US3739313A

US3739313A - Protectors for electric circuits

Info

Publication number: US3739313A
Application number: US00116819A
Authority: US
Inventors: A Gain; A Urani
Original assignee: McGraw Edison Co
Current assignee: Cooper Industries LLC
Priority date: 1971-02-19
Filing date: 1971-02-19
Publication date: 1973-06-12
Anticipated expiration: 1990-06-12

Abstract

An electric fuse has a cup-like housing that is subdivided into two separate compartments by a partition; and each compartment has a fusible element therein which is embedded within arcextinguishing material. A portion of the partition projects beyond the cup-like housing to enter a slot in a fuseholder to automatically align the terminals of the electric fuse with the fuse-receiving terminals of the fuseholder. An indicating lamp is connected in parallel with one of the fusible elements, and a second indicating lamp is connected in parallel with the other fusible element; and the conductors which connect those indicating lamps to the ''''load'''' terminals of the fuseholder are spaced far enough apart to prevent ''''arc over'''' but are close enough to each other to capacitively couple those lamps together in the event a transitory ''''fault'''' causes both of those fusible elements to ''''blow'''' and both of those lamps to become illuminated.

Description

United States Patent 91 Gaia et al.

1 1 PROTECTORS FOR ELECTRIC CIRCUITS [75 Inventors: Aldino J. Gaia, Angelo Urani, both of St. Louis, Mo.

[73] Assignee: McGraw-Edison Company, Elgin,

Ill.

[22] Filed: Feb. 19, 1971 [21] Appl. No.: 116,819

[52] U.S. Cl 337/206, 337/216, 340/250 [51] Int. CL. H0lh 85/02, H0111 85/32, HOlh 85/54 [58] Field of Search 337/186, 187, 188,

[56] References Cited UNITED STATES PATENTS 3,032,629 5/1962 Uecker 337/201 X 3,268,692 8/1966 Oldham 337/216 X 3,227,841 1/1966 Gaia 337/255 X [111 3,739,313 June 12, 1973 Primary ExaminerBernard A. Gilheany Assistant ExaminerF. E. Bell Att0rney-Edmund C. Rogers, Estill E. Ezell, Rey Eilers, Glenn K. Robbins and John T. Rogers 57] ABSTRACT An electric fuse has a cup-like housing that is subdivided into two separate compartments'by a partition; and each compartment has a fusible element therein which is embedded within arc-extinguishing material. A portion of the partition projects beyond the cup-like housing to enter a slot in a fuseholder to automatically align the terminals of the electric fuse with the fusereceiving terminals of the fuseholder. An indicating lamp is connected in parallel with one of the fusible elements, and a second indicating lamp is connected in parallel with the other fusible element; and the conductors which connect those indicating lamps to the load terminals of the fuseholder are spaced far enough apart to preventarc over but are close enough to each other to capacitively couple those lamps together in the event a transitory fault" causes both of those fusible elements to blow and both of those lamps to become illuminated.

15 Claims, 13 Drawing Figures PAIENIEU Jun v 2 ma SHEHZUFZ relates to improvements in electric fuses and fuseholders therefor.

It is, therefore, an object of the present invention to provide an improved electric fuse and an improved fuseholder therefor.

The electric fuse provided for the present invention has a cup-like housing that is subdivided into two separate compartments by a partition; and each compartment has a fusible element therein which is embedded within arc-extinguishing material. That partition will keep metal vapors, that may form as one or the other of the fusible elements blows, from passing into the other compartment. A portion of the partition projects beyond the cup-like housing to enter a slot in a fuseholder to automatically align the terminals of the electric fuse with the fuse-receiving terminals of the fuseholder. As a result, the partition of the electric fuse provided by the present invention performs a dual function namely, it subdivides the housing into two separate compartments, and it automatically aligns the terminals of the electric fuse with the fuse-receiving terminals of a fuse-holder. It is, therefore, an object of the present invention to provide an electric fuse with a partition which subdivides'the cup-like housing of that electric fuse into two separate compartments and which also acts as an aligning blade.

The cuplike housing of the electric fuse provided by the present invention is closed by a closure which has a slot therein that accommodates that part of the partition which acts as an aligning blade; and portions of that partition underlie portions of that closure. Sealing material seals the joint between the aligning blade and the slot in the closure, and further sealing material seals the periphery of the closure to the cup-like housing. As a result, that cup-like housing can prevent any loss of the arc-extinguishing material therein; and it also can prevent the escape therefrom of any metal vapors that develop as a fusible element, within thatcup-like housing, fuses. It is, therefore, an object of the present invention to provide the closure of a cup-like housing of an electric fuse with a slot that accommodates, and that can be sealed to, the aligning blade of that cup-like housing.

The fuseholder of the present invention has L-shaped line terminals and has L-shaped load" terminals. The feet of the line" terminals confront and extend toward each other, and thus space the remaining portions of those line" terminals apart appreciable distances. The feet of the load terminals confront and extend toward each other, and thus space the remaining portions of those load" terminals apart appreciable distances. The feet of the line" and load terminals are connected to the fuse-receiving terminals of the fuseholder; and hence the remaining portions of those line and load" terminals are spaced further apart than are those fuse-receiving terminals. It is,

therefore, an object of the present invention to provide a fuseholder with L-shaped line and load terminals that have the feet thereof confronting and extending toward each other and that are connected to the fusereceiving terminals of the fuseholder.

The fuseholder of the present invention hasan externallythreaded boss that has fuse-receiving terminals therein, has a second boss that is displaced from that externally threaded boss, has an indicating lamp in register with an opening in that second boss, and has a nut that coacts with the externally threaded boss to hold the fuseholder in assembled relation with a panel. That panel has an opening which accommodates the exter nally threaded boss and has a second opening which accommodates the second boss. A fuse, at the front side of the panel, will have the terminals thereof held by the fuse-receiving terminals in the externally threaded boss; and the blowing of that'fuse will be readily apparent because light will pass forwardly from the indicating lamp through the opening in the second boss.

In many installations where electric fuses are used, it is desirable that a neon lamp glow continuously subsequent to the blowing of a fuse; and, in recognition of that fact, fuse-holders have been proposed which would illuminate a neon lamp whenever a fuse therein opened a power-supply circuit. Where a fuse opens a power supply circuit in response to a fault" that is of a continuing nature, that fault can establish and maintain an indicating circuit which includes the neon lamp, and thus can keep that neon lamp glowing continuously. However, if the fault which causes the fuse to open the power-supplying circuit is of a transitory nature, that fault can establish an indicating circuit that will illuminate the neon lamp, but that fault" will be incapable of maintaining that indicating circuit and thus will be incapable of making certain that the neon lamp continues to glow. In some cases, the elongated conductors which extend from the fuse panel to the load are long enough, and are in such close proximity to each other, that they can act as the plates of a capacitor; and thus can keep the neon lamp of an indicat ing circuit flowing even though the fault which blew the fuse and illuminated the neon lamp subsequently clears." In certain installations, however, the lengths and placements of the conductors, which extend between the fuse panel and the load, can not be relied upon to provide sufficient capacitance to keep the neon lamp of an indicatingcircuit glowing after the fault has cleared. Consequently, it would be desir able toprovide a fuseholder which could assure continued energization of a neon lamp even where the fault, that caused the electric fuse in that fuseholder to blow, was of short duration. The present'invention provides such a fuseholder; and it does so by mounting within that fuseholder conductors which are interposed between the electric fuse and the load" terminals that fuse-holder and which are close enough to each other to act as a capacitor and thereby maintain a neon lamp aglow after a fault," of temporary nature, has blown the electric fuse and has initiated the glowing of that neon lamp. It is, therefore, an object of the present invention to provide a fuseholder which has conductors intermediate the electric fuse and the load terminals and which are so close to each other that they can act as the-plates of a capacitor, and can thus keep an indicating neon lamp glowing after a-fault" of short duration has blown" the fuse and has illuminated that neon lamp. The electric fuse provided by the present inventio has a circuit board on which the conductors between the fuse terminals and the load terminals are formed. As a result, the spacing between thoseconductors can be precisely determined and continuously maintained. The circuit board of the fuseholder provided by the present invention also has an indicating lamp thereon;

and, in addition, has a pin adjacent that indicating lamp. The fuseholder has a recess which accommodates the indicating lamp, and also has a small-diameter socket which receives the pin adjacent that indicating lamp. The pin on the circuit board and the socket for that pin will align the indicating lamp with the recess therefor in the'fuseholder; and the positioning of that pin within that socket will prevent appreciable shifting of that indicating lamp relative to the recess therefor. The lamp-receiving recess has a window therein, and the engagement between the pin on the circuit board and the socket in the fuseholder will hold the indicating lamp -in register with the window in that recess.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description, a preferred embodiment of the present invention is shown and described, but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing, FIG. 1 is a front elevational view of preferred embodiments of a fuseholder and electric fuse that are made in accordance with the principles and teachings of the present invention,

FIG. 2 is a sectional view, on a larger scale, through the fuseholder of FIG. 1, and it is taken along the plane indicated by the line 2-2 in FIG. 1,

FIG. 3 is a sectional view, on the scale of FIG. 2, through the electric fuse and fuseholder of FIG. 1, and it is taken along the plane indicated by the line 3-3 in FIG. 1,

FIG. 4 is a sectional view, on the scale of FIG. 2, through the electric fuse and fuseholder of FIG. 1, and it is taken along the plane indicated by the line 4-4 in FIG. 1,

FIG. 5 is a partially broken-away rear view, on the scale of FIG. 1, of the fuseholder shown in FIG. 1,

FIG. 6 is a sectional view, on the scale of FIG. 1, through the fuseholder of FIG. 1, and it is taken along the plane indicated by the line 66 in FIG. 5,

FIG. 7 is a sectional view, on the scale of FIG. 2, through the electric fuse and fuseholder of FIG. 1, and it is taken along the broke plane indicated by the broken line 77 in FIG. 5,

FIG. 8 is an exploded view of the fuseholder of FIG. 1, 1

FIG. 9 is an exploded view of the electric fuse of FIG.

FIG. 10 is a perspective view of the circuit board for the fuseholder of FIG. 1,

FIG. 11 is a perspective view of part of the electric fuse shown in FIG. 1,

FIG. 12 is an end view of the aligning blade of the electric fuse of FIG. 1, and it shows by dotted lines how that aligning blade'could be made with different widths, and

FIG. 13 is an end view of the aligning blade of the electric fuse of FIG. 1, and it shows by dotted lines how that'aligning blade could be made with different thicknesses.

Referring to the drawing in detail, the numeral generally denotes a preferred embodiment of fuseholder that is made in accordance with the principles and teachings of the present invention; and that fuseholder has an externally threaded boss 22. Four

shouldered recesses

24, 26, 28 and 30 are formed in the boss 22; and each of those shouldered recesses has a relatively large diameter portion that opens to the front surface of that boss and has a smaller-diameter portion that opens to the rear surface of the fuseholder 20. A slot 32 is formed in the boss 22, as shown particularly by FIG. 8; and that slot extends an appreciable distance inwardly of the front surface of that boss, as shown particularly in FIG. 7. An annular recess 34 is formed in the front surface of the boss 22, as shown particularly by FIGS. 7 and 8. The outer diameter of the annular recess 34 is slightly smaller than the root diameter of the external thread on the boss 22.

A generally L-shaped recess 36 is formed in the rear face of the fuseholder 20; and that recess communicates with the shouldered recess 26. A generally L- shaped recess 38 is formed in the rear face of the fuseholder 20; and that recess communicates with the shouldered recess 24. A short, transversely directed recess 40 is formed in the rear face of the fuseholder 20; and that recess communicates with the shouldered recess 28. A short, transversely directed recess 42 is formed in the rear face of the fuseholder 20; and that recess communicates with the shouldered recess 30. A partition 44, which is shown particularly in FIG. 4, is provided between the L-shaped recess 36 and the short, transversely directed recess 40. As shown particularly by FIG. 6, the partition 44 also extends between the L-shaped recess 38 and the short, transversely directed recess 42. A partition 46 is displaced from the partition 44 by ninety degrees; and one end of the partition 46 separates portions of the L-shaped

recesses

36 and 38, as shown by FIG. 7, while the other end of that partition separates portions of the short, transversely directed

recesses

40 and 42, as shown by FIG. 5.

A relatively large, rectangular recess 48 is formed in the rear face of the fuseholder 20; and part of that recess underlies a shallow cylindrical boss 56 that projects forwardly from the front surface of that fuseholder. A smaller but deeper rectangular recess 50 directly underlies the boss 56; and the rear of that recess is in communication with the recess 48, as shown by FIG. 3. A small diameter, cylindrical socket 52 is provided in the boss 56; and that socket extends from the forward surface of that boss to the recess 48, as shown by FIG. 3. A small diameter, cylindrical socket 54 also is formed in the boss 56; and that socket also extends from the forward surface of that boss to the recess 48, as shown by FIG. 3.

Circular openings

58 and 60 are formed in the front surface of the boss 56; and a transparent plate 62 is disposed within the recess 50 immediately adjacent the

openings

58 and 60 that transparent plate serving as windows for those openings. A transparent sealing material, not shown, is disposed within the

openings

58 and 60 to coact with the transparent plate 62 to provide a water-tight closing of those openings. A raised arrow 64 is formed on the forward face of the boss 56 adjacent the cylindrical socket 54', and a raised arrow 66 is formed on that forward face adjacent the cylindrical socket 52. As indicated particularly by FIGS. 1 and 8, the raised arrow 66 points to the left, and thus generally toward the opening 60; whereas the raised arrow 64 points to the right, and thus generally toward the opening 58. An opening 68 is provided in the fuseholder 20 adjacent one side of that fuseholder, as shown particularly by FIGS. 5 and 7. A similar opening, not shown, is provided in the fuseholder adjacent the opposite side of that fuseholder.

The numeral 69 denotes a. notch at one side of the rear face of the fuseholder 20, and the numeral 71 denotes a notch at the opposite side of that rear face; all as indicated by FIG. 5. The

numerals

73 and 75 denote notches at one end of the rear face of the fuseholder 20, as indicated by FIG. 8.

The numeral 72 denotes an O-ring which is disposed within the annular recess 34 in the forward surface of the boss 22. That O-ring is circular in cross section; and the normal, unstressed diameter of a circular cross section of that O-ring is greater than the depth ofthe annular recess 34. As a result, whenever the O-ring 72 is in its unstressed condition, the outer face of that O-ring will project outwardly beyond the outer face of the boss 22 of the fuseholder 20.

The numeral 74 denotes a shouldered conductor which is disposed within the shouldered recess 26 in the fuseholder 20. The large diameter portion of the shouldered recess 26 accommodates a tulip-type socket in the large diameter end of the conductor 74, the smaller diameter portion of the shouldered recess 26 accommodates an intermediate-diameter portion of the conductor 74, and a small diameter end portion of that conductor projects 'rearwardly beyond the recess 36. The

numerals

76, 78 and 80 denote conductors which are identical to the conductor 74; but those conductors are disposed, respectively, within the shouldered recesses 28, 30 and 24 of the fuseholder 20. A generally L- shaped conductor 82 has an opening 84 in the foot thereof which receives the intermediate-diameter portion of the conductor 80, as shown particularly by FIG. 7. The L-shaped conductor 82 has a reduced-width portion 86 adjacent the outer end thereof, and it has an offset 87 intermediate the opening 84 and the reducedwidth portion 86; all as shown by FIG. 8. The outer end of the L-shaped conductor 82 extends through the notch 73 in the rear face of the fuseholder 20. The numeral 88 denotes an L-shaped conductor which is the mirror image of the L-shaped conductor 82. The opening 90 in the foot of the L-shaped conductor 88 receives the intermediate-diameter portion of the conductor 74, as shown by FIG. 7. The L-shaped conductor 88 has a reduced-width portion 92 adjacent the outer end thereof, and it has an offset 93 between that reduced-width portion and the opening 90; all as shown by FIG. 8. The outer end of the L-shaped conductor 88 extends through the notch 75 in the rear face of the fuseholder 20. The numeral 94 denotes a wire-securing connector which is mounted on the reduced-width portion 86 of the L-shaped conductor 82; and the numeral 96 denotes a wire-securing connector which is mounted on 'thereduced-width portion 92 of the L- shaped conductor 88.

The numeral 98 denotes an L-shaped conductor which has an opening 100 in the foot thereof; and that opening accommodates the intermediate-diameter portion of conductor 78. The outer end of the L-shaped conductor 98 has a threaded opening 102 therein which receives the shank of a screw 104. A lock washer 106 will be telescoped over the shank of that screw before that shank is threaded into the opening 102. An offset 107 is provided intermediate the

openings

100 and 102 in the L-shaped conductor 98. The numeral 108 denotes an L-shaped conductor which is the mirror image of the L-shaped conductor 98. An opening 110 in the foot of the L-shaped conductor 108 accommodates the intermedia'te-diameter portion of the conductor 76. A threaded opening 111 in the outer end of the L-shaped conductor 108 accommodates the shank of a screw 112; and that shank will pass through a lock washer before it is seated in the threaded opening 111. An offset 113 is provided in the L-shaped conductor 108 intennediate the openings and 111.

The numeral 114 denotes s rivet which is mounted within the opening 68 in the fuseholder 20. A similar rivet, not shown, is disposed within the opening in the opposite side of the fuse-holder 20. The numeral 118 denotes a gasket which is generally rectangular in configuration, which has an opening that encircles and closely fits the externally threaded boss 22, and which has a second opening that encircles and closely fits the boss 56. As indicated particularly by FIGS. 1 and 8, the dimensions of the gasket 118 are just slightly smaller than the dimensions of the fuseholder 20.

The numeral 120 denotes a circuit board which is made of insulating material; and that circuit board is provided with openings 122 and 12 4 to accommodate shouldered

pins

154 and 156, respectively, as shown by FIG. 3. The

openings

122 and 124, and the shouldered

pins

154 and 156 held thereby, are in register with the

sockets

52 and 54 in the boss 56. The circuit board 120 also has

openings

126 and 128 which accommodate the rear ends of the glass envelopes for

neon lamps

158 and 160, respectively, as shown in FIG. 2. The circuit board 120 has

openings

130 and 132 for leads of the

neon lamps

158 and 160, respectively, as shown by FIG. 8; and the circuit board 120 has

openings

134 and 136 for terminals of resistors 166 and 170, as indicated by FIG. 8. The circuit board has

openings

138, 140, 142 and 144 to accommodate the small-diameter ends of

conductors

80, 74, 78 and 76, respectively.

Conductors

146, 148, 150 and 152 are provided on the rear surface of the circuit board 120, as shown by FIGS. 5 and 10. A mass of solder 162 connects one lead of the lamp 158 to the conductor 152; and a mass of solder 180 connects the other end of that conductor to.

the small-diameter end of conductor 78 which is disposed within the opening 142 in the circuit board 120. A mass of solder 164 connects one end of the conductor 146 to one terminal of the lamp 160; and a mass of solder 178 connects the other end of that conductor-to the small diameter end of the conductor 76 which is disposed within the opening 144 in the circuit board 120. The conductor 148 extends from the shouldered pin 154 to the small diameter end of the conductor 74, which is disposed within the opening in the circuit board 120; and a mass of solder 176 electrically connects the conductor 148 to the small diameter end of conductor 74 and also to oneterminal of resistor 170. The other terminal of that resistor is connected to the otherterminal of the lamp 160; and a sleeve 172 of insulation encases and protects that connection. The conductor extends from the shouldered pin 156 to the small diameter end of the conductor 80 which is disposed within the opening 138 in the circuit board 120; and a mass of solder 174 electrically'connects the conductor 150 to the small diameter end of the conductor 80 and also to one terminal of resistor 166. The other terminal of that resistor is connected to the other terminal of the lamp 158; and a sleeve 168 of insulation encases and protects that connection.

The circuit board 120 and the

conductors

146, 148, 150 and 152 thereon can be made in different ways, as desired. Preferably, however, that circuit board and those conductors are made by use of printed circuit board techniques starting with a metal-clad sheet of insulation, using acid-resistant ink to print a pattern on the metal layer of that sheet which is identical to the

conductors

146, 148, 150 and 152, and then etching away the rest of that metal layer. As a result, the circuit board 120 can be considered to be a printed circuit board.

The numeral 182 denotes a closure which is intended to underlie and to close the rear face of the fuseholder 20. That closure has a raised surface 184 which confronts and is close to the rear face of the circuit board 120.

Elongated bosses

186 and 188 project forwardly beyond the raised surface 184; and those bosses will be disposed within the

notches

69 and 71, respectively, at the sides of the rear face of the fuseholder 20. A shoul dered passage 190 is formed in the boss 186; and that passage accommodates one end of the rivet 114. As shown particularly by FIG. 7, the rivet 114 will coact with the shouldered passage 190 to help hold the closure 182 in assembled relation with the fuseholder 20. A shouldered passage 192 is provided in the boss 188; and that shouldered passage will receive one end of a rivet, not shown, which is similar to the rivet 114. A suitable sealing material 193 fills and seals the exposed end of the shouldered passage 192, as shown by FIG. 5. Similar sealing material, shown in FIG. 7, will be used to fill and seal the exposed end of the passage 190.

Elongated ribs

194 and 196 are provided at the rear face of the closure 182; and those ribs are parallel to the sides of the fuseholder 20. One end of the closure 182 is cut away to define

notches

195 and 197; and the notch 195 will expose the screw 104 while the notch 197 will expose the screw 112, when that closure is assembled with the rear face of the fuseholder 20.

The numeral 198 generally denotes an electric fuse which has a generally cup-like housing 200 with an outwardly extending annular flange 202 adjacent the open end thereof, as shown by FIG. 8. The housing 200 has a shallow cylindrical recess 204 in the outer face of the closed end thereof; and an indicia-bearing disc, not shown, can be disposed and held within that recess. That disc could bear the voltage rating and the ampere rating of that electric fuse. The housing 200 has a partition 206 therein; and that partition subdivides the interior of that housing into two separate compartments. In addition, one partition of the partition 206 projects outwardly beyond the open end of the housing 200, as shown particularly by FIG. 9, to constitute an aligning blade. An annular recess 208 is provided inwardly of the outwardly extending annular flange 202, as shown by FIG. 9. The portion of the partition 206 which extends between the annular recess 208 and the inner end of the housing 200 has a width that is equal to the inner diameter of that housing; but the portion of that partition which projects outwardly through and beyond the annular recess 208 has a reduced width, as shown particularly by FIGS. 3 and 9.

- A disc-like support 210 of insulating material has a slot 212 therein which is dimensioned to accommodate the outwardly extending portion of the partition 206 of the housing 200. The support 212 is dimensioned to fit neatly within the annular recess 208 in housing 200. Shouldered pins 214, 216, 218 and 220 are fixedly mounted within four openings in the support 210; and one end of the pin 216 is dimensioned to extend within and to be tightly gripped by the tulip-type socket in the outer end of the conductor 80. The

pins

214, 218, and 220 are dimensioned to have the outer ends thereof extend within and to be tightly gripped by the tulip-type sockets in the outer end of

conductors

74, 78 and 76, respectively. An opening 222 is formed in the support 210 intermediate the

pins

214 and 220; and an opening 224 is formed in that support intermediate the

pins

216 and 218. A fusible element 226 is suitably secured to the inner ends of the

pins

216 and 218; and a fusible element 228 is suitably secured to the inner ends of the

pins

214 and 220. The inner ends of the

pins

214, 216, 218 and 220 are dimensioned to hold the

fusible elements

226 and 228 within the two compartments defined within the housing 200 by the partition 206, and to hold those fusible elements in spaced relation to the inner surfaces of those compartments. Arc-quenching material 230 is provided within the two compartments in the housing 200 to quickly quench any are which forms as either of the

fusible elements

226 and 228 fuses.

Sealing material 233 is placed in the

openings

222 and 224 to close and seal those openings after the arcquenching material has been introduced into the two compartments of the housing 200 via those openings. In addition, sealing material 231 is used to close and seal the joint between the slot 212 in support 210 and the aligning portion of partition 206; and further sealing material 231 is used to close and seal the joint between the periphery of support 210 and the annular recess 208 in the housing 200. That sealing material will coact with that housing, with that partition, and with that support to prevent any leakage of arc-quenching material and to prevent any escape of vapors which develop as one or both of the

fusible elements

226 and 228 fuses.

The numeral 232 denotes a nut which has an internal thread that can mate with the external thread on the boss 22. A knurled nut 234 also has an internal thread which can mate with the external thread on the boss 22; and that knurled nut has an inwardly extending annular flange 236.,The inner diameter of the annular flange 236 is larger than the principal diameter of the housing 200 of the electric fuse 198, but is smaller than the outer diameter of the outwardly extending annular flange 202 on that housing. As a result, the knurled nut 234 can hold the electric fuse 198 in assembled relation with the fuseholder 20.

The feet and the forwardly offset portions of the L- shaped

conductors

82, 88, 98 and 108 are disposed within and are guided by the

recesses

38, 36, 42 and 40, respectively, in the rear face of the fuseholder 20. The

rearwardly offset outer ends of the L-shaped conduc--

tors

82 and 88 constitute the line" terminals of the fuseholder 20; and the rearwardly offset portions of the L-shaped

conductors

98 and 108 constitute the load" terminals of that fuseholder. The mass of solder which surrounds the opening 84 in the foot of the L-shaped conductor 82 electrically bonds and mechanically secures that L-shaped conductor to the conductor 80, and also mechanically secures both of those conductors to the fuseholder 20. Similarly, the masses of solder which surround the

openings

90, 100 and 110, respectively, in the L-shaped

conductors

88, 98 and 108 electrically bond and mechanically secure those L-shaped conductors to the

conductors

74, 78 and 76, respectively. Further, those masses of solder mechanically secure the L-shaped

conductors

88, 98, and 108 and the

conductors

74, 78 and 76 to the fuseholder 20. The masses of

solder

174, 176, 178 and 180 electrically bond conductor 150 to conductor 80, electrically bond conductor 148 to conductor 74, electrically bond conductor 146 to conductor 76, and electrically bond conductor 152 to conductor 78. In addition, the masses of the

solder

174, 176, 178 and 180 mechanically secure the circuit board 120 to the fuseholder 20. The shouldered pins 154 and 156 will coact with the

sockets

52 and 54 in the boss 56 to hold the

neon lamps

158 and 160, respectively, in register with the

openings

60 and 58 in that boss.

in the preferred embodiments of fuseholder and electric fuse shown in the drawing, the

conductors

74, 76, 78 and 88 are oriented and spaced to define a square; and the

pins

214, 220, 218 and 216 of the electric fuse 198 are oriented and spaced to define a congruent square. Manufacturing tolerances will, however, keep the orientation and spacing of the

pins

214, 220, 218

and 216 from being exactly congruent to the orientation and spacing of the

conductors

74, 76, 78 and 80; and this is desirable, because it will increase the contact pressures between those pins and those conductors. Specifically, if manufacturing tolerances cause the axes of the

pins

214 and 216 to be spaced further apart than the axes of the

conductors

74 and 80, those pins will apply forces to the tulip-type sockets in the forward ends of those conductors which will tend to force the more remotely located fingers of those tulip-type sockets apart with a force that is greater than normal. The shouldered recesses 26 and 24 closely encircle the fingers of the tulip-type sockets in the forward ends of the

conductors

74 and 80; and that close encircling plus the restorative forces within those fingers will enable those fingers to apply substantial contact pressures to the

pins

214 and 216. Conversely, if manufacturing tolerances causethe axes of the

pins

214 and 216 to be spaced closer together than the axes of the conductors 74 and 81), those pins will apply forces to the tulip-type sockets in the forward ends of those conductors which will tend to force the more close located fingers of those tulip-type sockets apart with a force that is greater than normal. The close encircling, by the shouldered recesses 26 and 24, of the fingers of the tuliptype sockets in the forward ends of the

conductors

74 and 80 will coact with the restorative forces within the fingers of those conductors to enable those fingers to apply substantial contact pressures to the

pins

214 and 216. Similarly, any increases or decreases in the spacings between the axes of the

pins

214, 216, 218 and 2211, due to manufacturing tolerances, and any increases or decreases in the spacings between the axes of the

conductors

74, 80, 78 and 76, due to manufacturing tolerances, will tend to increase the contact pressures between those pins and those conductors. Those increases and decreases in the spacings between the axes of the

pins

214, 216, 218 and 220, and those increases and decreases in the spacings between the axes of the

conductors

74, 80, 78 and 76, can be along any of the sides of the square defined by those pins and also can be along either of the diagonals of that square. Consequently, the manufacturing tolerances of those four pins, of those four conductors, of the support 210, and of the externally threaded boss 22 will make certain that higher-than normal contact pressures will be established and maintained between those pins and those conductors. Such higher-than normal contact pressures are desirable, because they increase the current-carrying capability of the combination of fuseholder and electric fuse. All of this means that by providing four fuse terminals on the electric fuse 198 and by providing four complementary fuse-receiving terminals on the fuseholder 20, the present invention enables manufacturing tolerances to effect the development of positive laterally directed and longitudinally directed forces which develop higher-than normal contact pres-' will flow from conductor 80 via conductor 150, a resistor 166, lamp 158, and conductor 152 to conductor 78; because the resistance of the fusible element 226 is so very much smaller than the combined resistances of resistor 166 and lamp 158. Similarly, essentially no current will flow from conductor 74 via conductor 148, resistor 170, lamp 160, and conductor 146to conductor 76; because the resistance of the fusible element 228 is so very much smaller than the combined resistances of resistor 170 and lamp 160. As a result, the lamps 158 and will normally remain unilluminated, and no light will be visible through the

openings

60 and 58 in the boss 56.

In the event a fault develops in the load, not shown, or between the conductors, not shown, which are connected to the

load terminals

98 and 108, either or both of the

fusible elements

226 and 228 may fuse. If the fusible element 226 fuses, but the fusible element 228 remains intact, current will flow from line terminal 82 via conductor 80, conductor 150, resistor 166, lamp 158, conductor 152, and conductor 78 to the load terminal 98; and that flow of current will illuminate that lamp. As long as the fusible element 228 remains intact, essentially no current will flow through resistor and lamp 160; and hence that lamp will remain un-illuminated. The light passing outwardly through the opening 60 in the boss 56 will pass through the opening in the panel, not shown, in which that boss is mounted; and that light will plainly indicate to the maintenance man that the fusible element 226 has blown. The maintenance man will, thereupon, rotate the knurled nut 234 in the counter-clockwise direction in FIG. 8, and thereby remove that nut from the externally threaded boss 22 which extends through a second opening in the panel, not shown. At such time, the maintenance man can apply an outwardly directed pull to the housing 200 of the electric fuse 198, and thereby separate that electric fuse from the fuseholder 20. A replacement fuse can then have the

terminals

214, 216, 218 and 220 thereof aligned, respectively, with the

conductors

74, 80, 78 and 76 of the fuse-holder 20; and the aligning portion of the partition 206 of that replacement fuse will coact with the slot 32 in the externally threaded boss 22 to insure that alignment. Specifically,

the portion of the partition 206 which projects outwardly beyond the annular recess 208 in the housing 200 of the replacement fuse will be longer than the portions of the

pins

214, 216, 218 and 220 which project outwardly from the support 210 of that fuse; and hence that portion of that partition will have to be aligned with, and will have to enter, the slot 32 before any of those pins can begin to enter the tulip-type socket therefor. As the replacement electric fuse is pressed into engagement with the fuseholder 20, it will apply force to that fuseholder which will tend to move that fuseholder rearwardly and away from the panel, not shown. However, the nut 232 will be solidly seated on the externally threaded boss 22 of that fuse-holder, and will thus prevent any such rearward movement. Once the

terminals

214, 216, 218 and 220 of the replacement electric fuse have been seated, respectively, within the tulip-type sockets in the forward ends of the

conduc tors

74, 80, 78 and 76, the knurled nut 234 will again be threaded onto the externally threaded boss 22. The annular flange 236 of that knurled nut will overlie the outwardly extending flange 202 on the housing 200 of the replacement electric fuse; and thus will thereby positively prevent accidental separation of that replacement electric fuse from the fuseholder 20.

At the time the fusible element 226 fused, flame and metal vapors may have been evolved; but that flame and those metal vapors could not escape from the housing 200 of the electric fuse 198. Specifically, the sealing material within the opening 224, the sealing material 231 in the joint between the projecting portion of the partition 206 and the slot 212 in the support 210, and the sealing material 231 which seals the circular joint between the periphery of the support 210 and the annular recess 208 in the housing 200 will effectively prevent any escape of flame or metal vapors. The user of the electric fuse and fuseholder provided by the present invention can be assured that the sealing material in the opening 224 and the sealing material 233 in the opening 222 will not be broken by nearby objects; because those openings are disposed, respectively, between the

pins

216 and 218 and between the

pins

214 and 220. Those pins will project outwardly from the support 210, and will thereby keep any nearby objects from contacting and injuring the sealing material within the

openings

224 and 222. The close proximity of the support 210 to the forward face of the externally threaded boss 22, whenever the electric fuse 198 is assembled with the fuseholder 20, and the fact that the O-ring 72 is disposed outwardly of and surrounds the circular joint between the support 210 and the annular recess 208 in the housing 200, will make certain that the said circular joint is protected from nearby objects whenever the electric fuse 198 is in assembled relation with the fuseholder 20. In addition, the knurled nut 234 will provide additional protection for the sealing material in the circular joint between the support 210 and the annular recess 208 in the housing 200, whenever the electric fuse 198 is assembled with the fuseholder and that knurled nut is holding that electric fuse and that fuseholder in such relation.

If the fusible element 228, rather than the fusible element 226, had blown in response to the fault which developed in the load, or in one or both of the conductors connected to the

load terminals

98 and 108, the lamp 160, rather than the lamp 158, would have become illuminated. Light from the lamp 160 would then pass outwardly through the opening 58 in the boss 56 and would pass through the opening in the panel, not shown, in which that boss is mounted. That light would plainly indicate to the maintenance man that the fusible element 228 had blown. The maintenance man would then replace the electric fuse 198.

If the fault in the load, or in the conductors connected to the

load terminals

98 and 108, had caused both of the

fusible elements

226 and 228 to blow," both of the

lamps

158 and 160 would have become illu minated. As long as that fault persisted, current would flow from line terminal 82 via conductor 80, conductor 150, resistor 166, lamp 158, conductor 152, conductor 78, load terminal 98, the conductor connected between that load terminal and the "fault," through the fault to the conductor connected to the load terminal 108, and then via conductor 76, the conductor 146, lamp 160, resistor 170, conductor 148, conductor 74, and line terminal 88. The values of the resistors 166 and 170 are high enough so those resistors will protect the

lamps

158 and 160 in the event only one of those lamps becomes illuminated; but those values are low enough to enable both of those lamps to become illuminated whenever both of the

fusible elements

226 and 228 blow.

In the event a fault which causes both of the

fusible elements

226 and 228 to blow is of a transitory nature, and disappears after it has blown those fusible elements and has caused both of the

lamps

158 and 160 to become illuminated, that fault" will be unable to maintain the circuit which illuminated those lamps. However, those lamps will continue to remain illuminated because of a capacitive effect which is provided by the closely spaced upper ends of

conductors

146 and 152, as those conductors are viewed in FIGS. 5 and 10. The spacing between those ends is great enough to prevent arcing over, but is small enough to provide a capacitance which will keep the

lamps

158 and 160 illuminated aftera transitory fault has caused both of the

fusible elements

226 and 228 to blow" and has caused those lamps to become illuminated. This is highly desirable; because it makes certain that the

lamps

158 and 160 will remain illuminated, and will thus indicate that a fault occurred, even if that fault subsequently disappears.

It will be noted that the outer ends of the

line terminals

82 and 88 are spaced further apart than are the

conductors

80 and 74; and it also will be noted that the outer ends of the

load terminals

98 and 108 are spaced further apart than are the

conductors

78 and 76. This is desirable because it will minimize the likelihood of any arcing over between conductors connected to the

line terminals

82 and 88, and also will minimize the likelihood of any arcing over between conductors connected to the load" terminals 98 and The electric fuse 198 and the fuseholder 20 provided by the present invention can be arranged to prevent the substitution of an electric fuse of an undesired ampere rating for an electric fuse of a desired ampere rating. Specifically, as shown by FIG. 12, the portion of the partition 206 which acts as an aligning blade can be made in different widths; and the slot 32 in the externally threaded boss 22 can be made in different lengths. To prevent over fusing, the smallest ampere-rating fuse to be used with the fuseholder 20 should have the narrowest aligning blade, the largest ampere-rating fuse should have the widest aligning blade, and electric fuses with intermediate ampere ratings should have aligning blades of widths intermediate those of the widest and narrowest aligning blades. The externally threaded boss 22 should have a slot 32 with a width that would correspond to the width of the aligning blade of the fuse having the desired ampere rating; and no fuse having a larger ampere rating could then be inserted in that-slot.

As indicated particularly by FIG. 13, the aligning portion of the partition 206 of the electric fuse 198 can be given different thicknesses, and the slot 32 in the externally threaded boss 22 of the fuseholder 20 can be provided with corresponding thicknesses. Specifically, the smallest ampere-rating electric fuse to be used with the fuseholder 20 should have the thinnest partition 206, and progressively larger ampere-rating fuses should have progressively thicker aligning blades. The externally threaded boss 22 should have a slot 32 with a thickness that would correspond to the thickness of the aligning blade of the fuse having the desired ampere rating; and no fuse having a larger ampere rating could then be inserted in that slot.

By varying the diameters and the orientations of the

pins

214, 216, 218 and 220 of the electric fuse 198, and by correspondingly varying the dimensions and orientations of the

conductors

74, 80, 78 and 76, and present invention also can prevent over fusing." As a result, the present invention makes it possible to provide a highly desirable, rating-regulated, combination of electric fuse and fuseholder therefor.

The electric fuse 198 and the fuseholder 20 can be used successfully in a location where moisture and dripping water can be anticipated. Specifically, in such an installation, the nut 232 will hold the front face of the gasket 118 in intimate engagement with the rear face of a panel, such as the panel indicated by dotted lines in FIG. 3; and that intimate engagement will enable that gasket to seal the openings in that panel which accommodate the

bosses

22 and 56. As a result, moisture or dripping water will be unable to pass through those openings. Also in such an installation, the O-ring 72 will engage the exposed face of the support 210 of the electric fuse 198, and will coact with that exposed face to form a moisture-resistant and water-proof seal. The overall result is that the electric fuse 198 and the fuseholder 20 can be used successfully in a location where moisture and dripping water can be anticipated.

The

lamps

158 and 160, that are mounted within the recess 50 in the boss 56, will preferably be neon lamps; because such lamps can be kept illuminated by the capacitance between the

conductors

146 and 152 after a fault has illuminated those lamps and then disappeared. However, in any installation where the anticipated circuit voltage is too low to illuminate a neon lamp, incandescent lamps will be substituted for the

neon lamps

158 and 160 while those incandescent lamps will respond to the fusing of the

fusible element

226 and 228 to become illuminated, and while those incandescent lamps will remain illuminated as long as the fault" which blew those fusible elements persists, those incandescent lamps will darken if that fault disappears. Consequently, the

lamps

158 and 160 will preferably be neon lamps.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What we claim is:

l. A fuseholder which has a line terminal, a load" terminal, a second line terminal, a second load terminal, fuse-receiving terminals intermediate the first said line" terminal and the first said load terminal which are adapted to be bridged by a fusible element, further fuse-receiving terminals intermediate said second line terminal and said second load terminal which are adapted to be bridged by a second fusible element, an indicating lamp connected in parallel with the first said fuse receiving terminals by a subcircuit including a conductor, and a second indicating lamp connected in parallel with said further fuse-receiving terminals by a second subcircuit including a second conductor, said said conductors being intermediate said load terminals and said indicating lamps and being spaced far enough apart from each other to prevent arcing over but being disposed close enough to each other to provide a capacitive effect that is large enough to maintain said indicating lamps illuminated in the event a short circuit" on the load side of said fuseholder causes both of said fusible elements to fuse and causes both of said indicating lamps to become illuminated and then disappears.

2. A fuseholder as claimed in claim 1 wherein said line terminals and said load terminals are adapted to connect the first said fusible element and said further fusible element and a load in series across a line, and wherein each of said lamps can be illuminated and can be kept illuminated by a voltage which is less than onehalf of the line voltage.

3. A fuseholder as claimed in claim 1 wherein said conductors are integral parts of a printed circuit board mounted within said fuseholder, whereby the spacing between said conductors is fixed and unvarying.

4. A fuseholder as claimed in claim 1 wherein a resistor is connected in the first said subcircuit and thus in series with the first said lamp between the first said line terminal and the first said load terminal, wherein a second resistor is connected in said second subcircuit and thus in series with said second lamp between said second line terminal and said second load" terminal, wherein the first said resistor will permit said first said lamp to become illuminated whether said resistor and said lamp have line voltage or approximately one-half of line voltage applied thereto, and wherein said second resistor will permit said second lamp to become illuminated whether said second resistor and said second lamp have line voltage or approximately one-half of line voltage applied thereto. 1

5. A fuseholder as claimed in claim 1 wherein said conductors are integral parts of a printed circuit board mounted within said fuseholder, whereby the spacing between said conductors is fixed and unvarying, wherein said lamps are disposed at one face of said printed circuit board, and wherein said conductors are on the opposite face of said printed" circuit board.

6. A fuseholder which has a recess therein to accommodate a plurality of indicating lamps, a plurality of sockets in said fuseholder adjacent to said recess, a support of insulating material within said fuseholder, a plurality of indicating lamps secured to said support of insulating material and disposed within said recess by said support of insulating material, rotation-resisting members which are secured to said support of insulating material and which are disposed within said sockets whenever said lamps are disposed within said recess, and said rotation-resisting members projecting from one surface of said support of insulating material a distance greaterthan the distance which said lamps project from said one surface of said support of insulating material, whereby said rotation-resisting members enter said sockets in said fuseholder before said lamps can enter said recess in said fuseholder and whereby said rotation-resisting members serve as aligning members.

7. A fuseholder which has a recess therein to accom modate a plurality of indicating lamps, a plurality of sockets in said fuseholder adjacent to said recess, a support of insulating material within said fuseholder, a plurality of indicating lamps secured to said support of insulating material and disposed within said recess by said support of insulating material, rotation-resisting members whichare secured to said support of insulating material and which are disposed within said sockets whenever said lamps are disposed within said recess, said rotation-resisting members being conductors that are dimensioned to extend into but not through said sockets, whereby the outer ends of said rotationresisting members are spaced short distances inwardly of the outer ends of said sockets, said outer ends of said sockets permitting probes of a test instrument to be inserted therein and to engage the-outer ends of said rotation-resisting members, a conductor extending between one of said rotation-resisting members and a fusereceiving terminal within said fuseholder, and a second conductor extending between the other of said rotation-resisting members and another fuse-receiving terminal within said fuseholder, whereby said rotationresisting members act as test points.

8. A fuseholder which has a recess therein dimensioned to accommodate a plurality of indicating lamps, a window in'said fuseholder providing visual communication'with said recess, a second window in said fuseholder providing visual communication with said recess, a plurality of sockets in said fuseholder adjacent to saidrecess, a first fuse-receiving conductor in said fuseholder, a second fuse-receiving conductor in said fuseholder, said first and second fuse-receiving conductors being spaced away from said recess, a support of insulating material within said fuseholder, means fixedly and permanently securing said first and second fuse-receiving conductors and said support of insulating material to each other and to said fuseholder, a plurality of indicating lamps fixedly and permanently secured to said support of insulating material and thereby fixedly and permanently secured to said fuseholder, said support of insulating material holding said plurality of indicating lamps within said recess, said support of insulating material holding one of said lamps in register with the first said window in said fuseholder, said support of insulating material holding another of said lamps in register with said second window in said fuseholder, rotation-resisting members which are fixedly and permanently secured to said support of insulating material and which are thereby fixedly and permanently secured to said fuseholder,v said rotationresisting members being disposed within and guided by said sockets in said fuseholder, said rotation-resisting members coacting with said sockets in said fuseholder to hold said one and said other lamps in register with the first said and said second windows, respectively, in said fuseholder, and said first and second fuse-receiving conductors being engageable by the terminals of an electric fuse which is in assembled relation with said fuseholder but is wholly external of said recess in said fuseholder.

9. A fuseholder which has a line" terminal and a load" terminal that are adapted to be electrically connected by a fusible element, a second line terminal and a second load terminal that are adapted to be electrically connected by a second fusible element, an indicating lamp connected in parallel with the first said fusible element by a subcircuit that includes a conductor, and a second indicating lamp connected in parallel with said second fusible element by a second subcircuit that includes a second conductor, said conductors being intermediate said load" terminals and said indicating lamps and being spaced far enough apart from each other to prevent arcing over but being disposed close enough to each other to provide a capacitive effect that is large enough to maintain said indicating lamps illuminated in the event a short circuit" on the load side of said fuseholder causes both of said fusible elements to fuse and causes both of said indicating lamps to become illuminated and then disappears.

10. A fuseholder which has a line" terminal and a load" terminal that are adapted to be electrically connected by a fusible element, a second line terminal and a second load terminal that are adapted to be electrically connected by a second fusible element, an indicating lamp connected in parallel with the first said fusible element by a subcircuit that includes a resistor, and a second indicating lamp connected in parallel with said second fusible element by a second subcircuit that includes a second resistor, said resistors having values enabling the first said resistor to protect the first said lamp in the event only the first said fusible element fuses and enabling said second resistor to protect said second lamp in the event only said second fusible element fuses but enabling both of said lamps to become illuminated in the event both of said fusible elements fuse.

11. A fuseholder that has a front face and an externally threaded boss which projects forwardly from said front face and which is adapted to extend through an opening in a panel, a second boss which projects forwardly from said front face and which is adapted to extend into a second opening in said panel, said second boss being spaced laterally from said externally threaded boss, a recess within said fuseholder in register with said second boss that accommodates an indicating lamp, an opening in the front of said second boss permitting light from said indicating lamp to pass forwardly through said second boss and through said second opening and thus to be visible from the front of said panel, fuse-receiving terminals within said externally threaded boss, an electric fuse that is disposed forwardly of said panel and that is securable to said fuse-receiving terminals within said externally threaded boss, conductors extending between said fuse-receiving terminals within said externally threaded boss and said lamp within said recess, in register with said second boss, that place said lamp in parallel with said electric fuse, and a nut that is threaded onto said externally threaded boss and that applies pressure to the front of said panel to hold said fuse-holder adjacent the rear of said panel with said second boss disposed within said second opening in said panel.

12. A fuseholder as claimed in claim 11 wherein said electric fuse has an outwardly projecting flange thereon, and wherein a second nut has an inwardly extending flange with a diameter larger than the principal diameter of said electric fuse but smaller than the outer diameter of said outwardly extending flange on said electric fuse, said second nut having a thread which mates with the thread on said externally threaded boss and which will enable said second nut to hold said electric fuse in assembled relation with said fuse-receiving terminals.

13. A fuseholder as claimed in claim 4 wherein said externally threaded boss has an annular groove in the outer face thereof, wherein an O-ring has a portion thereof disposed within said annular groove but has a further portion thereof projecting forwardly of said outer face of said externally threaded boss to engage and be compressed by said electric fuse, and wherein said second nut can coact with said outwardly extending flange on said electric fuse to force said electric fuse into compressing and sealing engagement with said further portion of said O-ring.

14. A fuseholder as claimed in claim 11 wherein said externally threaded boss has a slot therein and wherein said fuse has an aligning blade thereon, said aligning blade of said electric fuse being dimensioned to extend into and to be confined by said slot in said externally threaded boss, said slot in said externally threaded boss and said aligning blade on said electric fuse interacting to automatically align terminals on said electric fuse with said fuse-receiving terminals in said externally threaded boss, said aligning blade of said electric fuse projecting outwardly beyond the outer ends of said terminals on said electric fuse, whereby said aligning blade of said electric fuse must enter and be confined in said slot in said externally threaded boss before said terminals on said fuse can engage said fuse-receiving terminals in said externally threaded boss.

15. An electric fuse which has four pin-like fuse terminals projecting therefrom, said pin-like fuse termicontact pressures therebetween.

Claims

1. A fuseholder which has a ''''line'''' terminal, a ''''load'''' terminal, a second ''''line'''' terminal, a second ''''load'''' terminal, fuse-receiving terminals intermediate the first said ''''line'''' terminal and the first said ''''load'''' terminal which are adapted to be bridged by a fusible element, further fuse-receiving terminals intermediate said second ''''line'''' terminal and said second ''''load'''' terminal which are adapted to be bridged by a second fusible element, an indicating lamp connected in parallel with the first said fuse-receiving terminals by a subcircuit including a conductor, and a second indicating lamp connected in parallel with said further fuse-receiving terminals by a second subcircuit including a second conductor, said said conductors being intermediate said ''''load'''' terminals and said indicating lamps and being spaced far enough apart from each other to prevent arcing over but being disposed close enough to each other to provide a capacitive effect that is large enough to maintain said indicating lamps illuminated in the event a ''''short circuit'''' on the ''''load'''' side of said fuseholder causes both of said fusible elements to fuse and causes both of said indicating lamps to become illuminated and then disappears.

2. A fuseholder as claimed in claim 1 wherein said ''''line'''' terminals and said ''''load'''' terminals are adapted to connect the first said fusible element and said further fusible element and a load in series across a ''''line,'''' and wherein each of said lamps can be illuminated and can be kept illuminated by a voltage which is less than one-half of the ''''line'''' voltage.

3. A fuseholder as claimed in claim 1 wherein said conductors are integral parts of a ''''printed'''' circuit board mounted within said fuseholder, whereby the spacing between said conductors is fixed and unvarying.

4. A fuseholder as claimed in claim 1 wherein a resistor is connected in the first said subcircuit and thus in series with the first said lamp between the first said ''''line'''' terminal and the first said ''''load'''' terminal, wherein a second resistor is connected in said second subcircuit and thus in series with said second lamp between said second ''''line'''' terminal and said second ''''load'''' terminal, wherein the first said resistor will permit said first said lamp to become illuminated whether said resistor and said lamp have ''''line'''' voltage or approximately one-half of ''''line'''' voltage applied thereto, and wherein said second resistor will permit said second lamp to become illuminated whether said second resistor and said second lamp have ''''line'''' voltage or approximately one-half of ''''line'''' voltage applied thereto.

5. A fuseholder as claimed in claim 1 wherein said conductors are integral parts of a ''''printed'''' circuit board mounted within said fuseholder, whereby the spacing between said conductors is fixed and unvarying, wherein said lamps are disposed at one face of said ''''printed'''' circuit board, and wherein said conductors are on the opposite face of said ''''printed'''' circuit board.

6. A fuseholder which has a recess therein to accommodate a plurality of indicating lamps, a plurality of sockets in said fuseholder adjacent to said recess, a support of insulating material within said fuseholder, a plurality of indicating lamps secured to said support of insulating material and disposed within said recess by said support of insulating material, rotation-resisting members Which are secured to said support of insulating material and which are disposed within said sockets whenever said lamps are disposed within said recess, and said rotation-resisting members projecting from one surface of said support of insulating material a distance greater than the distance which said lamps project from said one surface of said support of insulating material, whereby said rotation-resisting members enter said sockets in said fuseholder before said lamps can enter said recess in said fuseholder and whereby said rotation-resisting members serve as aligning members.

7. A fuseholder which has a recess therein to accommodate a plurality of indicating lamps, a plurality of sockets in said fuseholder adjacent to said recess, a support of insulating material within said fuseholder, a plurality of indicating lamps secured to said support of insulating material and disposed within said recess by said support of insulating material, rotation-resisting members which are secured to said support of insulating material and which are disposed within said sockets whenever said lamps are disposed within said recess, said rotation-resisting members being conductors that are dimensioned to extend into but not through said sockets, whereby the outer ends of said rotation-resisting members are spaced short distances inwardly of the outer ends of said sockets, said outer ends of said sockets permitting probes of a test instrument to be inserted therein and to engage the outer ends of said rotation-resisting members, a conductor extending between one of said rotation-resisting members and a fuse-receiving terminal within said fuseholder, and a second conductor extending between the other of said rotation-resisting members and another fuse-receiving terminal within said fuseholder, whereby said rotation-resisting members act as test points.

8. A fuseholder which has a recess therein dimensioned to accommodate a plurality of indicating lamps, a window in said fuseholder providing visual communication with said recess, a second window in said fuseholder providing visual communication with said recess, a plurality of sockets in said fuseholder adjacent to said recess, a first fuse-receiving conductor in said fuseholder, a second fuse-receiving conductor in said fuseholder, said first and second fuse-receiving conductors being spaced away from said recess, a support of insulating material within said fuseholder, means fixedly and permanently securing said first and second fuse-receiving conductors and said support of insulating material to each other and to said fuseholder, a plurality of indicating lamps fixedly and permanently secured to said support of insulating material and thereby fixedly and permanently secured to said fuseholder, said support of insulating material holding said plurality of indicating lamps within said recess, said support of insulating material holding one of said lamps in register with the first said window in said fuseholder, said support of insulating material holding another of said lamps in register with said second window in said fuseholder, rotation-resisting members which are fixedly and permanently secured to said support of insulating material and which are thereby fixedly and permanently secured to said fuseholder, said rotation-resisting members being disposed within and guided by said sockets in said fuseholder, said rotation-resisting members coacting with said sockets in said fuseholder to hold said one and said other lamps in register with the first said and said second windows, respectively, in said fuseholder, and said first and second fuse-receiving conductors being engageable by the terminals of an electric fuse which is in assembled relation with said fuseholder but is wholly external of said recess in said fuseholder.

9. A fuseholder which has a ''''line'''' terminal and a ''''load'''' terminal that are adapted to be electrically connected by a fusible element, a second ''''line'''' terminal and a second ''''load'''' terminal that are adapted to be electrically connected by a second fusible element, an indicating lamp connected in parallel with the first said fusible element by a subcircuit that includes a conductor, and a second indicating lamp connected in parallel with said second fusible element by a second subcircuit that includes a second conductor, said conductors being intermediate said ''''load'''' terminals and said indicating lamps and being spaced far enough apart from each other to prevent arcing over but being disposed close enough to each other to provide a capacitive effect that is large enough to maintain said indicating lamps illuminated in the event a ''''short circuit'''' on the ''''load'''' side of said fuseholder causes both of said fusible elements to fuse and causes both of said indicating lamps to become illuminated and then disappears.

10. A fuseholder which has a ''''line'''' terminal and a ''''load'''' terminal that are adapted to be electrically connected by a fusible element, a second ''''line'''' terminal and a second ''''load'''' terminal that are adapted to be electrically connected by a second fusible element, an indicating lamp connected in parallel with the first said fusible element by a subcircuit that includes a resistor, and a second indicating lamp connected in parallel with said second fusible element by a second subcircuit that includes a second resistor, said resistors having values enabling the first said resistor to protect the first said lamp in the event only the first said fusible element fuses and enabling said second resistor to protect said second lamp in the event only said second fusible element fuses but enabling both of said lamps to become illuminated in the event both of said fusible elements fuse.

15. An electric fuse which has four pin-like fuse terminals projecting therefrom, said pin-like fuse terminals being spaced both laterally and longitudinally of said electric fuse to define a quadrilateral, said pin-like fuse terminals being fixedly spaced laterally of each other, and a fuseholder which has four fuse-receiving terminals, said fuse-receiving terminals being spaced both laterally and longitudinally of said fuseholder to define a quadrilateral essentially congruent to the first said quadrilateral, said fuse-receiving terminals being tulip-like terminals, said pin-like terminals coacting with said fuse-receiving terminals to provide substantial contact pressures therebetween and responding to the manufacturing tolerances thereof to provide increased contact pressures therebetween.