Note: Descriptions are shown in the official language in which they were submitted.
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~ECTRICAL CO~ECTOR
~ACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to electrical connectors for
electrical leads, particularly to electrical plugs which are
useful for making an electrical connection between an electrical
lead and an electrical power outlet.
- Introduction to the Invention
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It is often necessary to make an electrical connection to
an electrical lead, e.g. to splice two leads together or to
attach an electrical plug to a lead in order to apply power. It
is also known to insert a light, or other signal, into an
electrical circuit so that it is easy to determine whether
current is flowing through a heater or other operational
electrical device which forms part of the circuit. The light
can, for example, be placed in a plug through which the device
is connected to a wall outlet in a building or to another power
source. It is also known to insert a fuse, circuit breaker,
ground fault clrcuit interrupter (GFCI), or other circuit
protection device into an electrical circuit so that if the
current exceeds a safe level or otherwise behaves in an abnormal
fashion, the protection device is converted from its normal
state into an abnormal state in which it disconnects the c rcuit
from the power supply or otherwise prevents maintenance of the
abnormal current. The protection device can, for example, be
placed in a plug through which a heater or other operational
device is connected to a wall outlet in a building or to another
power source. When an electrical circuit contains both a signal
light and a protection device, absence of the signal light may
s1gnify failure of the operetional device itself, or failure of
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the electrical connections to the operational device, or
conversion of the protective device into its abnormal state,
e.g. failure ("blowing") of the fuse.
Self-regulating strip heaters which comprise elongate
electrodes connected by a conductive polymer resistive element
are well-known. In operation, the thermal output of these strip
heaters varies in response to changes in the thermal environment
and thus serves to limit the maximum temperature which the
heater achieves. Such heaters are often used to provide freeze
protection of pipes, such as domestic or commercial water lines,
or to maintain a constant temperature for pipes in process
industries. A number of measures have been proposed for
assisting the safe operation of such heaters. Reference may be
made, for example, to U.S. Patent No. 4,436,986 (Carlson) and
U.S. Patent No. 4,822,983 (Bremner et al).
SUMMARY OF THE INVENTION
I have now realized that when a conductive polymer strip
heater is connected to a power supply through an electrical plug
which is inserted into a conventional wall outlet and which
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contains a fuse or other protective device, it is ve*y useful to
include, as a part of the plug, a signal device, e.g. a light-
emitting diode, which is connected between the two legs of the
heater circuit so that it will provide a signal (e.g. will be
lit up) only~when the power is on and the protective device is
in its normal sta e.
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~ In a first aspect, this invention provides an electrical
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connector for connecting an electrical lead comprising a first
conductor-and a second conductor, which connector comprises
a conductor-receiving member which comprises
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(a) a first channel in which the first conductor can
be placed, and
(b) a second channel in which the second conductor
can be placed; and
(2) a conductor-connecting member which comprises
(a) a first conductor-contact section,
(b) a first connection-making section,
(c) a second conductor-contact section, and
(d) a second connection-making section;
the conductor-receiving member and the conductor-connecting
member being
(i) movable relative to each other between a unique
mated configuration and a plurality of demated
configurations;
(ii) such that in at least some of the demated
configurations, the first conductor can be
~ placed in the first channel and the second
~ conductor can be placed in the second channel;
.
(iii) such that if the first conductor has been placed
in the first channel and the second conductor
. . . has been placed in the second channel, the
conductor-recei~ing member with the conductors
placed therein and the conductor-connecting
. member can then be brought into the mated
configuratlon, in which mated configuration the
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first conductor makes physical and electrical
contact with the first conductor-contact section
: and the second conductor makes physical and
electrical contact with the second conductor-
contact section; and
.
(iv) such that they cannot be brought into the mated
configuration if the first conductor or the
second conductor has been placed in direct
physical contact with the respective conductor-
contact section instead of being placed in the
respective channel; and
(3) closure means for maintaining the conductor-receiving
member and the conductor-connecting member in the
mated configuration.
In a second aspect, this invention provides an electrical
connector which is in the form of an electrical plug for
connecting an electrical lead comprising a first conductor and a
' second conductor to an electrical power outlet.
'. In a third aspect, this invention provides an electrical
assembly~which comprises a plug according to the second aspect
: and an electrical fuse which is positioned between the first and
second contact sections.
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BRI~F DESCRIPTION OF THE DRAWING
Figure 1 is a schematic circuit diagram of an electrical
connector of the invention which is in the form of an electrical
plug;
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Figure 2 shows an exploded view of a plug of the invention;
and
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igure 3 shows a top view of another connector of the
invention.
`DETAILED D~SCRIPTIQN OF T~E_INV~TION
The connector of the invention is useful for connecting any
type of electrical lead which comprises a first conductor and a
second conductor. It is particularly useful when it is in the
form of an electrical plug which is used to connect an
electrical lead to an electrical power outlet. The power outlet
may be a wall outlet either inside or outside of a building, or
it may be part of a power supply or other suitahle source of
;power. The outlet may be two-hole for connection to a phase and
a neutral wire, or three-hole for connection to a phase, a
neutral, and a ground ~earth) wire. The electrical lead may be
any electrical component with a first conductor and a second
conductor, e.g. an electrical power cord. The plug is
particularly useful in making an electrical connection to a
strip heater, i.e. an elongate heating element which comprises
at least two electrodes. For a connection made with this type
of heater, the first conductor is one electrode of the heater
and the second conductor is the other electrode of the heater.
The strip heater may comprise a conductive polymer, i.e. a
composition in which a particulate conductive filler is
dispersed or otherwise distributed in a polymeric component.
Particularly preferred are self-regulating conductive polymer
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heaters, i.e. those which~exhibit PTC (positive temperature
coefficient) behavior. The electrodes of a self-regulating
` heater are generally elongate metal wires or braid which are
parallel and spaced apart. They are attached to or embedded in
a resistive element which comprises the conductive polymer and
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is often in the form of a continuous-strip. In order to provide
environmental protection and electrical insulation, it is common
ior the resistive element and the electrodes to be covered by a
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dielectric layer, e.g. a polymeric jacket. A metallic grounding
braid is often present over the dielectric layer in order to
provide physical reinforcement and a means of electrically
grounding the strip heater.
The term "PTC behavior" is used in this specification to
denote a composition or an electrical device which has an Rl4
value of at least 2.5 or an R1oo value of at least 10, and
preferably both, and particularly one which has an R30 value of
at least 6, where Rl4 is the ratio of the resistivitles at the
end and the beginning of a 14C range, Rloo is the ratio of the
resistivities at the end and the beginning of a 100C range, and
R30 is the ratio of the resistivities at the end and the
beginning of a 30C range. Self-regulating conductive polymer
j heaters which exhibit PTC behavior, and appropriate conductive
polymer compositions, are disclosed in U.S. Patents Nos.
3,858,144 (Bedard et al), 3,861,029 (Smith-Johannsen et al),
4,188,276 ~Lyons et al), 4,388,607 (Toy et al), and 4,426,339
(Kamath et al).
The invention is illustrated by the drawings. Figure 1
shows a schematic circuit di~gram for an electrical connector in
the form of a plug which is designed for insertion into an
electrical power outlet. A first contact member 2 comprises a
first prong 4 which can be inserted into one socket of the
outlet and a first fuse-contact section 6. A second contact
member 8 comprises a second fuse-contact section 10 and a first
conductor-contact section 12 to which a first conductor of an
electrical lead can be physically and electrically connected. A
third contact member 14 comprises a second conductor-contact
section 16 to which the second conductor of an electrical lead
can be physically and electrically connected and a second prong
~ 18 which can be inserted into the other socket of the outlet. A
; signal member 20 is electrically connected-between the second
and third contact members. In this embodiment, the signal
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member 20 is electrically in series with a first resistor 22 and
a second resistor 24. When the first and second prongs 4,18 are
inserted into the power outlet, the signal member 20 provides a
signal if a fuse 26 connects the first and second fuse-contact
sections 6,10. No signal is provided if there is no electrical
connection between the first and second fuse-contact sections
6,10. The signal member 20 may be a light, e.g. a light
emitting diode ~LED) which provides a visual signal, a bell or
other apparatus which provides an audio signal, or an electrical
switch which can generate an alarm signal. Other types of
signal members may be appropriate in different circumstances.
The first and second fuse-contact sections 6,10 are
positioned to receive a fuse 26. The selection of a specific
fuse is dependent on the normal operating conditions and the
anticipated fault conditions. Particularly preferred when the
connection is to be made to a strip heater is a very fast acting
fuse, i.e. a fuse which has little, if any intentional delay in
the overload region and which "trips" (opens) very rapidly when
the current in the circuit comprising the fuse exceeds the rated
value of the fuse. Appropriate fuses are very fast-acting
ceramic ferrule fuses with a current rating of 10 amperes and a
voltage rating of 125/250 volts. Such fuses are available, for
example, from the Bussman Division of Cooper Industries under
the name Buss GBB~-10. While it is possible to use one of the
measures disclosed in U.S. Patent No. 4,822,983 (Bremner et al)
in conjunction with this invention, I have found that, when a
fuse as just described is employed, excellent results can be
obtained without using a sensor.conductor as disclosed in that
patent. A switch or other component may be used in place of the
fuse for some applications. - i,
Figure 2 shows an exploded Yiew of one specific embodiment
of a connector in the form of a plug which is designed to
connect the conductors of a first-electrical lead 28 to an -
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electrical power outlet. In this figure the electrical lead 28
is a strip heater which comprises a resistive element 30, and
embedded therein, a first conductor 32 and a second conductor
34. The heater is surrounded by a metallic grounding braid 36.
Both the first conductor 32 and the second conductor 34 have
been stripped of the conductive polymer which comprises the
resistive element 30 to allow easy insertion into the conductor-
receiving member 38. For other types of leads, e.g. insulated
wires, it may not be desirable to remove the polymeric
insulation or jacketing material. The conductor-receiving
member 38 comprises a first channel 40, a second channel 42, and
a third channel 44, designed for insertion of the first
conductor 32, the second conductor 34, and the grounding lead
36, respectively. Each channel is a tunnel which has a frusto-
conical opening, both features sized so that the conductors
inserted in them can be held by frictional forces. The walls of
the channels serve to prevent contact between the conductors. A
radial opening 46,48,50 is cut through each tunnel to allow
electrical connection of the inserted conductor to the
conductor-contact sections. Once the conductors are inserted
into the conductor-receiving member 38, it is mated to the
conductor-connecting member 52. As a result of the design of
the conductor-receiving member, which may include positioning
pins or other design elements which are not shown, there is a
unique mated configuration. When the two pieces are mated, the
first conductor 32 is in physical and electrical contact with
the first conductor-contact section 12, the second conductor 34
is in physical and electrical contact with the second conductor-
contact section 16, and the grounding lead 36 is in physical and
electrical contact with the grounding contact section 5q. The
first and second conductor-contact sections 12, 16 and the
grounding contact section 54 may comprise insulation-piercing
means for use when the conductors are insulated with a polymeric
jacket. The conductor-connecting member further comprises first
and second fuse-contact sections 6,10 designed to receive a
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fuse. The first connection-making section 4 corresponds to the
first prong of Figure 1 and the second connection-making section
18 corresponds to the second prong. A ground-connection-making
section 56 is also present to connect to the ground in the
outlet. The embodiment shown also comprises a base 58 for the
conductor-connecting member 52 which can be welded, glued, or
snapped into place. A signal port 60 is positioned so that the
signal member 20 will be visible. Figure 2B shows the bottom of
the conductor-connecting member 52 with the base 58 removed.
The signal member 20, an LED, and first and second resistors
22,24 are visible. It is apparent that the first fuse-contact
section 6 and the first connection-making section 4 are made
from a single piece of metal, e.g. brass. In this embodiment,
the second conductor-contact section 16 and the second
connection-making section 18 are also made from a single piece
of metal, as are the second fuse-contact section 10 and the fuse
conductor-contact section 12.
The conductor-receiving member 38 is preferably made from
an insulating material, e.g. a polymer. It is particularly
preferred that it be made from a transparent polymer, e.g.
polycarbonate, so that there is a visual indication that the
conductors are properly positioned. The conductor-receiving
member 38 and the conductor-connecting member 52 are maintained
in position by a closure means 62, e.g. a screw or a clamp.
When mated properly, the plug provides adequate strain relief to
the electrical lead. A minimum pull force of 20 pounds on the
electrical lead is achieved. ~The "pull force" or "pullout
force" measures the amount of force required to pull the
electrical lead 0.125 inch (0.318 cm) out of the plug. This
procedure is described in U.S. Patent No. 4,883,945 ~Bautista)).
Proper mating of the conductor-receiving menber 38 and the
conductor-connecting member 52 cannot be achieved if either the
first conductor 32 or the second conductor 39 has been directly
connected to the respective conductor-contact section 12,16.
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; When the fuse 26 is in place but no conductors are inserted
into the conductor-receiving member, the plug may be used to
determine whether wall outlets are properly wired and/or live.
If the fuse is electrically intact and there is no signal when
the plug is placed into the outlet, that is an indication that
the outlet is defective. Additional signal members can be
incorporated into the plug to signal whether the phase and
neutral wires are wired correctly. When there is a ground
connection to the plug, additional signal members will indicate
whether there is actually a ground.
Figure 3 illustrates a connector 64 which is designed to
connect a first electrical lead 28 comprising first and second
conductors 32,34 and a second ectrical lead 66 comprising
third and fourth conductors 68,70. In this connector 64, there
are two conductor-receiving members 38,72. The second
conductor-receiving member 72 comprises two channels 74,76 for
insertion of the third and fourth conductors 66,68. A second
closure means 78 maintains the second conductor-receiving mem~er
72 in the mated configuration. In the mated configuration, the
third conductor 68 makes physical and electrical contact with
the first connection-making section 4 and the fourth conductor
70 makes physical and electrical contact with the second
connection-making section 18.
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