Two pole circuit breaker calibrated in assembled state

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to circuit breakers, and particularly to a two-pole miniature circuit breaker provided with an arrangement for calibrating the delayed trip function with the circuit breaker fully assembled.

2. Background Information

Circuit breakers designed for residential and light commercial applications are typically referred to as miniature circuit breakers. Such circuit breakers have pole mechanisms which include separable contacts, a spring powered operating mechanism with a handle for manual opening and closing of the separable contacts and a trip assembly for automatically opening the separable contacts. The trip assembly includes a bimetal providing a thermal or delayed trip in response to a persistent overcurrent condition, and a magnetic armature providing a magnetic or instantaneous trip in response to a higher level overcurrent. The pole mechanism is mounted in a housing molding of an insulative resin and having a compartment in which the pole mechanism is assembled. A molded cover is then secured in place to enclose the pole mechanism.

Industry standards require that the thermal trip device in these circuit breakers be calibrated to trip the breaker in response to an overcurrent of a predetermined magnitude within a specified time interval. Traditionally, this calibration of the thermal trip is performed “on the half shell”. That is, the pole mechanism is assembled within the compartment of the molded housing, and the thermal trip is calibrated before the mechanism is enclosed by the cover.

A common type of circuit breaker in which the thermal trip is calibrated in this manner is shown by way of example in U.S. Pat. No. 3,849,747. Such circuit breakers have been used for many years and their design has been refined to provide an effective, reliable circuit breaker which can be easily and economically manufactured on a large scale. This type of circuit breaker has a metal frame or support plate with an integral tab extending laterally from one end to which the bimetal of the thermal trip device is secured. The end of the support plate from which the tab extends is partially separated by a transverse slot from the remainder of the support plate which is fixed in the housing. The bimetal is calibrated by closing the circuit breaker and applying the prescribed overcurrent. A tool is inserted in the transverse slot in the support plate and when a specified time has expired, the tool is rotated to distort the free end of the support plate thereby adjusting the position of the support for the bimetal to cause the bimetal to trip the breaker. This calibration has traditionally been carried out automatically, “on the half shell” by a machine. With the calibration set, the cover is installed and riveted in place. The circuit breaker is then tested to validate the calibration. Circuit breakers which do not pass the calibration test are reworked by inserting a hook through a slot in the end of the circuit breaker to engage the free end of the bimetal to attempt to bring it within tolerance. Such reworking is done manually, and being difficult to perform only results in bringing about half of the rejected circuit breakers into tolerance.

It has been determined that the number of circuit breakers which fail the calibration test performed after the cover has been installed is due in part to minor changes in position and distortion of the mechanism resulting from the misalignment of the housing parts causing the breaker to fall out of calibration. In order to overcome these effects, U.S. Pat. No. 4,148,004 proposes a single pole circuit breaker of this type which is fully assembled with the cover riveted in place, and then calibrated by a plug rotatably mounted in the wall of the housing and having a bifurcated stem which engages the tab on the support plate carrying the fixed end of the bimetal. A tool inserted in apertures in the external face of the calibrating plug is rotated to set the calibration. Thus, the circuit breaker is calibrated after it is fully assembled and the parts are fixed in their final position. However, it also allows one to change the calibration which is not in conformance with electrical codes in the United States.

U.S. Pat. No. 5,008,645 discloses a single pole miniature circuit breaker which can be calibrated after full assembly and which provides an indication of any subsequent tampering with that calibration. This patent provides an opening in the housing which is aligned with the slot at the interface between the fixed portion of the metal support frame and the free end to which the bimetal is fixed. The automatic tool is inserted through this opening in the housing and rotated to bend the free end of the support plate relative to the fixed end to thereby adjust the trip point of the bimetal. The calibration is made tamper evident by applying a seal over the calibration opening once the thermal trip has been calibrated.

Both the U.S. Pat. Nos. 4,148,004 and 5,008,645 are directed to single pole miniature circuit breakers. Two-pole miniature circuit breakers are also available. These circuit breakers have identical pole mechanisms housed in side-by-side compartments within the molded housing. Such circuit breakers are commonly used in circuits where both pole mechanisms must be either open or closed. Thus, the handles are tied together so that the two poles are simultaneously opened and closed manually. A common trip device assures that when one pole mechanism trips, the other is tripped also. The common trip device includes actuating members in each pole compartment keyed on a common shaft so that when one actuating member is rotated the other is rotated also. The actuating members include a nose which is engaged by the tripping of a pole mechanism. Each of the actuating members also includes a finger which engages and trips the magnetic actuator of the associated pole when the common trip device is rotated. Thus, when either pole mechanism trips, either thermally or magnetically, the other pole is also tripped.

The metal support plate of one the poles of the two-pole miniature circuit breaker is adjacent to the outer wall of the associated pole compartment, and therefore, can be calibrated in the assembled state in the same manner as the single pole breaker of U.S. Pat. No. 5,008,645. That is, the tool can be inserted through an opening in the housing wall in direct alignment with the calibration slot in the metal support plate. However, since the two-pole mechanisms are identical, the metal support plate of the other pole is not adjacent an outer wall of the housing, but is separated from it by the remainder of the pole mechanism. More of a problem however, is that the actuating member of the common trip device interferes with the insertion of a calibrating tool into the calibration slot of this pole mechanism when the two-pole breaker is assembled. Thus, heretofore it has not been possible to calibrate the two-pole miniature circuit breaker while fully assembled. Consequently, the two-pole circuit breakers have continued to be calibrated “on the half shell” with all of the attendant problems discussed above, which are compounded by the need to achieve proper calibration of both poles.

There is a need therefor for an improved two-pole circuit breaker which can be calibrated when fully assembled.

SUMMARY OF THE INVENTION

This need and others are satisfied by the invention which is directed to a two-pole circuit breaker which can be calibrated when fully assembled. The circuit breaker comprises two pole mechanisms each having a bimetal and a metal frame on which the bimetal is mounted. The bimetal has a calibration opening in which a tool may be inserted to effect the calibration of the bimetal. The two-pole circuit breaker also includes a molded housing having two side-by-side outer compartments, each housing one of the pole mechanisms. The housing has calibration holes in sidewalls of the two outer compartments each of which is aligned with the calibration receptacle of the associated pole mechanism. The circuit breaker further includes a coupling member comprising a rod extending between the two outer compartments adjacent the calibration receptacles. The coupling member includes actuating members on opposite ends of the rod each engaging an associated one of the two pole mechanisms for simultaneous opening of both pole mechanisms. One of the actuating members associated with one of the poles is axially positioned on the rod between the calibration hole in the housing and the calibration receptacle in the associated frame. This actuating member has an actuating finger configured to permit direct, unobstructed access through the calibration hole to the calibration receptacle by the calibration tool with the breaker fully assembled. The least the one actuating member has a nose which is engaged by the associated pole mechanism when it is tripped to rotate the coupler. This actuating member also has a hub mounted on the rod and from which the nose and the finger extend. The nose and finger of the actuating member form a gap which is configured to permit the unobstructed, direct access to the associated calibration receptacle through the calibration opening even with rotation of the actuating member by engagement of the nose by the pole mechanism.

Each pole mechanism has a trip device, comprising a bimetal and a magnetic armature, which when actuated trips the pole mechanism open. The finger on the associated actuating member has a free end engaging the magnetic armature to actuate the trip device as the actuator is rotated. The finger is tapered toward the free end to distribute the load produced by engagement with the magnetic armature to preclude failure of the actuating member. The tapered actuating finger is substantially tangent to the hub of the actuating member on one face of the finger and has an arcuate interface with the hub on the opposite face. The calibration receptacle can be a slot in the metal frame of the pole mechanism. To this end, the metal frame has a fixed portion secured to the housing and a free section to which the bimetal is secured. The calibration receptacle is a slot at the interface between a fixed portion and the free section of the metal frame in which the calibration tool is manipulated to bend the free section of the frame relative to the fixed section.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:

FIG. 1

is an isometric view of a two-pole, ground fault circuit breaker incorporating the invention.

FIG. 2

is an end view of the circuit breaker of

FIG. 1

with parts broken away and with some parts shown schematically.

FIG. 3

is a vertical sectional view taken along the line

3

—

3

in

FIG. 1

of one of the mechanical poles shown in the closed position.

FIG. 4

is an isometric view of a support plate and its mount which form part of the circuit breaker.

FIG. 5

is a fragmentary view of a portion of the support plate of

FIG. 4

illustrating a calibration adjustment made in accordance with the invention.

FIG. 6

is a side elevation view of an actuating member which forms part of the circuit breaker of FIG.

3

.

FIG. 7

is an elevation view of the opposite side of the actuating member of FIG.

6

.

FIG. 8

is an end view of the actuating member of FIGS.

6

and

7

.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention will be described as implemented in a two-pole ground fault circuit breaker; however, it will become apparent seen that the invention is also applicable to two-pole circuit breakers with/without ground fault protection or other electronic protection such as arc fault protection.

Referring to

FIG. 1

, the two-pole ground fault circuit breaker

1

has a housing

3

which is molded in sections from an electrically insulative resin. The sections of the housing include a top base

5

, a top cover

7

, a bottom cover

9

, a bottom base

11

and a hollow centerbore

13

, all secured together such as by rivets

15

. A pigtail

17

connects a neutral conductor within the circuit breaker to a neutral bar (not shown) in a load center in which the circuit breaker

1

may be mounted.

Turning to

FIG. 2

, the top base

5

forms a partition

19

which forms where the top cover a first compartment

21

. The bottom base

11

similarly has a partition

23

which forms with the bottom cover

9

a second compartment

25

. The partition

19

of the top base

5

and the partition

23

of the bottom base

11

, together with the hollow center base

13

form a third compartment

27

between the first and second compartments. The three compartments

21

,

23

and

27

extend side-by-side. The two outer compartments

21

and

25

are pole compartments in which pole mechanism

29

and

31

(shown schematically in

FIG. 2

) are supported on the partitions

19

and

23

, respectively, in a manner to be described. The third or middle compartment

27

houses the electronics

33

(shown schematically) which provide the ground fault protection. If desired, the electronics

33

may also, or in the alternative, provide arc fault protection. A coupler

35

(also shown schematically) extends between the first and second compartments

21

and

25

to interconnect the pole mechanisms

29

,

31

in a manner to be discussed.

Referring to both

FIGS. 1 and 2

, each of the pole mechanism

29

and

31

had a handle

37

and

39

, respectively, which projects through the top of the housing

3

and is joined to the other by a handle tie

38

. As also shown in

FIG. 1

, a test button

40

is provided for testing the electronics

33

.

As the pole mechanisms

29

and

31

are identical, only the first pole mechanism

29

mounted in the first pole compartment

21

will be described. As can be seen in

FIG. 3

, the pole mechanism

29

has a set of separable contacts

41

including a fixed contact

43

connected to a line terminal

45

and a movable contact

47

. Pole mechanism

29

further includes an operating mechanism

49

, a thermal magnetic trip device

51

and a supporting metal frame

53

.

Briefly, the operating mechanism

49

includes a contact arm

55

carrying the moveable contact

47

at a lower end a cradle

57

pivoted about a pivot pin

59

molded in the partition

19

of the top base

5

. The contact arm

55

is connected to the cradle

57

by a helical tension spring

61

. The upper end of the contact arm

55

is engaged by the molded handle

37

. Movement of the handle

37

in the counterclockwise direction to the position shown in

FIG. 3

rotates the contacts arm

55

to close the separable contact

41

as is well known. When the handle

37

is moved clockwise in

FIG. 3

to the off position (not shown), the contact arm

55

moves away from the fixed contact

43

to open a separable contacts

41

, as is well known.

The contact arm

55

is electrically connected to the lower end of elongated bimetal element

63

by flexible conductor

65

. The bimetal

63

is part of the thermal-magnetic trip device

51

and is secured at its upper end to a flange

67

on the metal frame

53

. Another flexible conductor

69

connected to the upper end of the bimetal

63

passes through an opening

71

in the partition

19

into the third compartment

27

where it is connected to the ground fault electronics, and returns through the opening

71

and is connected to a tang

73

engaging a load connector

75

. Thus, with the separable contacts

41

closed as shown in

FIG. 3

, a closed circuit through the pole

29

extends from the line terminal

45

through the fixed contact

43

, the moveable contact

47

the contact arm

55

, the flexible conductor

65

, the bimetal

63

, the flexible conductor

69

, the tang

73

and load conductor

75

.

The thermal-magnetic trip device

51

includes in addition to the bimetal

63

, an elongated rigid magnetic armature or latch member

77

secured to the lower end of the bimetal

63

by flexible metal strip

79

, and a finger

81

on the cradle

57

. The magnetic armature

77

has an opening

83

which defines a latch surface on which the finger

81

of the cradle

57

is latched when the mechanical pole is reset by moving the handle slightly past the off position, as is well-known.

When the circuit breaker

1

is in the on position, as shown in

FIG. 3

, and a overload current above a first predetermined value persists, the bimetal

63

is heated by the current flowing through it which deflects the lower end counterclockwise to unlatch the finger

81

from the latch opening

83

. This releases the cradle

57

which allows the spring

61

to rotate the contact arm

55

counterclockwise as viewed in

FIG. 3

to a tripped position (not shown) in which the separable contacts

41

open. When a short circuit occurs with the circuit breaker in the on position shown in

FIG. 3

, the current generates a magnetic field which is channeled by a U-shaped pole piece

85

mounted on the bimetal

63

to attract the magnetic armature

77

toward the pole piece to unlatch the cradle

57

and thereby trip the separable contacts open.

As previously discussed in connection with

FIG. 2

, a coupler

35

couples the two pole mechanisms

29

and

31

together so that when one mechanical pole trips, the other pole trips simultaneously. This coupler

35

includes a coupling rod or shaft

89

extending through the third compartment

27

, the partition

19

into the first compartment

21

and partition

23

the second compartment

25

. On each end of the rod

89

is an actuating member

95

1

and

95

2

, respectively, for engaging the associated pole mechanism

29

,

31

. Each actuating member has an actuating finger

97

adjacent to the magnetic armature

77

of the associated pole. Each actuating member also has a nose

99

disposed adjacent a flange

101

on the cradle

57

of the associated pole mechanism. When one of the poles of the circuit breaker trips, the associated cradle

57

engages the nose

99

and rotates the coupling rod

89

. This in turn rotates the actuating member

95

on the other end of the rod

89

so that the actuating finger

97

of that actuating member engages the associated magnetic armature

77

to unlatch the cradle

57

and trip the other pole.

The bimetals

63

of the respective poles are designed to respond to low level overcurrents inversely as a function of time. That is, the greater the magnitude of the current the shorter the time for the thermal trip. While the construction of the bimetals is such that they conform to the overcurrent characteristic reliability, the circuit breaker

1

must be calibrated to assure that this inverse current response characteristic produces a trip at code specified conditions. For example, the circuit breaker can be calibrated so that at 250% of rated current a pole trips within 15 to 25 seconds. The circuit breaker

1

is calibrated by applying the specified overcurrent to a pole, and then adjusting the mechanism so that it trips within the specified time period. Thus, for example, in a case of a twenty amp circuit breaker, each pole is separately calibrated by applying 50 amperes to the pole in the closed position, and the mechanism is adjusted so that a trip occurs within 15 to 25 seconds.

In addition to the thermal-magnetic trip functions of the poles

29

and

31

, the circuit breaker

1

includes an electronic trip device

33

which can provide ground fault and/or arc-fault protection. As described in U.S. Pat. No. 5,483,211, the electronic trip device

33

is housed in the third compartment

27

and includes a solenoid, which in response to ground fault or arcing conditions detected in either pole actuates a finger

105

extending through and opening

107

in the partition

23

into the first compartment

21

where it bears against the magnetic armature

77

to trip the first pole mechanism

29

in a manner described above for a magnetic trip. As also described above, tripping of the first pole

29

results in tripping of the second pole

31

by the coupler

35

.

Calibration of the poles

29

and

31

of the circuit breaker

1

is effected through adjustment of the metal support frame

53

of the associated pole. This metal support frame

53

for the pole

29

is shown in more detail in

FIGS. 4 and 5

. The support plate

53

has opening

109

in a lobe

111

at one end which is keyed to and engaged by a projection

113

on the molded pivot

59

in the partition

19

of the top base

5

. An oval shaped opening

115

spaced from the opening

109

engages a molded pin (not shown) on partition

19

(not shown). The openings

109

and

115

fit snugly over the corresponding projections to firmly fix the position of the metal support frame

53

within the top base

5

. Bent over tabs

117

and

119

at the two upper ends of the metal support frame

53

butt against the top cover

7

of the housing to further maintain the fixed position of the metal support frame

53

when the circuit breaker

1

is assembled. A large aperture

121

near the right hand end of the metal support frame

53

accommodates the coupler

35

.

The opening

121

and an intersecting calibration receptacle or slot

123

partially separate a free end

125

from the remainder of the support

53

. A notch

126

in the top edge of the metal support frame

53

further weakens the connection of the free end

125

to the remainder of the support plate

53

. The flange

67

to which the bimetal

63

is secured extends laterally from the free end portion

125

of the metal support frame

53

.

Heretofore, the circuit breaker

1

has been calibrated by assembling the pole mechanism

29

within the cavity of the top base

5

, and before the top cover

7

is installed, applying the calibrating current between the terminals

45

and

75

with this pole mechanism closed. With the pole mechanism in this “on the half shell” condition, a tool

127

is inserted into the calibration receptacle or slot

123

as represented in FIG.

5

. When the prescribed time of application of the calibrating overcurrent has elapsed, the tool

127

is rotated to distort the free end

125

of the metal support frame

53

thereby rotating flange

67

carrying the bimetal

63

and forcing the breaker to trip. As seen in

FIG. 5

, the distortion of the metal support frame

53

causes the bimetal

63

to rotate from the phantom position to the full-line position. This calibration is performed automatically by a machine which applies current to the terminals, inserts the tool

127

into the slot

123

, and rotates the tool

127

to force the breaker to trip upon expiration of the prescribed time. Once the circuit breaker

1

has been calibrated, the top cover

7

is placed over the top base

5

to enclose the compartment

21

and is secured in place by the rivets

15

. The second pole

31

is similarly calibrated “on the half shell” before the circuit breaker is fully assembled. The circuit breaker is then tested by again applying the calibrating current and observing the breaker trips at the prescribed time within specified tolerances. If the circuit breaker

1

does not pass the test, a hook is inserted into an opening

129

molded in the housing top base

05

to engage the free end of the bimetal

63

and either push or pull the bimetal in an attempt to bring the thermal trip within the calibration limits. This repair is performed manually and is difficult to implement. While this repair procedure has increased the number of circuit breakers within calibration tolerance, it is time consuming and difficult to implement.

U.S. Pat. No. 5,008,645 teaches an arrangement and procedure for calibrating a single pole circuit breaker after it has been fully assembled. An opening molded into the housing wall and aligned with the calibration slot in the metal support frame allows the calibration tool to be inserted and rotated to adjust the bimetal calibration with the circuit breaker fully assembled. While this arrangement and method is suitable for calibrating the second pole mechanism

31

of the two-pole circuit breaker

1

where the metal support frame is adjacent to the outer wall of the bottom base

11

, it is not suitable for calibrating the pole mechanism

29

of the two-pole breaker such as that shown number in U.S. Pat. No. 5,483,211, because the actuating member

95

for this pole is between the outside wall formed by the top cover

7

and the metal support plate and blocks access to the slot

123

.

In accordance with the invention, the actuating member

95

, is configured so that the actuating finger

97

extends adjacent to, but is laterally displaced from, a direct line

131

from a calibration hole

133

in the top cover

7

to the calibration receptacle slot

123

, to permit insertion of the calibration tool

127

through the calibration hole

133

for engagement with the calibration slot

123

with a circuit breaker fully assembled. As can best be seen in

FIGS. 6 through 8

, this is accomplished by offsetting the actuating finger

97

from alignment with the center of the attachment member. More particularly, the actuating finger

97

is cantilevered from a hub

135

on the attachment actuating member

95

with the outer surface

137

of the actuating finger substantially tangent to the hub. The inner surface

139

of the actuating finger has an arcuate interface

141

with the hub

135

. Furthermore, the actuating finger

97

is tapered toward the free end

143

so that the stress is more evenly distributed along the actuating finger. In addition, the nose

99

is configured to form with the actuating finger

97

a gap

145

which is aligned with the path

131

for inserting of the calibration tool. The gap

145

is sized so that even with rotation of the actuating member

95

during tripping of the circuit breaker, the direct line

131

between the calibration opening

133

and the calibration slot

123

remains unobstructed by the attachment member. While the attachment member

952

for the second pole

31

need not be similarly configured because it is not between the calibration opening in the housing and the calibration slot of the metal support frame of the second pole frame mechanism

31

, it is preferred that a single actuating member configuration be established for both ends of the coupler to simplify assembly and reduce costs. Accordingly, the attachment member

95

has sockets

147

molded in each side face for engagement with the coupling rod

89

depending upon which pole the particular attachment member is used. As taught in U.S. Pat. No. 5,008,645 a tamper indicating seal

149

can be installed over the calibration opening

133

after the circuit breaker has been calibrated at the factory to preclude subsequent changing of the calibration.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.

Two pole circuit breaker calibrated in assembled state

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Abstract

Description

Claims