US3718894A

US3718894A - Resiliently reinforced nema contact

Info

Publication number: US3718894A
Application number: US00110892A
Authority: US
Inventors: W Schumacher
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1971-01-29
Filing date: 1971-01-29
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27

Abstract

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 resilient element acting between the contact and insulating housing.

Description

1 51 Feb. 27, 1973 Uniwd States Patet 1191 Schumacher' .339/255 A X ....339/255 R .339/14 R FOREIGN PATENTS OR APPLICATIONS 541 RESILIENTLY REINFORCEDNEMA 1,555,749 9 1925 Nielsen........................ CONTACT 2,619,516 11/1952 Schneider.... 2,686,297 8/1954 [75] Inventor: Walter C. Schumacher, Warw1ck,

Assignee: General Electric Company 7/1932 Great Britain...................

[22] Filed: Jan. 29, 1971 Primary Examiner-Marvin A. Champion Assistant Examiner-Robert A. Hafer 21 Appl. No.: 110,892

Attorney-Paul E. Rochford, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman [52] US. Cl........339/217 IS, 339/255 R, 339/259 R [51] Int. Cl. 9/08 ..339/l4,l54, 156,174, 217,

ABSTRACT Improved contact pressure on power blades of an [58] Field of Search......

electrical cap is provided by an electrical contact [56] References Cited UNITED STATES PATENTS 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 e h f n e e w e b g S .m m d g a i t F g m. .m g w mm m S WW D m 3 u S, .m Th m aw C vrm 3 Mm ea 3 a t .mm me 8 s n 295/ /559 922 WW 33 n. m1 mm m 6.1 TK 650 654 999 111 Ill 24 l 9l 11088 2 36002 3082 3223 2/1962 Stepoway.....................

PATENTED [[827 I873 In van for Ma Her C Sc/wmac/zer By PM swig! A ffwwey RESILIENTLY REINFORCED NEMA 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 furtherincreased. 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 ap preciated 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.

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 inches 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 inches. This standard is that specified by the National Electrical Manufacturers Association NEMA Standards, Publication No. WD2l9 63. According to Federal Specification W-D 596 b (G- SA-FSS) of Oct. 22, 1967 the finish on power blades used in suchtests must be an 8 microinch finish grind in a direction normal to the direction of insertion of the blades.

A co-pending application of the same assignee to i 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 isaccordingly 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 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 housings of outlets. A further object is to provide a means of utilizing existing non-NEMA contact structures in NEMA applications 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 the invention are achieved by a receptacle structure having power blade gripping capability below the NEMA standard in combination with resilient reinforcing elements mounted in the receptacle between the reverse side of the contact fingers thereof and the proximate internal walls of the receptacle to increase the finger gripping hold to above the NEMA level.

The manner in which the objects of the invention may be effectively achieved is described with reference to the accompanying drawings in which FIG. 1 is an exploded perspective view of a receptacle such as is provided pursuant to the present invention.

FIG. 2 is a partial sectional view taken along the line 2-2 of FIG. 1 of the receptacle of FIG. 1 in assembled form.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1 of the receptacle of FIG. 1 in assembled form.

Referring now first to FIG. 1, an exploded view of a conventional receptacle is shown. The receptacle has the usual components including an insulating base having cavities therein for receipt of metal parts. One of these metal parts, a contact strip 12, is shown in place in one of the cavities and another contact strip 14 is shown poised above the other cavity in position for insertion into the cavity.

A metal mounting strap 16 is disposed above the strip 14 so that it can be lowered to its position between the two strips and along the mid-ridge or divider 18 of the base 10.

Cover 20 fits over and holds the various metal parts in place in the base 10 for use with power blades to be inserted through the pairs of

parallel blade slots

22 and 24 in the face of cover 20 as well as perpendicular blade slots 23 and 25.

The pairs of parallel or perpendicular blades pass on either side of the

narrow sections

24 and 26 of mounting strap 16 and into contact with blade contact fingers of

contact strips

12 and 14.

A grounding blade passes through the

larger ports

28 or 30 and contacts

grounding contacts

32 or 34 respectively affixed to the mounting strap 16 in position to be inserted also into well 36 and cavity 38 of base 10.

The contact strips are brass of the conventional composition employed in electrical contacts and has relatively high conductivity and low spring strength. The strip is a'single strip of metal bent into the form of

fingered contacts

40 and 42 at each end of the strip, and having

wire terminals

44 and 46 between the end fingered contacts and a central break off tab 48. The base has side and bottom openings such as 50 for the screws and wires used in delivering power to the receptacle.

The improvement in gripping capability made feasible by this invention concerns use of elements in combination with a conventional receptacle structure such as that described herewith. The combination involves a resilient reinforcement of the more yieldable finger of the fingered contact. One illustration of this reinforcement is the use of neoprene or other high quality high temperature resilient material and the wedging of a piece of this material between the mid-section of the fingered contact and the adjoining insulating wall.

For convenience these resilient elements are referred to as resilient reinforcing elements although it will be understood that they may be formed of a wide variety of materials such as silicone rubbers and the like and may have a variety of forms or shapes. One convenient shape is cylindrical as the rubber can be extruded in cylindrical form and individual elements cut off to length. Other shapes of constant cross-section can also be extruded and cut to usable unit lengths.

center divider 18. The manner in which these elements increase the grip of contact on a blade inserted into the fingered contact will be clear from FIGS. 2 and 3.

Referring first to FIG. 2 a partial section along the line 2-2 of FIG. 1 shows a resilient reinforcing member 80 wedged between a tandem blade 82 and end wall 84. Ascension of member 80 is restrained by overhanging wall surface 86 of cover 20.

Insertion of a power blade between upwardly extending

fingers

87 and 88 increases the compressive force tending to squeeze member 80 against wall 84 and results in a greater gripping force being generated on the inserted blade. The NEMA standards of blade gripping referred to above are met by this cooperation of resilient reinforcing member 80 and

contact fingers

87 and 88 whereas in the absence of member 80 the NEMA blade gripping performance is not realized.

Referring now to FIG. 3, the use of resilient reinforcing elements to improve the blade gripping capability of a conventional receptacle for blades in parallel orientation is described.

FIG. 3 is a sectional view of the interior of the receptacle of FIG. 1 but in assembled form as viewed from one end of the receptacle. v

The contact strips 12 and 14 are seen from their respective ends. The base 10 and cover 20 are seen primarily in section.

The cylindrically shaped resilient reinforcing element 60 is compressed between finger 62 and surface 64 one of the internal surfaces formed by divider 18. A power blade entering the receptacle through port 24 separates finger 62 further from the other fingers and increases the compressive force on element 60. With the cooperation of the resilient reinforcing element the finger contacts exert NEMA standard of grip on power blades whereas in the absence of the resilient reinforcing elements the NEMA contact pressure is absent.

In the right side of the receptacle of FIG. 3 a rectangular resilient reinforcing element is present and is compressed into the shapeseen in the figure between finger 71 and divider 18.

What is claimed is:

1. An electrical receptacle comprising an insulating housing,

said housing including an insulating body and a cover, fingered contacts of brass of relatively high conductivity and low spring strength within said housing blade openings in said cover aligned with blade contact fingers rising from contact strips in said base,

at least one finger of said contacts being reinforced with a resilient rubber reinforcement wedged between the mid-section of the reverse side of said contact finger and an internal wall of said insulating-housing,

the upper portion of said finger being free to deflect against its inherent spring strength.

tact fingers rising from contact strips in said base, and at least one finger of said contacts being reinforced with a resilient rubber reinforcement wedged between the mid-section of the reverse side of said contact fingers and an internal wall of said insulating housing, said rubber reinforcing member being held in its wedged position by a shoulder of the cover pressing down on the member.

* a: a: a;

Claims

1. An electrical receptacle comprising an insulating housing, said housing including an insulating body and a cover, fingered contacts of brass of relatively high conductivity and low spring strength within said housing blade openings in said cover aligned with blade contact fingers rising from contact strips in said base, at least one finger of said contacts being reinforced with a resilient rubber reinforcement wedged between the mid-section of the reverse side of said contact finger and an internal wall of said insulating housing, the upper portion of said finger being free to deflect against its inherent spring strength.

2. The structure of claim 1 in which the rubber reinforcement is of the more yieldable finger of the fingered contact.

3. An electrical receptacle comprising an insulating housing, said housing including an insulating body and a cover, fingered contacts of brass of relatively high conductivity and low spring strength within said housing blade openings in said cover aligned with blade contact fingers rising from contact strips in said base, and at least one finger of said contacts being reinforced with a resilient rubber reinforcement wedged between the mid-section of the reverse side of said contact fingers and an internal wall of said insulating housing, said rubber reinforcing member being held in its wedged position by a shoulder of the cover pressing down on the member.