US3794948A - Blown fuse indicators - Google Patents

Abstract

A dead front electrical blown fuse indicator for all standard cartridge enclosed fuses of both the ferrule and knife-blade types each comprising a casing or tube molded from insulating materials having an indicator lamp and contact terminal connected in series encased within the tube and said tube being opaque as to prevent the lamp and its electrical connections from being visible and yet being sufficiently translucent as to permit the lamp to glow over a wide area so as to be visible at all angles and at great distances from the tube. Resilient conductors electrically connected to said terminal for the lamp and each having a cantilever connection with the tube for causing the free ends of said resilient conductors to have a direct and positive snap-on electrical contact with the outer walls of the terminals of a fuse even when the fuse is subjected to undue vibration or shock. Said tube having sufficient tensile strength so as to prevent the bending or breakage of the tube due to its repeated application to and withdrawals from a fuse.

Description

United States Patent 191 Linton et al.

1451 Feb. 26, 1974 1 BLOWN FUSE INDICATORS [75] Inventors: John C. Linton, Potomac; Gordon W. Berry, Beltsville, both of Md.

[73] Assignee: Fuse Indicator Corporation,

Rockville, Md.

[22] Filed: Oct. 2, 1970 21] Appl. No.: 77,532

[52] US. Cl 337/242, 337/206, 337/266, 240/151 [51] Int. Cl. I-I0lh 85/32 References Cited UNITED STATES PATENTS 2,225,912 12/1940 LaMar 337/242 2,206,783 7/1940 Linton 337/266 2,164,658 7/1939 Lyon 337/242 1,951,308 3/1934 Mar 337/242 2,206,784 7/1940 Linton 337/242 2,276,785 3/1942 Mar 337/242 3,457,535 7/1969 Poehlman 337/242 2,783,331 2/1957 Sundt 337/206 2,464,848 3/1949 Collins 340/250 FOREIGN PATENTS OR APPLICATIONS 743,178 l/l956 Great Britain 200/166 BF OTHER PUBLICATIONS Christopher & Fox, Polycarbonates," Reinhold Publishing Corp., New York, 1962, pages 46, 65, 136, 137 and 139 Primary ExaminerBernard A. Gilheany Assistant ExaminerD. A. Tone 57] ABSTRACT A dead front electrical blown fuse indicator for all standard cartridge enclosed fuses of both the ferrule and knife-blade types each comprising a casing or tube molded from insulating materials having an indicator lamp and contact terminal connected in series encased within the tube and saidtube being opaque as to prevent the lamp and .its electrical connections from being visible and yet being sufficiently translucent as to permit the lamp to glow over a wide area so as to be visible at all angles and at great distances from the tube. Resilient conductors electrically connected to said terminal for the lamp and each having a cantilever connection with the tube for causing the free ends of said resilient conductors to have a direct and positive snap-on electrical contact with the outer walls of the terminals of a fuse even when the fuse is subjected to undue vibration or shock. Said tube having sufficient tensile strength so as to prevent the bending or breakage of the tube due to its repeated application to and withdrawals from a fuse.

2 Claims, 30 Drawing Figures PATENTED FEB 2 6 I974 SHEET 2 [IF 3 FIG. )3 v INVENTORS JOHN C. LINTON & GORDON W. BERRY m4 CZ Wmwa PATENTEDFEBZSBH I SHEET 3 UF 3 FIG. 22

FIG. 25

INVENTORS JOHN C. L/NTON Ce GORDON WBERRY ATTORNEYS,

BLOWN FUSE INDICATORS PRIOR ART Dead front lamp blown fuse indicators employing an opaque tube require a light emitting opening formed therein and are undesirable not only in that moisture, dust, and other foreign matter may enter the tube opening, but the rays of light are constricted by the small sizeof the opening and visible from directly in front of the indicator only. Many tubes formed from translucent plastic materials do not have the high impact or tensile strength that is required of a blown fuse indicator without greatly enlarging the thickness of the walls of the tube which greatly reduces the light emitting qualities. Also sectional tubes are used with one section opaque for the lamp and another translucent section connected thereto which greatly adds to the cost thereof. Furthermore, the high ambient temperatures generated by the fuse electrical circuit and associated equipments as well as heat from the high brightness lamp and resistor housed within the tube tend to melt or distort these plastic tubes. Tubes formed from materials such as Pyrex or glass are too brittle or fragile to meet with the vibration and shock requirements of a blown fuse indicator, and are dangerous to personnel in the vicinity of the installed indicator. Many different forms of brackets are used for retaining the indicator tube upon cartridge enclosed fuses, but none have a direct and positive snap-on connection that prevent breaks in the current when a fuse is subjected to undue vibrations or shocks.

STATEMENT OF THE INVENTION The Underwriters Laboratories, lnc., list two classes of standard enclosed cartridge fuses, one for 250 volt or less circuits and the other for 600 volts circuits and each class lists six fuses according to their ampere ratings with two ferrule type fuses and four knife-blade type fuses. The overall lengths of the cartridges of the twelve fuses so listed each vary from 2 inches to 1 1 U8 inches, with allowable plus and minus tolerances of 1/32 of an inch for a ferrule type fuse and H16 of an inch for knife-blade fuses. The Underwriters Laboratories lnc., require that when these fuses are enclosed in a fuse box or cabinet that an allowable minimum distance must be maintained between the live parts of a fuse and the metal door of the cabinet. From a complete study of all standard enclosed cartridge fuses now on the market no two manufacturers thereof have the lengths and diameters of the cartridge for these fuses the same, yet all come with the allowable tolerances allowed. With the foregoing in mind, the tube of the indicator was produced having an outside diameter of 0.438 inches and inside diameter of 0.312 inches leaving a wall of about l/16 of an inch thick of the same length throughout which could be readily cut in the different lengths according to the length of the fuse to which it is to be attached and fit within the allowable minimum distance between the live parts of a fuse and the door of a cabinet when mounted therein. Among the modern day materials of which these tubes are made a polycarbonate resin sold under the trade name Lexan by the General Electric Co. is preferable. The natural color of this resin is amber, but a white coloring is added to render the tube about 85 percent opaque and sufficiently translucent to permit the rays of light from the indicator lamp to emit therefrom in a soft white glow. The tubes so formed have the required insulating qualities of a blown fuse indicator and are said to have a tensile strength equal to that of a tube produced from some metals. Within each indicator tube so formed there is encased a pair of contact terminals to which are connected in series a high light brightness or high intensity lamp and when necessary a resistor for different voltage requirements. To each terminal there is electrically and permanently connected one end of flexible conductors whereby all the above live parts are completely insulated so as to prevent contact therewith which might cause a personal shock or contact the metal door of a cabinet housing the fuse when the indicator tube is attached to the fuse.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 illustrates in side elevation the actual size of a standard cartridge enclosed ferrule type 0-30 ampere volt fuse as retained in the standard fuse clips mounted upon a fuse block, the latter being partly shown in section and one form of a blown fuse indicator attached to the fuse.

FIG. 2 is an end elevation of the same.

FIG. 3 is a greatly enlarged sectional view of a protective boot or cap for the blown fuse indicator as illustrated above.

FIG. 4 is a greatly enlarged longitudinal sectional view of the blown fuse indicator as shown in FIG. 1 with a protective cap at the left hand terminal thereof.

FIG. 5 isa side view of the actual size of a standard cartridge enclosed ferrule type 31-60 ampere 250 volt fuse with a slightly modified blown fuse indicator attached thereto.

FIG. 6 is an enlarged detail sectional view of one end of the indicator shown in FIG. 5.

FIG. 7 illustrates the same blown fuse indicator with the fuse therefore of less over all length than that of the fuse shown in FIG. 5 and having ferrule end walls of concave configuration as indicated in dotted lines.

FIG. 8 is an end elevation of the same.

FIG. 9 illustrates in side elevation still another modified form of blown fuse indicators as applied to a fuse of the same overall length as that shown in FIG. 5 having convex end wall ferrules.

FIG. 10 is an end view of the same.

FIG. 11 is a plan view of a bracket to be used on all standard enclosed cartridge type fuses.

FIG. 12 is a side view of the same.

FIG. 13 illustrates in side view another embodient of the indicator with one end thereof in section.

FIG. 14 illustrates in top plan view another modified embodient of the indicator.

FIG. 15 is an end view of the same.

FIG. 16 is a diagram of the indicator as shown in FIG. 14 included in an electrical circuit.

FIG. 17 illustrates another type of cartridge enclosed fuse for use on high potential circuits with a blown fuse indicator attached.

FIG. 18 is an end view of the same.

FIG. 19 is an opposite end view of the same.

FIG. 20 is an enlarged sectional view through one split ring washer of FIG. 17 with one end of a bracket connected thereto.

FIG. 21 is an enlarged sectional view through the other washer of FIG. 17 with one end of a bracket connected thereto.

FIG. 22 illustrates in side view a standard cartridge enclosed fuse of the knife-blade type retained in fuse clips supported upon a panel board and a blown fuse indicator applied thereto.

FIG. 23 is an enlarged plan view of the knife-blade contact bracket.

FIG. 24 is a vertical section through the same.

FIG. 25 illustrates in side view another type of knifeblade fuse with blown fuse indicator applied thereto through a modified form of brackets for top mounting.

FIG. 26 is an end view of the same.

FIG. 27 is a detail plan view of the same.

FIG. 28 illustrates in side view another type of knifeblade cartridge enclosed fuse having brackets for the side mounting of the blown fuse indicator.

FIG. 29 is an end view of the same, and

FIG. 30 is an enlarged transverse sectional view taken on the line 30-30 of FIG. 28 in the direction of the arrow points.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Each embodiment as shown in the drawings employs a tube 1 extruded from Lexan resin with a white color added, of the same outside diameter for housing a neon lamp 2 for high potential circuits or an incandescent lamp for low potential circuits as well as resistors 3 when required and contact terminals 4 connected in series therewith. A conductive bracket 5 is electrically connected to each terminal for supporting the tube 1 at not more than I 16 of an inch above the cartridge of the fuse in parallel with the fusible element thereof and in series with the fuse terminals so that when the fusible elements becomes ruptured or blown the lamp will glow emitting soft white rays of light no matter what may be the position of the lamp within the tube 1.

All brackets are preferably stamped from a sheet of beryllium copper alloy or equal of a thickness of about 0.031 of an inch and then heated for about 2 hours at 625 degrees F. to increase their tensile strength. The brackets 5 for all ferrule type fuses as best shown in FIGS. 11 and 12 of the drawings, are all of the same length or about 0.875 inches with a disc shaped upper end 6 having an aperture 7 extending therethrough. A reduced neck 8 connects the disc 6 with a blade 9 having a width of about 0. l 87 inches. The lower extremity of each blade 9 terminates in an outwardly flared end 10 to assist in applying the bracket over the ferrule of a fuse. Each of the'blades 9 have undulations formed therewith providing two spaced apart crests 11 extending entirely across the blade and projecting about 0.046 inches therefrom and the dimples thereof are on a radius of 0.062 inches. The distance from a center line extending through the aperture 7 and the peak of the upper crest II is about.0.346 inches and that of the lower crest 11 is about 0.546 inches. All of the above dimensions are critical in that at least one of said knobs will have direct and positive'contact with the outer walls of the fuse ferrules whether they be straight, concave, or convex.

The contact terminals as best shown in FIG. 4 of the drawings fit entirely over the ends of the tube 1 with an inner sleeve 12 that fits tightly within the tube 1 for re taining contact therewith and a lead wire 13 from either the lamp 2 or resistor 3 and each sleeve 12 is retained by means of the drive screws 14. An outer concentric flange 15 is also formed with each contact terminal and extends over the outer periphery of the tube 1. A rivet 16 connects each bracket 5 to each contact terminals 4.

To enclose the ends of the blown fuse indicator, as best illustrated in FIG. 4, to provide a dead-front, the exposed live parts are covered by a boot or cap 17 preferably molded from rubber so as to have a snap-on connection and if desired an extension 18 may be formed therewith which extends over the outer face of the blade portion of a bracket.

In FIG. 13 of the drawings there is illustrated a modified form of contact between a bracket 5 and contact terminals 4 in that screw bolts 19 are used in place of the rivets 16 as shown in FIG. 6 of the drawings. A coil spring 20 is positioned between the nut 21 on each bolt 19 and the inner wall of the terminal 4 whereby the tension of the coil spring may be adjusted for establishing a flexible connection between a bracket 5 and contact terminal 4 for giving the brackets 5 more play when applying or withdrawing an indicator relative to a fuse.

The modified forms of indicators as applied to the fuses in FIGS. 5 to 10 of the drawings, each have the contact terminals 22 retained by drive screws 22 a short distance from the opposite ends of the tube 1 and a plug 23 of insulating material completely closing the opened ends of the tube 1. A threaded stud 24 is integral with the plug 23 and extends through the opening 7 of the bracket 5 and has engagement with a threaded opening 22a within the contact terminals 22 for retainingthe bracket 5 in electrical contact with said terminals. An insulated handle 25 is molded with the plug 23. A slot 26 is cut in the tube 1 of a length and width so that the neck portion 8 of the bracket 5 fits therein so as to prevent the latter from turning in the tube.

In FIG. 5 of the drawing there is illustrated a 31-6- O-250 volt fuse which is 3 inches in over all length including the ferrules thereof with straight end walls with the knobs 11 both in contact therewith. The peak ends of these knobs ll of each pair of brackets 5 normally rest at a distance therebetween which is l/32 of an inch less than the over all length of that fuse, that is 2 and 3l/32 of an inch so as to have a gripping contact with the ferrule of the fuse.

In FIGS. 7 and 8 of the drawing the fuse as illustrated is 1/32 of an inch less than that of the fuse shown in FIG. 5 or the minimum allowable tolerance. The outer walls of the ferrule are concaved as at 27 so that both knobs ll of a bracket 5 may be seated therein.

The fuse as shown in FIGS. 9 and 10 of the drawings is of the same over all length as the fuse shown in FIG. 5 of the drawings, but the outer wall of each ferrule is convexed as of 29, increasing the over all length of the fuse to about 3 and 1/32 of an inch or the maximum tol erance allowed. In this application, the brackets 5 have only the lower knobs ll in contact with the convexed surface 29. The indicator tube 1 of this modification does not need the end handles 25 as it has formed with its opposite side walls the handle extensions 30.

These handles 25 and 30 are desirable as they greatly assist in moving the indicator to and from a fuse.

From actual tests it was found that a pull of 6 and U2 pounds were needed to remove the indicator from a fuse due to the positive gripping contacts between the knobs l 1 and the ferrules of the fuse. Also it has proven that the Lexan tubes ll, no matter how long they were, did not bend or break during the repeated application or withdrawal of the indicator from a fuse.

The embodiment of the invention as shown in FIGS. 14, 15, and 16 is for use with a cartridge enclosed type fuse 31 having high current interrupting capacity which when it blows instantly opening the switch 32 of the electrical circuit to protect and stop motors or instruments arranged within branch circuits as may be connected to the main supply circuit. The indicator tube 1 has a neon lamp 2 and resistor 3 connected in series with the terminals of the fuse 31 but in parallel with the fusible element thereof so that as long as the switch 32 is closed the lamp will glow, but when the switch is opened as illustrated in FIG. 16 of the drawings the current will flow to the side terminal 33 and then through the lead wire 34 having a resistor 35 included therein to a contact 36 located at a point beyond the switch where the current is grounded. However, should the switch fail to open when the fuse 31 blows the lamp will indicate its blown condition. It takes more than 90 volts to cause the lamp 2 to strike and having runaway chardently touch other live parts located adjacent to the indicator as maycause damage and therefore these contacts should be covered by a boot 17 so as to enclose the indicator and give the same a dead front.

In FIG. 17 of the drawings there is illustrated another type of cartridge enclosed fuse for use in very high potential circuits having a threaded terminal 37 connected to a buss bar 38 and another round stud termi nal 39 with an opening 40 therein for receiving a cable connection. To apply the blown fuse indicator to this fuse a split ring washer 41 engages the stud terminal 39 and another washer 43 has an opening therein through which passes the other threaded stud terminal 37 of the fuse and is retained between the buss bar 38 and the hex nut 43 of the fuse. An outer knob 44 is formed with the outer extremities of each washer for a snap-on cngagement with the freeends ofa bracket of the fuse indicator as best shown in FIGS. and'2l. This arrangement permits the indicator to be moved around the fuse to any desired position whereby the indicator can be visible at all angles from the fuse.

Theblown fuse indicator as illustrated in FIG.22 of the drawings has a tube 1 the same as that shown in FIG. 5, but of greater length and is provided .with brackets 45 for mounting upon a knife-blade cartridge enclosed fuse'46. These brackets 45 as best shown in FIGS. 23 and 24 are each stamped from a thin sheet of Beryllium Copper having an 'apertured circular portion 47 that extends within the tube 1 and is connectedto the contactterminals therein. The blade sections 48 of each bracket 45 is positioned between the ferrules 49 of the fuse and the fuse clips 50. The blade sections 48 of each bracket have an opened end slot 54 formed therein for receiving a blade 51 of the fuse 46. In applying a bracket to a fuse blade 51 the opposite jaws of the blade sections 48 are spread apart until the upper edge of a blade 51 is seated within the circular portion 52 and the knob 54 of each said jaw grips the opposite side of the fuse blades 51 thereby insuring a direct and positive electrical contact therewith.

The blown fuse indicator as illustrated in FIGS. 25,

26 and 27 of the drawings have a tube 1 the same as that shown in FIG. 9 as it does not require any handles to assist in the removal of the tube indicators from that type of knife-blade contacts of the fuse 55. The fuse blades 56 extend horizontally from the fuse and are connected to the buss terminals 57 by means of the bolts 58. The brackets 59 are L-shaped having one end extending within the tube 1 and connected to the contact terminals arranged therein whereas the base section 60 of each said bracket is slotted for receiving the bolts 56. To remove a blown fuse, the bolts 56 have to first be separated therefrom and the indicator with the brackets attached thereto can be separated from the fuse and applied to another fuse.

In FIGS. 28 29 and the blown fuse indicator is for side mounting upon another type of cartridge enclosed fuse 61 with horizontally extending blade 62 connected to the terminals 63 by means of the bolts and nuts 64.-

The bracket 65 consist of a base section 66 connected to the terminals 62 by means of the bolts 64 and a section67 extending at an angle from the base 66. The outer extremity of each extension 66 is connected to the tube 1 in the manner as is illustrated in FIG. 4. To remove a blown fuse 61, the bolts 64 have to be first removed whereupon the indicator and its attached brackets can be separated from the fuse and applied to another good fuse. As will be noted from FIG.30 the bolt 64 has a wedge fit 70 with the base 66 so that when the nut thereof is removed the bolt can be separated from the buss terminal 63 and blade 62 of the fuse and it will be carried by the bracket 66 so as to prevent it from becoming lost.

We claim: v

1. A dead-front electrical blown fuse indicator fo cartridge enclosed fuses comprising a one piece flat end tube having only end openings, an inner bore and being of an insulating material, an indicator lamp positioned in said'tube, contact terminals connected inseries with said lamp, each of said contact terminals having a flat base mounted across the exterior of and closing one of said tube open ends, an inner sleeve extending from said base within said one of said tube end openings intosaid tube bore in contact with said tube and an outer annular flange concentric with its sleeve and extending over a portion of .the outer periphery of said tube, said tube being sufficiently opague such as to prevent said lamp from being visible and yet sufficiently translucent so as to permit the glow from said lamp when lit to be visible through said tube, a pair of resilient conductor brackets, means electrically attaching an end portion of each of said brackets to a different one of said contact terminal bases providing a cantilever connection between said tube and said end of each bracket whereby the opposite free ends of said brackets can have direct and positive snap-on electrical contact with the terminals of a fuse.

2. A dead-front electrical blown fuse indicator for cartridge enclosed fuses as claimed in claim 1 including caps each of a flexible insulating material and having a side opening, each of said caps having a snap-on fit over one of said contact terminals base, outer annular flange and the end portion of the bracket connected to said base with said bracket extending through said cap side opening.

Claims (2)

1. A dead-front electrical blown fuse indicator for cartridge enclosed fuses comprising a one piece flat end tube having only end openings, an inner bore and being of an insulating material, an indicator lamp positioned in said tube, contact terminals connected in series with said lamp, each of said contact terminals having a flat base mounted across the exterior of and closing one of said tube open ends, an inner sleeve extending from said base within said one of said tube end openings into said tube bore in contact with said tube and an outer annular flange concentric with its sleeve and extending over a portion of the outer periphery of said tube, said tube being sufficiently opague such as to prevent said lamp from being visible and yet sufficiently translucent so as to permit the glow from said lamp when lit to be visible through said tube, a pair of resilient conductor brackets, means electrically attaching an end portion of each of said brackets to a different one of said contact terminal bases providing a cantilever connection between said tube and said end of each bracket whereby the opposite free ends of said brackets can have direct and positive snap-on electrical contact with the terminals of a fuse.

2. A dead-front electrical blown fuse indicator for cartridge enclosed fuses as claimed in claim 1 including caps each of a flexible insulating material and having a side opening, each of said caps having a snap-on fit over one of said contact terminals base, outer annular flange and the end portion of the bracket connected to said base with said bracket extending through said cap side opening.

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