a larger prong of a male electrical plug.
The cable 11 includes the conductor 44 and a return conductor 50.
The conductor 50 is connected directly to a female terminal 51 positioned in
20 the aperture 30 and adapted to receive a smaller prong of a male electrical
plug. The cable 11 also includes a ground conductor 52 which is connected
directly to a female terminal 53 positioned in the aperture 32 and adapted to
receive a ground prong of a male electrical plug.
The circuit breaker 42 functions to provide overcurrent protection to
25 any electrical device which is to be provided with power from the electrical
outlet 13. The circuit breaker 42 is set at a predetermined amperage rating
to interrupt the electric current flow through the conductor 44 when the
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current flow therein exceeds the predetermined amperage rating for any
reason. The current rating of the circuit breaker 42 is selected to correspond
to the amperage rating of the electrical devices to be protected which rating
is lower than the current rating of the electrical circuit connected to the
5 outlet 13.
When the circuit breaker 42 is actuated to open the current path in
the conductor 44, the reset button 36 is extended outwardly from the position
shown in solid line in the Fig. 3 to the position shown in phantom line.
Thus, the reset button 36 serves to indicate that the amperage rating of the
10 cord assembly 10 has been exceeded and the circuit breaker 42 has been
actuated. Typically, the circuit breaker 42 includes a thermally responsive
element (not shown) which is heated by current flow and opens the circuit
when excess current flow heats the element above a predetermined
temperature. Upon actuation, the circuit breaker 42 cannot be reset until
lS the thermally responsive element has cooled for a period even if the reset
button 36 is urged inwardly. When the element has cooled sufficiently, the
button 36 can be positively locked in the position shown in solid line and
current will flow.
Often, it is desirable to prevent the accidental turning on or off of an
20 electrical device. The guard walls 38 and 40 protect against accidental
actuation of the button 36 when it is in the solid line position such that a
connected electrical device is not turned off. The walls also protect against
accidental actuation of the button 36 when it is in the phantom line position
such that a connected electrical device is not turned on before the cause of
25 the current overload is corrected.
An alternate embodiment of the present invention is shown in the
Figs. 6-8. A female plug 58 has a body 60 extending along a longitudinal
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8378-20
axis 61 (Fig. 7) and formed of an electrically insulating material. The body
60 has a generally rectangular cross section with rounded edges and an
enlarged central portion 62 connected between a first or rear end portion 64
and a second or front end portion 66. The first end portion 64 has a
S generally cylindrical cross-section and is adapted to receive and encapsulate
the adjacent end portion of the electrical cable 11. The cable 11 extends in
the direction of the longitudinal axis 61 of the body 60 and exits a rear
surface 65 of the end portion 64.
The second end portion 66 is generally rectangular in cross section
and has a generally planar front surface 67. The end portion 66 is
configured as three of the second end portions 26 positioned side-by-side.
The surface 67 has three sets of three apertures formed therein for receiving
the prongs of a typical male electrical plugs. In the center, an aperture 68
and an aperture 70 are formed as horizontally spaced, vertically extending
lS slots with the aperture 68 at the left being longer as is typical of a polarized
plug. An aperture 72 is semi-circular and positioned between and below the
apertures 68 and 70 for receiving a ground prong of the male plug.
An upper surface 73 of the end portion 66 has a projection 74 formed
thereon. The projection 74 is centered between the apertures 68 and 70 and
is generally semi-circular in cross section with a planar front surface 75
coextensive with the front surface 67.
A reset button 76 extends outwardly from a left side surface 77 of the
central portion 62. The reset button 76 is positioned between a pair of
upstanding guard walls 78 and 80 which extend outwardly from the surface
77 in parallel planes perpendicular to the longitudinal axis 61 of the body 60.
The reset button 76 is connected to a circuit breaker (not shown) similar to
the circuit breaker 42 and encapsulated within the central portion 62.
21~61i95
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At either side of the front surface 67 are provided an additional set of
apertures, the set 82, 83 and 84 and the set 85, 86 and 87, for cooperating
with the prongs of two male plugs (not shown). As shown in the Fig. 8, the
cable 11 includes the conductors 44, 50 and 52 which extend into the body 60
5 in the same manner as in the plug 18. Provided inside the body 60 are the
circuit breaker 42, the conductor 47, and the terminals 48, 51 and 53.
Positioned in the apertures 82, 83 and 84 are female terminals 87, 88 and 89
respectively, electrically connected to the terminals 48, 51 and 53
respectively. Positioned in the apertures 85, 86 and 87 are female terminals
90, 91 and 92 respectively, electrically connected to the terminals 48, 51 and
53 respectively. Thus, the three sets of female terminals are connected in
parallel and are protected by the circuit breaker 42.
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8378-20
In accordance with the provisions of the patent statutes, the present
invention has been described in what is considered to represent its preferred
embodiment. However, it should be noted that the invention can be
practiced otherwise than as specifically illustrated and described without
S departing from its spirit or scope.
