US 3710287 A
An electrical plug of the type used with convenience outlet receptacles, but improved by having insulation integral with and effectively faired-in with the prong structure adjacent the plug body so that the conductive portions of the prongs can never be exposed while the plug is carrying current; in various embodiments the prongs are undercut to receive and retain the insulation, are fitted with insulative sleeves of effectively zero obstruction thickness, and have divided portions to receive and retain molded-in-place insulation.
Description (OCR text may contain errors)
United States Patent 1 Eckert 1 Jan. 9, 1973  INSULATED PLUG FOREIGN PATENTS OR APPLICATIONS  Inventor: William F. Eckert, 729 Milyer Lane, 1,048,309 l/ 1959 Germany ..339/196 R Baltimore, Md, 21229 1,181,370 2/1970 Great Britain ..339/196 M Primary Examiner-James A. Leppink V Assistant ExaminerLawrence J. Staab Attorney-John F. McClellan, Sr.
 ABSTRACT An electrical plug of the type used with convenience outlet receptacles, but improved by having insulation integral with and effectively faired-in with the prong structure adjacent the plug body so that the conductive portions of the prongs can never be exposed while the plug is carrying current; in various embodiments the prongs are undercut to receive and retain the insulation, are fitted with insulative sleeves of effectively zero obstruction thickness, and have divided portions to receive and retain molded-in-place insulation.
1 Claim, 6 Drawing Figures PATENTEDJAN 9 I975 3,710,2 7
ATTORNEY INSULATED PLUG can be made by means of paperclips, knife blades, portions of toys, or even in some cases, by direct contact with a portion of the body of the user, particularly when the plug is being inserted or withdrawn.
The problem would arise less often if it were not for the necessity of connecting receptacles and prongs in a positively retentive manner, to avoid too-easy disconnection by dislodging the plug.
Some plugs are provided with cam-locking devices which secure them in place, but in most cases the spring-action of the parts is relied on. in ordinary spring-action plugs, considerable overlap between conductive parts of the plug and of the receptacle is provided, so that when the plug is pushed all the way into the receptacle, substantial friction can be applied.
sures have been made which involve loose or working.
parts, such as, for example, those which can be found in military multi-prong insulators which involve the use of springdoaded precision blocks of insulation sliding on the prongs of the connector or sliding on special ways provided for the purpose.
Some fixed-insulation prongs have been used in the past ,as in jacks, but it is believed that prior to the present invention no flush-insulated convenience outlet plug prongs have been known or used.
Accordingly, it is a principal object of this invention to provide as a new and useful article of commercea safety plug having prongs with continuous, effectively flush insulation fixed along the base portions of the prongs to such extent that contact with the conductor of a receptacle is made only after a portion of the insulated length of the prong is inside the receptacle, and this object comprises also a brief summary of the invention.
The above and other objects and advantages of the invention will become more readily apparent upon examination of the following description, including .the drawings to which reference is now made as follows:
FIG. 1 is a face view and FIG. 2 is a side view of a plug according to this invention;
FlG. 3 is a face view and FIG. 4 is a side view of another embodiment of a plug according to this inven tion; and
FIG. 6 is a side view of yet another embodiment. of a plug according to this invention.
In the Figures, like reference numerals designate like parts.
Referring in detail to FIGS. 1 and 2, there is shown at 10 a two prong electrical plug of the type supplied for use with ordinary household electrical convenience outlets. Each of the flat-shaped metallic prongs, l2 and 14, is reduced in section, at 16 and 18 respectively, in the mannerof undercuts.
The reduced section portion of each prong extends from the insulative base 20 about halfway the length of the prong and includes reductions in both length and breadth of the section. The terminal half including the free end of the prong remains the standard size provided in present electrical practice, as does the electricallead'22 connective portion (not shown) in the base.
An insulator 24, 26 covers each reduced-section portion of the prongs l2, 14, extending from the base 20 to the full-size terminal portion of the prongs. The insulators are made of such dimension as to fill out the undercut portions to the full size of the terminal portions of the prongs, fairing in smoothly with the prongs in both length and breadth.
In operation, the plug is used in the accepted manner, being inserted in the normal way into any ordinary convenience outlet and withdrawn to break the connection when desired. The insulation does not interfere in the leastwith the oper'ationof the plug, since there is no insulative protrusion to catch on the receptacle structure.
However, it will be noted that shook hazards arewith the exposed portions, and no danger of short circuiting. Even when an electrolyte such as salt-water is poured over a wall-outlet towhich a plug made according to this invention is connected, the chance of shorting the plug is very small.
Material for the insulators 24; 26 can be transparent polyvinyl chloride, as indicated in the drawings, or polyethylene, or any other suitable insulation.
The insulation ispreferably molded in place, but if it is rubber, or similarly elastic, it can be stretched over the full-sized ends of the prongs and slid into the recesses. i
With the molded construction, a positive fit'can be assured and danger of cutting the insulation on installation is eliminated,
In either case, the insulation is positively constrained by the width and thickness ledges at the end of the reduced section so thatit cannot be dragged over the prong ends, and abut the plug body in a tight fit at the other end. The tight fit assures that even a knife blade cannot be inserted between the plug body and the insulation without forcing it, in the elastic slip-on insulation version of the invention. In the molded insulation version of the" invention, the insulation flows into all minute irregularities of the reduced section, throughout the length and breadth of the reduced section, so that the insulation cannot be resiliently collapsed on itself, and cannot be displaced without using force sufficient to rip the insulation.
FIGS. 3 and 4 illustrate a molded insulation construction, installed on a plug 300 which is even more tenacious in gripping to retain itself and in protecting the prongs gripped, than the FIG. 1 and 2 embodiment.
In FIGS. 3 and 4, the reduced sections 316, 318 of the prongs 312, 314, extend the same distances along the prongs as in the previous embodiment, but the prongs themselves are divided into plural lengthsjoined at one end at the plug base and at the other end at the full size terminal portion of the prongs.
As shown these lengths may be in four parts, 316a, b, c (d not shown) and 318a, b, c (d not shown).
Insulation 324, 326 is molded on the respective prongs as before, but in this embodiment the insulation also flows into and around the spaces between the plural portions of the prongs. The result is that even though the insulation may be torn loose from the underlying prong structure, it cannot slip off. The insulation can even be slit lengthwise without any possibility of coming loose from the prongs.
The prongs are made to have the divided structure described by punching-out sections of the prong blanks during manufacture, or by any other suitable means. Even though this reduces the theoretical current carrying capacity of the prongs, no conductive problem arises practically since the remaining section is easily left heavier than the cross-section of the wiring 322 used with it. Wear problems are confined to the terminal portion of the prongs, which are full size as noted. Bending stiffness and strength are sufficiently bolstered by application of the plastic reinforcement to prevent distortion in normal use. If desired, rigid porcelain insulation or semi-rigid insulation such as solid Nylon can be molded in place to assure exceptional rigidity.
FIGS. 5, a side view with the near prong removed for exposition, illustrates a version 500 of the invention in which a resilient clip of insulation 524 is snapped in place around each recessed prong base to achieve the same result of insulating it safely. Material for the resilient clip can be insulatively coated spring steel, or merely resilient plastic as shown. The clip is in the form ofa squared C in section, and the ends of the C" do not necessarily abut on installation, but preferably should. If the ends fail to meet, due to individual variation in prong size to which the clip is applied, the line of conductor exposed between the ends of the C should be on the inside of the prong, facing the other prong. This location is least accessible for accidental contact. In addition, there is less chance of opening the ends of the C by accidental contact with external structure when the seam is between the prongs.
It will be appreciated that instead of being merely clipped to the prongs, the squared C structures may be cemented in place.
Taking advantage of extremely thin, tenacious, wearresistant films such as high density polyethylene and the like, it has become possible to provide a plug which has such thin insulation extending along the prongs that, particularly for seldom removed plugs, protection can be provided without recessing the prongs to receive the insulation.
FIG. 6, a side view, shows this embodiment 600 in which the film is preferably thermoplastically applied directly to the base portions of the prongs 614, 612 (not shown). The film can also be applied as a pullover sleeve, as previously described.
This arrangement IS the cheapest n that it can be apthe scope of the appended claims the invention may be practiced otherwise than as specifically described.
What is claimed and desired to be secured by United States Letters Patent is:
1. In a plural prong insulated-base electrical plug of the type adapted for insertion into convenience outlet receptacles and the like, the improvement comprising: each prong having a uniform-depth recessed portion extending from said insulative base to a point intermediate the length of the prong and terminating in a shoulder at said point intermediate the length of the prong, each prong recessed portion being divided by slits into lengthwise extending strips spaced apart and joined at the ends, at least one said slit being through the thickness of each prong and another said slit being through the width of each prong, an insulative covering secured to each prong over said portion of'the prong extending from said insulated base to said point intermediate the length of the prong, the insulative covering extending integrally through and along all said slits between the lengthwise extending strips and being flush with the exterior of the prongs adjacent the recessed portions, thereby preventing the insulative coverings from coming loose from the prongs even when out lengthwise.