US 3662324 A
Improved contact pressure on power blades of an electrical cap is provided by an electrical contact formed to accept power blades in two orientations at right angles. The contact is made of a strip of metal of high conductivity and low spring properties and is reinforced by a metal clip of lower conductivity and higher spring properties of a general "U" configuration.
Description (OCR text may contain errors)
I United States Patent [151 3,662,324 Schumacher May 9, 1972 54] REINFORCED ELECTRICAL CONTACT FOREIGN PATENTS OR APPLICATIONS  Inventor: Walter C- S h m h W k, R 1,487,407 2/1966 Germany ..339/259 F  Assignee: General Electric Company Primary E.\'ammerMarvin A. Champion  Flled: 1971 Assistant Examiner-Robert A. Hafer  Appl. No.: 111,020 Attorney-Paul E. Rochford, Frank L. Neuhauser, Oscar B.
Waddell and Joseph B. F orman  US. Cl. ..339/255 R, 339/259 R 7 T T  lnt.Cl ..l-l0lr ll/22 [5 1 ABS RAC  Field of Search ..339/252, 253, 255, 256, 259, Improved contact pressure on power blades of an electrical /2 I 165.217 cap is provided by an electrical contact formed to accept power blades in two orientations at right angles, The contact is  References cued made of a strip of metal of high conductivity and low spring UNITED STATES PATENTS properties and is reinforced by a metal clip of lower conductivity and higher spring properties of a general U configural,969,99l 8/1934 Robinson ..339/259 X i 1,990,087 2/1935 Nichols et al. 3,032,736 5/1962 Howells ..339/14 R 1 Claim, 5 Drawing Figures PATENTEDHM 9 I912 3, 662,324
In yen/or [Ha/fer C Scfiumacher Afforn REINFORCED ELECTRICAL CONTACT The present invention relates to an electrical wiring device and more particularly to a wiring device having electrical contacts of strong prong retaining capability.
The effectiveness of a wiring device for its intended purpose of conveniencing the temporary making and subsequent breaking of electrical connections has been developed to a degree where electrical outlets are provided in most buildings having electrical service. Heavier and heavier currents are available from such outlets for normal household, factory and institutional use as equipment requiring heavier temporary supply of electrical current and greater reliability of supply of current have come into more common use.
Reliability of connection is ensured by use of the locking device type of electrical connector but special electrical caps and receptacles must be provided and these must have specially shaped power blades and receiving connectors.
Greater reliability of maintained connection can be ensured in part by increasing the retentive pressure exerted on a prong by the prong receiving contacts of an electrical connector. However, it is known that materials which have greater capability to conduct electricity will generally have poorer physical and work resistance properties.
One difficulty resulting from the poorer mechanical properties of highly conductive metals used in electrical receptacles is the tendency of the contacts to be sprung by the repeated insertion of the power blades as required to make electrical contact. This is familiar to most persons who have used convenience outlets in older homes. As the contact fingers of conventional convenience outlets are sprung there is a tendency to employ power blades of greater thickness to ensure contact. This has a tendency to cause further spreading of contact fingers and can cause the separation of the contact fingers of new convenience outlets beyond that satisfactory for retaining the thinner power blades under acceptable blade retaining pressure. Poor contact results in heating of the connection. As heating results in oxidation, resistance at the contact is increased and the heating effect is further increased. Hazardous heating under higher loads can result.
While it is highly desirable that the spacing between contact fingers of a convenience outlet remain essentially constant and that the contact pressure exerted on blades inserted between the fingers not diminish due to prolonged usage or due to use of blades of first greater and subsequently of lesser thickness, it will be appreciated that too great a contact pressure can also be detrimental. This is particularly so where the metal of the contact fingers is sufficiently hard as to cause a scoring or cutting of the surface of the blades inserted between the contact fingers. Also, too great a pressure between the contact fingers can require use of an excessive pressure to insert the power blades. This, in turn, can cause too great a pressure of the contact on the housing and can cause deforming or even a breaking of the housing itself.
Similarly where the inserted power blade is held between contact fingers with excessive pressure the withdrawal of the connector can cause excessive force to be used on the current carrying cable attached to the connector. Safety considerations require that the connector be disconnected when the connector or cord is pulled with a force which is reasonable for the intended usage. I
Accordingly, for reliable and safe use the attainment of a contact pressure required for a convenience outlet, such as is described above, is preferably the result of developing between the contact fingers a spring pressure which does not change under repeated cycling with power blades of different thickness.
The National Electrical Manufacturers Association has established standards of blade retention known in the wiring device industry as NEMA standards.
The prescribed standards include the capability of a fingered contact to develop sufficient spring pressure on a smooth steel blade having a thickness of 0.055 inch to hold the blade in the grip of the fingered contact under a pull of 1.5 pounds for 60 seconds after said contact has been subjected to 20 conditioning .cycles comprising the insertion and withdrawal of a smooth steel blade without holes having a thickness between 0.073 to 0.075 inch. This standard is that specified by the National Electrical Manufacturers Association NEMA Standards, Publication No. WD2-l963. According to Federal Specification W-C 596 b (GSAFSS) of Oct. 22, 1967 the finish on power blades used in such tests must be an 8 microinch finish grind in a direction normal to the direction of insertion of the blades.
A copending application of the same assignee to which this application is assigned Ser. No. 871,415 filed Sept. 16, 1968 teaches the formation of a NEMA contact employing an alloy of beryllium in copper. While the contacts formed by this method have the highly desirable properties taught in the application, their cost is high in comparison to contacts and receptacles which do not meet the NEMA standards.
It is accordingly an object of the present invention to provide an electrical contact which meets the NEMA standards.
It is another object of the present invention to provide an electrical contact strip which has the desirable high spring contacts at the fingered end portion thereof but which also has an easily broken off circuit separating tab at the mid-portion thereof.
Another object of the present invention is to provide a low cost contact and contact strip which meets the NEMA standards.
Still another object of the present invention is to provide a reinforced contact for a receptacle which fits into the existing housing of outlets by a reinforcement of the contact which consumes a minimum of space.
Other objects will be in part apparent and in part pointed out in the description which follows.
In one of its broader aspects the objects of this invention are achieved by providing an electrical contact comprising a contact strip of metal of high conductivity and low spring properties, said strip having three contact fingers extending up from a common base to provide two contact slots in T formation, two fingers of said contact being parallel to the base of the T and on opposite sides thereof and a third or cross finger being parallel to the cross member of the T and disposed above said cross member, a spring reinforcing clip for said contact, said clip being generally U-shaped, one upright of said U embracing the cross finger of saidcontact and having its upper end bent inwardly to bear against an upper portion of said cross finger, the other upright of said U being forked at its upper portion and the upper end of said fork being bent inwardly to engage the outer surfaces of said parallel fingers to add spring bias to resist the spread of said fingers.
The manner of achievement of the above objects will be better understood by reference to the accompanying drawings in the description which follows wherein:
FIG. 1 is an exploded view of a receptacle of the present invention showing the relation of a spring clip to the contact strip.
FIG. 2 is a top plan view of the receptacle showing the clip in place on the contact fingers.
FIG. 3 is a vertical section taken along the line 3-3 of FIG. 2 and showing power blades in place in the receptacle.
FIG. 4 is a detailed perspective view of a form of clip as used in this invention prior to bending into form for use.
FIG. 5 is a'perspective view of the clip of FIG. 4 after being bent into form for use.
Referring first now to FIG. 1, the several parts of a conventional receptacle are seen.
This includes the base 10, contact strip 12, mounting strap 14, and top or cover 16.
One of the contact strips is shown with its reinforcing clips provided pursuant to this invention in place in base 10.
The other contact strip is seen in its exploded position poised above the cavity into which it fits in base 10. One clip is in place at the upper contact and the other clip is shown in its exploded position between the contact with which it is as sociated and the cavity into which the clip reinforced contact fits.
Above both the base and contact strip the mounting strap is disposed to display the parts thereof and its relation to the receptacle base as well as the cover.
The base has the conventional array of parts and in fact one feature of the present invention is that improved receptacle performance can be achieved for receptacles of conventional construction without modification of the molded plastic or of the formed metal parts but simply by use in conjunction with an existing receptacle of unique reinforcing spring clips.
Accordingly, base 10 is a molded base of a conventional receptacle and is used without modification in connection with the present invention. Base 10 has four cavities, two of which are elongated longitudinally extending cavities and 22 into which contact strips 12 and 24 are insertable.
These cavities have conventional side and bottom openings and internal ribs and other configuration which receives the contact strips and holds them securely during use of the receptacle.
The two other cavities are grounding cavities 26 and 28. Contact 30 of mounting strap 14 fits into cavity 26 so that grounding blades received through blade port 32 of cover 16 are accommodated in the receptacle.
- Similarly grounding port 34 of cover 16 receives grounding blades and these blades pass into cavity 28 of base 10 contacting grounding contact 36.
Turning now to contact strip 12 it is evident that this strip has a conventional form having fingered blade contacts at each end, two wire terminals 38 and 40 adjoining the end blade contacts and having a break off tab 42 at the mid-section of the strip.
The mounting strap 14 has screw holes 44 and 46 at each end for screws used in mounting the assembled device into a wall box. Conventional plaster ears, and holes for assembly screws are also incorporated in the strap. Grounding wires may be attached at screw terminals formed in grounding tabs 50 and 52 as needed.
Cover 16 has two pairs of power blade entry ports 54 and 56. Each pair has a single parallel slot and a slot in T form with the cross member of the T parallel to the parallel slot. Power blades are inserted in pairs into these pairs of slots, each blade pair being either alligned in parallel relation or at right angles.
The action of the reinforcing clips of this invention in improving the gripping action of the contacts on power blades inserted into contact therewith is described with reference to FIGS. 2, 3, and 4.
Referring first to FIG. 4 one form of reinforcing spring clip usable in connection with this invention is illustrated. The clip has a unique capability of reinforcing the contact fingers alligned to receive the parallel blades i.e., the blades lying generally parallel to the longitudinal axis of the receptacle as well as the perpendicular blades, i.e., the blades the lateral extent of which is positioned generally perpendicular to the longitudinal axis of the receptacle.
The clip as illustrated in FIG. 4 is in an open position in which mounting on a contact strip is facilitated and may be done with hand pressure. After mounting on the strip, the clip fits into the cavity by an interference fit so that as it is pressed into the cavity it closes about and comes into position to exert spring pressure on the blades.
The form of the clip as it is aligned after being pressed into the base is seen in FIG. 5.
Referring now to FIG. 5, the clip is seen to have a general U formation with each of the uprights of the U bent inward at their upper portions. The base 60 of the U is generally flat to match the flat bottom of the cavities in the receptacle base and the fiat configuration of the bottom of the fingered contacts at each end of strip 12 of FIG. 1. The right hand upright 62 reinforces the finger which receives the parallel blade.
This reinforcement is evident in FIG. 3 for example where base 60 is seen bottomed in the cavity of base 10 and upright 62 rises between the lower part 82 of finger 84 and the insulating wall 86 of base 10.
An upper part 64 of the clip is bent in to bear against the upper portion of finger 84 and to urge it toward the opposing upright of the clip.
T e manner in which the finger such as 84 bears against a parallel blade under the urging of a clip is seen in the right hand portion of the FIG. 3. Blade is shown inserted in place and bearing against the vertical edges 92 of the fingers positioned to receive a blade oriented perpendicularly to the long axis of the receptacle.
The flat forward surface of finger 94 bears against the opposite side of blade 90 under the urging of the spring clip upright 64 pressing against the back of the finger 94.
In the left hand side of FIG. 3 a blade is shown inserted into the fingered contact to the left side of the figure and oriented perpendicular to the long axis of the receptacle of FIG. 3.
The left upright 66 of the clip is seen bent into position to bring the prongs 67 and 68 onto either side of the upwardly extending fingers 87 and 88 as best seen in FIG. 2.
Referring again to both FIG. 3 in which blades are illustrated in place in the receptacle and to FIG. 2 where the blades are absent, a blade 100 brought into position through port 57 in cover 16 spreads blades 87 and 88 apart and into spring contact with prongs 67 and 68 of upright 66 of the reinforcing U clip. Blade 100 may also press against finger 84 but this is not necessary to achieve the N EMA contact performance as the blades 87 and 88 as reinforced by spring clip upright 66 achieve this level of blade retaining performance.
As is seen at the right hand side of FIG. 3 the straight portion 66 of the forked upright of the clip bears against the lower portion of the parallel fingers 106. Accordingly, the clip exerts a first compressive spring pressure on the fingers when a blade such as 90 is in place in the fingered contact. This is distinct from a second compressive spring pressure exerted at right an gles to the first pressure in urging the parallel fingers together when a blade such as 100 is therebetween as seen in the left hand side of FIG. 3.
A novel feature of the present invention is the use of a metal contact of higher conductivity and lower spring compression properties to receive power blades in two orientations at right angles to each other in combination with a metal clip of lower conductivity and higher spring compression properties where the reinforcing spring clip acts on the fingered contact to compress the fingers thereof together in two directions at right angles to each other.
The reinforcing clip may be made from spring steel as for I example SAE 1095 and having a Hardness and Temper of Rockwell A 73-75. A strip of 0.0l8 mil has been demonstrated satisfactory.
What is claimed is: 1. An electrical contact comprising a contact strip of metal of high conductivity and a low spring properties said strip having three contact fingers extending up from a common base to provide two contact slots in T formation therebetween, two fingers being parallel to the base of the T and on opposite sides thereof a third finger being parallel to the cross member of the T and disposed above said cross member, a spring reinforcing clip for said contact said clip being generally U shaped one upright of said U embracing the cross finger of said contact and having its upper end bent inwardly to bear against said cross finger, the other upright being forked at its upper portion and the upper end of said fork being bent inwardly to engage the outer surface of said parallel fingers to add spring bias to resist the spread of said fingers.