US3753191A - Low profile glass enclosed hermetically sealed circuit breaker - Google Patents

Abstract

A circuit breaker comprises a bimetal snap-action element disposed within a hermetically sealed glass envelope. The snapaction element opens an electrical circuit upon thermal or current overload. The glass envelope has two substantially flat parallel sides in order to provide a low profile to the circuit breaker and to improve thermal transfer to the snap-action element.

Description

United States Patent [1 1 Dennis Aug. 14, 1973 {5 LOW PROFILE GLASS ENCLOSED 3.227.842 1/1966 Salem 337/112 x HERMETICALLY SEALED cmcun 3,278,705 10/1966 Dennis 337/362 BREAKER Inventor: Philip J. Dennis, Cape Elizabeth,

Maine Assignee: GTE Sylvnnla Incorporated,

Danvers, Mass.

Filed: Mar. 20, 1972 Appl. No.: 235,903

US. Cl. 337/112, 337/89, 337/365, 337/380 Int. Cl. "01h 45/02 Fleldolsearch 337/112, 113, 89, 337/365, 380, 362

References Cited UNITED STATES PATENTS Dales 337/380 X Primary Examiner-Bernard A. Gilheany Assistant Examiner-F. E. Bell A norne v Norman OMalley and James Theodosopoulos [57] ABSTRACT A circuit breaker comprises a bimetal snap-action element disposed within a hermetically sealed glass envelope. The snap-action element opens an electrical circuit upon thermal or current overload. The glass envelope has two substantially flat parallel sides in order to provide a low profile to the circuit breaker and to improve thermal transfer to the snap-action element.

3 Claims, 2 Drawing Figures I l N Patented Aug. 14, 1973 FIG. 1

. art glass enclosed circuit breakers.

1 LOW PROFILE GLASS ENCLOSED IIERMETICALLY SEALED CIRCUIT BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention pertains to glass enclosed hermetically sealed circuit breakers containing a bimetal snapaction element which is normally in a closed position.

2. Description of the Prior Art Circuit breakers of the type with which this invention is concerned are shown in the following U. S. Pat. Nos. 3,272,944; 3,278,705; 3,278,706; 3,307,126; 3,555,478; 3,573,696; 3,573,697; and 3,597,838.

The breakers comprise two lead-in wires extending through a seal of a hermetically sealed glass envelope, a bimetal snap-action element mounted on one of the lead-in wires and a contact mounted on the other leadin wire. In normal operation the snap-action element is closed, that is to say, is in electrical contact with the contact mounted on the other lead-in wire. The circuit breaker is attached to an electrical device being protected, such as a motor, fluorescent lamp ballast, electrical heater and the like, so that some or all of the electric current passes. through the snap-action element. Thus, when a fault occurs and the electrical device starts to draw excessive current, said current will overheat (1 R losses) the snap-action element and cause it to snap open, thereby opening the electrical circuit.

In addition, the circuit breaker is physically located in such proximity to the electrical device that if thermal overload of the device occurs, the snap-action element will eventually be heated above its snap temperature and open the circuit. It can be seen, then, that it is advantageous to mount the circuit breaker as close to the heated part of the electrical device as possible and with efficient heat transfer therebetwe'en, in order to obtain prompt circuit interruption upon abnormal temperature rise of the device.

In motors, for example, a desirable location for a circuit breaker is adjacent the stationary field coils. However, the cyindrical shape of glass envelopes of the prior art circuit breakers often obviates such a location where the motor housing is a close fit around the stationary field coils. And although prior art metal or plastic enclosed circuit breakers have flat shapes to fit into tighter locations than glass enclosed circuit breakers, they do not have the advantages of the latter, especially as relates to hermetic sealing, low cost and ease of adjusting snap temperature just prior to final sealing.

It is an object of this invention to provide a glass enclosed hermetically sealed circuit breaker that has a lower profile and better heat transfer than such prior SUMMARY OF THE INVENTION A circuit breaker in accordance with this invention comprises a hermetically sealed glass envelope having a flat press seal at one end thereof. Extending through The glass envelope has two substantially flat parallel sides, roughly describable as a flattened ellipse, and is made by heating cylindrical tubing to the softening point and then pressing between parallel jaws to obtain the desired flattened shape. The snap-action element is mounted within the envelope so as to be substantially parallel to the flat sides thereof.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is an elevational view and FIG. 2 a crosssectional view of a circuit breaker in accordance with this invention.

DESCRIPTION or THE PREFERRED EMBODIMENT As shown in the drawing, a circuit breaker has a glass envelope 1 having a flattened elliptical shape. One end of envelope 1 is sealed by a press seal 2. Embedded within press seal 2 and extending interiorly and exteriorly therefrom are lead-in wires 3 and 4. Welded to the upper end of lead-in wire 4 is a substantially flat bir'netal snap-action element 5 having a contact button 6 welded thereto at the upper end thereof. A similar contact button 7 is welded to the upper end of lead-in wire 3. Normally, the circuit breaker is in a closed position, that is to say, buttons 6 and 7 are touching.

In order to provide a low profile to the circuit breaker, element 5, which is the widest component within envelope 1, is mounted substantially parallel to the flat sides of envelope 1.

In one aspect of the invention, the distance between element 5 and the flat glass wall therebehind is kept small,,say, about 30 to mils, so that the glass limits the movement of element 5 when it snaps open. The reason for this is to limit the gap distance between buttons 6 and 7 and thereby prevent excessive arcing, as discussed in U. S. Pat. No. 3,555,478 which is incorporated herein by reference.

In the manufacture of the circuit breaker, a length of open-ended glass tubing was prepared, longer than the finished length of envelope 1. For example, for a circuit breaker having an overall envelope length of 1 inches, the glass tubing had a length of 2 :6 inches. The outside diameter of the tubing was 9/32 inch.

About 1 inch of the tubing was heated and pressed, as described previously, so that the width of the glass between the flats was 13/64 inch outside. This increased the elliptical diameter to 11/32 inch outside.

The circuit breaker assembly, consisting of wires 3 and 4 with elements 5, 6 and 7 mounted thereon,was inserted into the flattened glass tubing and supported externally by means of wires 3 and 4. An elongated tool was inserted into the other end of the tubing to support.

snap element 5 and wire 4. The reason for this was to prevent any change in the position of wire 4 relative to wire 3 and in the predetermined snap temperature of element 5, which could result from the intense heat of the flames used to form press seal 2. Press seal 2 was then formed, using suitable pressing jaws, after the glass was heated to the softening temperature. The pressing was perpendicular to the plane formed by wires 3 and 4 in order to prevent reduction of the gap between wires 3 and 4. Also, the jaws were shaped to contain the glass somewhat in order that press seal 2 be within the perimeter of envelope 1. Envelope 1 was then hermetically sealed by conventionally sealing the open end of the tubing, which had not been flattened,

leaving residual sealed tip 8. If desired, envelope 1 could be filled with a suitable inert atomsphere, such as nitrogen, through the open tubular end prior to final sealing.

I claim:

1. A glass enclosed, hermetically sealed circuit breaker comprising: a glass envelope having a flattened elliptical shape, the flattened sides thereof being substantially parallel to each other; a press seal at one end of said envelope; two spaced apart lead-in wires embedded in said press seal extending interiorly and exteriorly therefrom; a substantially flat bimetal snapaction element disposed within said envelope and mounted on the upper end of one of said lead-in wires, said element being substantially parallel to said flattened sides of said envelope; a first contact button centrally disposed on the upper end of said element; a second contact button mounted on the upper end of the other of said lead-in wires, said buttons normally being in physical and electrical contact with each other; and said element having a predetermined snapping temperature whereby, upon attainment of said temperature, said element snaps open and interrupts an electrical circuit, the gap between said element and the proximate flattened side of said envelope being small so that the envelope limits the travel of said element upon opening thereof.

2. The circuit breaker of claim 1 wherein the distance between the flattened sides of said envelope is less than the distance between the curved sides of said elliptical shape.

3. The circuit breaker of claim 2 wherein the gap between said element and the proximate flattened side of said envelope is about 30 to mils.

l i l

Claims (3)

1. A glass enclosed, hermetically sealed circuit breaker comprising: a glass envelope having a flattened elliptical shape, the flattened sides thereof being sUbstantially parallel to each other; a press seal at one end of said envelope; two spaced apart lead-in wires embedded in said press seal extending interiorly and exteriorly therefrom; a substantially flat bimetal snapaction element disposed within said envelope and mounted on the upper end of one of said lead-in wires, said element being substantially parallel to said flattened sides of said envelope; a first contact button centrally disposed on the upper end of said element; a second contact button mounted on the upper end of the other of said lead-in wires, said buttons normally being in physical and electrical contact with each other; and said element having a predetermined snapping temperature whereby, upon attainment of said temperature, said element snaps open and interrupts an electrical circuit, the gap between said element and the proximate flattened side of said envelope being small so that the envelope limits the travel of said element upon opening thereof.

2. The circuit breaker of claim 1 wherein the distance between the flattened sides of said envelope is less than the distance between the curved sides of said elliptical shape.

3. The circuit breaker of claim 2 wherein the gap between said element and the proximate flattened side of said envelope is about 30 to 60 mils.

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