US 3829819 A
A dead front, back-wired electrical plug having a front accessible fuse mounted in a fuse well in the front face, a pivotable safety cover on the front face swingable into covering and uncovering relationship with the well, and a hollow plug housing with back-wired terminal posts for the respective contact blades and ground pin which project from the front face.
Description (OCR text may contain errors)
[ Aug. 13, 1974 United States Patent 1191 Eckart FUSED ELECTRICAL PLUG  Inventor: George R. Eckart, Lake Zurich, Ill.
Daniel Woodhead Inc, Northbrook, Ill.
ll/l922 Great Britain 339/44 M 122 Filed: 01.30, 1972 21 App]. No.: 302,230
Primary ExaminerRichard E. Moore Attorney, Agent, or Firm lohnston, Keil, Thompson & Shurtleff 339/206 P H0lr 13/58, HOlr l3/68 ABSTRACT I  337/196 339/39 44 A dead front, back-wired electrical plug having a front 339/1'47 206 accessible fuse mounted in a fuse well in the front face, a pivotable safety cover on the front face swingable into covering and uncovering relationship with the well, and a hollow plug housing with back-wired terminal posts for the respective contact blades and ground pin which project from the front face.
 References Cited UNITED STATES PATENTS l,92l,447 8/1933 Barnett 339/63 R 1,974,790 9/l934 Barth 339/63 R 2,636 097 4/l953 Shapiro........,...... 337/201 X 8 Claims, 8 Drawing Figures FUSED ELECTRICAL PLUG The invention herein concerns improvements in fused electrical'plugs, particularly those having a dead front and back-wiring of the terminal posts of the blades and ground pin, having a well for a fuse in the front face of the plug, the well having a safety cover movable into and out of covering relationship with the well. The fuse is connected in the plugs circuit between a terminal post and its contact blade. Other improvements of the invention reside in the configuration of the contact blade-mounting block to provide a compact assembly of the fuse contacts, the contact blades, the ground pin and the terminal post therefor.
A fused plug will protect motors, test instruments, data processing equipment, and other similar machines or equipment against damage caused by brown-outs, unexpected voltage drops or other electrical malfunctions. The amperage reading for the fuses may be tailored to the safety needs for each particular motor, instrument, piece of equipment, or machine, e.g., over a fuse range of 0.25 amps.
The location of the fuse well in the dead front of the I plug and the provision of a fuse well cover on the dead front has several advantages. For added safety, the fuse can be removed only after the plug has been removed from the receptacle. When removed, the cover plate is readily moved into and out of covering relationship relative to the fuse well whereby fuses-may be quickly checked or replaced.
One previously known type of fuse plug is a frontwired plug in which the terminal posts for one contact blade and the ground pin are recessed in forwardly opening wells immediately behind the front face of the plug. The terminal post for the other contact blade is positioned in a fuse well located next to the aforesaid wells. One of the fuse clips is electrically connected with the latter terminal post, while the other fuse clip is electrically connected with the latter blade.
The front face of said known plug is a removable dielectric cover plate with openings for the contact blades and ground pin. A body with a cylindrical passage is integrally molded on the back face of the dielectric cover plate. This body holds the midportion of a cylindrical fuse and slips between the fuse-mounting clips in the well when the cover plate is slid over the blades and ground pin and mounted on the plug body. The
THE INVENTION HEREIN This invention provides improvements over the known fused electrical plug described above and other fusing arrangements for electrical plugs by providing a dead front, back-wired electrical plug with a frontaccessible fuse. The plug of the invention comprises a hollow plug body of dielectric material with a blademounting body of dielectric material mounted in one end of the hollow plug body. The blade-mounting body has electrical contact blades, and optionally a ground pin, projecting from its front face, which also serves as the front face of the plug. The plug has circuit means for connecting its blades to the current wires of an electrical cord or cable and, where provided, for connecting the ground pin to the ground wire of such cord or cable.
The circuit means includes a fuse in the circuit for the blade connected to the hot wire. This fuse is located in a well in the front face of the plug. Two fusemounting clips are seated in the well. A cover member of dielectric material is mounted on the front face of the plug and is movable into and out of covering relationship with relation to the well.
Preferably. the cover member is a thin plate of dielectric material connected by pivot means to the front face providing for the swinging of the cover member into and out of covering relationship with the well. The pivot means advantageously is provided with an arm projecting from the side of the thin plate, the base of the arm being pivotally connected to the front face.
The terminal posts for the respective blades and ground pin are located on the rearward side of the blade-mounting body. These terminal posts are seated in wells or recesses in the rear face of the blademounting body. A separable cap covers the rear face and the wells or recesses therein to keep the bare ends of the wires well separated and isolated where they are attached to the respective terminal posts. The cap has passages or apertures through which the wires can pass into the respective wells or recesses.
The rearward end of the plug has a clamp for securely clamping the sheathed portion of the electrical cord or cable for the plug. Such clamp preferably has one section integrally molded with the rear portion of the hollow body of the plug and a removable section attached by bolts to the first-mentioned section. The cord is clamped between the sections by a bevelled, arcuate wall provided in the clamping face of the firstmentioned section and a pair of arcuate walls provided in the clamping face of the removable section. These arcuate walls accommodate cords or cables of various sizes and securely clamp such cords or cables by a biting action of the respective arcuate walls into the outer, insulated sheath of such cords or cables.
THE DRAWINGS A preferred embodiment of the invention is illustrated in the drawings, wherein:
FIG. I is a rear perspective view of the embodiment with the removable, electric cord or cable-clamping member also shown in phantom in exploded position;
FIG. 2 is a front perspective view of the embodiment with the cover plate for the fuse well in closed position;
FIG. 3 is a view similar to FIG. 2 with the cover plate in open position and the fuse in exploded, perspective view;
FIG. 4 is an exploded, front, perspective view of the three major components of the electrical plug, i.e., the hollow plug body, the contact blade-mounting block, and the removable electrical cable or cord clamp member;
FIG. 5 is an exploded, rear perspective view of the blade-mounting block, and its rear cap with one contact blade and the ground pin in exploded view and the other contact blade mounted in the block;
FIG. 6 is an exploded, front perspective view of the contact blade-mounting block with the other contact blade, its terminal post assembly, and the fusemounting clips in exploded view;
FIG. 7 is a side plan view of the blade-mounting block as viewed from plane 77 of FIG. 2; and
FIG. 8 is a schematic diagram of the wiring of the electrical components of the plug.
THE ILLUSTRATED EMBODIMENT The electrical plug 10 has as its main components a dielectric hollow plug body 11 made of an opaque, translucent or transparent thermoplastic or thermosetting synthetic polymer and a dielectric, contact blademounting block 12 molded from like or different thermoplastic or thermosetting synthetic polymer, e.g., Lexan (trademark), a polycarbonate polymer or resin. The block 12 has a dead front face 13. The so-called dead face results from back-wiring of the rearwardly located terminal posts 16 and 17 for the contact blades 14 and which project from the dead front face. The ground pin 18 also projects from the front face with its terminal post 19 also being back-wired.
The block 12 fits into the end 20 of the plug body 11 with its groove 21 mating with the internal rib 22 in the body 11. The block has a blade-accommodating passage 23, a ground pin-accommodating passage 24, and a blade-accommodating slot 25. The latter extends transversely across the inner side wall 94 of a fusereceiving well 95 extending longitudinally along one side of the front face.
The blade 14 lies in slot 25. Its base has a diagonal leg 26 and an apertured car 27. The latter is conductively connected by rivet 28 to the apertured spring metal fuse-mounting clip 29. The diagonal leg 26 lies on the diagonal surface 30 on the rear face of the block 12. The rivet extends through hole 31 extending from the rear face to the bottom wall of well 95.
The other fuse-mounting clip 32 is also made of spring metal and is seated at the opposite end of the well 95. It is connected conductively with the terminal post 16 by a rivet 33 which extends through the apertured ear 34 of the terminal bracket 35, the latter having mounted thereon a bolt 36 with a wire-holding nut 37. An insulating gasket 38 with an apertured car 39 lies on the bottom wall of the recess 40 which extends diagonally into the rear face from the side 41 of the block 12. The terminal post 16 is thus conductively connected with the blade 14 via the fuse 42 and its fuse-mounting contacts 29 and 32. The gasket 38 lies between the terminal post 16 and the contact blade 14 and its diagonal leg 26. It shields the latter against accidental contact by the wire attached to terminal post 16 and also prevents conductive foreign material from accidentally bridging the gap therebetween.
The other blade 15 projects through passage 23, the rearward end of which intersects a recess 43 which opens into the rear face edge portion 44 and the rear portion of the side wall 45 of the block 12. The wall 46 of recess 43 is slotted for the purpose of receiving one edge of the base 47 of the blade 15. The bolt 49 and nut 48 serve the purpose of clamping a wire to the terminal post 17. The arched portion 50 of the third wall of the recess 43 accommodates the projecting end of the bolt, the slotted head of which isaccessible through the slotted opening in the side wall 45.
The terminal post 19 of the ground pin 18 is seated in the same manner in a recess 51 of like configuration to the recess 43 with an edge of the base 52 seated in the slot 53. The wire clamping nut 54 is threaded on the bolt 55, the projecting end of which is accommodated by the arched portion 56.
The block 12 has a rear cap 57 composed of a rear. cover plate 58 and side walls 59 and 60 dimensioned to enclose the two open sides of the rear corner notch 61 of the block 12.
The cover plate 58 has a pair of apertures 62 and 63 for passage of the two wires to be connected to the terminal posts 16 and 17. A short tubular member 64 serves as a passage for the grounding wire to be connected to the terminal post 19.
The block 12 and its rear cap 57 are held in the hollow housing 11 by bolts 64 and 65, the shanks of which extend through countersunk passages 66 and 67 in the block 12 and apertures 68 and 69 in the cover plate 58. The threads at the ends of the shanks are threaded in integrally molded tubular columns 70 and 71 formed in two inner corners of the rearward portion of the housing 11. The bolts 64 and 65 hold the cover plate 58 against an inner, peripheral lip 72 extending along the inner faces of the four sides of the rear portion of the housing 11.
The hollow housing 11 has at its rearward end an electrical cable or cord clamping unit 73. A half section 74 thereof is molded integrally with the housing 11. This section has solid side portions 75 and 76 with respective bolt-receiving passages 77 and 78. Its midportion has a bevelled, semi-circular opening 79 in its clamping face 80. An electrical cable or cord passes through the semi-circular opening 79 and is gripped on one side by the relatively sharp, bevelled edge of the opening 79 when the removable clamp section 81 is drawn against the cable by bolts 82 and 83.
The removable clamp section 81 is a molded plastic body having end wells 84 and 85 for receiving said bolts. Its clamping face 86 has planar end faces 87 and 88 with bolt passages 89 and 90 connecting said faces and the respective wells 84 and 85. At the midportion of the face 86 is a recess or well 91, the front and rear edges of which have arcuate, cable or cord gripping walls 92 and 93 projecting outwardly therefrom. These walls oppose and coact with the semi-circular passage 79 in the secure gripping of electrical cables or cords of various diameters.
The fuse-mounting well 95 has a cover plate 96 which is movable into and out of covering relationship with relation to the well. The cover has a free end 97 which may overlie or cover, in the well-covering position, the well and an offset shoulder 98' (FIG. 3) in the face of the front face 13. Its narrower neck 98 provides a notched edge portion 99 in which the blade 14 is positioned with the cover plate in well-covering position (FIG. 2). An arm 100 projects laterally from the base of the cover plate, the arm being pivotally joined at its base by a plastic pin 101 having its end deformed into a rivet-like head. The base of the arm lies in an offset corner 102 in the front face 13 (FIG. 4) whereby the front surfaces of the cover plate, its neck and its arm are substantially flush with the plane of the front face 13.
As can be seen fron FIGS. 2 and 3, the swingable cover plate 96 and the position of the fuse-mounting well 95 along one side of the front face 13 gives ready, convenient access to the fuse 42 for its inspection or replacement by simply swinging the cover plate 96 to the position shown in FIG. 3. Removal of the fuse cannot be done without removal of the plug from the receptacle. It is not necessary, as is the case with previous known fused plugs, to remove completely any part of the plug, e.g., a front cover plate or its dielectric housing, to gain access to the fuse.
The back-wiring feature of the invention allows the plug to be wired by removing the blade-mounting body 12 and its rear cap 57 from the hollow plug body 11, e.g., as shown in FIG. 4. The respective bolts of the terminal posts are loosened. The wires of the cable or cord are stripped of their insulating sheath to a depth about equal to the depth of the respective wells or recesses in which the respective terminal posts are mounted. The bare wire ends are inserted through the respective apertures 62, 63 and 64 in the rear cap 57 and pass between the respective nuts and the terminal post portions 35, 47 and 52. The bolts are thereupon turned by a screwdriver to securely clamp the wires on the respective terminal posts.
The back-wiring feature provides complete isolation of the respective ends of the wires from each other. Each bare wire end is located in a well or recess with dielectric material separating the wells or recesses. This arrangement provides one very safe wiring arrangement which guards against accidental short-circuiting between wires in the plug, voltage leakages across wires in the plug and the like.
The configuration and orientation of contact blades 14 and 15 and the optional ground pin 18 on the front face 13 is but one type of many which may be used. Other configurations and orientations for contact blade and ground pins of the non-locking or locking type (such as those approved by the National Electrical Manufacturers Association for various voltages and amperages) may be used instead of that shown in the illustrated embodiment.
It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description, and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing any of its attendant advantages, the form herein disclosed being a preferred embodiment for the purpose of illustrating the invention.
The invention is hereby claimed as follows:
1. A dead front, back-wired electrical plug with a front-accessible fuse comprising a hollow plug body of dielectric material, a blade-mounting body of dielectric material mounted in one end of said hollow plug body, the blade-mounting body having electrical contact blades projecting from its front face, means on the rear of said blade-mounting body for connecting said blades to current wires of an electrical cord or cable, a well in an offset segment of said front face, said offset segment and the well therein extending longitudinally across one side of said face, fuse means in the circuit of one blade, said fuse means including fuse-mounting clips in said well, and a thin plate cover member of dielectric material swingably mounted on said front face and movable into and out of covering relationship with relation to said well and lying flush with said front face when said plate is swung to overlie said offset segment and the well therein.
2. An electrical plug as claimed in claim 1, said thin plate being connected by pivot means in said offset segment to said front face.
3. An electrical plug as claimed in claim 2, said a thin plate having a projecting arm, and said pivot means being a pin pivotally connecting said arm to said front face, and said arm lying flush with said front face and said plate when said plate is swung to overlie said offset segment and the well therein.
4. A dead front, back-wired electrical plug with a front-accessible fuse comprising a hollow plug body of dielectric material, a blade-mounting body of dielectric material mounted in one end of said hollow plug body, the blade-mounting body having electrical contact blades projecting from its front face, means on the rear of said blade-mounting body for connecting said blades to current wires of an electrical cord or cable, a well in and extending longitudinally across one side of said front face, said fuse means including fuse-mounting clips in said well, a slot extending transversely across a side wall of said well, and one of said blades being mounted in said slot and extending across said side wall.
5. A dead front, back wired electrical plug with a front-accessible fuse comprising a hollow plug body of dielectric material, a blade-mounting body of dielectric material mounted in one end of said hollow plug body, the blade-mounting body having electrical contact blades projecting from its front face, means on the rear of said blade-mounting body for connecting said blades to current wires of an electrical cord or cable, a well in said front face, fuse means in the circuit of one blade, said fuse means including fuse-mounting clips in said well, said fuse mounting clips being a pair of spaced, fuse-mounting clips mounted in said well, a plurality of recesses in the rearward portion of said blade-mounting body, means mounting one of said blades in one of said recesses in electrical contact with one of said clips, a terminal post with wire-clamping means mounted in one of said recesses by means providing electrical contact with the other of said clips, and the other of said blades extending through said body and having a rearward terminal post positioned in another of said recesses.
6. An electrical plug as claimed in claim 5, said well being located along one side of said front face, a slot extending transversely across a side wall of said well, and said one of said blades being mounted in said slot and extending across said side wall.
7. A dead front, back-wired electrical plug with a front-accessible fuse comprising a hollow plug body of dielectric material, a blade-mounting body of dielectric material mounted in one end of said hollow plug body, the blade-mounting body having electrical contact blades projecting from its front face, means on the rear of said blade-mounting body for connecting said blades to current wires of an electrical cord or cable, a well in said front face, fuse means in the circuit of one blade, said fuse means including fuse-mounting clips in said well, said one of said blades having a laterally extending base portion seated in a recess in the rearward portion of said body directly behind said well, an aperture through said body connecting one end of said well and said recess, and a metal fastener in said aperture and connecting and mounting one fuse-mounting clip in said well and said base portion in said recess.
8. An electrical plug as claimed in claim 7, a terminal post mounted in a further recess in the rearward portion of said body in spaced relation to said one of said blades and its base portion, a second aperture through said body connecting the other end of said well and said last-mentioned recess, and a second metal fastener in said second aperture and connecting and mounting another fuse-mounting clip in said well and said terminal post in said last-mentioned recess.