US3394338A - Explosion-proof electrical connector - Google Patents

Description

July 23, 1968 w. F. HICKES ET AL 3,394,333

EXPLOSION-PROOF ELECTRICAL CONNECTOR Filed May 24, 1967 5 Sheets-Sheet l FIG. I FIG. 11

FIG. III

INVENTORS WILLIS F HICKES RICHARD B. NEWELL AGENT July 23. 1968 w, H| ET AL EXPLOSION-PROOF ELECT CCCCCCCCCCCC OR eeeeeeeeeeee t2 FIG. I

W l L H I C K ES RRRRRRRRRRRRR LL July 23, w c s ET AL EXPLOS I ON- PROOF ELECTRI CAL CONNECTOR 5 Sheets-Sheet 5 Filed May 24. 1967 FIG. I

FIG. If

FIGFSZIIE L m L TSE EW 8 KE 0 W m a E F G S fl A H mm W M Y F B Dim United States Patent 3,394,338 EXPLOSION-PROOF ELECTRICAL CONNECTOR Willis F. I-Iickes, Sharon, and Richard B. Newell, Attleboro, Mass, assignors to The Foxboro Company, Foxboro, Mass., a corporation of Massachusetts Filed May 24, 1967, ,Ser. No. 640,900 Claims. (Cl. 339111) ABSTRACT OF THE DISCLOSURE An electrical connector for operation at normal commercial supply voltages, typically 117 volts at 60 cycles, having explosion-proof characteristics by virtue of a relatively small volume connector chamber, with quenching surface area within said chamber which is in relatively high ratio to the volume of said chamber, this combination functioning, in assembly, with a length of flame path significantly shorter than conventional usage while permitting the use of a relatively large net cross-section of flame path on the order of the like net cross-section commonly used in non-explosion-proof applications.

This invention relates to electrical connectors of the separable plug or plug-in type, with male-female mating structure combinations.

It particularly relates to explosion-proof connectors which are switching connectors in the sense that electrical circuits are made and broken within protective housings. Explosions occur from flame arcs between connectors at the point and time of separation or joining. Devices of this nature break the electrical circuit before final separation and make the circuit after preliminary joining. Thus, explosion-proofing is provided at the time of arcing.

The protective housing are provided with flame path relief passages from the interior to the exterior of the housings. These flame paths may be the clearance of a male connector pin in an entrance to the protective housing. Prior art devices use long flame paths in combination with an extremely close fit between the connector pin and the wall of the housing entrance so that only a net clearance in the order of a thousandth of an inch is permitted.

This prior art tight fit makes manufacturing tolerances difficult and costly. In a multiple pin connector the spacing between the pins becomes critical, and temperature change provides problems. Use of such connectors in the field becomes diflicult.

An advantage of this invention is that tolerances are provided which are normal to household appliances.

This invention provides a new and useful explosionproof device which makes possible the use of a small, compact connector which is easily and surely operable, and which permits the use of a short flame path, in a concept of application and explosion-proofing which is a novel and substantial departure from and improvement over past concepts.

The device of this invention is particularly appropriate in normal commercial supply voltage applications of up to 240 volts, with current up to one and a half ampereS in a combustible mixture of air and hydrocarbon vapor. It is also useful in other combustible mixtures such as hydrogen and air over a range of voltage-ampere combinations. It is compact and easily handled. As a male-female assembly, one half may be permanently fixed on a mounting plate and the other half engaged with the first half and locked to the mounting plate with straight, simple, snap-in pressure. It may be separated by manual spring release and straight line pull. Both operations are quick, positive, and easily executed by one hand. It provides an explosion-proof structure within an outer protective and 3,394,338 Patented July 23, 1968 mounting structure. It is mechanically highly rugged and secure through a combination of plasti molding and mechanical clamping of electrical leads.

In addition, by virtue of the unusually large net crosssectional area allowed .for the flame path of this invention, for example, between one and two orders of magnitude greater than that normally considered to be necessary, the connector may readily be employed in a multipin configuration without encountering the manufacturing and handling difficulties normally inherent in precision tolerances in the order of one thousandth of an inch as in the prior art.

This invention relates to a chambered connector for use with its counterpart connector. The chambered connector may be male or female, as desired. Both mating connectors may be free. One may be free and the other snapped into a support, or one may be permanently fixed to -a support, and the other snapped into the support as it is joined with its counterpart.

Explosion-proofing in this invention may be defined as providing an enclosure with internal quenching areas about a potential source of ignition in combination with quenching means in the form of relief passages from the interior to the exterior of the enclosure. The enclosure is made strong enough to resist without damage, a possible internal explosion, and tight enough so that any escape of products of combustion from the enclosure is limited to small flame path passage means provided for this purpose. An internal low power explosion is thus quenched within the enclosure and in the small passage means, and the products of combustion are cooled within the enclosure and in passing through the small pass-age means to such an extent as to be incapable of thereafter causing ignition of the outer atmosphere.

In this invention, the chamber volume is enough to allow necessary movement of the connector members, and defines a chamber in which much of a low energy explosion can occur and be quenched by means of relatively extensive internal surface quenching area. This area combines the surfaces of contacts with the internal wall surfaces of the chamber. Beyond this, the volume is minimal, and for this purpose each male-female combination is provided with a separate chamber.

The prior art provides flame paths that are long and highly restrictive. This invention provides the more convenient and desirable condition of relatively short flame paths that are not so highly restrictive. This is made possible by using a novel combination of small internal volume as related to a substantial internal quenching surface area.

The combination provided by this invention does not result from the application of standard guidelines of exposion-proof design parameters.

In this invention, a small internal volume, with considerable exposed connector area within this volume, provides a large area to volume ratio as an important quenching factor.

This connector is used in low power applications, less than 500 watts, so that the electrical energy at the make and break is limited. The co-ordinated design of this invention establishes new, practical, and tested flame path configuration, instead of following conventional explosion-proofing guide lines developed for larger systems.

Other objects and advantages will be in part apparent and in part pointed out hereinafter and in the accompanying drawings, wherein:

FIGURE I is a central section of a female connector unit according to this invention;

FIGURE II is a right end face view of the FIGURE I structure, as if it were whole;

FIGURE III is a further showing of the structure of FIGURE I, assembled with its male counterpart;

FIGURE IV is an exploded perspective of the female connector unit assembly according to this invention;

FIGURE V is a schematic of one contact to the connector assembly, as disengaged;

FIGURE VI is a schematic of one contact to the connector assembly, as engaged;

FIGURE VII illustrates the point of possible arcing between the connector units, as the units are being engaged or disengaged; and

FIGURE VIII shows the unit of FIGURE IV, as assembled and mounted in a support plate.

The FIGURE I female assembly is shown in FIG- URES IV and VIII in relation to the whole connector device. This assembly 10 has a housing 11 made of glass filled diallyl phthalate, a self-extinguishing plastic Which will not support combustion. The housing 11 is provided with three separate chambers 12, 13, 14, which are elongate, parallel and of small volume. Each of these chambers contains a spring electrical connector clip as at 15, 16, and 17, for receiving male connector pins, FIGURE III, 18, 19, and 20.

The FIGURE I connector clips are electrically connected to individual wires in a cable 21 through a molding 22 of thermoplastic material, and the clips are mounted on a sandwich of two strips 23 and 24 of thermosetting phenolic with a body of thermoplastic material 25 therebetween. This sandwich and the molding 22 seal off the inner ends of the connector chambers 12, 13 and 14. Thus the clips 15, 16, and 17 are separately housed in individual chambers, and fixed in relation to each other even under adverse heat conditions.

If the assembly is exposed to fire, the clips 15, 16 and 17 and their leads are still held separate by the sandwich strips and no direct electrical contact between them can occur. FIGURE III is shown without the molding 22 and without the sandwich strips 23 and 24. Each of the chambers 12, 13, and 14, has a single and only passage to the exterior of the housing 11, respectively at 26, 27 and 28.

As in FIGURE III, these passages receive the male connector pins 18, 19, and for extension into the chambers 12, 13, and 14 and into mechanical spring clamping engagement nad consequent electrical connection with their respective electrical connector clips 15, 16, and 17.

FIGURE IV illustrates the full assembly of the unit of FIGURE I with its protective coverFIGURE VIII shows this full assembly as snap mounted in an opening in a support plate 29.

In FIGURE IV the housing 11 is shown as nestable in a mounting spring clip 31, which in turn is nestable in the protectable cover 32. The cable 21 extends through the spring clip 31 and the cover 32. Thereafter, in the full assembly, clamp members 33 and 34 are bolted to the outer end of the cover 32 in such fashion as to firmly grip the cable 21. Thus the cable is doubly fixed, first by the molding 22 (FIGURE I) and then by the clamps 33 and 34. The housing 11 is secured within the cover 32 by bolts 35 and 36. Thus the spring clip 31 is firmly nested inside the cover and held therein by the housing 11.

The cover has inside guide formations as at 37 which locate the spring clip 31 by means of cooperating forms on the spring clip as at 38.

The cover 32 has top and bottom apertures 39 through which serrated portions 40 of the spring clip extend outwardly, limited by spring tabs 41 engaging inwardly facing cover shoulders 42. The spring clip 31 has forwardly facing beveled ends 43 and transverse locking slots 44.

The front of the housing 11 in FIGURE IV shows a round receptor hole for receiving the round ground connector pin 18, and two rectangular holes for receiving the rectangular cross-section connector pins 19 and 20. The ground pin is the longer, and makes contact first, and disconnects last.

Accordingly, as in FIGURE VIII, the entire unit may be simply pushed together in a mounting plate opening aided by the bevel end 43, so that the spring then snaps outward to engage the locking slots 44 in the mounting plate. Thereafter, simple squeezing together of the spring portions 40 will release the unit from the plate. The male unit 30 is ordinarily fixed to the mounting plate 29 as indicated by the dotted line bracket, and the female unit then joined with the mounting plate and the male unit. The mounting plate is customarily a part of a housing containing the apparatus to which this connector provides power supply. This arrangement limits the power supplied through the connector to that used by the apparatus, and assures that large loads beyond the safe power limits of this connector shall not be applied.

FIGURES V, VI, and VII schematically illustrate the structure, form, and function of the device according to this invention in terms of explosion proofing, and in terms of a single chamber within the housing 11 of FIGURE I. Minimal volume for the potential explosion is achieved by establishing each connection in its separate chamber.

FIGURE V relates to FIGURE VIII, and FIGURE VI relates to FIGURE III. The arcing point, either engaging or disengaging, of FIGURE VII, is indicated as protectively enclosed at that moment, by dotted line 45.

In illustration of all the male connector pins, note in FIGURE VI that the male insert 46 essentially fills the flame path passage 47. It is a somewhat loose fit to allow a small flame path around the insert 46. Because of the small volume of the chamber, a somewhat loose fit is permissible, without danger of propagation of an internal explosion. The loose fit permits larger tolerances on dimensions, and in the alignment between the connector plIlS.

As a guiding example, the passage 47 may be one sixteenth of an inch long, with a clearance of five thousandths of an inch. The internal free volume of the individual chamber may be one hundredth of a cubic inch. The internal surface area available to this volume for explosion quenching may be one square inch. The overall body of assembly, male and female together may be five cubic inches in volume.

An explosion in such a chamber is presented with sulficient volume to allow a small explosion, and with suflicient internal surface area and flame path to quench such an explosion to such an extent as to prevent a secondary external explosion.

This invention, therefore, provides electrical connector means which is compact, mechanically and electrically eflicient, and which is explosion-proof on a basis which is new and useful. It involves a combination of small volume and large internal surface area to volume ratio, co-ordinated with a conveniently short and loose flame path.

As many embodiments may be made of the above invention, and as changes may be made in the embodiment set forth above without departing from the scope of the invention it is to be understood that all matter hereinbefore set forth and in the accompanying drawings is to be interpreted as illustrative only and not in a limiting sense.

We claim:

1. An electrical connector adapted for making and breaking an electrical circuit in conjunction with a separable mating connector in an explosive environment without igniting same comprising,

a housing having a passage from its exterior to a chamber therein with said passage adapted for receiving the mating inserting element of said mating connector with a loose fit therebetween whereby the cross section of said mating inserting element substantially occupies the cross section of said passage while permitting unimpeded insertion and withdrawal of said mating inserting element through said passage and with said passage having a short length and sufficiently small open volume while said passage is substantially occupied by said mating inserting element to extinguish the remainder effect of an explosion occurring at the chamber end of said passage.

with said housing enclosing said chamber communicating with the inner end of said passage, with said chamber being of a small volume adequate only for enclosing the element making electrical contact with said inserting element so that explosions ignited within said chamber as a consequence of separation and contact between said mating elements are consequently explosions of minimal force owing to the small volume of explosive vapor possible to be contained in said chamber, said chamber having a high ratio of internal surface quenching area to the free volume of said chamber, and

electrical conduction means for completing the electrical circuit from said elements being in a scalable fit with said housing between said chamber and the exterior of said housing whereby said passage is the only access to the exterior for said chamber.

2. A female electrical connector adapted for making and breaking an electrical circuit in conjunction with a separable male connector in an explosive type of environment without igniting said explosive environment comprising,

means to minimize explosions occurring within said female electrical connector as a consequence of electrical arcing during making and breaking of electrical contact with an enclosed female electrical contacting element by the male electrical contacting element of said separable male connector, said means including a minimal volume chamber enclosing the operative section of said female electrical contractor so that explosions occurring within said chamber represent a relatively minor release of explosive energy, and said means including a relatively high ratio of surface quenching area within said chamber to the free volume of said chamber, and

means for damping explosions occurring within said chamber before reaching said explosive environment immediately surrounding said female electrical connector including passage means connecting said chamber to the exterior of said female electrical connector which passage means in combination with a conforming inserted male contacting element provides a loosely restricted access to atmosphere from said chamber with said restricted access thereby formed having a relatively short length and a relatively large net cross section between said male contacting element and the walls of said passage which length and cross section in combination prevents propagation of effects of the explosion occurring within said chamber.

3. A connector as in claim 1, with provision for multiple contacts, with each female connector enclosed in a separate compartment, having minimum internal volume, with each compartment substantially gas tight except for the restricted access to atmosphere between each connector pin of the male plug and the corresponding opening in the compartment surrounding each female connector.

4. An electrical connector according to claim 1, wherein, as connected, open volume of said chamber and passage is of the order of one hundredth of a cubic inch, and interior quenching surface is of the order of one square inch for explosion proofing over a range of normal commercial voltage applications.

5. An electrical connector according to claim 1, which is explosion-proof in low energy applications in the presence of a combustible mixture of air and hydrocarbon vapor.

6. An electrical connector according to claim 1, which is explosion-proof in low energy applications, and in which the open volume in said passage in the presence of said inserting element comprises a short flame path.

7. An explosion-proof electrical connector male-female assembly for use with voltages up to 240 volts and current up to one and a half amperes,

said assembly comprising means for providing a suificient internal volume to permit not more than a small primary explosion,

said quenching means comprising internal surface area of the order of one square inch exposed to said explosion, said internal volume being of the order of one hundredth of a cubic inch, and said assembly having a flame path of the order of one sixteenth of an inch in length, with a clearance of the order of five thousandths of an inch.

8. An explosion-proof electrical connector male-female assembly including a connector according to claim 1 with over all size in the order of five cubic inches, for use in systems up to 240 volts and current up to one and one half amperes, primarily for use in a combustible mixture of air and hydrocarbon vapor and useful in a combustible mixture of hydrogen and air, under limited voltageampere situations, and with said (claim 1) passage as a flame path of the order of one sixteenth of an inch in length and five thousandths of an inch clearance,

said assembly comprising a sufficient internal volume to permit not more than a small primary explosion, and sufficient means for quenching said small explosion, said quenching means comprising internal surface area of the order of one square inch exposed to said small explosion in an internal volume of the order of one hundredth of a cubic inch.

9. An electrical connector according to claim 1, comprising three connector means each in a separate chamber and each according to claim 1, and thermally protective means for maintaining said connector means in their separate chambers to prevent contact therebetween in the event of high heat of the nature of fire and explosion.

10. An electrical connector according to claim 1, wherein the structure is contained in an outer housing with spring snap-in means for mounting in a plate opening.

References Cited UNITED STATES PATENTS 2,626,975 1/1953 Rockwell et a1 33991 3,337,836 8/1967 Churla 339-217 3,360,763 12/1967 Rongey et al 339-111 FOREIGN PATENTS 614,636 2/ 1961 Canada.

RICHARD E. MOORE, Primary Examiner.

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