US3789346A

US3789346A - Electrical coupling with pressure contacts and multiple conductance paths

Info

Publication number: US3789346A
Application number: US00286012A
Authority: US
Inventors: Brick E De
Original assignee: West Virginia Armature Co Inc
Current assignee: Baker Mine Services Inc
Priority date: 1972-09-05
Filing date: 1972-09-05
Publication date: 1974-01-29
Anticipated expiration: 1991-01-29
Also published as: CA956715A

Abstract

Electrical coupling includes a plug and receptacle. The plug has multiple pin contacts engageable within socket contacts in the receptacle. The pin contacts are split expandable tubes telescopically engageable within bores in the socket contacts which are non-expandable. Auxiliary pressure and contact means includes tapered plugs within the socket contacts, pressed outwardly by springs to engage tapered bores in the tubular pin contacts to expand the latter into substantial electrically conductive engagement with the bores of the socket contacts. Two conductive paths are thereby created between each corresponding pin contact and socket contact. One conductive path is established through the outer surface of the pin contact and the bore of the socket contact, and another conductive path is established through the bore of the pin contact and the tapered plug.

Description

United States Patent [1 1 De Brick ELECTRICAL COUPLING WITH PRESSURE CONTACTS AND MULTIPLE CONDUCTANCE PATHS [52] U.S. Cl. 339/89 R, 339/94 R, 339/259 R [51] Int. Cl H01! 13/54 [58] Field of Search... 339/45, 89, 90, 94, 177, 258,

[56] References Cited UNITED STATES PATENTS 5/1966 Harrison et al. 339/89 C 8/1968 Piaget 339/94 R FOREIGN PATENTS OR APPLICATIONS 1/1944 Great Britain 339/89 C 7/1968 1,120,358 Great Britain 339/89 R Jan. 29, 1974 fiiflflEXWi H-IQ QPh Ii-MQQXPQ Attorney, Agent, or F irm-Davis, McCaleb & Lucas [5 7] ABSTRACT Electrical coupling includes a plug and receptacle. The plug has multiple pin contacts engageable within socket contacts in the receptacle. The pin contacts are split expandable tubes telescopically engageable within bores in the socket contacts which are nonexpandable. Auxiliary pressure and contact means includes tapered plugs within the socket contacts, pressed outwardly by springs to engage tapered bores in the tubular pin contacts to expand the latter into substantial electrically conductive engagement with the bores of the socket contacts. Two conductive paths are thereby created between each corresponding pin contact and socket contact. One conductive path is established through the outer surface of the pin contact and the bore of the socket contact, and another conductive path is established through the bore of the pin contact and the tapered plug.

6 Claims, 7 Drawing Figures PATENTEUJAN 29 I974 SHEET 2 OF 3 .om mm ELECTRICAL COUPLING WITH PRESSURE CONTACTS AND MULTIPLE CONDUCTANCE PATHS BACKGROUND OF THE INVENTION The field of invention includes electrical cable couplings and is particularly applicable to electrical couplings for transmitting power to machinery which is rated permissible by United States Bureau of Mines Standards for operation in explosive atmospheres such as those in certain underground mines.

With no significant exception, all underground mining machinery is powered by electricity. Much of this equipment, such as continuous miners, loading machines, shuttle cars, and many kinds of conveyors, are highly mobile so they can follow an advancing mine face. Further, they require substantial amounts of power involving high voltages and high currents. Operating voltages for this equipment are as high as 4,160 volts, and higher voltages are under serious consideration. Current requirements for a single machine may be as high as 1,200 amperes.

Electrical power for such mobile equipment must be supplied through flexible cables which are extended from time to time by additional lengths connected through electrical couplings.

Typically, an electrical coupling of this kind, whether used at a relatively stationary power output board or junction box, or in the flexible cable itself, includes a plug and a receptacle, the plug having pin contacts telescopically inserted within corresponding socket contacts in the receptacle. Either the plug contacts or socket contacts are deflectible and elastic, to facilitate connection and disconnection and at least initial positive metal-to-metal contact. A serious shortcoming of these conventional electrical couplings is that the flexible contacts lose their elasticity after extended use. This reduces the contact pressure and current-carrying capacity, causing heating which in turn causes more loss of elasticity and more heating, further limiting the current-carrying capacity.

BRIEF SUMMARY OF THE INVENTION A general object of the invention is to provide an electrical coupling for use in a power transmission cable which is explosion-proof in hazardous atmospheres, will carry high voltages and currents without overheating, and is easily, quickly and safely connected and disconnected by one man.

Another object is to provide an electrical coupling in which deflectible, elastic pin contacts are pressed into substantial electrically conductive engagement within socket contacts to maintain a uniformly high currentcarrying ability over a long service life. A feature of the invention is that the pin contacts are split or hollow and are held expanded by spring-loaded tapered plugs or wedges within the socket contacts to maintain substantial pin-to-socket surface engagement while the coupling is connected.

Another object is to provide an electrical coupling having multiple conductance paths for maintaining current-carrying capacity over a long service life. A feature of the improved coupling is that a first conductive path between each corresponding pin and socket contact is established through the outer surface of the pin contact and the inner surface of the bore in the socket contacts, and a second conductive path is established through an inner surface of the pin contact and the main body portion of the socket contact via a spring-loaded wedge.

Another object is to provide a locking ring which positively connects the coupling by camming the pin contacts into the socket contacts when turned in one direction, and positively disconnects the coupling by camming the pin contacts out of the socket contacts when turned in the opposite direction.

Another object is to provide a coupling which presents all the above advantages in a housing that is sealed when connected, to thereby comply with United States Bureau of Mines requirements for operation in explosive atmospheres. The coupling is water-tight, impactand shatter-resistant, and both explosionand corrosion-proof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view of an electrical coupling shown in connected or assembled condition intermediate the ends of an electrical cable, and illustrates a preferred form of the present invention;

FIGS. 2 and 3, when viewed together, show a fragmentary view similar to FIG. 1, in disconnected or disassembled condition, FIG. 2 showing the connecting portion of the plug, and FIG. 3 showing the connecting portion of the receptacle;

FIG. 4 is an enlarged fragmentary view of FIG. 3 showing a tapered plug or wedge which is carried out within each power socket contact for engagement within a tapered bore of the corresponding hollow pin contact;

FIG. 5 is an enlarged fragmentary view of FIG. 1 illustrating how the tapered plug or wedge shown in FIG. 4 expands the corresponding hollow pin contact into substantial electrically conductive engagement with the inner bore of the corresponding socket contact, while providing dual conductive paths between the pin and socket contacts; and

FIGS. 6 and 7 are views of FIGS. 2 and 3 as seen in the direction of arrows 6 6 and 7-7, respectively.

Like parts are referred to by like reference characters through the figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The electrical coupling shown assembled in FIG. I is indicated generally by the reference numeral 20. This particular embodiment is for use in interconnecting separate lengths of cable. It will be obvious as the description proceeds, that one or the other of the coupling housing shells could be modified suitably to connect a cable either directly to a power source such as a junction box, or to a point of use such as a mining machine.

The electrical coupling 20 has a two part, fully enclosed, explosion-proof housing generally designated 22 interconnected by sealing and locking means to be described This consists of a plug housing shell 24, part of which is separately shown in FIG. 2; and a receptacle housing shell 26 partly shown in FIG. 3.

The cable end of each

housing shell

24 and 26 consists of a bell-shaped aluminum body 28 with forward internal threads 30 at its open end and external threads 32 at its cable end, the latter threads being engaged by an internally threaded adjustment nut 34 which is part of a bell mouth packing gland generally designated 36.

This may be a conventional packing gland, forming no part of the present invention, and therefore will not be described in detail. Briefly, the packing glands 36 provide fluid-tight seals in the usual manner where

cables

38 and 40 enter the plug and receptacle housing shells.

Each housing shell is provided with a series of set screws about its open end for a purpose to be described, and each has two or more integral supporting or anchor lugs 44. Each body section 28 has a forwardly or outwardly disposed annular stop surface or flange 46. This facilitates assembly during manufacture, and disconnection of the plug from the receptacle by reverse rotation of the locking ring to be described.

A generally cylindrical sleeve member 48 has a rear section 50 with external threads 52 engaging the threads 30 in the plug housing shell 24. Likewise a generally cylindrical sleeve member 54 has a rear section 56 with external threads 58 engaged within threads 30 of the receptacle housing shell 26.

Sleeve member 48 has a forward external flange 60 with an annular abutment surface 62 on the back side and a beveled sealing surface 64 on the forward side.

A locking ring 66 is rotatably secured on and limitedly axially movable relative to the plug housing shell 24. The locking ring has coarse internal screw threads 68 and a rear, inner flange 70 between the previously described

abutment surfaces

46 and 62, the spacing between these abutment surfaces being determined by the degree of screw engagement of the sleeve member 48 within the plug body 28 and is held by set screws 42 bearing against the sleeve member. Thus, it will be apparent that the locking ring 66, when the coupling is disconnected as shown in FIG. 2, is freely rotatable in the space between

flange surfaces

46 and 62 and is limitedly movable in an axial direction depending on the spacing between those flange surfaces. To assemble the plug during manufacture, the locking ring 66 will first be placed on the sleeve member 48 behind the flange 60. Then the entire sub-assembly, including the insulation and pin contacts within the sleeve member (to be described) will be turned into the threads 30 of the plug and held in place by tightening set screws 42. External lugs 72 on the locking ring enable engagement by a spanner wrench or the like.

Receptacle sleeve member 54 has an intermediate external flange 74 with spanner wrench engaging lugs 76, and coarse external screw threads 78 engageable with locking ring threads 68, and a forward beveled sealing surface 80 engageable with plug sealing surface 64. A forward cylindrical portion 82 is telescopically assembled within a forward cylindrical bore 84 of the plug.

If the electrical coupling were to be used at a power outlet such as a junction box, the body 28 for the receptacle housing shell 26 would not be used; instead, the flange 74 would be bolted (by means not shown) directly to a panel. Similarly, if the coupling were to be used at a use point such as a mining machine, the body 28 of plug housing shell 24 would not be used; instead, some component similar to the sleeve member 48 would be screwed or otherwise fastened directly to the control box of the machine. The other, internal components of the coupling will now be described.

Insulating material 86 such as epoxy resin is preferably cast or molded in place within the sleeve member 48 and comprises in effect an electrically insulating integral portion thereof. Potted or molded integrally therein are three power-carrying pin contact members 88 and one, somewhat smaller cross-section, ground pin contact member 90. Additional pilot pin contacts in the plug, and pilot socket contacts in the receptacle may and usually will be employed in commercial couplings but they form no part of the present invention and therefore are shown only in dotted lines and indicated by reference numerals 92 and 94 in FIGS. 6 and 7, respectively. Each power carrying pin contact member 88 comprises a hexagonal crosssection body portion 96 embedded in the insulating material 86. It has a rearwardly open bore 98. receiving the bared end of one of three power conductors 100 extending from cable 38, these bared ends being held in the bore by set screws 102. The forward, reduced diameter end portion 104 of the pin contact member 88 is tubular, having an outside cylindrical surface 106, an inside bore 108 with a forwardly enlarging tapered bore portion 110 and is longitudinally split at locations numbered 112 to provide elasticity and expansibility. The ground pin contact member 90, and its corresponding socket contact member to be described, do not form any essential part of the invention but are shown merely to exemplify one arrangement which may be used. It comprises a shank 114 with set screws 116 holding the bared end of ground conductor 118 within bore 120; and a reduced diameter forward portion 112 longitudinally split for flexibility at 124.

Insulating material 126 in the receptacle housing shell 26 may be the same as insulating material 86 and is cast or molded in sleeve member 54, forming an electrically insulating portion thereof. Potted or molded integrally therein are three power-carrying socket contact members 128 and one somewhat smaller crosssection ground socket contat member 130.

Each power-carrying socket contact member 128 comprises a hexagonal cross-section body portion 132 embedded in the insulating material 126. It has a rearwardly open bore 134 with the bared end of one-of three power conductors 136 extending from cable 40 held by set screws 138. The forward ends of the powercarrying socket contact members 138 are wholly contained within the insulating material 126 and each comprises a tubular section with a forwardly open cylindrical bore 140. This forward tubular section is continuous in cross-section, not being split as in the case of the pin contacts, to provide the solid cylindrical bearing surface 140 against which the pin contact outer surfaces 106 are pressed when the coupling is connected. The ground socket contact member 130 is generally similar to the power-carrying socket contact members 128 so far described and comprises a hexagonal body portion 142 embedded in insulating material 126, with set screws 144 holding the bared end of ground conductor 146 within rearward bore 148. A fowardly open cylindrical bore 150 is of proper size and position to receive the ground pin contact member 90 and provide a snug, electrically conductive fit.

An important part of the present invention is the auxiliary pressure and contact means generally designated 152 and contained within the socket contact members 128. As shown in FIGS. 4 and 5, a tapered plug or wedge 154 has a cylindrical body 156 with a reduced diameter section 158 and a forward tapered section 160 matching the taper of the bore portion 110 in the corresponding power pin contact. The tapered plug for each socket contact is axially slidable within a reduced diameter, inner bore 162 and is urged in an outward direction by a coil spring 164 compressibly interposed between the end of the tapered plug and the end of the bore 162. A pair of pins 166 is mounted in the socket contact member wall, with inner ends extending into the reduced diameter section 158 to limit axial movement of the tapered plug.

The taper on the

surfaces

110 and 160 will preferably be quite steep, such as a Morse taper of approxiamtely 3 from the axis, enabling a relatively small axial force exerted by spring 164 to exert a substantial outward, expanding force on the forward tubular portions of the pin contacts to maintain high pressure and good, uniform, conductive engagement between

surfaces

106 and 140.

It will be appreciated that, because of the aforementioned wedging effect of the tapered plugs within the hollow pin contacts and the consequent high bearing pressures achieved between

surfaces

106 and 140, it is important to provide means which insures that the pin contacts can be forced all the way in to fully inserted position when the coupling is connected, and subsequently broken loose readily when disconnected. For this purpose the locking ring 66 provides a beneficial two-way function in driving the contacts home when the coupling is connected, and in breaking them loose when disconnected.

In view of the above description, it is believed that use and operation of the improved coupling is obvious. Briefly, however, assuming the plug 24 and receptacle 26 are first brought into facing position as shown in FIGS. 2 and 3, they will then be moved together with ground pin contact member 90 inserted in the corresponding ground socket contact member 130, and with the three power-carrying pin contact members 88 inserted in the corresponding power-carrying socket contact members 128. These will be telescoped together until screw threads 68 on the locking ring 66 engage screw threads 78 on sleeve member 54. Rotation of the locking ring, preferably with spanner

wrenches engaging lugs

72 and 76, then seats the pin contacts in the socket contacts as shown in FIG. 1 and engages beveled sealing

surfaces

64 and 80 to seal the interior of the coupling. In drawing the plug and receptacle together by means of the locking ring, it bears upon the annular abutment surface 62 of flange 60. Conversely, when the coupling is disconnected, the locking ring 66 is rotated in the opposite direction until it engages the annular abutment surface or flange 46 on the plug 24,

t and continued rotation of the locking ring in the same direction pries the plug and receptacle apart.

The improved electrical coupling has been shown to have significant improvements over conventional couplings which do not employ anything comparable to the tapered plugs 154. Without increasing the size of the plug and receptacle housing shells overthe sizes conventionally used,'the voltage drop across the coupling has actually been measured as less than an equivalent length of the cable used with it. This increased conductance is accompanied, of course, by reduced heat generation across the contacts. A primary reason for this improved performance is the outward pressure exerted by the tapered plugs 154 which press and maintain the expandable hollow pin contact members 88 against the inner walls 140 of the socket contact members 128. In addition to the improved conductivity thus obtained from pin surfaces 106 to socket surfaces 140, there is substantial current transmitted through the tapered plugs 154, springs 164, and the solid hexagonal body portions 132. Thus, two conductive paths are established, one being through the outer surfaces of the pin contact members 88 into the inner surfaces of the socket contact members 130, and the other being through the bores of the pin contacts and the tapered plugs.

While one preferred embodiment of the invention has been illustrated and described for use in connecting two lengths of cable, and modifications have been described for connecting a cable either to a power junction box or to the input control box of a mining machine, it will be apparent to those skilled in the art that other specific constructions, arrangements and uses in the mining industry as well as other applications are possible within the scope and spirit of the invention as covered by the following claims.

I claim as my invention:

1. A detachable two-part multiple pin and socket electrical coupling comprising:

a housing including a pair of housing shells with open-ended confronting portions;

one of said housing shells being a plug housing shell and having a plurality of pin contacts embedded in a body of electrical insulating material therein, said pin contacts having expandible forward tubular portions extending from the insulating material in said plug housing shell and having forwardly open axial bores;

the other of said housing shells being a receptacle housing shell and having a plurality of socket contacts embedded in a body of electrical insulating material therein, said socket contacts having bores suitably dimensioned and suitably disposed in said receptacle housing shell to telescopically receive said pin contacts in electrically conductive relation when said plug and receptacle housing shells are assembled;

auxiliary pressure and contact means including tapered plugs independently telescopically movable within the bores of said socket contacts and electrically connected thereto and biasing means within the bores of said socket contacts biasing said tapered plugs in an outward direction and engageable with said forwardly open axial bores in said pin contacts effective to expand said pin contacts and press the outer surfaces thereof into substantial electrically conductive engagement with the bores of corresponding socket contacts;

whereby a first conductive path between each corresponding pin and socket contact is established through the outer surface of the pin contact and the bore of the socket contact, and a second conductive path is established through the bore of the pin contact and the socket contact.

2. A detachable two-part multiple pin and socket electrical coupling according to claim 1 in which said biasing means comprises separate spring-like elements in the bores of said socket contacts acting to press said tapered plug independently into said forwardly open axial bores in said pin contacts to thereby independently expand said pin contacts into electrically conductive engagement with the bores of the corresponding socket contacts.

3. A detachable two-part multiple pin and socket electrical coupling comprising:

one of said housing shells being a plug housing shell and having a plurality of pin contacts embedded in a body of electrical insulating material therein, said pin contacts having expandible forward tubular portions extending from the insulating material in said plug housing shell and having forwardly enlarging tapered bores;

auxiliary pressure and contact means including tapered plugs within said socket contacts and electrically connected thereto and engageable with said tapered bores in said pin contacts effective to expand said pin contacts and press the outer surfaces thereof into substantial electrically conductive engagement with the bores of corresponding socket contacts, and said tapered plugs are guided for limited telescopic movement within the respective socket contacts and are urged in an outward direction by spring-biasing means;

4. A detachable two-part multiple pin and socket electrical coupling according to claim 3 in which said spring-biasing means comprises a spring seated in the bore of each socket contact compressibly interposed between the inner ends of each socket contact and the tapered plug contained therein.

5. A detachable two-part multiple pin and socket electrical coupling comprising:

sealing means between said housing shells including mutually engageable continuous peripheral seats extending about said open-ended confronting portions;

positive assembling and disassembling means between said housing shells including a locking ring rotatably secured on and limitedly axially movable relative to one of said housing shells; said locking ring being threadedly connected with the other of said housing shells, for moving said housing shells and locking them together in assembled position with said seats engaged to seal the interior of said housing in response to rotation of said locking ring in one direction, and for moving said housing shells apart to disassemble them in response to rotation of said locking ring in the opposite direction: said locking ring being engageable with said one housing shell while threadedly engaged with said other housing shell to enable said locking ring to cam said shells apart and forcibly disengage said seats in response to rotation of said locking ring in said opposite direction; one of said housing shells bieng a plug housing shell and having a plurality of pin contacts embedded in a body of electrical insulating material therein, said pin contacts having expandible forward tubular portions extending from the insulating material in said plug housing shell and having forwardly open axial bores; the other of said housing shells being a receptcle housing shell and having a plurality of socket contacts embedded in a body of electrical insulating material therein, said socket contacts having bores suitably dimensioned and suitably disposed in said receptacle housing shell to telescopically receive said pin contacts in electrically conductive relation when said plug and receptacle housing shells are in said assembled position; and

6. A detachable two-part multiple pin and socket electrical coupling according to claim 6 in which the plug housing shell includes a main shell member with a first annular flange encircling an open end thereof, a sleeve member threadedly engaged with said main shell member within said open end and having a second annular flange disposed forwardly of said first annular flange, the axial spacing between said flanges being determined by rotational adjustment of said sleeve member, said peripheral seat on said plug housing shell being disposed on the forward end of said sleeve member, and said locking ring having an inner flange disposed in said axial spacing between said first and second flanges and engageable respectively therewith upon rotation of said locking ring in one direction or the other.

a: n: a a a:

P'J-ww UNITED STATES PATENT. OFFICE CER'lIFlCA'IE O1 CORRIbCflON Patent No. 3 ,789,346 Dated January 29 1974 Inventor) Eric DeBrick It is certified that error appears in the above-identified patent and thet said Letters Patent are hereby corrected as shown below:

zlol. 2, line 29, delete "out";

Col. 4, line 35, "contat" should be -contact-;

line 55, "fowardly" should be forw-ardly-; Col. 5, line 9, "approxiamtely" should be -approximately-; Col. 6, line 61', "plug" should be -plugs--.

Signed and sealed th is 7th day of May 197M.

(SEAL) Attest:

C. MARSl-iALL DAHN Commissionerof Patents EDWARD 1 I.FLETCI-IER, JR. Attesting Officer

Claims

1. A detachable two-part multiple pin and socket electrical coupling comprising: a housing including a pair of housing shells with open-ended confronting portions; one of said housing shells being a plug housing shell and having a plurality of pin contacts embedded in a body of electrical insulating material therein, said pin contacts having expandible forward tubular portions extending from the insulating material in said plug housing shell and having forwardly open axial bores; the other of said housing shells being a receptacle housing shell and having a plurality of socket contacts embedded in a body of electrical insulating material therein, said socket contacts having bores suitably dimensioned and suitably disposed in said receptacle housing shell to telescopically receive said pin contacts in electrically conductive relation when said plug and receptacle housing shells are assembled; auxiliary pressure and contact means including tapered plugs independently telescopically movable within the bores of said socket contacts and electrically connected thereto and biasing means within the bores of said socket contacts biasing said tapered plugs in an outward direction and engageable with said forwardly open axial bores in said pin contacts effective to expand said pin contacts and press the outer surfaces thereof into substantial electrically conductive engagement with the bores of corresponding socket contacts; whereby a first conductive path between each corresponding pin and socket contact is established through the outer surface of the pin contact and the bore of the socket contact, and a second conductive path is established through the bore of the pin contact and the socket contact.

3. A detachable two-part multiple pin and socket electrical coupling comprising: a housing including a pair of housing shells with open-ended confronting portions; one of said housing shells being a plug housing shell and having a plurality of pin contacts embedded in a body of electrical insulating material therein, said pin contacts having expandible forward tubular portions extending from the insulating material in said plug housing shell and having forwardly enlarging tapered bores; the other of said housing shells being a receptacle housing shell and having a plurality of socket contacts embedded in a body of electrical insulating material therein, said socket contacts having bores suitably dimensioned and suitably disposed in said receptacle housing shell to telescopically receive said pin contacts in electrically conductive relation when said plug and receptacle housing shells are assembled; auxiliary pressure and contact means including tapered plugs within said socket contacts and electrically connected thereto and engageable with said tapered bores in said pin contacts effective to expand said pin contacts and press the outer surfaces thereof into substantial electrically conductive engagement with the bores of corresponding socket contacts, and said tapered plugs are guided for limited telescopic movement within the respective socket contacts and are urged in an outward direction by spring-biasing means; whereby a first conductive path between each corresponding pin and socket contact is established through the outer surface of the pin contact and the bore of the socket contact, and a second conductive path is established through the bore of the pin contact and the socket contact.

5. A detachable two-part multiple pin and socket electrical coupling comprising: a housing including a pair of housing shells with open-ended confronting portions; sealing means between said housing shells including mutually engageable continuous peripheral seats extending about said open-ended confronting portions; positive assembling and disassembling means between said housing shells including a locking ring rotatably secured on and limitedly axially movable relative to one of said housing shells; said locking ring being threadedly connected with the other of said housinG shells, for moving said housing shells and locking them together in assembled position with said seats engaged to seal the interior of said housing in response to rotation of said locking ring in one direction, and for moving said housing shells apart to disassemble them in response to rotation of said locking ring in the opposite direction: said locking ring being engageable with said one housing shell while threadedly engaged with said other housing shell to enable said locking ring to cam said shells apart and forcibly disengage said seats in response to rotation of said locking ring in said opposite direction; one of said housing shells bieng a plug housing shell and having a plurality of pin contacts embedded in a body of electrical insulating material therein, said pin contacts having expandible forward tubular portions extending from the insulating material in said plug housing shell and having forwardly open axial bores; the other of said housing shells being a receptcle housing shell and having a plurality of socket contacts embedded in a body of electrical insulating material therein, said socket contacts having bores suitably dimensioned and suitably disposed in said receptacle housing shell to telescopically receive said pin contacts in electrically conductive relation when said plug and receptacle housing shells are in said assembled position; and auxiliary pressure and contact means including tapered plugs independently telescopically movable within the bores of said socket contacts and electrically connected thereto and biasing means within the bores of said socket contacts biasing said tapered plugs in an outward direction and engageable with said forwardly open axial bores in said pin contacts effective to expand said pin contacts and press the outer surfaces thereof into substantial electrically conductive engagement with the bores of corresponding socket contacts; whereby a first conductive path between each corresponding pin and socket contact is established through the outer surface of the pin contact and the bore of the socket contact, and a second conductive path is established through the bore of the pin contact and the socket contact.