US2505193A - Fuse plug - Google Patents

Description

April 25, 1950 F. LOPORTO 2,505,193

FUSE PLUG Filed Feb. 8, 1946 Patented Apr. 25, 1950 UNITED STATES PATENT OFFICE FUSE PLUG Frank Lopolto, Cicero, lll.

Application February 8, 1946, Serial No. 648,323

1 Claim. (Cl. 20G- 113) This invention relates to protective devices for electrical circuits of the type which include a current carrying conductor adapted to be ruptured when heated by the overloading of the circuit.

One object of the invention is to provide a, new and improved fuse plug in which a slender iliament of mercury is employed as one of the conductors, said mercury being overheated and expelled from its current conducting position by an overload in the circuit but being retained vwithin the plug so that it is adapted to be replaced in conducting position without unsealing the plug or otherwise altering its structure.

Another object oi the invention is to provide a fuse plug in which a. quantity of mercury is employed as the current conductor sensitive to overload and in which the displacement of said conductor from its normal position serves to close an alarm circuit for indicating the condition of the principal circuit in which the plug is contained.

It is also an object of the invention to provide a new and improved fuse plug of the type employing a liquid current carrying medium which is displaced from its normal current carrying position by an overload in the circuit, said plug comprising a substantially transparent body through which the displaced liquid is readily visible.

A further object of the invention is to provide equipment for protecting a, plurality of circuits including a new and improved fuse plug of the type employing a liquid current carrying medium Which is displaced from its normal current carrying position by an overload in the circuit, said plug including a contact element positioned in the body of the plug to contact the displaced liquid medium and to be connected therethrough with one side f a feed circuit, said element extending outside the body of the plug so that by means of a signal device and test wire connected to the other side of the circuit any such plug may be tested without removal from its mounting for determining the circuit in which the overload occurred.

Other objects and advantages of the invention will appear from the following description taken in connection with the drawings, in which:

Fig. 1 is an axial sectional view showing a fuse plug embodying this invention, with a wiring diagram therefor.

Fig. 2 is a face view of a panel board having installed thereon a plurality oi fuse plugs similar to that shown in Fig. l, with an indicator lamp for each plug;

2 a modiiied form of the invention, with its wiring diagram.

Fig. 4 is a face view of a panel board provided with a plurality of fuse plugs like that shown in Fig. 3 and with a single indicator lamp and means for connecting it alternatively to any of the fuse plugs;

Fig. 5 is an axial sectional view of a fuse plug embodying this invention with an individual indicator lamp mounted directly on the plug, and a wiring diagram.

Fig. 6 is a transverse section taken as indicated at line 6-6 on Fig. 5.

In the form shown in Fig. 1, the fuse plug embodying this invention is provided with a body I6 which is preferably of transparent material, such as glass or synthetic plastic, and which is formed with an axially disposed chamber I2 communicating with an axial bore I4 which is slightly larger than the chamber and in which there is inserted a bushing I6 o1' conducting material such as brass or copper. The bushing has a slender axial channel I8 which connects with a similar channel 2li in a plug 22 of insulating 26 material, said plug being tted into a recess in Fig. 3 is an elevation partly in section showing 55 the lower end of the conducting bushing I6 and extending through a plate or washer 24 of conducting material. Said plate 24 contacts the threaded metallic shell 26 of the plug and said shell 26 is anchored to the body I 0 in any convenient manner.

The plate or washer 24 is retained in position by means of an insulating cap 28 which is held in place by the overlapping ange 3,0 of the shell 26 and which carries the center contact element 32 disposed axially in the cap 26 and engaged with the end of the insulating plug 22. 'Ihe conducting plate 24 engages the lower end portion of the conducting bushing I6 which encircles the insulating plug 22. A small quantity of liquid current conducting material 34. preferably mercury, normally occupies the axial channel 20 in the insulating plug 22 and extends into the axial channel I8 of the conductor I6. Thus when the fuse plug is screwed into a socket connected in the circuit to be protected. the center contact 32 of the plug engages the center contact of the socket, and the shell 26 engages the threaded shell of the socket. The circuit is completed by the column or filament of mercury 34 which engages the center contact 32 and connects it with the conductor bushing I6, while the latter is connected by the plate 24 with the shell 26.

The upper or outer end of the conducting bushing I6 is formed with an inverted conical recess 36 communicating with the bore or channel I6.

In the event of a short circuit or overload, the momentary overheating of the mercury 88 causes a portion of 1t to vaporize and expand rapidly, forcing the entire column into the chamber I2 of the body I8. This breaks the circuit and the mercury instantly cools and falls back into the recess .or cup 88 into the position indicated in dotted lines at 88; but the restricted character of the channel I8 prevents the mercury from flowing by gravity into said channel and reestablishlng the circuit. If the fuse plug be removed from the socket and shaken sharply, the mercury is readily forced back into the restricted channels I8 and 28, thus renewing the plug for further service, and such renewal can be repeated indefinitely.

By reason of the fact that the body I8 is made of transparent material, an installation of fuse plugs of this type can be easily and readily inspected without removal from their supporting sockets, and if any of the plugs has blown" as a result of a short circuit or overload, this fact will be readily apparent because the globule of mercury resting in the chamber I2 if the plug is in horizontal position, or in the cup 88 at 88 if the plug is installed vertically, can be seen through the transparent body I8.

The present invention provides additional means for readily and definitely identifying the plug which has been "blown by a short circuit, and this means may be embodied in the fuse plug whether it be made of transparent or of opaque material, such as porcelain. Said means includes a conductorl I8 which is permanently embedded in the body I8 so as to extend into the chamber I2 and toward the recess 88, as shown in Fig. 1. In the event of an overload or short circuit, the mercury globule formed at 88 will extend into contact with the conductor 88. Outside the body I Ii the conductor is threaded so as to serve as a binding po'st and is provided with a knurled nut 82 for clamping one end of conductor wire 88. This wire is connected to one terminal of a sisnal lamp 88, while the other terminal of the lamp extends to the line wire or feed wire L1, as diagrammatically shown in Fig. l. The lamp or other appliance in the circuit protected by the fuse is shown at A, connected between line wires L1 and L with the fuse in series with the element A. When the fuse is blown, a new circuit is established from Irl through lamp 58, conductor 88, conductor 88. mercury 88, bushing I8, plate 28, and shell 28 which is already connected to line wire L. The lighting of the lamp 88 thus indicates that the fuse has fimctioned. ^f As sho'wn in Fig. 2, each section of the panel board 88 includes a fuse plug body I8 and a corresponding indlcamr lamp nto which a wire u extends. Thus, whenever a short circuit causes the mercury 8l in a fuse plug to'be expelled from its normal position in the channels I8 and .28 to its position at 38 in the recess 88, it will complete the circuit of the corresponding lamp 88 which will glow as a signal to identify the fuse plug requiring attention for renewal.

Fig. 3 illustrates a slight modiiication of the fuse plug structure and Fig. 4 shows a modified arrangement of the panel board. In Fig. 8 the functioning-portions of the fuse device as such may be understood as similar to those of Fig. 1 already described, but instead of the conductor 48 with its binding post 42 the body portion Ila of the plug shown in Fig. 3 carries a conductor 88 having merely a smoothly rounded head 82 conductor 88 carries a single indicator lamp 18 and a single, preferably flexible, conductor 88 hangs from its connection to the socket of the lamp 18 in a position in which its contact terminal 88 is normally clear of all the fuse plug bodies I8a on the board. In the event of an overload or short circuit causing one of the plugs to blow, the defective circuit can be promptly identified by swinging the conductor 88 so as to bring its terminal 88 selectively into contact with the exposed contact heads 82 of the several fuse plugs until such engagement causes lighting of the signal lamp 18. As a matter of convenience, the fuse plugs are shown arranged on the panel board 88 in an arc concentric with the axis of the lamp 18.

Figures 5 and 6 illustrate a further modification of the fuse plug in which it is arranged to carry its own signal lamp. The body IIIb may be of transparent or opaque insulating material, and the internal portions of the fuse device itself are similar to those shown in Fig. l and are identified by corresponding numerals. The outer end of the plug body IUb is shown surmounted by a washer 12 which may be of nbre or like material, and serves to seat the in-turned base flange of a metallic socket 18, the base portion of the socket being bent over and enclosing an insulating disc 'I8 through which a bolt 18 extends into the body I8b of the fuse plug. The threaded end of the bolt extends into the chamber I2 in the plug body and is secured therein by a nut 88 which thus clampsithe socket 18 in position on the outer end of the body I8b. The head of the bolt 18 serves as a center contact for the small indicator lamp 82 which is supported in the socket 'I8. The socket itself is provided vwith a lug 88, and a 88 extends therefrom to the line wire L1. p

With this arrangement, it will be evident that as long as the filament or column of mercury 88 functions to complete the circuit for the lamp or other device at A through the contact element 82 and the conducting bushing I8, the lamp 82 will not be energized, but that in the event of a short circuit which causes the mercury to leave the bores I8 and 28 and to settle in the cup or recess 88, the globule of mercury thus formed at 88 will provide a connection between the line wire L, shell 28, plate 28, bushing I8 and the bolt 18 which is in contact with the center of the base of the indicator lamp 82. The other side of the circuit for the lamp 82 is already completed through the socket 18, lug 88, and conductor 88, leading to line wire L1. Thus in any panel board containing a considerable number of fuse plugs oi'` this type, the failure of any circuit will be indicated immediately by the glowing of the indicator lamp 82 on the plug which has been affected. The plug then may be removed and shaken down to restore the mercury to the channels I8 and 28 and thus renew the plug for further service. If the defective circuit is known to be yagain in safe condition, the plug will be replaced at once in its socket to resume service.

While I have shown and described herein certain structure embodying my invention and illustrative thereof, it is to be understood that the invention is not limited thereto or thereby but'embraces all changes and modifications in its various features which may come within the scope of the appended claim.

I claim:

A fuse including an insulating, centrally aperexposed outside the body I8a. The panel board 'IISA tured body, a conducting bushing seated therein,

somos closing the outer portion of the aperture and at its outer end ush with the end of the body, an insulating plug socketed in the conducting bushing and extending beyond the end of the body, a conducting washer encircling the plug, engaging the end of the body and the end of the conducting bushing, an insulating cap socketed to contain the outer end of the insulating bushing and to engage the outer face of the conducting washer, a threaded conducting shell encircling the fuse body, engaging the washer throughout substantially its entire periphery and ilanged to overlie the insulating cap and hold it iirmly against the washer, a conducting pin extending axially through the insulating cap, the insulating plug and conducting bushing being each centrally apertux'ed to dene an aligned capillary tube extending from the conducting pin to the inner end of the conducting bushing, the capillary tube being adapted to contain a liquid conn The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,531,756 Roach Mar. 31, 1925 1,705,678 Pierce Mar. 19, 1929 1,813,344 Gilbert July 7, 1931 1,958,977 Riv-ers May '15, 1934 2,038,970 Tessier Apr. 23, 1936 2,059,681 Crimmins Nov. 3, 1936 2,060,819 McHugh Nov. 17, 1936 2,063,813 Kellendorfer Dec. 8, 1936 2,079,462 McHugh May 4, 1937 2,097,406 Jenkins Oct. 26, 1937

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