Fused Plug Assembly With Spare Fuse Elements

1. Field of the Invention

The present invention relates to fused electrical plugs and particularly to those for use with Christmas tree light sets and other decorative light sets.

2. Description of the Prior Art

Electrical plugs having internal fuses for opening an electrical circuit responsive to excess current flow are in use on decorative light sets. Typical designs are shown in U.S. Pat. Nos. 3,976,967; 4,080,039 and 4,178,061.

Need has arisen for a safe, reliable, cheaper and simpler plug unit having a minimum of parts and in which a fuse is easy to change. There is also a need for a plug unit providing its own spare fuse. The present invention aims to meet these needs.

In accordance with the present invention the use of fuse carriers and fuse access covers has been eliminated by providing a push-in fuse unit having an enlarged head located between the prongs and which can be gripped for removal. The fuse unit is preferably square in cross-section and has an active pair and a spare pair of fuse elements along its four sides, the active pair engaging two sets of contacts provided by the prong members and the wire leads at opposite sides of a socket receiving the fuse unit. The spares can be put into use by removing the fuse unit from the socket and reinserting it after turning it ninety degrees.

FIG. 1 is a side elevational view of a fused plug assembly embodying the present invention;

FIG. 2 is a front plan view of the plug assembly with part of the head of the fuse unit broken away and taken as indicated by line 2--2 of FIG. 1;

FIG. 3 is an enlarged side elevation view of the fuse unit;

FIG. 4 is a rear plan view of the fuse unit taken as indicated by line 4--4 of FIG. 3;

FIG. 5 is a side elevational view of a contact element blank to an enlarged scale;

FIG. 6 is a side elevational view of the contact element when attached to a wire lead;

FIG. 7 is taken as indicated in line 7--7 of FIG. 6; and

FIG. 8 is an enlarged fragmentary longitudinal sectional view taken as indicated by line 8--8 in FIG. 2.

Referring to the drawings it is seen that the fused plug assembly of the present invention comprises a plug body 10, a push-in fuse unit 12, a pair of prong members 14-15, and a pair of wire contacts 16-17 connected to a pair of leads 18-19. The plug body 10 is formed with a central square fuse receiving socket 10a at the front and a pair of standard prong sockets 10b, 10c at the rear.

The fuse unit 12 has a hollow body 12a preferably generally square in transverse cross-section and formed with an enlarged head 12b. Two pairs of fuse element strips 20a-d extend along the four outer faces of the fuse body 12a, one opposite pair 12a, 12c of these strips electrically interconnecting the prong members 14-15 with the wire contacts 16-17 while the other pair 12b, 12d remain as spares.

The prong members 14-15 are alike, but positioned with opposite orientation; hence, only prong member 14 will be described in detail. It is formed by doubling back the brass prong stock from the projecting tip 14a to form an exposed prong 14b of double thickness for insertion into a wall socket or other plug. Within the plug body the prong member has two separated legs, one leg 14c being outwardly offset to extend along the outer side of the prong socket 10b to engage the respective prong 22 of an add-on plug when plugged into the plug body 10. The other leg is bent inwardly and then rearwardly to provide a contact portion 14d exposed to the fuse socket 10a near the mouth thereof. This contact portion 14d is opposed by a contact portion 15d on the opposite side of the fuse socket. The contacts 16-17 are alined with and spaced rearwardly from the contact portions 14d, 15d so that the fuse elements 20a, 20c will engage and electrically interconnect the contacts 16-17 with the contact portions 14d, 15d of the prong members.

As indicated in FIGS. 5-7, contact 16, for example, is formed by slitting a rectangular brass blank at 16a to form an arm 16b which is crimped over the exposed terminal wire portion 18a of lead insulated wire lead 18. The leads 18-19 extend from the contacts 16-17 out the sides of the plug body through a boss portion 10d to connect with the sockets of the first and last light in a string of lights.

It will be noted that the front portion of the plug body 10 between the prongs 14-15 is recessed and tapered to the mouth of the fuse socket 10a to match the enlarged head 12b of the fuse unit. The width of the front part of the plug body 10 is given the same dimension as the standard distance between the prongs 14-15 so that the square head 12b will extend on two of its side edges to the sides 10e, 10f of the plug body while its other two side edges extend into frictional engagement with the opposing inner faces of the prongs 14-15. This frictional engagement together with a relatively snug fit of the fuse body 12 in the fuse cavity 10a keeps the fuse unit 12 in pushed-in position relative to the plug body 10. If desired, one or both of the prong members 14-15 can be dimpled inwardly adjacent the top face of the fuse body to provide a small locking knob 14e (FIG. 8). The fuse body is molded from a sufficiently resilient plastic as to permit the enlarged head 12b to pass the knob 14e when the fuse unit is pushed into the fuse socket 10a. In this regard, it is also preferred to have the fuse body hollow through a major part of its length so that it can yield inwardly to allow for a snug fit of the fuse body in the fuse cavity so that there will be good contact between the fuse elements 10a, 10c and the wire contacts 16-17 and prong contact portions 14d, 15d. At the inner end of the fuse socket 10a it is preferred to provide a projecting portion 10g extending into the open end of the fuse body 12a to guarantee separation of the adjacent ends of the fuse elements 20a, 20c. The fuse elements 20a-d are formed from zinc or aluminum foil about 0.001 inches thick and are secured by a suitable adhesive to the fuse body. The exact thickness and width of the fuse elements of course depend upon the desired fuse rating.

It will be appreciated that the plug body 10 can be injection molded in one piece with the prong members 14-15 and contacts 16-17 and connected wires 18-19 in place in the mold. The body of the fuse 12 can also be injection molded as one piece whereupon the fuse elements 10a-d are attached as by a suitable pressure sensitive adhesive. Hence the plug assembly need only have two plastic parts.

If one of the fuse elements 20a, 20c should sever because of an overload or short circuit, after the difficulty is corrected, the spare elements 20b, 20c can be placed in operation merely by removal of the fuse unit, turning it ninety degrees, and pushing it back into the fuse socket as before. To assist in removal of the fuse unit when desired, the portions 10e', 10f' at the front edges of the sides 10e, 10f of the plug body can be beveled to expose the underside of the overlying portions of the enlarged head 12b of the fuse body.