US 2988617 A
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Description (OCR text may contain errors)
June 13, 1961 M. GRAZIQSI 2,988,617
THREE WIRE SAFETY FUSE ADAPTER, GROUNDING TYPE Filed July 25, 1959 INVENTOR. MICHAEL 6RAZ|0$I FIG 8 0 BY mwmuk ATTORNEYS United States Patent 2,988,617 THREE WIRE SAFETY FUSE ADAPTER, GROUNDING TYPE Michael Graziosi, 383 2nd St., Jersey City, N .J Filed July 23, 1959, Ser. No. 829,020 8 Claims. (Cl. 200'115.5)
This invention relates to electrical plug connectors, and more specifically to a new and advantageous form of fused electrical connecting device adapted for making a grounding connection.
Attachment caps in common use employ two parallel and identical blades for insertion into a receptacle. An indeterminate one of the blades is thereby connected to the energized or hot line, while the other is connected to a wire which ordinarily is grounded. In some specialized applications, such as for shipboard use, neither line is grounded, and in no case by this system is it possible to identify with certainty any wire at the appliance itself which will be connected to ground when the appliance is plugged in. When an appliance has any portion of its exterior made of metal or a conductive material, leakage or fault current can flow into this conductive portion, and if touched by a person who is himself grounded as by standing on the ground, such current can cause an undesired shock unless such frame is reliably grounded. Even in the absence of leakage or fault current, such an effect is common when the electrical capacity to the frame is sufficient, and this effect is usually the more pronounced when a better grade of insulation is used. So serious are these dangers in the case of electrical devices used in damp locations or outdoors that the numerous resultant fatalities have induced changes in the National Electrical Code promulgated by insurance underwriters groups and embodied in many codes and ordinances having the effect of law. Positive grounding of the exterior conductive frame of such devices by means of a third supply wire is thereby required and manufacturers now frequently provide devices equipped with such a third and grounding wire in the supply cable of the device. The supply cable is terminated either in a three-prong connector plug, which can not be used with most of the receptacles now in existence, or in a common parallel blade plug and an extended grounding wire, dangling and unconnected. Neither of these arrangements can provide a convenient means for quickly connecting such an appliance to an ordinary outlet in a safe manner, and it is a purpose of this invention to provide means for doing so.
Branch circuits in domestic use for accommodating the type of equipment described are ordinarily of the kind rated for amperes maximum load, but because of the increasing use of electricity in the home are often fused well in excess of this rating, or even provided with slow blow fuses capable of sustaining for a short time, very heavy loads such as are requested for starting large motors.
Under these circumstances, safety of portable equipment and tools is prejudiced, even where a third wire ground is used as described above, because short circuit currents can develop a dangerous voltage drop in the long third wire and the connections thereto, which in this case, is necessarily directly communicated to the erson, under the most efiective contact conditions. Even when the circuit is properly fused, it is often the case that the ground wire connection is formed through a steel sheath on the house wiring cable, and includes numerous mechanical connections of indifferent electrical quality.
For these reasons I find it desirable to provide a connecting device which contains its own fuses, of an appropriate rating less than that of the branch circuit fuses,
Patented June 13, 1961 "ice and by which means the above described difficulties peculiar to third Wire portable electrical devices are entirely overcome. In addition to the advantages above mentioned, it will be apparent that by using smaller fuses than the branch circuit fuses in the instant device, they can be induced to blow preferentially, thus protecting the larger fuses from damage.
There is thereby avoided the difficult task of locating and replacing blown branch circuit fuses, the interruption of current to other devices operating from the same branch circuit which may include electric clocks which require resetting upon fuse replacement, and the possibility of blowing the more expensive main fuses which occasionally blow in preference to the branch circuit fuses upon occurrence of a short circuit.
These and other objects of the instant invention I obtain by the employment of a wiring device which comprises, in one of its forms, an insulative body member containing a pair of removable fuse cartridges and having a parallel bladed connector body provided with either a third pin for ground wire connection or a loose wire for making permanent ground connection to a convenient grounding screw usually provided On the outlet box, or elsewhere, and having a three pin receptacle comprising a part of the device.
Another object of this invention is to provide an attachment means for portable appliances having a grounding connection which is usable with safety on any branch circuit regardless of how heavily such circuit may be fused.
A further object of the invention is to provide such a means wherein a grounding connection to the appliance is maintained when the appliance is turned off by means of a switch on the appliance which interrupts the normally grounded line.
Still another object is to provide such a means wherein an appliance ground is maintained despite the blowing or absence of one or more fuses in the attachment means.
A fuller understanding of these and other objects of the invention and their mode of attainment may be had by reference to the drawings, wherein:
FIG. 1 is a view of the assembled connector of the instant invention;
FIG. 2 is a view of the interior portion of FIG. 1;
FIG. 3 is a view of the cover portion of FIG. 1;
FIG. 4 is a top view of FIG. 2;
FIG. 5 is a section taken on the line 5-5 of FIG. 4;
FIG. 6 is a view of conductive portions of FIG. 2;
FIG. 7 is a view of conductive portions of FIG. 2;
FIG. 8 is a view of a modification of FIG. 7;
FIG. 8a is a view of a portion of FIG. 8; and
FIG. 9 is a view of a section taken on line 9-9 of FIG. 5.
Turning now to the drawings, it will be seen that the numeral 10 designates the instant appliance generally, and that the same comprises an open ended exterior casing 12 retained on the body section 14 by a screw 16 through a hole '18 in the casing and into a tapped hole 20' in the body section. Casing 12 is preferably constructed of an insulating material such as a laminated phenolic plastic material, but this is not imperative, and metal may be used in cases where extreme strength and durability are of importance. Body section 14 must be constructed of an insulating material and because of its shape, which contains no undercuts or blind cavities may be molded conveniently and at a high rate of speed on plastic molding machines.
One end of fuses 20 is retained in fuse clips 22 and fuses may be of the widely available glass, or of the ceramic body type, appropriately sized to the load. Clips 22 are retained in convolutions of fitting 24 which is of conductive material and convoluted to form an adequate spring loaded female prong connector socket portion 26 on one end thereof, fastened to body section 14 by the screws 26 into tapped holes therein, the threads whereof may be formed by the employment of self tapping screws as the screws 26'. The other ends of fuses 20 are retained in fuse clips 28 fastened to fittings 32 having contact prong portions 34 protuberant from the body section 14, and retained therein by the screws 36 therethrough. Clips 28 have no portions convergent over the ends of fuses 20, and are aligned with holes 38 in the casing 12, which are larger in diameter than the diameter of fuses 20. Small holes 42 in the body section 14 thus enable any round instrument of small diameter to be thrust into holes 42 to eject the fuses through the holes 38 without opening the device, and fuses may be replaced by a reverse procedure. For this reason it is unnecessary to open the device under any circumstances, and possibility of damage to the internal components is greatly reduced.
A grounding pin socket 44 is fastened to a mounting member 46 by a flat head screw 48 through a septum 52 in body portion 14, access thereto being had through opening 54 into the cavity wherein it is retained. A prong 56 is fastened to member 46 by bolt 57 for insertion into an outlet having provision therefor. In cases where no such provision is made, a flexible wire 58 having terminals 6'2 and 64 is employed in substitution of the prong 56, fastened to the member 46 through the terminal 62 in the same manner by bolt 57, and protruding through a slot 66 in casing 12 for connection to the mounting screw 68 customarily used for retaining the wall plate of a receptacle to the outlet box, and solidly grounded thereby. The use of a spade lug terminal 64 on the distal end of wire 58 renders it unnecessary to completely remove such mounting screw in order to make connection thereto, which is advantageous because such screws are frequently long, and the wall plate will drop off if they are completely removed although this will not occur if they are merely loosened enough to permit engagement thereunder of the terminal spade lug 64.
Although this invention has been described in terms of a specific illustration example thereof comprising the preferred embodiment, it is to be understood that various modifications and elaborations thereof will occur to those skilled in the art which do not, however, depart from the essential spirit of the invention. It is therefore intended that the invention be limited only by the appended claims.
What is claimed is:
1. In a fused connector for an electrical appliance, a body member of insulating material having cutaway portions for fuse retention and a pair of fuse-aligned fuse ejection access holes substantially smaller than a fuse diameter, a pair of parallel contact blade means protruding from one end of said body member and fastened thereto, first fuse clip means on each of said blade means comprising a pair of jaws adapted for resilient engagement of only the circumference of one end of a generally cylindrical fuse body, a pair of contact blade socket means adapted by reentrant curvature for resilient blade engagement and fastened to said body member in said cutaway portions for engaging blades inserted in an opposite end thereof, second fuse clip means on each of said socket means aligned with and spaced from said first fuse clip means a fuse length distance, grounding blade socket means comprising a resilient clip in parallel alignment with said blade means and fastened to said body member, grounding means therefor, and an open ended housing slidable over said body member and said blade means having apertures of greater than fuse diameter aligned with said clip means, and apertures for said blade means and said grounding means.
2. The article of claim 1 wherein said grounding means comprises a blade of resilient metal having a substantially U-shaped cross section and disposed generally parallel to said pair of parallel contact blades.
3. The article of claim 1 wherein said grounding means comprises a terminal lug on said grounding blade socket means, a length of stranded and insulated wire conductor means having one end thereof electrically connected to said terminal lug, and a terminal spade lug electrically connected to the other end of said conductor means.
4. A safety device for energizing single phase electrical appliances having a distinct grounding wire which comprises a receptacle assembly having dissimilar jacks for connection to a three-pronged polarized cord connector, plug means mounted in opposition thereto and including a pair of parallel contact blades for making connection to a convenience outlet, retaining means for cylindrical fuses mounted on said receptacle assembly, one of said means being connected between each of the parallel blades of said plug means and a different one of said receptacle jacks and characterized by having an open ended construction whereby fuse removal and insertion is accomplished by endwise fuse sliding, grounding means connected to a remaining said jack, and a cover slidably installable over said receptacle and having apertures for fuse removal without removal of said cover.
5. The article of claim 4 wherein said grounding means comprises a grounding pin.
6. The article of claim 4 wherein said grounding means comprises a ground wire and a spade lug termination connected to said ground wire.
7. The article of claim 4 wherein said grounding means comprises a grounding pin of folded sheet metal having a U-shaped cross section.
8. The article of claim 4 wherein said grounding means comprises a grounding pin of folded sheet metal having a U-shaped cross section, the protruding length of said grounding pin being substantially greater than that of said pair of parallel contact blades.
References Cited in the file of this patent UNITED STATES PATENTS 1,291,443 Dorsey Jan. 14, 1919 1,892,567 Craddock Dec. 27, 1932 1,990,176 Fried Feb. 5, 1935 2,597,600 Shapiro May 20, 1952 2,649,522 Marcus Aug. 18, 1953 FOREIGN PATENTS 144,338 Australia Nov. 28, 1951