High current auxiliary switch for a circuit breaker

FIELD OF THE INVENTION

The present invention relates generally to circuit breakers. More specifically, the present invention relates to an auxiliary switch for a circuit breaker which is capable of switching substantially the rated interrupt current of the circuit breaker.

BACKGROUND OF THE INVENTION

Control panel systems, having a variety of panel mounted circuit breakers mounted thereon, are often sold in both the United States and Europe to provide branch circuit protection or supplementary (equipment) protection. By way of example, circuit breakers are often mounted in theater lighting control panel systems to provide protection for branch circuits which supply electrical power to the various lights of a theater. Alternatively, circuit breakers can also be mounted in control panels to provide dedicated supplementary protection to equipment such as computers, power supplies or copying machines.

Circuit protection standards vary between the United States and Europe, and impose different performance requirements on the circuit breakers involved. For example, U.S. standards rarely allow the provision of a disconnect to the neutral (return) side of a circuit load, while European standards often require it. European standards for a neutral disconnect effectively requires the addition of another switch, capable of handling the rated interrupt current capacity of the circuit breaker, when connected in series with the circuit breaker and the load. Rated interrupt current, i.e., interrupting rating, is defined in article 100 of the 1996 edition of the National Electric Code, published by the National Fire Protection Association, Quincy, Mass., as: “the highest current at rated voltage that a device is intended to interrupt under standard test conditions”. The interrupt current and the standard test conditions for a device, such as a circuit breaker, would typically be specified in an industry excepted standard, e.g., UL 1077, titled Standard For Supplementary Protectors For Use In Electrical Equipment, or UL489, titled Standard For Molded Case Circuit Breakers And Circuit Breaker Enclosures. Prior art attempts to modify existing U.S. circuit breakers to provide neutral side disconnects involved stacking a second pole up against the single pole circuit breaker, effectively doubling the width and size of such an assembly.

However, space is a premium in control panel systems. In the telecommunication industry, for example, telecommunication equipment designers can earn bonuses of up to $1000 for every square inch of panel space saved. Consequently, there is often very little panel space to accommodate the additional second pole for the circuit breakers without an expensive redesign of the system. This is especially critical when the additional requirements increase the overall package width, since the circuit breakers are often stacked side by side, leaving very little space in between for growth.

Auxiliary switches are often mounted to the bottom portions of circuit breakers to provide an extra set of switching contacts without a significant increase in overall package size or width. However, auxiliary switches are primarily used to indicate status of the circuit breaker, e.g., whether the circuit breaker is open or closed, and typically have current switching capacities which are much lower than the interrupt current capacity rating of the main breaker. The low power auxiliary switches are constructed of much smaller components and require much less space to actuate than the main contacts of the circuit breaker.

To construct an auxiliary switch capable of switching the rated interrupt current capacity of its associated circuit breaker with a minimum impact in overall package width is problematic for several reasons. For example, the contact gap spaces and spring forces for the auxiliary switch must increase, tending to increase the package size and width. Also, since the auxiliary contacts are mechanically actuated by the main breaker contacts, the increased spring forces from the auxiliary switch actuator acting on the main breaker contacts may significantly change the main breaker contact pressure. This can result in excessive arcing and premature circuit breaker contact wear.

Another significant factor which tends to make the auxiliary switch package grow is that the higher power requirements can result in greater arcing during make (make contact) or break (break contact) of the auxiliary contacts. This increases the possibility of welding the contacts together or leaving debris and carbon deposits on the contacts. This problem is often minimized in the main circuit breaker with a lateral wiping action designed between the movable and stationary contacts of the main breaker. The wiping action is used to clean the contacts and shear away any welds as the contacts make or break. That is, the moveable contacts of the main circuit breaker pivots on a moveable contact lever to make contact with the stationary contact. A generally kidney shaped slot at the pivot point of the movable contact lever is fundamental to this arcuate motion. This slot is easily elongated to provide for over travel in the lateral directions of the contacts relative to each other, which results in the wiping action.

However, auxiliary switch contacts are typically designed to have a substantially linear motion when bridging the contact gaps (bridge contacts), rather than the arcuate motion described above for the main breaker contacts. Problematically, the bridge contacts are not conducive to providing a wiping action in the lateral direction. The arcing problem can be compensated for by increasing the size of the auxiliary contacts and their associated contact gaps, but this tends to unduly increase the overall package size and width.

Accordingly, there is a need for an improved auxiliary switch for a circuit breaker, which is capable of switching the rated interrupt current capacity of the associated circuit breaker.

SUMMARY OF THE INVENTION

The present invention offers advantages and alternative over the prior art by providing an auxiliary switch for a circuit breaker capable of switching the rated interrupt current capacity of the breaker. The auxiliary switch/circuit breaker assembly can be used to provide neutral disconnects to an existing control panel system to meet European standards.

These and other advantages are accomplished in an exemplary embodiment of the invention by providing a circuit breaker assembly comprising a circuit breaker and an auxiliary switch. The circuit breaker has a predetermined rated interrupt current capacity, and includes a movable contact lever having a circuit breaker moveable contact disposed thereon. The contact lever has an open position and a closed position. The auxiliary switch includes a switch housing mounted in an opening defined by the circuit breaker. An auxiliary actuator is movably mounted within the switch housing and has an upper portion of the auxiliary actuator protruding into the opening of the circuit breaker from the switch housing. An auxiliary moveable contact member has an auxiliary moveable contact disposed thereon, the member is moveably mounted to the auxiliary actuator. A contact spring acts between the auxiliary actuator and the auxiliary moveable contact member. An auxiliary stationary contact is arranged in the switch housing for engagement with the auxiliary moveable contact. A return spring is disposed between the switch housing and auxiliary actuator urging the auxiliary stationary and moveable contacts apart. The auxiliary switch is adapted to switch substantially the rated interrupt current of the circuit breaker through the moveable and stationary auxiliary contacts when the moveable contact lever of the circuit breaker moves from the open position to the close position, thereby depressing the auxiliary actuator to have the auxiliary moveable contact make contact with the auxiliary stationary contact.

In an alternative embodiment of the invention the overall width of the auxiliary switch is substantially equal to or less than the overall width of the circuit breaker.

Several embodiments of the auxiliary switch disclose various features which contribute to increasing the interrupt current rating and/or down sizing the width of the auxiliary switch. Among them are:

an early make, late break of the auxiliary contacts compared to the circuit breaker contacts;

an inertia dampening fly wheel attached to the actuator of the switch to enhance the early make/late break feature;

a wiping action between the moveable and stationary contacts of the auxiliary switch to clean off welding and debris deposited from arcing;

dual auxiliary contacts to enhance the contact area with little impact on package size and width; and

a positioning of the auxiliary actuator on the contact lever of the circuit breaker to prevent the spring forces acting on the actuator from affecting circuit breaker contact pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a side view of a circuit breaker assembly in accordance with the present invention;

FIG. 2

is a side view of

FIG. 1

;

FIG. 3

is a perspective view of the interior of the circuit breaker assembly with the circuit breaker moveable contact lever in the open position;

FIG. 4

is a perspective view of the interior of the circuit breaker assembly with the circuit breaker moveable contact lever in the closed position;

FIG. 5

is a perspective view of an embodiment of the auxiliary switch showing an inertia dampening fly wheel in accordance with the present invention;

FIG. 6

is a perspective view of an embodiment of the auxiliary switch showing a canted moveable contact member in accordance with the present invention;

FIG. 7

is a side view of the actuator of the switch in

FIG. 6

;

FIG. 8

is an enlarged view of the moveable and stationary contact of the auxiliary switch of

FIG. 6

with their centerlines offset;

FIG. 9

is an enlarged view of the moveable and stationary contact of the auxiliary switch of

FIG. 6

with their centerlines aligned;

FIG. 10

is a force balance diagram on the moveable contact lever of the circuit breaker of

FIG. 4

in the closed position;

FIG. 11

is a schematic diagram of the auxiliary switch contacts having a single pole, single throw, double break arrangement;

FIG. 12

is a schematic diagram of the auxiliary switch contacts having a single pole, double throw, double break arrangement;

FIG. 13

is a wiring diagram of the auxiliary switch used as a neutral disconnect with the circuit breaker; and

FIG. 14

is a wiring diagram of the auxiliary switch wired in series with the circuit breaker to increase interrupt capability of the circuit breaker in a DC circuit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to

FIGS. 1 and 2

, front and side views respectively, of an exemplary embodiment of a circuit breaker assembly in accordance with the present invention is shown generally at

10

. The circuit breaker assembly

10

includes a circuit breaker

12

with an auxiliary switch

14

mounted thereon. Half shells

16

and

18

form a split case enclosure

20

which encloses the interior components of the circuit breaker

12

. Toggle handle

22

, extending out of the top of circuit breaker

12

, is pivotally mounted to the interior of the split case

20

to provide manual actuation of the circuit breaker

12

, and circuit breaker terminals

24

and

26

, extending through the bottom of circuit breaker

20

, provide electrical connection to load and source lines (not shown). The auxiliary switch

14

includes a switch housing

28

mounted in an opening defined by the circuit breaker

12

, and has a pair of auxiliary terminals

30

and

32

extending straight through the bottom of switch housing

28

. The auxiliary terminals include a center hole

33

through which a wire, e.g., a source line or load line, can be attached.

As will be discussed in greater detail hereinafter, the auxiliary switch

14

is adapted to switch substantially the rated interrupt current of circuit breaker

12

without substantially changing the overall package width of the circuit breaker assembly

10

. That is the overall width of the auxiliary switch

14

is substantially equal to or less than the overall width of the circuit breaker

12

.

Typically, the auxiliary switch

14

and circuit breaker

12

fall into a general industry classification of “Low Voltage” circuit protection devices, which have normal operation ratings that range up to 100 amps at 300 volts AC or 100 amps at 80 volts DC. In addition to the normal operation ratings, circuit protection devices are required to be rated for the maximum current they can safely interrupt under standard test conditions at their rated voltage. This rating is known as the interrupt current capacity of the circuit protection device. The auxiliary switch

14

is typically rated for use, in series with the circuit breaker, with an interrupt current capacity of 5000 amps at 120 volts AC, 3000 amps at 240 volts AC, and 5000 amps at 80 volts DC.

Comparatively, prior art auxiliary switches in these voltage ranges are not rated for handling substantially higher interrupt currents than the normal operation current ratings and are therefore limited to use for indicating circuit breaker status, e.g., on/off or make/break.

Though this embodiment describes a split case circuit breaker, the circuit beaker can be any switch that automatically interrupts an electric circuit under an infrequent abnormal condition, e.g., current overload.

Referring to

FIGS. 3 and 4

, the circuit breaker

12

includes a collapsible linkage assembly

34

engaged between a moveable contact lever

36

and the handle

22

which is pivotally mounted to the circuit breaker enclosure

20

. The moveable contact lever

36

includes a circuit breaker moveable contact

38

disposed thereon which traverses from an open position

40

to a closed position

42

across a predetermined first distance

43

, to make electrical contact (make) with circuit breaker stationary contact

44

. Typically, when the contact lever

36

is in the closed position, a source current will conduct through terminal

26

to the stationary contact

44

. The current is conducted through the stationary contact

44

, through the movable contact

38

, to the movable contact lever

36

. The movable contact lever

36

is connected to the current sensing electromagnetic coil

48

through lead

52

. The coil

48

is connected through lead

50

to the terminal

24

and out to a load. When the current in the coil exceeds a predetermined rated current capacity, e.g. rated operational current or rated interrupt current, the coil will cause the circuit breaker to trip, thereby collapsing the linkage assemble

34

, pivoting the moveable contact lever

36

from the closed position

42

to the open position

40

and breaking contact (break) between the moveable and stationary contacts

38

and

44

to open the circuit. An auxiliary coil

45

may be provided for allowing remote or relay opening of the contacts

42

/

44

. The auxiliary coil

45

is preferably on a separate bobbin from the main coil

48

rather than simply supplied as an alternative to the usual circuit breaker configuration with a single main coil. See U.S. Pat. No. 4,982,174 for such an arrangement. In

FIGS. 3 and 4

, the auxiliary coil bobbin is made in two parts so as to surround the coil

45

completely. The arrangement assures that failure of the coil

45

will not interfere with normal circuit breaker operation.

The auxiliary switch housing

28

, of the auxiliary switch

14

, includes flanges

54

which slidably engages circuit breaker mounting grooves

56

to mount the housing

28

into opening

58

defined by the circuit breaker enclosure

20

. The auxiliary switch

14

also includes an auxiliary actuator

60

slidably mounted within the switch housing

28

. An upper portion

62

of the auxiliary actuator

60

protrudes into the opening

58

of the circuit breaker

12

from the switch housing

28

. An auxiliary moveable contact member

64

extends laterally out of opposing sides of a hollow lower portion

66

of the auxiliary actuator

60

and has a pair of auxiliary moveable contacts

68

disposed thereon. The moveable contact member

64

is moveably mounted and retained by the hollow lower portion

66

of the auxiliary actuator

60

. A contact spring

70

(shown in dotted lines) acts between the auxiliary actuator

60

and the auxiliary moveable contact member

64

to urge the moveable contact member

64

against the bottom of the auxiliary actuator

60

. A return spring

72

is disposed between the switch housing

28

and the auxiliary actuator

60

urging the upper portion

62

of the auxiliary actuator

60

into engagement against the movable contact lever

36

of the circuit breaker

12

. A pair of auxiliary stationary contacts

74

are arranged in the switch housing

28

for engagement with the auxiliary moveable contacts

68

and are spaced a second predetermined distance

76

therefrom. When the moveable contact lever

36

of the circuit breaker

12

moves from the open position

40

to the close position

42

, the contact lever

36

depresses the auxiliary actuator

60

to have the auxiliary moveable contact

68

traverse the second predetermined distance

76

and make contact with the auxiliary stationary contact

74

.

Typically, when the auxiliary switch

14

is used as a neutral disconnect for a protected load, the auxiliary contacts

68

and

74

of the auxiliary switch

14

will be wired on the neutral side of the load in series with the load and the circuit breaker contacts

38

and

44

of the circuit breaker

12

. In this case, when the auxiliary contacts

68

and

74

are closed, load current will conduct from terminal

30

, through one of the moveable and stationary contacts

68

and

74

, across the moveable contact member

64

, through the other moveable and stationary contacts

68

and

74

, and out terminal

32

to the source. Since the auxiliary actuator

60

of the auxiliary switch

14

is mechanically actuated by circuit breaker contact lever

36

, when the circuit breaker

12

trips the actuator switch

14

will also trip, thereby causing the auxiliary contacts

68

and

74

to separate and disconnect the neutral line from the load.

By utilizing the dual pair of moveable and stationary auxiliary contacts

68

and

74

rather than a single set of contacts, the contact surface area and gap size are effectively doubled without significantly affecting the overall width of the auxiliary switch

14

. The dual contacts are therefor a contributing factor to the increased current capacity of the auxiliary switch

14

.

Another factor that reduces arcing in the auxiliary switch

14

and enables the auxiliary switch

14

to switch substantially the rated interrupt current of the circuit breaker

12

, is a late break, early make feature. That is, the predetermined second distance

76

through which the auxiliary moveable contacts

68

must traverse is designed to be less than the predetermined first distance

43

through which the circuit breaker moveable contact

38

must traverse. Consequently, the moveable and stationary contacts

68

and

74

of the auxiliary switch

14

will make earlier and break later, than the moveable and stationary contacts

38

and

44

of the circuit breaker

12

. Therefore, most of the arcing occurs across the larger circuit breaker contacts when they make or break first, enabling the smaller auxiliary contacts to be reduced in size for the same interrupt current rating.

Though the circuit breaker moveable contact lever

36

is shown as a pivotally mounted moveable contact arm, other moveable contact lever embodiments are also considered within the scope of this invention. By way of example, the lever

36

may have a dual contact bridge configuration similar to that of the moveable contact member

64

.

Though the auxiliary actuator

60

is shown in this embodiment as being slidably mounted within the switch housing

28

, one skilled in the art would recognize that the auxiliary actuator

60

may be moveably mounted in other ways, e.g., pivotally mounted. Additionally, though the auxiliary actuator

60

is shown in this embodiment as making contact with the moveable contact lever

36

when it is in the open position

40

, a gap may exist between the auxiliary actuator

60

and the moveable contact lever

36

when it is in this position

40

. In that case, the gap will be closed as the moveable contact lever

36

moves from the open position

40

to the closed position

41

to contact and depress the auxiliary actuator

60

.

Referring to

FIG. 5

, another embodiment of the auxiliary actuator switch

14

shows an enhancement to the early make, late break feature whereby an inertia dampening flywheel

73

is pivotally attached to the switch housing

28

via flywheel pivot axis

75

. The flywheel has an engagement slot

77

slidably engaged to a mounting pin

79

located on the lower portion

66

of the auxiliary actuator

60

.

The fly wheel

73

engaged with the auxiliary switch actuator

60

provides inertia dampening to the auxiliary switch

14

such that the moveable and stationary contacts

68

and

74

of the auxiliary switch

14

break later than the moveable and stationary contacts

38

and

44

of the circuit breaker

12

. When the inertia dampening of the flywheel is combined with the early make, late break design discussed previously, the arcing across the auxiliary contacts

68

and

74

is further reduced, allowing the auxiliary switch

14

to be further down sized.

Referring to

FIGS. 6 and 7

, an alternative embodiment of the auxiliary switch

14

is shown where case

28

further includes an upper portion

78

removeably attached to a lower portion

80

. The lower portion

80

covers and protects right angle terminals

82

and has lower portion hooks

84

extending upwardly to removably engage with upper portion hooks

86

extending downwardly from the bottom of the upper portion

78

of case

28

.

This embodiment also shows the auxiliary moveable contact member

64

canted (tilted) relative to the substantially horizontal stationary contacts

74

which enables a contact wiping action when the moveable and stationary contacts

68

and

74

make and break. The lower portion

66

of the auxiliary actuator

60

has a hollow section

88

with a canted bottom surface

89

which slidably retains the contact spring

70

and contact member

64

. The contact spring

70

urges the contact member

64

flush against the canted surface

89

when the actuator

60

is fully extended, i.e., when the moveable contact lever

38

is in the open position

40

.

Referring to

FIGS. 8 and 9

, a convex surface

90

is disposed on the auxiliary moveable contacts

68

having a centerline

92

substantially normal to the surface

90

. Additionally, a convex surface

94

is disposed on the auxiliary stationary contacts

74

having a centerline

96

substantially normal to the surface

94

, and facing the convex surface

90

of the auxiliary moveable contacts

68

. When the moveable contact lever

36

pivots from the open position

40

to the closed position

42

, the actuator

60

is depressed. The moveable and stationary contacts

68

and

74

move linearly toward each other until their convex surfaces

90

and

94

make contact with their centerlines

92

and

96

being offset. The pair of stationary contacts

74

then lift the moveable contact member

64

off of the canted surface

89

of the actuator

60

such that the contact spring

70

generates a force along the centerline

92

of the moveable contacts

68

. Consequently, a reactionary force is generated along the centerline

96

of the stationary contact

74

. This misalignment of forces creates a moment that rotates the moveable contact member

64

. Since the contact member

64

is retained by the hollow section

88

of actuator

60

, it is forced to pivot about a pivot point

98

urging the centerlines

92

and

96

of the contacts

68

and

74

substantially into alignment. This rotation causes a relative lateral motion between the moveable and stationary contacts

68

and

74

, wiping the surfaces

90

and

94

clean of welds and debris caused by arcing on break. On break, the slanted surface

89

of the actuator

60

contacts one side of the moveable contact member

64

first, generating a twisting moment that will shear any contact welds caused by arcing on make. The wiping action enables the spring forces and contact surface areas to be downsized, and therefore is an additional factor in enabling the switch to keep a small package size and a high interrupt current rating.

Referring to

FIG. 10

, a force balance diagram on the moveable contact lever

36

in the closed position

42

is shown. A toggle compression force F

T

is generated by the collapsible linkage assembly

34

on the contact lever

36

. The toggle compression force F

T

has a line of direction which passes through toggle attachment point

100

and fulcrum point

101

which is located on the moveable contact

38

side of the moveable contact lever

36

. A main spring force F

MS

through the main spring pin

102

reacts to the toggle compression force F

T

to generate a moment M

MS

defined by the equation M

MS

=F

MS

(A), where “A” is the distance between the line of direction of F

MS

and the fulcrum point

101

. This moment M

MS

is reacted to by the moveable contact

38

on the stationary contact

44

to generate a predetermined contact pressure force F

C

and an equal and opposite contact pressure moment M

C

. The contact pressure moment M

C

is defined by the equation M

C

=F

C

(B) where “B” is the distance between the line of direction of F

C

and the fulcrum point

101

. The upper portion

62

of the auxiliary actuator

60

is positioned at the fulcrum point

101

and generates an auxiliary actuator force F

AUX

which is substantially in line with the direction of the opposing toggle compression force F

T

.

It is important to maintain the predetermined contact pressure F

C

between the moveable and stationary contacts

38

and

44

to insure proper circuit breaker

12

performance and to prevent premature wear on the contacts

38

and

44

. By positioning the actuator

60

at the fulcrum point

101

, the larger springs required to enable the auxiliary switch

14

to handle the higher interrupt current ratings of the circuit breaker

12

can be utilized without affecting the contact pressure F

C

or the performance of the circuit breaker

12

.

Referring to

FIG. 11

, as is well known, the auxiliary switch contacts are discussed above as having a single pole, single throw, double break arrangement. However, it is also considered within the scope of this invention to have other contact arrangements as well. By way of example, a single pole, double throw, double break embodiment is shown in FIG.

12

.

Referring to

FIG. 12

, the contact lever

64

of the auxiliary switch

14

has an additional pair of moveable contacts

104

disposed on its opposing side. An additional pair of terminals

106

and

108

are connected to an additional pair of stationary contacts

110

. The terminals

30

and

32

could be connected in one circuit, and the terminals

106

and

108

could be connected to a separate circuit. Alternatively, terminals

30

and

106

or terminals

32

and

108

could be tied together in the same circuit.

Referring to

FIG. 13

, a wiring diagram of the auxiliary switch used as a neutral disconnect is shown. The line side of the source

112

is connected to terminal

26

which is in series with the circuit breaker contacts

38

and

44

, current sensing coil

48

and terminal

24

of the circuit breaker. The load line is connected in series to load

114

. The return side of the load is connected to auxiliary terminal

32

which is in series with auxiliary contacts

74

and

68

, and auxiliary terminal

30

. Auxiliary terminal

30

is in turn connected to the return side of the source

112

to complete the circuit. The full load current must conduct through both the circuit breaker contacts

38

and

44

on the line side of the circuit, and the auxiliary contacts

68

and

74

on the load side of the circuit. Since the auxiliary contacts

68

and

74

are mechanically tied to the circuit breaker contacts

38

and

44

, when the circuit breaker

12

disconnects the line side, the auxiliary switch

14

will disconnect the neutral side.

Referring to

FIG. 14

, a wiring diagram of the auxiliary switch

14

used in series with the circuit breaker

12

in a DC circuit is shown. In this embodiment the circuit breaker contacts

38

and

44

are in series connection with the auxiliary contacts

68

and

74

on the high side of a DC circuit between a DC source

116

and a load

118

. By connecting the auxiliary switch in this fashion, the DC interrupt capacity of the circuit breaker can be increased.

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.