US3775727A

US3775727A - Electrical adapter for converting two-hole receptacle into three-hole receptacle with equipment ground

Info

Publication number: US3775727A
Application number: US00224582A
Authority: US
Inventors: M Wise
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-02-08
Filing date: 1972-02-08
Publication date: 1973-11-27
Anticipated expiration: 1990-11-27

Abstract

An electrical adapter which will convert a standard two-hole receptacle into a three-hole receptacle having an equipment ground. The equipment ground connection is established by the adapter through the two-hole receptacle by selective arrangements within the adapter utilizing the grounded housing or selectively the grounded neutral conductor of the two hole receptacle. Means to indicate the polarity of the receptacle and adapter conductors as well as indicating whether equipment ground has been established are additional features associated with the adapter.

Description

United States Patent 1191 Wise Nov. 27, 1973 [5 ELECTRICAL ADAPTER FOR FOREIGN PATENTS OR APPLICATIONS CONVERTING TWO-HOLE REC PT C 1,447,370 6/1966 France 339/14 P INTO THREE-HOLE RECEPTACLE WITH 1,359,840 3/1964 France 339/32 M EQUIPMENT GROUND P E M A Ch ,3 3 V rzma xammerarvm am 1011 [76] Inventor: Melvm wlse 223 Beliewood Assisu zt Examiner-Robert A. Hafer w Avenue Daytonlohlo 45406 Attorney-Melvin Wiviott [22] Filed: Feb. 8, 1972 [21] Appli No.: 224,582 [57] T T An electrlcal adapter WhlCh W111 convert a standard two-hole receptacle into a three-hole receptacle hav- 14 339/31 5 R ing an equipment ground. The equipment ground con- Ilft. action i established the adapter through the

twoof Search

32, 33, 34, hole receptacle selective arrangements the 14, 154, 155, 157 adapter utilizing the grounded housing or selectively the grounded neutral conductor of the two hole recep- 1 References Cited tacle. Means to indicate the polarity of the receptacle UNITED STATES PATENTS and adapter conductors as well as indicating whether 3,131,013 4/1964 Carlson 339/14 R equipment ground has been established are additional 3,171,113 2/1965 McNamara... 340 255 features associated with the p 3,626,354 12/1971 Banner 339/14 R 2,792,561 5 1957 Cohen 339 157 11 Clams 6 "3" F'gures 3,382,355 5/1968 Prifogle et a1 339/14 R X 2! Z] 3 /Z 13 1 & 1 e

3.9 g j 1 17$ -35 fixfi 5 I Z/ 20 I! PATENTED NOV 2 71975 SHEET 1 [1F 2 PATENTEB NUV 2 7 I975 SHEET 2 [IF 2 FIG-6 ELECTRICAL ADAPTER FOR CONVERTING TWO-HOLE RECEPTACLE INTO THREE-HOLE RECEPTACLE WITH EQUIPMENT GROUND This invention relates to an electrical adapter which converts a standard two-hole receptacle for use with a three pronged electrical plug having an equipment ground. This adapter also provides means to establish an equipment ground from the three pronged plug through the receptacle by selective utilization of the housing or neutral wire of this receptacle. In addition, means are also provided to indicate the polarizion of the receptacle conductors as well as to show whether equipment ground has been established from the three pronged plug through this receptacle.

Because of a need to provide increased electrical safety features, modern electrical equipment is generally manufactured with a three wire electrical cord having a three pronged electrical plug. The third wire of this cord is electrically connected to the outer exposed portion of the equipment which may be electrically conductive, such as a metal housing. The other end of the third wire is normally electrically connected to equipment ground when the three pronged plug is attached to a modern threehole receptacle having an equipment ground. If by accident the hot, high potential wire of the electric cord accidentally makes contact with the equipment housing, a short circuit to ground is provided by the third ground wire of the three-wire grounded system. Thus the operator of the electrical equipment who is in physical contact with the equipment housing does not act as aground and is prevented from receiving an electrical shock and possible injury to himself.

Although virtually all modern electrical equipment is provided with a three-wire electric cord system containing a plug with a corresponding number of three prongs, a basic problem may occur when this equipment is to be used in older facilities. In these older facilities, generally, the only electrical wall receptacles available are two-wire receptacles. Consequently, the question arises as to how to connect a three pronged plug to a two-hole receptacle and still maintain equipment ground. This problem has purportedly been resolved in the past by various means.

One method used in the past has been to employ an adapter having two prongs to plug into the two-hole receptacle and three female elements for receiving the three prongs of a three wire plug. In this type of connection the hot and neutral" wires of the three wire cord are connected through the adapter to the hot and neutral conductors of the two-hole receptacle. The third equipment ground wire from the cord terminates at the adapter and consequently no equipment ground is established from the electrical equipment through the receptacle. With this type of adapter, the equipment operator still is likely to receive a shock if the equipment housing comes into contact with the hot, high potential wire of the electric cord.

Attempts have been made to establish equipment ground by a variety of methods arranged in conjunction with the adapter connecting a three pronged plug to a two-hole receptacle. One method has been to have a ground wire connected to the third equipment ground conductor within the adapter with suitable connection means at the distal end of the ground wire for attachment to the cover plate mounting screw of the two-wire receptacle. The screw holding the cover plate unto the receptacle is grounded through this receptacle housing when the housing is at ground potential. Industrial and commercial installations have been required for a number of years by the National Electrical Code to use a metalic covered conductor, such as B-X cabling orconduit, when installing wall receptacles. Consequently, the receptacle housing is normally grounded through the B-X cabling or conduit.

Another method of establishing equipment ground in the past has been to remove the fastening screw holding the receptacle cover plate in place. A second longer electrically conductive screw having the same diameter and thread dimensions is affixed onto and penetrates through the adapter with electrical contact made within this adapter to the third equipment ground conductor. The threaded end of this second screw is fastened to the receptacle in place of the original fastening screw. If the receptacle housing is at ground potential, the third equipment ground conductor is grounded through the receptacle by being in electrical contact with the second screw which in turn is grounded through the receptacle housing.

One of the biggest problems previously existing in attempting to establish an equipment ground through the two-hole receptacle housing occurred when the receptacle housing for one reason or antoher was not at ground potential. In that event, of course, any electrical connection from an adapter equipment ground conductor to the receptacle housing does not complete the equipment ground circuit and equipment ground does not take place. Quite often the equipment operator using one of the methods previously used in the past to establish ground through the receptacle housing is not aware the receptacle housing is not grounded. Consequently, the operator may not realize he is still susceptible to an electrical shock" if the electrical equipment housing inadvertently comes into contact with the hot, high potential wire of the electric cord.

Other problems existing with past methods of attempting to ground the equipment ground by use of an adapter has been the inability to ascertain whether the two-wire receptacle conductors are properly polarized and whether proper equipment grounding has taken place. Electrical indicating equipment to give polarization and grounding information is frequently not immediately available to the individual using an electrical adapter. Consequently, the user of an adapter generally does not check for correct polarization or whether equipment ground has taken place and just assumes they are correct, This could lead to a potential short circuit and/or lack of correctequipment ground without knowledge of the user of the adapter.

To avoid the problems discussed above, it is desirable to provide an electrical adapter which not only will provide an equipment ground through the two-wire receptacle housing when possible; but also has the capability of providing a second source to equipment ground through the receptacle when receptacle housing ground is not established. This second source of equipment ground can be obtained by utilizing the neutral conductor of the two-wire receptacle. This neutral wire, in older installations, is normally grounded by a lead from the fuse box to a point of ground, such as water pipe. The use of a separate ground and neutral conductor in an old installation may therefore be superfluous since they would normally be grounded to the same source. It is also desirable to have indicating means to show whether there is proper receptacle conductor polarization and equipment ground.

A feature of this invention is to provide a novel type of electrical adapter which has the capability of establishing equipment ground through the neutral conductor of a two-conductor receptacle.

Another feature of this invention is the capability of this electrical adapter to provide equipment ground se- Iectively through a grounded two-wire receptacle hous' ing as well as through the neutral" conductor of this receptacle.

Still another feature of this invention is the utilization of indicating means as a function of the electrical adapter to indicate whether there exists proper polarization of the electrical conductors within the two-wire receptacle with resulting safe use of the adapter.

A further feature of this invention is the utilization of indicating means as a function of the electrical adapter to indicate whether there is proper equipment ground from the adapter through the two-wire receptacle.

Other features and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is an exploded perspective view showing a conventional duplex receptacle, adapter in conformance with the present invention, and three pronged p g;

FIG. 2 is a perspective face view of adapter;

FIG. 3 is a sectional side view of FIG. 2 and attached p g;

FIG. 4 is a front elevational view of adapter with parts broken away;

FIG. 5 is a secitonal view taken along line 55 of FIG. 4;

FIG. 6 is a fragmentary view of adapter similar to FIG. 4 with polarity and ground indicating circuits shown.

In the embodiment shown by FIGS. 1 and 2, electrical adapter 10 contains two pair of male

electrical connector elements

11, 12 and 13, 14, respectively. These male connector elements are inserted into associated female

electrical connector elements

41, 42, and 43, 44, respectively, of two-hole receptacle 40 when the electrical adapter 10 is attached to receptacle 40. Female

electrical connector elements

42 and 44 of receptacle 40 are oriented to be at an electrically hot potential in a normal standardized polarized position. Female

electrical connector elements

41 and 43 of receptacle 40 are oriented as being electrically neutral. Consequently, when electrical adapter 10 is attached to receptacle 40,

male connector elements

12 and 14 are electrically hot and male connector elements 11 and 13 are electrically neutral.

Also on the face surface 15 of adapter 10 is affixed a conductive contact element 16. This conductive contact element 16 is in physical abutment with electrically conductive cover plate fastener 45 of receptacle 40 when adapter 10 is attached to receptacle 40. The coverplate fastener 45 is at ground potential when the receptacle housing it is attached to is at ground potential. The receptacle housing would be at ground potential when there is electrical contact with B-X cabling attached thereto or some other grounding means. Consequently, conductive contact element 16 is at ground potential when in abutment with coverplate fastener 45 at ground potential.

As shown by FIG. 3, a three pronged plug 30 is attached to adapter 10 to enable plug 30 to become electrically connected through adapter 10 to two-hole re ceptacle 40.

Prongs

31 and 32 of electric cord plug 30 are inserted into

female elements

17 and 18 of adapter 10.

Female elements

17 and 18 of adapter 10, in turn, are electrically connected to male elements 1 1 and 12, respectively, of adapter 10. Accordingly, when adapter 10 is attached to receptacle 40; male element 12 of adapter 10, female element 18 of adapter 10 and prong 32 of plug 30 are all at an electrically hot potential when receptacle 40 is in a normal standardized polarized position. Simultaneously, male element 11 0f adapter 10, female element 17 of adapter 10 and prong 31 of plug 30 are all at an electrically neutral potential. The remaining prong 33 of plug 30 is an equipment ground prong and is inserted into female electrical ground element 19 of adapter 10. Female element 19 is electrically connected to contact element 16 of adapter 10. When contact element 16 is at ground potential due to electrical contact with coverplate fastener 45 which is established at ground potential, female element 19 of adapter 10 is at ground potential. This in turn grounds equipment ground prong 33 of plug 30 which is in electrical contact with female element 19 of adapter 10 when inserted therein.

Similarly,

female elements

24 and 25 of adapter 10 are electrically connected to

male elements

13 and 14, respectively, of adapter 10. Female electrical ground element 26 is electrically connected to contact element 16 of adapter 10.

In order to have a more secure attachment of adapter 10 to receptacle 40, an additional fastening device is used. Fastener 20 is inserted through adapter 10 and is oriented therein so that the front end 21 of fastener 20 is opposite cover plate fastener 45 of receptacle 40 when adapter 10 is attached to receptacle 40. In order to achieve a more secure attachment of adapter 10 to receptacle 40, cover plate fastener 45 is removed prior to attachment of adapter 10 to receptacle 40. When adapter 10 is engaged to receptacle 40, adapter fastener 20 (which is a screw like device having the same thread and diameter dimensions as removed cover plate fastener 45) is screwed into the threaded'opening of receptacle 40 from which cover plate fastener 45 was removed. When fastener 20 is screwed into receptacle 40 a sufficient depth, the head portion 22 of fastener 20 abuts the rear portion of adapter 10 and consequently holds adapter 10 securely against receptacle 40.

In addition to fastener 20 holding adapter 10 to receptacle 40, fastener 20 is electrically conductive and makes electrical contact with

female elements

19, 26 and conductive contact element 16 affixed to adapter 10. Consequently, when fastener 20 is screwed into the housing of receptacle 40 which is at ground potential, fastener 20 is at ground potential and thereby places at ground potential

female elements

19, 26 of adapter 10 to which it is electrically connected. In turn, ground prong 33 of plug 30 which is inserted into female element 19 of adapter 10 is placed at ground potential. Thus it can be seen that fastener 20 serves two functions. One function is to securely fasten adapter 10 to receptacle 40 and the other function is to place prong 33 of plug 30 at ground potential.

In the embodiment shown by FIGS. 4 and 5, features are shown which allow equipment ground to be obtained when the housing of receptacle 40 is not at ground potential and consequently grounding through contact element 16 and fastener 21 is not possible.

Female connector elements

17 and 24 of adapter are electrically and physically connected together by electrically conductive bar 23. Thus

female connector elements

17, 24 and conductive bar 23 are all at the same electrical potential, which is normally electrically neutral.

Female connector elements

18 and 25 of adapter 10 are electrically and physcially connected together by electrically conductive bar 27. Thus

female connector elements

18, 25 and conductive bar 27 are consequently all at the same electrical potential, which is normally electrically positive or hot.

Female ground elements

19 and 26 of adapter 10 are electrically and physically connected together by electrically conductive bar 28.

When ground is not established by conductive bar 28 through electrical contact 16 and/or fastener 21 because the housing of receptacle 40 is not at ground potential, ground can still be obtained by utilizing inventive features embodied within adapter 10. Electrically conductive set screw 35 is threaded through neutral conductive bar 23. The set screw 35 is prevented from being completely unscrewed from bar 23 and is captured in place by means such as pin 36 which is inserted through the end portion 37 of setscrew 35. The setscrew 35 cannot be completely withdrawn from bar 23 because pin 36 thereon will abut bar 23 before setscrew 35 can be completely removed and thereby prevent such removal. When setscrew 35 is rotated in a clockwise direction about its longitudinal axis, the set screw moves forward through bar 23 because of its threaded engagement within bar 23. When setscrew 35 is sufficiently rotated, end portion 37 of setscrew 35 comes into abutment against electrically conductive ground bar 28. Since setscrew 35 is electrically conductive, an electrical connection has been set up between ground conductive bar 28 and neutral conductive bar 23. Consequently, when adapter 10 is attached to receptacle 40 and electric cord plug 30 is attached to adapter 10, the equipment ground prong 33 of plug 30 is electrically connected through female ground element 19 of adapter 10 to ground bar 28; from ground bar 28, electrical connection is made through abutting set screw 35 to neutral conductive bar 23; neutral conductive bar 23 is electrically connected to neutral male electrical connector elements 11 and 13 of adapter 10 which in turn are electrically connected to neutral

female connector elements

41 and 43, respectively, of receptacle 40. Thus the equipment ground prong 33 of plug 30 is electrically grounded through adapter 10 to the neutral conductors of receptacle 40. Consequently, equipment ground is achieved through receptacle 40 even though the housing of receptacle 40 is not at ground potential.

In order to make it relatively easy to adjust setscrew 35 within adapter 10, an access opening 38 in adapter 10 permits a screw driver to be inserted within adapter 10 to allow adjustment of setscrew 35. This access opening 38 would normally be covered by coverplate 39 or other means when access to setscrew 35 is not required.

Another embodiment of this invention is shown by FIG. 6. When adapter 10 is attached to a normally polarized receptacle 40, conductive bar 27 is electrically hot" and conductor bar 23 is electrically neutral."

With this receptacle orientation established, proper equipment ground is established through the housing of receptacle 40 and/or receptacle 40 neutral conductors. Occasionally, however, an older receptacle has been wired backwards and could cause electrical problems with any plug and/or adapter plugged into it. To ascertain whether receptacle 40 is correctly polarized, adapter 10 embodies a polarity indicating electrical circuit which indicates what the actual polarity of receptacle 40 is prior to the time a piece of electrical equipment is plugged into electrical connection with this receptacle. This polarity indicating circuit is electrically connected at one end 51 to conductive bar 27. The other end 52 of this circuit is electrically connected to a conductive push button element 53 which protrudes through chassis 54 of adapter 10. This conductive element 53 could be a washer or other such piece of hardware but is shown as a conductive push button element 53 of electrical switch 55. Intermediate ends 51 and 52 of the polarity indicating circuit is an indicating device, such as neon lamp 56. When electrical switch 55 is in a normally open position, there is electrical connection from conductive bar 27 through neon lamp 56 to conductive push button element 53. When adapter 10 is attached to receptacle 40 which is correctly polarized, conductive bar 27 is electrically hot. This polarization is indicated by placing conductive push button 53 at ground potential by attachment to a ground. This grounding could be done simply by a person touching push button 53 and establishing a weak ground through his body. Thus when conductive bar 27 is electrically hot at one end of the polarity indicating circuit and electrically conductive push putton 53 is placed at ground potential at the other end of the circuit, current flow takes place through this circuit and goes through neon lamp 56 which then glows. This glowing indicates that conductive bar 27 is at a hot potential reflecting the current polarization of receptacle 40. If the polarization of receptacle 40 was not correct, conductive bar 27 would not be hot and consequently no current would flow through the circuit to push button 53 which is at ground potential. The neon lamp 56 would not light up and it would immediately be established that receptacle 40 was not properly oriented. If this were true, receptacle 40 might have to be rewired to establish correct polarization; or the adapter 10 rotated around to put the adapter 10 male elements (if the prongs are not polarized) into opposite receptacle 40 female elements and thereby reverse the polarity.

There is very little risk that a person touching push button 53 would get little more than a tingle when conductive bar 27 is at a hot potential. There is little current flow due to neon lamp 56 being in the circuit between the push button 53 and conductive bar 27 and also because of the weakness of a ground caused by a person touching conductive push button 53. However, as an extra safety feature, a current limiting device 57 can be inserted in the circuit to positively assure that the current flow is sufficiently limited to prevent injury to a person touching conductive push button 53.

Still another embodiment of this invention is shown by FIG. 6. To ascertain whether equipment ground has been properly established, adapter 10 comprises a ground indicating electrical circuit. This circuit shares a part of the polarity indicating circuit described above. When push button 53 is depressed, switch 55 contact at switch contact element 58 is broken and a new contact at switch contact element 59 is made. This new switching arrangement establishes a ground indicating circuit from electrically conductive bar 27 (at electrical connection 51) through neon lamp 56 and switch contact element 59 to electrically conductive bar 28 (at electrical connection 61). When adapter 10 is attached to normally polarized receptacle 40, electrically conductive bar 27 is at a hot potential. Simultaneously, electrically conductive bar 28 is at ground potential by electrical connection through either conductive contact element 16 (FIG. 2) and/or fastener 20 (FIG. 3) when they are in electrical contact with the grounded housing of receptacle 40. As a result, an electrical current flows from conductive bar 27 to electrically conductive bar 28. This current flow causes neon lamp 56 in the circuit to glow which indicates that proper grounding has taken place.

If for some reason the housing of receptacle 40 is not at ground potential, obviously conductive element 16 (FIG. 2) and/or fastener 20 (FIG. 3) are not at ground potential. Therefore, electrical connection of conductive element 16 and/or fastener 20 with conductive bar 28 will not put conductive bar 28 at ground potential. Consequently, there wil! be no current flow from electrically hot conductive bar 27 to conductive bar 28 and neon lamp 56 will not glow. Conversely, it can be seen that when the neon lamp does not glow, it indicates there is not current flow and ground has not been established. In the event that ground has not been established because the housing of receptacle 40 is not grounded, another method of grounding must be applied. As previously described, electrically conductive set screw 35 in conductive bar 23 is rotated until it advances sufficiently to make contact with conductive bar 28. Thus an electrical connection is established between

conductive bars

23 and 28. Conductive bar 23 is at a negative potential when adapter 10 is attached to a normally polarized receptacle 40. Consequently, conductive bar 28 is at a negative potential and current will flow to it from conductive bar 27 which is at a hot potential. This current flow will cause neon lamp 56 to glow indicating a proper equipment ground has been established through receptacle 40.

It is rare, but possible, that due to incorrect polarization of receptacle 40, conductive bar 23 might be at a hot" potential. This would, through electrically conductive setscrew 35, make conductive bar 28 hot. When push button 53 is depressed to close the ground indicating circuit, a large current flow could then go through switch contact element 59. Therefore, as a safety precaution, electrical insulation material 60 is affixed between push button 53 and switch 55. The person depressing the push button would then be isolated from the current flow and safe from any shock which could result from a large current going through the ground indicating circuit.

While certain embodiments of my invention have been shown and described, it is understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention.

l claim:

1. An electrical adapter attachable to a standard two hole duplex wall receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said electrical adapter comprising a plurality of pairs of male elements, said male elements attachable to said two hole duplex receptacle, the electrically neutral male element of each said pair of male elements being electrically joined together by a first electrically conductive joining element, said electrical adapter comprising a plurality of triple groupings of female elements for receiving the prongs of conventional triple pronged electric plugs, a first and second of said female elements of each grouping electrically connected to the electrical hot and neutral prongs, respectively, and the third of said female elements electrically connected to the electrical equipment ground prong, respectively, of said triple pronged plug during engagement of said triple pronged electric plug with said adapter, said first and second female elements of said adapter electrically connected to first electrically hot and second neutral male elements, respectively, within said adapter which in turn are respectively electrically connected to a first electrically hot conductor and a second neutral conductor of said two hole receptacle when said adapter is attached to said receptacle, the electrical equipment ground conducting third female element of each said triple groupings of female elements being electrically joined together by a second electrically conductive joining element, an electrically conductive elongated member movably engaged to and in electrical contact with one of said electrically conductive joining elements, said elongated member being of a configuration and so positioned as to maintain electrical contact with said one of said joining elements while being selectively projected towards the other of said electrically conductive joining elements until contact is made therewith, said first and second electrically conductive joining elements thereby being electrically connected and thereby electrically connecting said neutral male elements of said adapter with said electrical equipment ground conducting third female elemnts of said adapter and establishing an equipment ground through said adapter neutral male elements and associated said electrically grounded neutral conductors of said duplex receptacle to which there would be connective reception when said adapter is attached to said receptacle.

2. An electrical adapter attachable to a standard two hole duplex wall receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said electrical adapter comprising two pair of male elements attachable to said two hole duplex wall receptacle, the electrically neutral male element of each said pair of male elements being electrically joined together by a first electrically conductive joining element, said electrical adapter comprising a plurality of triple groupings of female elements for receiving the prongs of conventional triple pronged electric plugs, a first and second of said female elements of each grouping electrically connected to the electrical hot and neutral prongs, respectively, and the third of said female elements electrically connected to the electrical equipment ground prong, respectively, of said triple pronged plug during engagement of said triple pronged electric plug with said adapter, said first and second female elements of said adapter electrically connected to first electrically hot and second neutral male elements, respectively, within said adapter which in turn are respectively electrically connected to a first electrically hot conductor and a seocnd neutral conductor of said two hole receptacle when said adapter is attached to said receptacle, the electrical equipment ground conducting third female elements of each said triple groupings of female elements being electrically joined together by a second electrically conductive joining element, an electrically conductive screw-like device engaged to and in electrical contact with one of said electrically conductive joining elements by being threaded therein, said screw-like device being of a configuration and so positioned that rotation thereof advances said screw-like device until contact is made with the other of said electrically conductive joining elements, said first and second electrically conductive joining elements thereby being electrically connected and thereby electrically connecting said neutral male elements with said electrical equipment ground conducting female elements of said adapter and establishing an equipment ground through said adapter neutral male elements and associated said electrically grounded neutral conductors of said duplex receptacle to which there would be connective reception when said adapter is attached to said receptacle.

3. The structure of claim 2 wherein the exterior housing of said electrical adapter defines an access opening therein whereby said electrically conductive screw-like device is accessible without removal of said exterior housing of said adapter, a cover encompassing the defined opening when accessibility to said screw like device is not necessary.

4. An electrical adapter attachable to a standard two hole receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectively electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter further comprising a second selective means of electrically connecting said equipment ground of said adapter to said receptacle when the electrically conductive housing of said receptacle is electrically connected to a source of ground, said second selective means electrically connecting said adapter equipment ground to said receptacle housing thereby establishing an equipment ground between said adapter and said receptacle, said adapter still further comprising a polarity indicating means for indicating the polarity of the electrical cir cuit between said receptacle and said attached adapter, said polarity indicating means indicating whether the electrically hot and grounded neutral conductors within said receptacle are correctly oriented in normal standardized polarized positions therein and thereby establishing whether said adapter and said receptacle are electrically connected to provide a proper ground between said adapter and said receptacle, said polarity indicating means comprising a polarity indicating electrical circuit within said adapter with one terminal point electrically connected to a normally polarized electrically hot male element within said adapter when said adapter is attached to said receptacle, the other terminal point being electrically connected to an electrically conductive hardware item mounted in such a manner as to protrude through the chassis of said adapter, intermediate said terminal points of said circuit and electrically connected within said circuit is an indicating device, said circuit being closed and current flowing therein when said normally hot male element is correctly polarized as a hot male element and said externally accessible electrically conductive hardware item is placed at ground potential by contact with an external ground to complete said circuit, said indicating device activated by such current flow and indicating proper polarization of said receptacle conductors.

5. The structure of claim 4 wherein said polarity indicating electrical circuit comprises a current limiting device therein to limit the magnitude of current within said circuit thereby making said circuit and contact with said externally accessible electrically conductive hardware item therein non-hazardous to humans.

6. An electrical adapter attachable to a standard two hole receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectively electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter further comprising a second selective means of electrically connecting said equipment ground of said adapter to said receptacle when the electrically conductive housing of said receptacle is electrically connected to a source of ground, said second selective means electrically connecting said adapter equipment ground to said receptacle housing thereby establishing an equipment ground between said adapter and said receptacle, said adapter further comprising a ground indicating means to indicate whether there is proper grounding of said equipment ground through said attached receptacle, said ground indicating means comprising a ground indicating electrical circuit with a terminal point electrically connected to an electrically hot male element within said adapter when said adapter is attached to said receptacle, the other terminal point being electrically connected to an equipment ground element within said adapter, intermediate said terminal points of said ground indicating electric circuit are an indicating device and an electrical switch, said electrical switch in a normally open position to interrupt current flow within said ground indicating electrical circuit, said electrical switch selectively positioned in a closed position, said switch in said closed position completing an electrical circuit between said electrically hot male element and said equipment ground element within said adapter when said equipment ground element is connected to ground through said receptacle, said completed electrical circuit activating said indicating device to indicate that equipment ground has been established.

7. The structure of claim 6 wherein said adapter still further comprises a polarity indicating electrical circuit with one terminal point electrically connected to a normally polarized electrically hot male element within said adapter when said adapter is attached to said receptacle, the other terminal point being electrically connected to an electrically conductive hardware item mounted on said adapter, intermediate said terminal points of said polarity indicating electrical circuit and electrically connected within said circuit are an indicating device and said electrical switch, said electrical switch when in a closed position for said polarity indicating circuit completes said circuit allowing current flow therein when said normally hot male element is correctly polarized as a hot male element and said electrically conductive hardware item is placed at ground potential by contact with a grounding element, said indicating device being activated by such current flow and indicating the presence of proper polarization, both said polarity indicating electrical circuit and said ground indicating electrical circuit contain said electrical switch, said electrical switch in a first selective position completing said polarity indicating circuit and disrupting current through said ground indicating electrical circuit, said electrical switch in a second selective position completing said ground indicating electrical circuit and disrupting current through said polarity indicating electrical circuit.

8. The structure of claim 7. wherein said electrically conductive hardware item of said polarity indicating circuit is electrically connected to said electrical switch, said electrical switch in said first selective position completing said polarity indicating electrical circuit comprising said electrically conductive hardware item, current limiting means within said polarity indicating electrical circuit to limit the magnitude of current within said circuit and thereby making said circuit and contact with said electrically conductive hardware item therein non-hazardous to humans; said electrical switch in said second selective position disrupting current flow through said polarity indicating electrical circuit as well as electrically isolating said electrically conductive hardware item from said ground indicating electrical circuit thereby making contact with said electrically conductive hardware item non-hazardous to humans regardless of the magnitude of current within said ground indicating electrical circuit.

9. The structure of claim 7. wherein said indicating device selectively indicates the polarity of said receptacle conductors when said indicating device functions in said polarity indicating electrical circuit and selectively indicates the establishment of proper grounding of said equipment ground when said indicating device functions in said ground indicating electrical circuit.

10. An electrical adapter attachable to a standard two hole wall receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectiveiy electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter comprising a second selective means of electrically connecting said equipment ground of said adapter to said receptacle when the electrically conductive housing of said receptacle is electrically connected to a source of ground, said second selective means electrically connecting said adapter equipment ground to said housing thereby establishing an equipment ground between said adapter and said receptacle, said adapter additionally comprising a polarity indicating means affixed thereto for indicating the polarity of the electrical circuit between said receptacle and said attached adapter, said polarity indicating means indicating whether the electrically hot and grounded neutral conductors within said receptacle are correctly oriented in normal standard-ized polarized positions therein, said adapter comprising a ground indicating means affixed thereto, upon said ground indicating means indicating improper grounding taking place through said receptacle housing and said polarity indicating means indicating correct polarity, said adapter being capable of selectively utilizing said first selective means electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle to establish proper grounding of said adapter equipment ground.

11. An electrical adapter attachable to a standard two hole wall receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectively electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter further comprising a plurality of triple groupings of female elements for receiving engagement with conventional triple pronged electric plugs, the electrical equipment ground conducting third female elements of each said grouping being electrically joined together by a conductive joining element, said conductive joining element being electrically connected to an electrically conductive contact element mounted on the exterior of said adapter, said conductive contact element being in abutment with the electrically conductive cover plate fastener affixed to the housing of said two hole receptacle when said adapter is attached to said receptacle, a second selective means of equipment ground thereby being established from said conductive contact element of said adapter through said receptacle conductive cover plate fastener to said electrically conductive housing of said receptacle which is connected to a source of ground, said adapter still further comprising a second electrically conductive fastener, said second electrically conductive fastener removably affixed selectively to replace said fastener holding said cover plate to said two wire receptacle, said conductive contact element mounted on the exterior of said adapter being of a configuration defining an opening therein of a magnitude allowing said second electrically conductive fastener access there through, said second electrically conductive fastener selectively affixed to said adapter with a portion of said second conductive fastener penetrating said adapter and making electrical contact with said conductive joining element of said electrical equipment ground conducting third female elements, an end portion of said second electrically conductive fastener with a configuration extending beyond said adapter exterior through the opening of said conductive contact element and oriented when said adapter is attached to said receptacle for threaded engagement into the female threaded portion of said receptacle from which said cover plate fastener was selectively removed, said second electrically conductive fastener thereby mechanically hoiding said adapter to said receptacle in addition to selectively establishing another equipment ground from said equipment ground conducting third female elements of said adapter through said electrically conductive housing of said receptacle.

IF 4 l

Claims

4. An electrical adapter attachable to a standard two hole receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectively electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter further comprising a second selective means of electrically connecting said equipment ground of said adapter to said receptacle when the electrically conductive housing of said receptacle is electrically connected to a source of ground, said second selective means electrically connecting said adapter equipment ground to said receptacle housing thereby establishing an equipment ground between said adapter and said receptacle, said adapter still further comprising a polarity indicating means for indicating the polarity of the electrical circuit between said receptacle and said attached adapter, said polarity indicating means indicating whether the electrically hot and grounded neutral conductors within said receptacle are correctly oriented in normal standardized polarized positions therein and thereby establishing whether said adApter and said receptacle are electrically connected to provide a proper ground between said adapter and said receptacle, said polarity indicating means comprising a polarity indicating electrical circuit within said adapter with one terminal point electrically connected to a normally polarized electrically hot male element within said adapter when said adapter is attached to said receptacle, the other terminal point being electrically connected to an electrically conductive hardware item mounted in such a manner as to protrude through the chassis of said adapter, intermediate said terminal points of said circuit and electrically connected within said circuit is an indicating device, said circuit being closed and current flowing therein when said normally hot male element is correctly polarized as a hot male element and said externally accessible electrically conductive hardware item is placed at ground potential by contact with an external ground to complete said circuit, said indicating device activated by such current flow and indicating proper polarization of said receptacle conductors.

10. An electrical adapter attachable to a standard two hole wall receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectively electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter comprising a second selective means of electrically connecting said equipment ground of said adapter to said receptacle when the electrically conductive housing of said receptacle is electrically connected to a source of ground, said second selective means electrically connecting said adapter equipment ground to said housing thereby establishing an equipment ground between said adapter and said receptacle, said adapter additionally comprising a polarity indicating means affixed thereto for indicating the polarity of the electrical circuit between said receptacle and said attached adapter, said polarity indicating means indicating whether the electrically hot and grounded neutral conductors within said receptacle are correctly oriented in normal standard-ized polarized positions therein, said adapter comprising a ground indicating means affixed thereto, upon said ground indicating means indicating improper grounding taking plaCe through said receptacle housing and said polarity indicating means indicating correct polarity, said adapter being capable of selectively utilizing said first selective means electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle to establish proper grounding of said adapter equipment ground.

11. An electrical adapter attachable to a standard two hole wall receptacle, said adapter converting said receptacle into a three hole receptacle having an equipment ground, said adapter comprising means for selectively electrically connecting the equipment ground of said adapter to said receptacle, a first selective means of electrically connecting said adapter equipment ground to the neutral conductor of said adapter and thereby through the grounded neutral conductor of said attached receptacle establishing an equipment ground between said adapter and said receptacle, said adapter further comprising a plurality of triple groupings of female elements for receiving engagement with conventional triple pronged electric plugs, the electrical equipment ground conducting third female elements of each said grouping being electrically joined together by a conductive joining element, said conductive joining element being electrically connected to an electrically conductive contact element mounted on the exterior of said adapter, said conductive contact element being in abutment with the electrically conductive cover plate fastener affixed to the housing of said two hole receptacle when said adapter is attached to said receptacle, a second selective means of equipment ground thereby being established from said conductive contact element of said adapter through said receptacle conductive cover plate fastener to said electrically conductive housing of said receptacle which is connected to a source of ground, said adapter still further comprising a second electrically conductive fastener, said second electrically conductive fastener removably affixed selectively to replace said fastener holding said cover plate to said two wire receptacle, said conductive contact element mounted on the exterior of said adapter being of a configuration defining an opening therein of a magnitude allowing said second electrically conductive fastener access there through, said second electrically conductive fastener selectively affixed to said adapter with a portion of said second conductive fastener penetrating said adapter and making electrical contact with said conductive joining element of said electrical equipment ground conducting third female elements, an end portion of said second electrically conductive fastener with a configuration extending beyond said adapter exterior through the opening of said conductive contact element and oriented when said adapter is attached to said receptacle for threaded engagement into the female threaded portion of said receptacle from which said cover plate fastener was selectively removed, said second electrically conductive fastener thereby mechanically holding said adapter to said receptacle in addition to selectively establishing another equipment ground from said equipment ground conducting third female elements of said adapter through said electrically conductive housing of said receptacle.