Note: Descriptions are shown in the official language in which they were submitted.
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FUSE STATE INDICATOR
BACKGROUND OF THE INVENTION
[0002] This invention relates generally to fuses and, more
particularly, to fuses with a fuse state indicator.
[0003] Fuses are widely used as overcurrent protection devices to
prevent costly damage to electrical circuits. Fuse end caps typically form an
electrical
connection between an electrical power source and an electrical component or a
combination of components arranged in an electrical circuit. A fusible link is
connected between the fuse end caps, so that when electrical current flowing
through
the fuse exceeds a predetermined limit, the fusible link melts and opens the
circuit
through the fuse to prevent electrical component damage.
[0004] Various types of fuse state indicators have been developed in
an attempt to more efficiently locate opened fuses for replacement. For
example, U.S.
Patent No. 6,566,996 to Douglass et al., is directed toward a combustible fuse
state
indicator which is notable both for its low cost construction and its
reliability in
comparison to other types of indicators. The combustible fuse state indicator
of the
`996 patent includes a combustible substance located adjacent a transparent
lens
extending through a side of a rectangularly shaped fuse module. A secondary
fuse
link extends adjacent the combustible substance and heat associated with
opening of
the secondary fuse link ignites the combustible substance to reveal a backing
layer of
a contrasting color. The fuse state indicator of the `996 patent, however, is
designed
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for use with a rectangular fuse module, and implementing such an indicator in
other
types of fuses presents a number of issues.
[0005] For example, in a cylindrical or cartridge fuse, the fuse indicator
assembly must be accommodated in a comparatively smaller space than in a
rectangular fuse module. Also, the secondary fuse link for the indicator must
be
electrically connected interior to the fuse body to conductive end caps or
terminal
elements coupled to the fuse body. Reliably establishing the electrical
connection
and properly orienting the secondary fuse link with respect to the combustible
substance is difficult. Also, due to the curvature of the fuse body, the
backing layer
beneath the combustible substance can be difficult to see when the combustible
substance is consumed.
[0006] It would therefore be desirable to provide a fuse state indicator
that is more amenable to use in other types of fuses, such as cylindrical
fuses, than
the indicator described in the `996 patent for a rectangular fuse module.
BRIEF DESCRIPTION OF THE INVENTION
[0007] According to one aspect of the present invention, there is
provided a fuse state indicator for a fuse including a cylindrical fuse body
and a
primary fuse element therein, said fuse state indicator comprising: an
extension
member having an outer surface, the outer surface having a curvature
complementary to a curvature of the cylindrical fuse body; a transparent lens
coupled
to said extension member; a readily combustible substance adjacent the lens; a
secondary fuse link adjacent said combustible substance, said readily
combustible
substance substantially completely ignited and consumed when said secondary
fuse
link opens; and a curved backing layer adjacent said secondary fuse link, the
backing
layer having a major surface and a minor surface peripheral to the major
surface, the
major surface having a curvature complementary to the curvature of the
extension
member, said backing layer at least partially concealed by said combustible
substance when viewed through said transparent lens before the fuse has
opened,
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said backing layer maintaining said secondary fuse link in position with
respect to
said combustible substance.
[0008] Optionally, the extension member is elongated in a longitudinal
direction and curved in a lateral direction. Conductive clips may be provided
to
electrically connect the secondary fuse link to end caps of a fuse.
Alternatively, the
secondary fuse link comprises a high resistance portion and a low resistance
portion
for termination with the fuse end caps.
[0009] According to another aspect, there is provided an electric fuse
comprising: a tubular fuse body having a first end, a second end, and an
aperture for
fuse state identification; first and second end caps coupled to said body; a
primary
fuse element electrically connected between said first and second end caps;
and a
fuse indicator assembly comprising a secondary fuse link electrically
connected
between said first and second end caps, a readily ignitable and combustible
substance adjacent said secondary fuse link, and a flexible backing layer
coupled to
an extension member and maintaining said secondary fuse link in position with
respect to said combustible substance, said flexible backing layer assuming a
curvature complementary to a curvature of the tubular fuse body.
[0010] According to another aspect, there is provided an electric fuse
comprising: a tubular fuse body having a first end and a second end and an
aperture
for fuse state identification; first and second end caps coupled to said body;
a primary
fuse element electrically connected between said first and second end caps;
and a
fuse indicator assembly comprising: an extension member having an outer
surface,
the outer surface having curvature complementary to an outer surface of the
tubular
body; a secondary fuse link electrically connected between said first and
second end
caps; a readily ignitable and combustible substance adjacent said secondary
fuse
link; and a flexible backing layer coupled to said extension member and
adjacent said
secondary fuse link, said flexible backing layer assuming the curvature of the
extension member when secured thereto and maintaining said secondary fuse link
in
position proximate said combustible substance for visible fuse state
indication
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through said aperture of said fuse body by the presence or absence of said
combustible substance, wherein said combustible substance is substantially
completely combusted after said primary fuse element has opened.
[0011 ] In still another aspect, there is provided a fuse state indicator for
a fuse including a primary fuse element in an insulative body, the insulative
body
having an aperture therethrough for fuse state identification, said fuse state
indicator
comprising: an insulative extension member having a body defining a
substantially
cylindrical outer surface and defining a cavity extending from the cylindrical
outer
surface; an ignitable and combustible substance received within said cavity; a
secondary fuse link extending across said extension member and said cavity
such
that said secondary fuse link is positioned adjacent said combustible
substance; and
a backing layer coupled to said extension member and closing said cavity over
said
combustible substance, wherein said secondary fuse link is positioned between
said
backing layer and said combustible substance, said backing layer being flexed
to
conform to the cylindrical shape of the extension member and at least
partially
concealed by said combustible substance when viewed through the aperture in
said
insulative fuse body before the primary fuse element has opened, said backing
layer
maintaining said secondary fuse link in position with respect to said
combustible
substance, said combustible substance being ignited and combusted to reveal
said
backing layer when said secondary fuse link opens.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Figure 1 is a perspective view of an exemplary fuse including a
state indicator.
[0013] Figure 2 is a cross sectional view of the fuse shown in Figure 1.
[0014] Figure 3 is an exploded bottom perspective view of a fuse state
indicator assembly for the fuse shown in Figures 1 and 2.
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[0015] Figure 4 is a cross sectional view of a portion of the fuse shown
in Figures 1 and 2.
[0016] Figure 5 is an exploded view of an embodiment of a fuse
including a state indicator.
[0017] Figure 6 is an exploded view similar to Figure 5 but illustrating
another embodiment of a fuse having a state indicator.
[0018] Figure 7 is an exploded view of another exemplary embodiment
of a fuse state indicator.
DETAILED DESCRIPTION OF THE INVENTION
[0019] Figure 1 is a perspective view of an exemplary embodiment of a
fuse 100 including a cylindrical fuse tube or body 110 having an aperture 150
extending therethrough at a location proximate to a first end of fuse body
110, and
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conductive ferrules or end caps 122, 124 are attached to the fuse body 110 on
either
end thereof. In an exemplary embodiment, the end caps 122, 124 include knife
blades
126, 128 respectively, which may be connected to line side and load side
electrical
circuitry (not shown), thereby forming a current path through a primary fuse
element
(not shown in Figure 1). In accordance with known fuses, the primary fuse
element
may include one or more fusible links or a fuse element assembly extending
through
the fuse body 110 between the end caps 122, 124.
[0020] A fuse state indicator assembly (not shown in Figure 1)
extends interior to the fuse body 110 and a portion of the fuse state
indicator is visible
through the aperture 150 in the body 110 to indicate an operating condition or
state of
the fuse 100. The fuse state indictor is electrically connected to the end
caps 122, 124
in the manner explained below, and indicates the state of the primary fuse
element
(i.e. an unopened state wherein current is conducted through the fuse element
or an
opened state wherein the circuit through the fuse element is broken).
[0021] In an exemplary embodiment, the fuse body 110 is elongated
and is generally cylindrical, although it is appreciated that the benefits of
the instant
invention may apply to non-cylindrical fuses in alternative embodiments.
Further, it
is understood that the invention is applicable to a wide variety of fuses
intended for a
wide variety of applications and having a wide variety of fuse ratings.
Therefore, the
embodiments of the invention shown and described herein are for illustrative
purposes
only, and the invention is not intended to be restricted to a particular fuse
shape type,
class or rating.
[0022] Figure 2 is a cross sectional view of the fuse 100 illustrating
the fuse body 110 having a first end 112, a second end 114 and an interior
bore 116
which contains a primary fuse element assembly 130. In the illustrated
embodiment,
the primary fuse element assembly 130 is a known dual element, time delay fuse
element assembly. In alternative embodiments, a wire fuse link, a fuse element
strip,
or other known fuse element or fusible link construction may be employed in
the fuse
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100. Additionally, more than one fuse link or element assembly may be employed
in
further embodiments of the invention.
[0023] The first end cap 122 and the second end cap 124 include
inner surfaces that fit over the first end 112 and the second end 114,
respectively, of
the fuse body 110. The fuse element assembly 130 and a fuse state indicator
assembly 200 are electrically connected in parallel between the end caps 122,
124 in
the interior of the bore 116 extending through the body 110. The aperture 150
of the
body 110 extends from the interior of the bore to the exterior of the body 110
and is
adapted to accept a portion of the fuse state indicator assembly 200 in the
manner
explained below when the fuse state indicator assembly 200 is installed in the
fuse
body 110. In accordance with known fuses, the fuse body 110 is filled with an
arc
energy absorbing material (not shown in Figure 2), such as quartz sand which
absorbs
heat generated in the primary fuse element assembly 130 in an overcurrent
condition
as the primary fuse element opens.
[0024] Figure 3 is an exploded view of an exemplary embodiment of
the fuse state indicator assembly 200. In the illustrative embodiment, the
fuse state
indicator assembly 200 includes an insulative extension member 210 having a
recessed cylindrical housing 216 extending therefrom, a transparent lens 230
coupled
to the housing 216, a combustible substance 232 disposed within the housing
216, a
secondary fuse link 234 extending across the extension member 210, and a
flexible
backing layer 236.
[0025] In an exemplary embodiment, the extension member 210 is
generally bowed or curved, and has a radius substantially equal to an inner
radius of
the fuse body 100 (as shown in Figures 1 and 2) so that a top surface 218 of
the
extension member 210 maintains contact with an inner surface of the fuse body
1 10.
The extension member 210 is elongated in a longitudinal direction and curved
in a
lateral direction so that the extension member maintains contact with the
inner surface
of the fuse body 110. The curvature of the extension member 210 is
substantially
complementary to the curvature of the fuse body 110 (shown in Figure 2)
although at
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a slightly reduced curvature, such that a top surface 218 of the extension
member may
underlie the interior surface of the bore 116 of the body 110 (shown in Figure
2) when
the fuse state indicator assembly 200 is installed.
[0026] The extension member 210 includes the recessed cylindrical
housing 216 extending from the top surface 218 of the extension member 210,
and the
housing defines an opening or cavity 219 extending therein from a bottom
surface 221
of the extension member 210. In one embodiment, the housing 216 includes crush
ribs (not shown in Figure 3) on the outer surfaces thereof which anchor the
housing
216 and the extension member 210 to the body 110 (shown in Figures 1 and 2)
when
the housing 216 is extended through the aperture 150 (shown in Figures 1 and
2)
during installation of the indicator assembly 200.
[0027] The housing 216 contains the transparent lens 230 at an outer
surface of the recessed cylindrical housing 216 at a distance from the top
surface 218
of the extension member. In an exemplary embodiment, the transparent lens 230
is
fabricated from suitable materials known in the art, including, but not
limited to,
polycarbonate, polysulfone, polyethersuifone, and acrylic. The recessed
cylindrical
housing 216 receives the combustible substance 232 in the cavity 219 for fuse
state
indication as described below.
[0028] In an exemplary embodiment, the combustible substance 232
is a tuft of nitrocellulose cotton that is easily ignitable and substantially
fills the
recessed cylindrical housing 216. The combustible substance 232 rests upon the
flexible backing layer 236 at a distance below the transparent lens 230. In
one
embodiment, the combustible substance 232 fills the cylindrical housing and
contacts
the transparent lens 230. In an alternative embodiment, the combustible
substance
232 only partially fills the cylindrical housing 216, thereby creating an
insulating air
gap (not shown) between the transparent lens 230 and the combustible substance
232
that both provides for combustion of the combustible substance and protects
the
transparent lens 230 from the associated heat when the secondary fuse link 234
ignites
the combustible substance 232. The combustible substance 232 has a contrasting
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color relative to the flexible backing layer 236, which may be any contrasting
color
relative to the combustible substance 232 for ready indication of the fuse
state, as
described further below. In one embodiment, the combustible substance 232 is
white
and the flexible backing layer 236 is black.
[0029] In a further embodiment, a known energetic chemical
compound may be used to assist ignition of the combustible substance 232. One
such
energetic chemical compound is described in commonly owned U.S. Patent No.
6,556,996. It is contemplated, however, that other compounds may be employed
in
other embodiments to assist or facilitate ignition and combustion of the
combustible
substance 232.
[0030] In alternative embodiments, other readily combustible
materials known in the art may be used in lieu of nitrocellulose cotton as the
combustible substance 232. For example, pure nitrocellulose, combustible
substances
such as cellulose paper, polymer film, polymer felt, and cellulose felt may be
used
within the scope of the present invention. In such embodiments, the
combustible
substance 232 is located adjacent and/or within the recessed cylindrical
housing 216
in various forms, including but not limited to circular disks that are, for
example,
0.001 inches to 0.010 inches thick. The disks may be dimensioned to be larger
in
circular dimension than the housing 216 and/or the transparent lens 230 so
that the
combustible substance 232 extends beyond the transparent lens 230 and the
recessed
cylindrical housing 216.
[0031] In an exemplary embodiment, the secondary fuse link 234 of
the fuse state indicator 200 is electrically connected in parallel with the
primary fuse
element assembly 130 (shown in Figure 2) through a first clip 222 and a second
clip
224 as described below. The secondary fuse link 234 has a much higher
electrical
resistance than the primary fuse element assembly 130 so that, during normal
operation of the fuse, substantially all of the current passing through the
fuse passes
through the primary fuse element assembly 130. In one embodiment, the
secondary
fuse link 234 is a fine wire selected to melt at a designated current in
accordance with
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a desired amperage rating of fuse. In alternative embodiments, the secondary
fuse
link 234 may be fabricated from a variety of materials known in the art,
including but
not limited to copper, and copper alloys including zinc, nickel, chromium,
tin, iron,
molybdenum, aluminum, berylium, and silicon.
[0032] The flexible backing layer 236 is disposed adjacent and
extends beyond the combustible substance 232 so as to be concealed or hidden
from
view by the combustible substance 232 when viewed through the top of the
transparent lens 230. The flexible backing layer 236 is of a contrasting color
relative
to the combustible substance 232, and is generally coextensive with the
combustible
substance 232. Disposed between the combustible substance 232 and the flexible
backing layer 236 is the secondary fuse link 234.
[0033] In an exemplary embodiment, the flexible backing layer 236
includes an adhesive or tacky layer on one side thereof. The flexible backing
layer
236 is applied to the extension member 210 adjacent the secondary fuse link
234 and
the combustible substance 232, thereby keeping the combustible substance 232
in
place within the recessed cylindrical housing 216 and maintaining the position
of the
secondary fuse link 234 with respect to the extension member 210. The flexible
backing layer 236 is fabricated from a relatively noncombustible material
relative to
the combustible substance 232, and is contrasting in color relative to the
combustible
substance 232. In an illustrative embodiment, the flexible backing layer 236
is
fabricated from, for example, black electrical tape having a sharp color
contrast with
the combustible substance 232, and the electrical tape secures the secondary
fuse link
234 to the extension member 210 proximate the combustible substance 232. The
flexibility of the electrical tape accommodates the curvilinear shape of the
extension
member 210 while reliably positioning the secondary fuse link 234 in proper
position
relative to the combustible substance 232 to ensure reliable ignition thereof
upon the
occurrence of a specified overcurrent condition. In further, and/or
alternative
embodiments, other insulative (i.e., nonconductive) materials, whether
flexible or
rigid, may be employed by adhesive or other attachment methods in lieu of
electrical
tape to accommodate the curved shape of the extension member 210.
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[0034] In an exemplary embodiment, the extension member 210
further includes mounting flanges 212, 214 located on opposite ends of the
extension
member 210, which interface with the first clip 222 and the second clip 224
and
which further interface with the secondary fuse link 234. The mounting flanges
212,
214 may be fabricated from a variety of materials known in the art, and in an
exemplary embodiment, are fabricated from plastic.
[0035] In an exemplary embodiment, the first clip 222 and the
second clip 224 engage both the fuse state indicator assembly 200 and the fuse
body
ends 112, 114. The clips 222, 224 are fabricated from a conductive material,
and in
the illustrative embodiment, are fabricated from strips or ribbons of
conductive
material, such as copper or copper alloys, including but not limited to alloys
including
zinc, nickel, chromium, tin, iron, molybdenum, aluminum, berylium, and
silicon. The
conductive clips 222 and 224 both position the extension member 210 relative
to the
fuse body 110 (shown in Figures 1 and 2) and establish an electrical
connection
through the secondary fuse link 234. Specifically, the clips 222 and 224
mechanically
and electrically contact the fuse end caps 122 and 124 (shown in Figures 1 and
2) and
provide a conductive path through the secondary fuse link 234 when the end
caps 122
and 124 are connected to an energized circuit (not shown).
[0036] In an exemplary embodiment, the clips 222, 224 are formed
or folded into a serpentine shape which engages the fuse state indicator 200
and the
fuse body ends 112, 114. More specifically, the clips 222, 224 include an
elongated
center 227 section having each ends 226, 228 displaced from and extending
generally
parallel to the center section in opposite directions from the center section
227.
[0037] In an exemplary embodiment, the mounting flanges 212, 214
are positioned adjacent an aperture 240 located at each end of the extension
member
210 which allows the clips 222, 224 to interface the mounting flanges 212,
214. The
mounting flanges 212, 214 include apertures 242 coextensive with similarly
shaped
apertures 244 on either end of extension member 210. The clips 222, 224 also
contain
mounting apertures 246, whereby a fastener (not shown) can be inserted through
each
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of the apertures 244, 242, and 246 in the extension member 210, the mounting
flanges
212, 214, and the clips 222, 224 respectively, to secure the clips 222, 224 to
the
extension member 210. The fastener can be any known fastener, for example, a
rivet
or a screw.
[0038] The secondary fuse link 234 is electrically fastened to the
clips 222, 224 so that the secondary fuse link 234 is connected in parallel
with the
primary fuse element assembly 130 as described above. The secondary fuse link
234
can be electrically and/or mechanically connected to the clips 222, 224 in a
known
manner such as soldering. In a further embodiment, the secondary fuse link 234
is
inserted into the aperture 242 located within the mounting flanges 212, 214
and
thereafter secured to the clips 222, 224 once the clips 222, 224 engages the
mounting
flanges 212, 214. In yet another embodiment, each end of the secondary fuse
link 234
engages the clips 222, 224 when the respective clips 222, 224 are positioned
relative
to the mounting flanges 212, 214.
[0039] In an exemplary embodiment, the fuse state indicator
assembly 200 functions as follows. When the primary fuse element assembly 130
opens due to a fault current, the current flows through the parallel secondary
fuse link
234, which causes the secondary fuse link 234 to melt or vaporize. The
resultant heat
ignites the combustible substance 232, and the combustible substance 232 is
consumed by confined burning within the recessed cylindrical housing 216, When
the combustion is complete, the flexible backing layer 236 is visible through
the
transparent lens 230.
[0040] Thus, an operative condition or state of the fuse 100 is readily
indicated by a visible change of color from, for example, a light color to a
dark color,
as seen through the transparent lens 230. The color visible through the lens
230
reflects the respective colors of the combustible substance 232 in an unopened
or
operative condition and the flexible backing layer 236 in an opened or
inoperative
state after the primary fuse element has opened. That is, to an observer
viewing the
transparent lens 230, when the primary fuse element assembly 130 is operable,
i.e.,
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has not melted or opened, the light-colored combustible substance is visible
through
the transparent lens 230. However, when the primary fuse element assembly 130
is
inoperable due to melting or opening from a fault current, the current
vaporizes the
secondary fuse link 234, ignites and consumes the combustible substance 232,
and
thereby reveals the contrasting dark-colored flexible backing layer 236 so
that it is
visible through the transparent lens 230.
[0041] In alternative embodiments, the flexible backing layer 236 is
only partially concealed by the combustible substance 232 when primary fuse
element
assembly 130 has not opened. For example, a light-colored stripe of the
combustible
substance 232 may cross a dark-colored flexible backing layer 236 such that
the stripe
is visible when the primary fuse element assembly 130 has not opened, and the
stripe
is combusted when the primary fuse element assembly 130 has opened so that
only
the colored flexible backing layer 236 is visible through the top of
transparent lens
230. In a further alternative embodiment, the flexible backing layer 236
includes text
and/or graphics that become visible when the combustible substance 232 is
combusted to indicate the state of the fuse 100.
[0042] Figure 4 is a cross sectional view of the fuse 100 showing the
placement of the first clip 222 in an exemplary embodiment. The second clip
224
(not shown in Figure 4) is placed around the second end 114 of the fuse body
110 in a
similar manner. In an exemplary embodiment, as shown in Figure 4, when the
fuse
state indicator assembly 200 is inserted into the aperture 150, second end 228
of the
clip 222 engages the fuse body 110 by folding the second end 228 over the
first end
112 of the fuse body 110 as shown. The first end 226 of the clip 222 engages
the
mounting flange 212 of the extension member 210 as described above. The
elongated
center 227 of the clip 222 is positioned adjacent the fuse body 110 and
extends from
the extension member 210 to the fuse body first end 112, and each clip end 226
and
228 extends generally parallel to the center section in opposite directions.
[0043] The second end 228 of the clip 222 is folded over the fuse
body first end 112. The end 228 of the first clip 222 is electrically
connected to the
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first end cap 122 when the end cap 122 is installed over the first end 112 of
the fuse
body 1.10. The first end cap 122 is connected to the fuse body 110 as
generally
known in the art, for example by crimping.
[0044] Figure 5 is an exploded view of an exemplary embodiment of
the fuse 100 including the fuse state indicator assembly 200. In this
embodiment, the
fuse 100 includes the cylindrical fuse body 110 having the first end 112, the
second
end 114 and the fuse bore 116 extending therebetween which receives the fuse
state
indicator 200 and the fuse element assembly 130. The fuse state indicator 200
is
elongated in the longitudinal direction and curved in the lateral direction so
that the
fuse state indicator maintains contact with the inner surface of the fuse body
110. The
fuse body 110 further includes the aperture 150 extending therethrough at a
location
proximate to the fuse body first end 112. The fuse state indicator is located
proximate
to the aperture 150 so that the transparent lens is visible through the
aperture 150 and
substantially flush with an outer surface of the fuse body 110. The end caps
122, 124
are attached to the fuse body 110 on either end thereof.
[0045] The fuse element assembly 130 is placed into the fuse bore
116 and is a known dual element time delay fuse element assembly having first
and
second short circuit strips 132 and 134 with a time delay element 136 in
between.
The first short circuit strip 132 and the second short circuit strip 134
include one or
more weak spots or areas of reduced cross sectional area therein. The first
and second
short circuit strips 132, 134 are mechanically and electrically connected to
the end
caps 112, 114 in a known manner such as, for example, via conductive washers
250.
[0046] In an exemplary embodiment, the first and second short
circuit strips 132, 134 are axially offset from one another on either side of
the time
delay element 136. The offset short circuit strip 132 is positioned in the
fuse bore 116
relative to the fuse state indicator 200 and is spaced a distance from the
fuse state
indicator assembly 200. As such, heat and potential arc energy released when
the
short circuit strip 132 opens is less likely to damage the fuse state
indicator assembly
200.
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[0047] The fuse state indicator assembly 200 is adapted to be
inserted into the fuse bore 116. The fuse state indicator assembly 200 extends
on the
interior of fuse body 110 and is positioned proximate to the aperture 150
within the
fuse body 110. When the fuse state indicator assembly 200 is so positioned,
the
transparent lens 230 extends across the aperture 150 and is generally flush
with the
outer surface of the fuse body 110. The aperture 150 is positioned at a
location
proximate to the fuse body first end 112 so as to minimize the effects of
electrical
arcing caused by the fuse element assembly 130. The fuse state indicator
assembly
200 is further held in place by the first clip 222 and the second clip 224 as
indicated
above. The first clip 222 and the second clip 224 are of differing lengths so
that the
fuse state indicator assembly 200 can be appropriately positioned with respect
to the
aperture 150.
[0048] Figure 6 shows an exploded view of an alternative
embodiment of a fuse 300 in which common elements of fuses 300 and 100 are
numbered with like reference characters. The fuse 300 includes a fuse body 110
having an aperture 150 and end caps 112, 114. The fuse 300 further includes a
fuse
state indicator assembly 200 as generally described above. In this embodiment
the
fuse element assembly 130 is a known "class J" fuse element. An open side of a
short
circuit strip 138 is positioned to face the fuse state indicator assembly 200
so that heat
and potential arc energy released when the short circuit strip 138 opens is
less likely
to damage the fuse state indicator assembly 200.
[0049] Having now described different embodiments of cylindrical
fuses having different types of fuse element assemblies, it should now be
understood
that the above described fuse state indicator may be adapted to accommodate a
variety
of different types of fuses. With appropriate modification of the conductive
clips
which connect the indicator to the fuse end caps, the indicator may be
securely
positioned at a desired location within the fuse body to appropriately space
the
indicator from primary fuse elements. Reliable fuse state indication is
therefore
provided for substantially universal use across a full product line of fuses.
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[0050] Figure 7 is an exploded view of another exemplary
embodiment of a fuse state indicator assembly 350 which may utilized with an
insulative body, such as the body 110 (shown in Figures 1 and 2), to construct
a fuse
with a local fuse state indication feature which is visible through the an
aperture in the
body, such as the aperture 150 (shown in Figures 1 and 2) in the body 110.
[0051 ] Like the indicator assembly 200 described above, the fuse
state indicator assembly 350 includes an insulative extension member 352
having a
recessed cylindrical housing 354 extending therefrom, a transparent lens 356
coupled
to the housing 354, a combustible substance 358 disposed within the housing
354, a
secondary fuse link 360 extending across the extension member 352, and a
flexible
backing layer 362.
[0052] Unlike the indicator assembly 200 having a secondary fuse
link 234 coupled to conductive clips 222, 224 (shown in Figures 3-6) for
terminating
the secondary fuse link to the end caps of the fuse, the assembly 350 employs
a
secondary fuse link or element 360 having a high resistance portion 363 and
integrated lower resistance portions 364 and 366 on either side of the high
resistance
portion 363. The low resistance portions 364 and 366 of the fuse link 360 may
be
directly coupled to the fuse end caps without external connecting elements,
such as
the clips 222 and 224 described above. As such, the external clips 222 and 224
and
associated fasteners may be eliminated and a simpler construction of the fuse
is
provided.
[0053] In an exemplary embodiment, the secondary fuse link 360 is
fabricated from a fine fuse wire, such as, for example, a thin wire fabricated
from
copper, a copper alloy, or chrome, having a predetermined resistance which
forms the
high resistance portion 363. A second wire, which is different from fuse wire,
is
wrapped or twisted about the fine fuse wire on the ends thereof to form the
lower
resistance portions 364, 366 on either side of the high resistance portion
363. A
central portion of the fuse wire (i.e., the high resistance portion 363) in
the vicinity of
the combustible substance 358, however, does not include the second wire
twisted
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thereabout. In an illustrative embodiment, the second wire has a comparatively
lower
resistance than the fuse wire and is for example, wound about the fuse wire
for about
60 twists to form the lower resistance portions 364 and 366 in the fuse link
360. The
twisted wire on the fuse wire of the secondary fuse link 360 effectively
creates lower
resistance termination portions 364 and 366 which may be mechanically and
electrically connected to the fuse end caps in a known manner (e.g.,
soldering), while
providing a high resistance portion 363 proximate the combustible substance
358.
The high resistance portion 363 ensures reliable ignition and consumption of
the
combustible substance 350 in an overcurrent condition to reveal the
contrasting
backing layer 362 and identify the operative state of the fuse as described
above.
[0054] In an alternative embodiment, the fuse link 360 having a high
resistance portion 363 and lower resistance portions 364 and 366 may be
fabricated
from a high resistance fine fuse wire coated, plated or overlaid with, for
example,
copper or another suitable material having a lower resistance. A portion of
the copper
plating may be stripped, cut, or otherwise removed from the plated wire to
form the
high resistance portion 363. The remaining plated portions of the wire
flanking the
high resistance portion 363 form the lower resistance portions 364 and 366 for
termination to the end caps.
[0055] In an illustrative embodiment, slots 368, 370 are provided in
the extension member 352 which receive the secondary fuse link 360 to assist
in
orienting or positioning the fuse link 360 in relation to the combustible
substance 358.
The flexible backing layer 362 is coupled to the extension member 352 as
described
above to maintain the fuse link 360 in a desired position relative to the
combustible
substance 358 and the transparent lens 356.
[0056] The assembly 350 is readily adaptable to a variety of bodies
used in the fabrication of fuses, and in particular may be utilized in
cylindrical fuses
having various types of fuse element assemblies, including but not limited to
the
primary fuse elements and assembles described above. By adjusting the lengths
of the
low resistance portions 364, 366 of the secondary fuse link 360, the indicator
may be
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securely positioned at a desired location within the fuse body to
appropriately space
the indicator from primary fuse elements, and establishing electrical
connection to the
end caps of the fuse may be greatly simplified. Reliable fuse state indication
is
therefore provided for substantially universal use across a full product line
of fuses.
[0057] While the invention has been described in terms of various
specific embodiments, those skilled in the art will recognize that the
invention can be
practiced with modification within the spirit and scope of the claims.
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