US3157766A

US3157766A - Dead front fuse with improved terminal clamping means

Info

Publication number: US3157766A
Application number: US243483A
Authority: US
Inventors: William S Edsall
Original assignee: Chase Shawmut Co
Current assignee: Chase Shawmut Co
Priority date: 1962-12-10
Filing date: 1962-12-10
Publication date: 1964-11-17
Anticipated expiration: 1981-11-17

Description

ICL

Nov. 17, 1964 w. s. EDSALL 3,157,765

DEAD FRONT FUSE WITH IMPROVED TERMINAL CLAMPING MEANS Filed Dec. 10, 1962 2 Sheets-Sheet 1 Nov. 17, 1964 Filed D90. 10, 1962 w. s. EDSALL 3,157,766

DEAD FRONT FUSE WITH IMPROVED TERMINAL CLAMPING MEANS 2 Sheets-Sheet 2 United States Patent 3,157,766 DEAD FRQNT FUiE W TMPRQVED TERMTNAL QLAMPTNG lidEANh William S. Edsali, Boston, Mass, assignor to The Shawrnut Company, New! uryport, Mass.

Filed Bee. it), 1962, No. 24 3,483 2 Claims. (8i. 2tl l132) This invention relates to electric fuses, and more particularly to so-called dead-front electric fuses.

Conventional electric fuses--be it fuses of the ferrule type, or fuses of the blade type-are normally applied in connection with fuse holders having exposed contacts, and such fuses are intended to be applied in connection with such fuse holders. The provision of exposed confacts is an ever present danger to maintenance personnel, particularly in instances where such personnel is not highly skilled, in damp locations, and where the circuit voltage is relatively high.

It is, therefore, one object of this invention to provide electric fuses precluding immediate access to the contact structures thereof and thus eliminating the danger to human life and safety resulting from the provision of exposed or readily accessible contact structures.

Arrangements of fuses and fuse holders wherein all live parts are arranged on the rear side and are inaccessible from the front side of the fuses, are referred to as dead-front arrangements.

It is another object of this invention to provide in proved dead-front fuse and fuse holder arrangements.

Generally dead-front fuse and fuse holder arrangements involve shrouds upporting the fuse and shielding the contacts thereof. Such arrangements are, however, relatively bulky and relatively expensive.

It is, therefore, another object of this invention to provide shroudless, compact and relatively inexpensive dead-front fuses.

Prior art dead-front fuses lend themselves to low current ratings as well as to high current ratings.

Other objects and advantages of the invention will become apparent to those versed in the art upon making reference to the ensuing description and drawings in which a preferred structural embodiment of the invention is shown by Way of illustrative example.

In the drawings:

FIG. 1 is mainly a section along lll of FIG. 2 and shows an electric fuse and a cooperating fuse holder forming part of a panelboard, some parts of the structure being shown in elevation rather than in section;

FIG. 2 is mainly a section along of FIG. 1, some parts being shown therein in elevation rather than in section; and

FIG. 3 is a section along 3-3 of FIG. 1, some of the parts of FIG. 3 being again shown in elevation rather than in section.

Referring now to the drawings, numerm 1 has been up pllied to indicate a casing of insulating material having a predetermined length L and forming a pair of annular rims 1:: at the axially outer ends thereof. Casing i may be of a melamine-glass-cloth laminate. it houses a pair of spaced aligned electric terminals in form of plates or blocks 4.. Reference letter i has been. applied to indicate the spacing between terminals or terminal plates or blocks 4. It is apparent that the latter is less than the length L of easing l, i.e.

L' L Terminals d are arranged in their entirety inside of housing 1, the latter being closed on both ends thereof by insulating plugs 3, preferably made of a fairly heat resistant synthetic resin. Each of insulating plugs 3 supports one of terminals 4 in a fashion set forth below more in detail.

3,l57,766 Patented Nov. 17, 1964 Each insulating plug 3 comprises an axially inner portion 3:: having a relatively small outer diameter and fitted into casing 1 and an axially outer portion 311 having a relatively large outer diameter. The axially outer portion 35b of each plug 3 abuts against one of the annular rims fa of casing 1 and is cemented to it by a cement having a relatively high tensile strength. Each insulating plug 3 is provided with a recess 30 extending in a direction longitudinally of casing 1 and closed at the axially outer end thereof. Thus recesses 3c form dead-end passageways. Each recess 30 accommodates a terminal element or terminal block l, preferably formed by a rectangular stamping of bar copper. Each insulating plug 3 is further provided with a bore 3d formin a pasageway extending radially with respect to casing 1 and at right angles to the eneral plane defined by terminal plates 4. Terminal plates 4 are conductively interconnected by a pair of spaced ribbon fuse links 5 of copper or silver, each arranged at opposite sides of terminal plates 4 and sandwiching the axially inner ends of terminal plates 4. Fuse links 5 comprise a plurality of transverse lines So of circular perforations and each fuse link 5 supports an overlay 5b of a link-severing low fusing point metal, e.g. tin. Regarding the geometry and arrangement of overlays 5b on fuse links 5, I prefer to follow the teaching given in U.S. Patent 2,988,620 to F. l. Kozacka, Time-Lag Fuses, issued June 13, 1961, and reference may be had to that patent as to particulars of the geometry and arrangement of overlays 5b. Fuse links 5 are submersed in a pulverulent arc-quenching filler 6 such as, for instance, quartz sand. Each terminal plate 4 is provided with a hole or bore 4a which is internally screw-threaded and receives the radially inner end of a screw-threaded bolt or stud 7 forming part of a stab-connector or stab contact. Bolt or stud '7 is arranged inside of bore 3d in each insulating plug 3 and has a radially outer screw-threaded end supporting a current-carrying contact 8. The radially inner end of current-carrying contact 8 rests against a washer 9 which, in turn, rests against an insulating member 10 hugging the outer surface of casing 1. The radially inner end surface of contact 8 presses against washer 9 which, in turn, compresses insulating member 10. The higher the pressure upon insulating member 10, the tighter the sealing effect thereof limiting venting of products of arcing from the inside of casing 1 to the outside thereof. As a general rule, a limited degree of venting of products of arcing from casing It is believed to be desirable.

Current carrying contacts may be provided with a transverse bore So for receiving a key or tool for screwing contact 8 against parts 9, 10.

it will be understood that bolts or studs 7 are normally under tension and insulating plugs 3 are normally under compression.

(Zurrent carrying contacts 8 engage a pair of tulip type contacts ll. Contacts 11 are made up of a plurality of stampings 11a arranged in a circular pattern around contacts 8 and kept in engagement under pressure with contacts 8 by garter springs 11b. Garter springs 11b cause also engagement under pressure of stampings 11a with current carrying studs 11c. Tulip type contacts 11 may be accommodated in an insulating housing 2 closed by a front panel 12 of insulating material having a pair of apertures 12a for the passage of stab connectors 7, 8.

When assembling a structure embodying this invention a subassembly comprising fuse links 5 and terminal plates 4 is inserted into casing 1 and then one side of casing 1 is closed by an insulating plug 3 and that plug is held in position by insertion of a stab connector assembly 7, 8. Thereafter filler 6 is poured into casing 1, the latter is closed by second insulating plug 3, and the latter is held in position by insertion of the second stab connector assembly 7, 3.

It will be understood that I have illustrated and described herein a preferred embodiment of my invention, and that various alterations may he made therein without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. An electric dead-front fuse comprising:

(a) .a tubular casing of insulating material having a predetermined inner diameter and a predetermined length and forming a pair of annular rims at the axially outer ends thereof;

(b) ribbon-shaped fuse link'means having a predetermined thickness arranged inside of said casing extending in a direction longitudinally thereof;

(c) a pair of insulating plugs having axially inner ends of relatively small diameter equal to said predetermined inner diameter of said casing fitted into said casing and having axially outer ends equal in di ameter to the outer diameter of said casing and arranged in abutting relation to said pair of rims, each of said pair of plugsdefining an axially extending recess closed at the axially outer end thereof and open at the axially inner end thereof, and each of said pair of plugs defining aradialpassageway having a radially inner end communicating with said recess;

(d) a pair oft'erminal blocks each having a thickness being a multiple of said predetermined thickness of said fuse link means and each being inserted into said axially extending recess of one of said pair of insulating plugs, each of said pair of terminal blocks defining a radially extending internally screwthreaded passageway in registry with said radial passageway in one of said pair of insulating plugs;

(e) means conductively connecting each of the axially outer ends of said fuse link means to one of said pair of terminal blocks;

(f) a pair of studs each projecting transversely through said casing and through said radial passageway in one of said pair of insulating plugs, each of said pair of studs having a radially inner screw-threaded end cooperatively engaging said internally screw-thread ed passageway in one of said pair of insulating plugs, and each of said pair of studs having a radially outer screw-threaded end; and

(g) a pair of screw nuts each mounted on said radially outer screw-threaded end of one of said pair of studs and each stressing one of said pair of studs in a direction longitudinally thereof and thereby clamping one of said pair of terminal blocks in position inside said recess of one of said pair of insulating plugs, each of said pair of screw nuts having an outer substantially cylindrical contact surface.

2. An electric dead-front fuse comprising:

(a) a tubular casing of insulating material having a predetermined inner diameter and a predetermined length and forming a pair of annular rims at the axially outer ends thereof;

(b) ribbon-shaped fuse link means having a predetermined thickness arranged inside of said casing extending in a direction longitudinally thereof;

(c) a pair of insulating plugs having axially inner ends of relatively small diameter equal to said predetermined inner diameter of said casing fitted into said casing and having axially outer ends equal in diameter to the outer diameter of said casingand arranged in abutting relation to said pair of rims, each of said pair of plugs defining an axially extending recess closed at the axially outer end thereof and open at the axially inner end thereof, and each of said pair of plugs defining a radial passageway having a radially inner end communicating with said recess;

(d) a pair of terminal blocks each having a thickness being a multiple of said predetermined thickness of said fuse link means and each being inserted into said axially extending recess of one of said pair of insulating plugs, each of said pair of terminal blocks defining a radially extending internally screw-threaded passageway in registry with said radial passageway in one of said pair of insulating plugs;

(6) means conductively connecting each of the axially outer ends of said fuse link means to one of said pair of terminal blocks;

(f) a'pair -of studs each projecting transversely through said casing and through said radial passageway in one of said pair of insulating plugs, each of said pair of studs having a radially'inner screw-threaded end cooperatively engaging said internally screwthreaded passageway in one of said pair of insulating plugs, and each of said pair of studs having a radially outer screw-threaded end;

(g) a pair of substantially cylindrical contact mem-- bers each having an axial internally screw-threaded bore, each of said pair of contact members being mounted on said radially outer screw-threaded end of one of said pair of studs stressing one of said pair of studs in a direction longitudinally thereof and thereby clamping one of said pair of terminal blocks in position inside said recess of one of said pair of insulating plugs; and

(h) a pair of compressible seal-s each mounted on one of said pair of studs and each interposed between the outer surface of said casing and one of said pair of contact members to limit the flow of products of arcing along said pair of studs out of said casing.

References Cited by the Examiner UNrrED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner.

iiii Julius is is I V I i W flilfii of. ii I I UNITED STATES RATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 157,766 November 17, 1964 William 5. Ed sall It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, lines 38 and 39, strike out "Prior art deadfront fuses lend themselves to low current ratings as well as to high current ratings. column 2, line 14, for "pasageway" read passageway column 3, line 43, andocolumn 4, lines 31 and 32, for "insulating plugs", each occurrence, read terminal blocks Signed and sealed this 13th day of April 1965,

(SEAL) Attest:

ERNEST W. SWIDER' EDWARD J. BRENNER Attesting Officer Commissioner of Patents UNITED STATES RATENT OFFICE CERTIFICATE OF CORRECTION William S. Edsall s in the above numbered petthat error appear nt should read as It is hereby certified ent requiring correction and that the said Letters Pate corrected below.

Column 1 lines 38 and 39, strike out "Prior art deadtings as well as front fuses lend themselves to low current ra for "pasageway" to high current ratingsg"; column 2, line l4 read passageway column 3, line 43, andocolumn 41, lines 31 and 32, for "insulating plugs", each occurrence read terminal blocks Signed and sealed this 13th day of April 1965.,

(SEAL) Attest:

EDWARD J. BRENNER ERNEST W. SWIDER' I Avttesting Officer Comm ssioner of Patents

Claims

1. AN ELECTRIC DEAD-FRONT FUSE COMPRISING: (A) A TUBULAR CASING OF INSULATING MATERIAL HAVING A PREDETERMINED INNER DIAMETER AND A PREDETERMINED LENGTH AND FORMING A PAIR OF ANNULAR RIMS AT THE AXIALLY OUTER ENDS THEREOF; (B) RIBBON-SHAPED FUSE LINK MEANS HAVING A PREDETERMINED THICKNESS ARRANGED INSIDE OF SAID CASING EXTENDING IN A DIRECTION LONGITUDINALLY THEREOF; (C) A PAIR OF INSULATING PLUGS HAVING AXIALLY INNER ENDS OF RELATIVELY SMALL DIAMETER EQUAL TO SAID PREDETERMINED INNER DIAMETER OF SAID CASING FITTED INTO SAID CASING AND HAVING AXIALLY OUTER ENDS EQUAL IN DIAMETER TO THE OUTER DIAMETER OF SAID CASING AND ARRANGED IN ABUTTING RELATION TO SAID PAIR OF RIMS, EACH OF SAID PAIR OF PLUGS DEFINING AN AXIALLY EXTENDING RECESS CLOSED AT THE AXIALLY OUTER END THEREOF AND OPEN AT THE AXIALLY INNER END THEREOF, AND EACH OF SAID PAIR OF PLUGS DEFINING A RADIAL PASSAGEWAY HAVING A RADIALLY INNER END COMMUNICATING WITH SAID RECESS; (D) A PAIR OF TERMINAL BLOCKS EACH HAVING A THICKNESS BEING A MULTIPLE OF SAID PREDETERMINED THICKNESS OF SAID FUSE LINK MEANS AND EACH BEING INSERTED INTO SAID AXIALLY EXTENDING RECESS OF ONE OF SAID PAIR OF INSULATING PLUGS, EACH OF SAID PAIR OF TERMINAL BLOCKS DEFINING A RADIALLY EXTENDING INTERNALLY SCREWTHREADED PASSAGEWAY IN REGISTRY WITH SAID RADIAL PASSAGEWAY IN ONE OF SAID PAIR OF INSULATING PLUGS; (E) MEANS CONDUCTIVELY CONNECTING EACH OF THE AXIALLY OUTER ENDS OF SAID FUSE LINK MEANS TO ONE OF SAID PAIR OF TERMINAL BLOCKS; (F) A PAIR OF STUDS EACH PROJECTING TRANSVERSELY THROUGH SAID CASING AND THROUGH SAID RADIAL PASSAGEWAY IN ONE OF SAID PAIR OF INSULATING PLUGS, EACH OF SAID PAIR OF STUDS HAVING A RADIALLY INNER SCREW-THREADED END COOPERATIVELY ENGAGING SAID INTERNALLY SCREW-THREADED PASSAGEWAY IN ONE OF SAID PAIR OF INSULATING PLUGS, AND EACH OF SAID PAIR OF STUDS HAVING A RADIALLY OUTER SCREW-THREADED END; AND (G) A PAIR OF SCREW NUTS EACH MOUNTED ON SAID RADIALLY OUTER SCREW-THREADED END OF ONE OF SAID PAIR OF STUDS AND EACH STRESSING ONE OF SAID PAIR OF STUDS IN A DIRECTION LONGITUDINALLY THEREOF AND THEREBY CLAMPING ONE OF SAID PAIR OF TERMINAL BLOCKS IN POSITION INSIDE SAID RECESS OF ONE OF SAID PAIR OF INSULATING PLUGS, EACH OF SAID PAIR OF SCREW NUTS HAVING AN OUTER SUBSTANTIALLY CYLINDRICAL CONTACT SURFACE.