ELECTRICAL DISTRIBUTION DEVICE
INCLUDING PROTECTION FOR OVERHEATING CONDITIONS
BACKGROUND OF THE INVENTION
1. Field of the Invention
[00011 The invention relates to electrical distribution devices and, more particularly,
electrical distribution devices, such as, for example, receptacle outlets, wiring devices,
wall, light or other power switches, lamp bases, extension cord outlet boxes, or wire
union junction boxes, having an arrangement for protecting against overheating
conditions.
2. Description of the Prior Art
10002] Electrical connections, especially where wires are terminated (e.g., at outlets,
switches, or other electrical distribution devices), are susceptible to overheating
conditions that can potentially cause a fire. The overheating conditions can be caused
by a number of conditions, such as a loose, damaged or degraded connection between
an electrical conductor and a terminal. A loose, damaged or degraded connection in
and of itself may not be a hazard, but it is known that such connections can cause arcs
when current is flowing and/or cause fretting of the electrical conductor. The arcing
and/or fretting can lead to problems that result in overheating conditions, such as a
glowing contact.
[0003] A glowing contact is a high resistance connection which can form at the
interface of, for example, a copper wire and a screw terminal of, for example, a
receptacle. The high resistance connection results from a build up of copper oxide
that is produced during arcing and/or fretting at the interface. During a glowing
contact fault in, for example, a receptacle, the copper wire reaches a glowing
temperature value at which time the wire looks like an electric heater coil. First, the
wire's insulation melts at the terminal. The melting then slowly progresses away from
the terminal toward other wires in the receptacle's outlet box. The melting and
decomposition of the plastic insulation from the wire and outlet can produce ignitable
gasses (e.g., hydrogen, methane, ethane, ethylene, or acetylene) which can be ignited
1

by an arc. Plastics and surrounding materials (wood, wallboard, etc.) may also be
ignited solely from the high temperature produced from the glowing connection.
[0004] Furthermore, the current that flows both during and after the formation of a
glowing contact is typically normal, since the voltage drop across a glowing contact,
depending on the current, can range from 2 Vrms to 10 Vrms, with the higher voltage
level occurring at the lower current levels. The existence of a glowing contact,
therefore, is not reliably detectable by a conventional upstream current protective
device (e.g., a conventional circuit breaker or fuse).
[0005] It is thus desirable to be able to detect glowing contacts or other conditions
that lead to overheating conditions and interrupt the current before the fault progresses
to a hazardous condition.
SUMMARY OF THE INVENTION
[0006] The present invention relates to an electrical distribution device that includes
a terminal, such as a screw, for providing an electrical connection to a first conductor,
a spring mechanism, such as a piece of spring copper or other metal, having a first end
that is electrically connected to the terminal and a second conductor electrically
connected to one or more internal components of the electrical distribution device.
The spring mechanism has a first condition and a second condition. In the first
condition, the second end of the spring mechanism is electrically connected to the
second conductor by solder. When the solder is caused to melt, such as by being
exposed to overheating conditions (e.g., from a glowing contact or series arcing at the
terminal) that exceed the melting point of the solder, the spring mechanism moves
from the first condition to the second condition. In the second condition, the second
end of the spring mechanism is no longer electrically connected to the second
conductor, thereby protecting the internal components from the fault condition that
lead to the overheating. This spring mechanism would preferably be present on all
line and neutral conductor paths. In the example of the wall outlet, there would be
four spring mechanisms since there are two plug receptacles present.
[0007] The electrical distribution device may further include a condition indicator
for indicating that a fault condition has occurred. The condition indicator is
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operatively coupled to the second end of the spring mechanism. The condition
indicator is caused to move to a fault indicating condition when the spring mechanism
moves from the first condition to the second condition. Preferably, the condition
indicator includes an indicator element, such as a sliding element provided in a
channel, operatively coupled to the second end of the spring mechanism that is
movable from a first position to a second position, wherein the second position
indicates a fault condition. The condition indicator may include a window through
which the indicator element is visible when in the second position.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008} A full understanding of the invention can be gained from the following
description of the preferred embodiments when read in conjunction with the
accompanying drawings in which:
[0009J Figure 1 is a front elevational view of a receptacle that includes an
arrangement for protecting against overheating conditions, such as are caused by
glowing contacts, according to the present invention;
|0010] Figures 2 and 3 are schematic illustrations of the arrangement for protecting
the receptacle from overheating conditions forming a part of the receptacle of
Figure 1;
[0011J Figure 4 is a front elevational view of a receptacle having a condition
indicator according to a further aspect of the present invention; and
[0012} Figures 5 and 6 are schematic representations showing the operation of the
condition indicator of Figure 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Figure 1 is a front elevational view of a receptacle 5 that includes an
arrangement for protecting against overheating conditions, such as may be caused by
a glowing contact or series arcing, according to the present invention. As will be
appreciated, receptacle 5 includes many components of common prior art receptacles.
For instance, receptacle 5 includes a body 10 consisting of a two-piece molding made
of thermoplastic insulating material. The receptacle 5 also includes a conventional
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ground-mounting plate 15 for mounting the receptacle 5 in a conventional outlet box
20 and two conventional receptacle outlets 25 and 30. The receptacle 5 includes two
screws 35 and 40 for electrically connecting a power line such as line wiring 45 and
two screws 50 and 55 for electrically connecting a neutral line such as neutral wiring
60 of a conventional 120-volt AC power source. A threaded mounting bore 65 is
adapted to receive a fastener, such as a screw, which is received through a mounting
aperture of a cover plate (not shown) in order to fasten the cover plate to the
receptacle 5. The receptacle 5 further includes a screw 70 for electrically connecting
a ground line 75, which grounds the ground-mounting plate 15. Although screws 35,
40, 50, 55 and 70 are shown, any suitable connection or terminal (e.g., without
limitation, compression terminals) may be employed.
|0014| Figures 2 and 3 are schematic illustrations of an arrangement for protecting
the receptacle 5 from overheating conditions, such as may be caused by a glowing
contact or series arcing, according to the present invention. As seen in Figure 2, a
conductive spring mechanism 80, such as a piece of spring metal (e.g., spring copper)
or other suitable conductive material, is attached to the screw 40 in a manner such thai
the spring mechanism 80 is electrically connected to the line wiring 45 at a first end of
the spring mechanism 80. A second end 90 of the spring mechanism 80 is electrically
and physically connected to conductor 95 by solder 100. Conductor 95 leads to the
internal components of the receptacle 5. As is known, solder 100 will have a
particular melting temperature depending on the specific type of solder used for solder
100. The use of screw 40 in Figures 2 and 3 is meant to be exemplary only, and it
will be appreciated that the arrangement of the present invention may also be used
with any combination of the screws 35, 40, 50 and 55 (and the associated wiring such
as neutral wiring 60), or other suitable terminals. In the preferred embodiment, the
arrangement of Figures 2 and 3 is used with each of the screws 35, 40, 50 and 55 (and
the associated wiring).
[0015] Under normal operating conditions, the arrangement appears as shown in
Figure 2 such that the line wiring 45 is electrically connected to the conductor 95
(through the solder 100), and therefore the internal components of the receptacle 5.
Spring mechanism 80, being made of a conductive material, will conduct heat. Thus,
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05-KDP-131
when the temperature at or near the junction of the screw 40, the line wiring 45 and
the first end 85 of the spring mechanism 80 becomes elevated, such as during
overheating conditions caused by, for example, a glowing contact or scries arcing, the
heat that is generated will be conducted by spring mechanism 80 to the second end 90
of the spring mechanism 80. When the temperature at the second end 90 of the spring
mechanism 80 is high enough, i.e., above the melting point of the solder 100, the
solder 100 will melt, thereby causing spring mechanism 80, and in particular the
second end 90 thereof, to move away from the conductor 95 under the spring tension
as shown in Figure 3. As a result, the electrical connection between the second end
90 of the spring mechanism 80 (and thus the line wiring 45) and the conductor 95 will
be broken, thereby isolating the internal components of the receptacle 5 and
protecting them from the overheating conditions.
[0016] As noted above, the particular melting point of solder 100 will depend on the
particular solder that is chosen. In addition, the time between the initiation of an
overheating condition, e.g., the initiation of a glowing contact, and the opening of the
connection the second end 90 of the spring mechanism 80 and the conductor 95 will
depend on the particular melting point of the solder 100. Thus, that time period can
be controlled, for a given current, by the type of solder that is chosen for solder 100.
The lower the melting point of the solder chosen for solder 100, the more sensitive il
will be to a temperature rise and the more quickly it will melt following the initiation
of the overheating condition, resulting in the separation of the second end 90 of the
spring mechanism 80 and the conductor 95. As will be appreciated, care should be
taken in choosing a solder for solder 100, as too low a melting point will cause the
solder to melt (and therefore allow the second end 90 of the spring mechanism 80 to
separate from the conductor 95) as a result of the heat generated under normal
operating conditions, particularly in applications having high ambient conditions.
[0017] A number of commercially available lead based solders that may be used for
solder 100 and their corresponding melting points are shown in 'fable 1 below.

Solder Type Melting Point
CC)
Cerrobend 70
Cerrosafe 71-88
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05-KDP-131

Cerroshield 95
Cerromatrix 103-227
Cerrobase
Cerrotru 124
138
Cerrolow-117 47
Cerrolow-136 58
57-65
Cerrolow-140

Cerrolow-147 61-65
Cerroseal Wire 116-127
Roses metal 95-110
Woods metal 70
Pb/Sn 60/40 188
Indalloy#117 47
Indalloy #136 58
Indalloy#158 70
Indalloy #42
Indalloy #255 96
124 """
Indalloy #181 145
Indalloy #2 154
Indalloy #97 163
Indalloy #9 167
Indalloy #204 175
Sn62 179
[0018] In light of new environmental regulations, it may be desirable or necessary to
use a lead free solder for solder 100. A number of commercially available lead free
solders that may be used for solder 100 and their corresponding melting points are
shown in Table 2 below.

Solder Type Melting Point
Indalloy #19 60
Indalloy #162 | 72
Indalloy #174 79
Indalloy #8 93
Indalloy #224 108
Indalloy #1 118
Cerrocast 138-170
Indalloy #281 138
Indalloy #290 143
Indalloy #4 157
Indalloy #133 240
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05-EDP-131
Indalloy#3 ] 247 J
[00I9| Figure 4 is a front elevational view of a receptacle 105 having a condition
indicator 110 according to a further aspect of the present invention. The receptacle
105 is similar to the receptacle 5 shown in Figure 1 and includes at least a line
terminal (e.g., screw 40) and a neutral terminal (e.g., screw 50), each one of which is
provided with an arrangement as shown in Figures 2 and 3 (not shown in Figure 4).
The condition indicator 110 is able to indicate whether a line or neutral fault condition
exists inside of the receptacle 105 as a result of the separation of the second end 90 of
the spring mechanism 80 and the conductor 95 for a particular terminal (line or
neutral terminal).
[0020] The condition indicator 110 includes sliding elements 115A and 115B that
are slideably mounted within a channel 120 provided on the front face of the
receptacle 105. The condition indicator 110 further includes a window 125,
preferably made of a colored, transparent or translucent material such as a colored
(e.g., red) plastic. The channel may be covered so that the sliding elements 115A and
115B are not visible except through the window 125 as described below.
(0021 ] As seen in Figure 4, the sliding element 115A is provided with the letter "I,"
thereon to indicate load. The sliding element 115A is coupled, such as through a rod
or lever mechanism, to the spring mechanism 80 attached to the load terminal of the
receptacle 105 so that, when the spring mechanism 80 is caused to separate from the
associated conductor 95, it will in turn cause the sliding element 115A to move to the
right as shown in Figure 5 and within the window 125. The presence of the sliding
element 115A within the window 125 will indicate that a load fault has occurred.
Similarly, the sliding element 115B is provided with the letter "N" thereon to indicate
neutral. The sliding element 115B is coupled, such as through a rod or lever
mechanism, to the spring mechanism 80 attached to the neutral terminal of the
receptacle 105 so that, when the spring mechanism 80 is caused to separate from the
associated conductor 95, it will in turn cause the sliding element 115B to move to the
left as shown in Figure 6 and within the window 125. The presence of the sliding
element 115B within the window 125 will indicate that a neutral fault has occurred.
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05-KDP-131
[0022] While specific embodiments of the invention have been described in detail, it
will be appreciated by those skilled in the art that various modifications and
alternatives to those details could be developed in light of the overall teachings of the
disclosure. For example, while the arrangement shown in Figures 2 and 3 is described
in connection with the receptacle 5, it may be used in the terminals of other electrical
distribution devices, such as, for example, receptacle outlets, wiring devices, wall,
light or other power switches, lamp bases, extension cord outlet boxes, or wire union
junction boxes. Accordingly, the particular arrangements disclosed are meant to be
illustrative only and not limiting as to the scope of the invention which is to be given
the full breadth of the claims appended and any and all equivalents thereof.
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05-KMM31
What is claimed is:
1. An electrical distribution device (5), comprising:
a terminal (35, 40, 50, 55) for providing an electrical connection to a
first conductor (45, 60);
a spring mechanism (80) having a first end (85) and a second end (90),
said first end being electrically connected to said terminal (35, 40, 50, 55); and
a second conductor (95) electrically connected to one or more internal
components of the electrical distribution device (5);
wherein said spring mechanism (80) has a first condition and a second
condition, wherein in said first condition said second end (90) of said spring
mechanism (80) is electrically connected to said second conductor (95) by solder
(100), wherein said spring mechanism (80) moves from said first condition to said
second condition when said solder (100) is caused to melt, and wherein in said second
condition said second end (90) of said spring mechanism (80) is not electrically
connected to said second conductor (95).
2. The electrical distribution device (5) according to claim 1, wherein
said terminal (35, 40, 50, 55) is a screw.
3. The electrical distribution device (5) according to claim 1, wherein
said spring mechanism (80) is a piece of spring metal.
4. The electrical distribution device (5) according to claim 1, wherein
said solder (100) is a lead based solder.
5. The electrical distribution device (5) according to claim 1, wherein
said solder (100) is a lead free solder.
6. The electrical distribution device (5) according to claim 1, wherein
said terminal (35, 40, 50, 55) is a load terminal.
7. The electrical distribution device (5) according to claim 1, wherein
said terminal (35, 40, 50, 55) is a neutral terminal.
8. An electrical distribution device (105), comprising:
a terminal (35, 40, 50, 55) for providing an electrical connection to a
first conductor (45, 60);
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05-EDP-131
a spring mechanism (80) having a first end (85) and a second end (90),
said first end being electrically connected to said terminal (35, 40, 50, 55);
a second conductor (95) electrically connected to one or more internal
components of the electrical distribution device (5); and
a condition indicator (110) operatively coupled to said second end (90)
of said spring mechanism (80);
wherein said spring mechanism (80) has a first condition and a
second condition, wherein in said first condition said second end (90) of said spring
mechanism (80) is electrically connected to said second conductor (95) by solder
(100), wherein said spring mechanism (80) moves from said first condition to said
second condition when said solder (100) is caused to melt, wherein in said second
condition said second end (90) of said spring mechanism (80) is not electrically
connected to said second conductor (95), and wherein said condition indicator (110) is
caused to move to a fault indicating condition when said spring mechanism (80)
moves from said first condition to said second condition.
9. The electrical distribution device according to claim 8, wherein said
condition indicator (110) includes an indicator element (115 A, 115B), said indicator
element (115A, 115B) being operatively coupled to said second end (90) of said
spring mechanism (80), said indicator element (115 A, 115B) being movable from a
first position to a second position, said second position indicating a fault condition
10. The electrical distribution device (105) according to claim 9, wherein
said condition indicator (110) includes a window (125), said indicator element (115 A,
115B) being visible through said window (125) in said second position.
11. The electrical distribution device (105) according to claim 9, wherein
said condition indicator (110) includes a channel (120), wherein said indicator
clement (115A, 115B) is a sliding element slideable within said channel (120), and
wherein said indicator element (115A, 115B) moves from said first position to said
second position by sliding within said channel (120).
12. The electrical distribution device (105) according to claim 11, wherein
said condition indicator (110) includes a window (125), said indicator element (115A,
115B) being visible through said window (125) in said second position.
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05-EDP-131
13. The electrical distribution device (105) according to claim 10, wherein
said indicator element (115 A, 115B) includes one of the letter "L" and the letter "N"
thereon.
14. The electrical distribution device (105) according to claim 8, wherein
said terminal (35, 40, 50, 55) is a screw.
15. The electrical distribution device (105) according to claim 8, wherein
said spring mechanism (80) is a piece of spring metal.
16. The electrical distribution device (105) according to claim 8, wherein
said solder (100) is a lead based solder.
11
17. The electrical distribution device (105) according to claim 8, wherein
said solder (100) is a lead free solder.
18. The electrical distribution device (105) according to claim 8, wherein
said terminal (35, 40, 50, 55) is a load terminal.
19. The electrical distribution device (105) according to claim 8, wherein
said terminal (35, 40, 50, 55) is a neutral terminal.

An electrical distribution device that includes a terminal for providing
a connection to a first conductor, a spring mechanism having a first end that is
electrically connected to the terminal, and a second conductor electrically connected
to one or more internal components of the device. The spring mechanism has a first
condition and a second condition. In the first condition, the second end is electrically
connected to the second conductor by solder. When the solder melts, the spring
mechanism moves from to the second condition in which the second end is no longer
electrically connected to the second conductor, thereby protecting the internal
components from the fault condition that lead to the overheating. A condition
indicator may also be provided for indicating a fault condition.