SLOT MOTOR AND CIRCUIT BREAKER INCLUDING THE SAME
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to electrical switching apparatus, such as, for
example, circuit breakers and, more particularly, to circuit breakers including a slot
motor.
Background Information
Circuit breakers are used to protect electrical circuitry from damage
due to an overcurrent condition, such as an overload condition or a relatively high
level short circuit or fault condition. Circuit breakers include at least one pair of
separable contacts. A first contact is fixed within the circuit breaker housing and a
second movable contact is coupled to an operating mechanism. These separable
contacts are in electrical communication with either the line or the load coupled to the
circuit breaker. The operating mechanism moves the movable contact between a first,
open position wherein the movable contact is spaced from the fixed contact, and a
second, closed position wherein the fixed and movable contacts are in contact and in
electrical communication. The operating mechanism may be operated manually or by
a trip mechanism.
In order to enhance the speed of separation of the separable contacts,
the contacts may be disposed within a slot motor, which increases interruption
performance. The slot motor is a ring-shaped, loop-shaped or U-shaped device made
of magnetically permeable material (e.g., steel), which at least generally surrounds the
separable contacts and a movable contact arm of the operating mechanism. When the
circuit is live, an electrical arc may be drawn between the contacts during separation.
The electrical current interacts electro magnetically with the slot motor to induce a
magnetic field in the magnetic material of the slot motor, which, in turns, interacts
with the separating contacts and the movable contact arm to accelerate the contact
opening process. Examples of slot motors are disclosed in U.S. Patent Nos.
4,375,021; 4,546,336; 4,546,337; 4,549,153; 4,970,482; 5,694,098, and 6,281,459.
Ring-shaped or loop-shaped slot motors typically have two assemblies,
an upper assembly and a lower assembly. Both upper and lower assemblies include a

corresponding housing and a plurality of plates composed of the magnetically
permeable material. The lower assembly is disposed below the fixed contact.
Upon interruption of a short circuit or other fault condition by a circuit
breaker, molten metal may be deposited throughout the internals of the circuit
breaker, which may impair its performance.
Hence, there is room for improvement in electrical switching
apparatus, such as circuit breakers, and in components therefor.
SUMMARY OF THE INVENTION
This need and others are met by embodiments of the invention, which
provide a debris shield as part of an insulative slot motor housing. The debris shield
obstructs debris from entering internal circuit breaker areas, such as the operating
mechanism, where it could, otherwise, cause a functional problem. For example,
extensions are disposed from a portion of the insulative slot motor housing proximate
a number of the are plates, in order to shield the internal environment of the operating
mechanism from the are chamber.
In accordance with one aspect of the invention, a circuit breaker
comprises: a fixed contact; a movable contact; an operating mechanism comprising a
movable arm carrying the movable contact; an are chute comprising a plurality of
spaced apart are plates including a number of first are plates and a number of second
are plates; and a slot motor comprising: a slot motor structure disposed about the fixed
and movable contacts and a portion of the movable arm, and an insulative housing at
least substantially covering the slor motor structure and insulating the slot motor
structure from the movable arm and the fixed and movable contacts, the insulative
housing comprising a base and a pair of anus disposed from the base, wherein each of
the arms includes a first portion disposed proximate the first are plates and a second
portion disposed proximate the second are plates, wherein a space extending from the
first portion of the arms, which is noi occupied by the second portion of the arms, is
generally occupied by part of the are chute including a portion of the second are
plates, and wherein the second portion of the insulative housing forms a debris shield
between the second are plates and the operating mechanism.
The first and second are plates may include ends forming a generally
arcuate path. The movable arm may have a first position wherein the fixed and

movable contacts are closed and a second position wherein the fixed and movable
contacts are open. The movable contact may generally follow the generally arcuate
path from a position intermediate the first and second positions toward the second
position. The second portion of the insulative housing may include an edge which
approximates the arcuate path. The second portion of the insuiative housing may
obstruct debris from the second are plates from entering the operating mechanism.
As another aspect of the invention, a slot motor comprises: a slot motor
structure structured to be disposed about a fixed contact, a movable contact and a
portion of a movable arm carrying the movable contact, and an insulative housing at
least substantially covering the slot motor structure, the insulative housing being
structured to insulate the slot motor structure from the movable arm and the fixed and
movable contacts, the insulative housing comprising a base and a pair of arms
disposed from the base, wherein each of the arms includes a first portion structured to
be disposed proximate a number of first are plates and a second portion structured to
be disposed proximate a number of second are plates, and wherein a space extending
from the first portion of the arms, which is not occupied by the second portion of the
arms, is structured to be generally occupied by part of an are chute including a portion
of the second are plates.
As another aspect of the invention, a circuit breaker comprises: a
housing; a fixed contact; a movable contact; an operating mechanism comprising a
movable arm carrying the movable contact, the movable arm being pivotally mounted
with respect to the housing, the movable arm having a first position wherein the fixed
and movable contacts are closed and a second position wherein the fixed and movable
contacts are open; an are chute comprising a plurality of spaced apart are plates
including a number of first are plates and a number of second are plates; and a slot
motor comprising: a slot motor structure disposed about the fixed and movable
contacts and a portion of the movable arm, and an insulative housing at least
substantially covering the slot motor structure and insulating the slot motor structure
from the movable arm and the fixed and movable contacts, wherein the fixed contact
includes a first end disposed toward the are chute, a contact portion and a second end
disposed toward the operating mechanism, wherein the movable contact includes a
first end, a contact portion electrically contacting the contact portion of the fixed

contact in the first position of the movable arm, a second end and a side opposite the
contact portion of the movable contact, wherein the first are plates include a first end
distal from the operating mechanism and a second end facing the operating
mechanism, wherein the second are plates include a first end distal from the operating
mechanism and a second end facing the operating mechanism, wherein at least one of
the first are plates is disposed proximate the first end of the fixed and movable
contacts in the first position of the movable arm, wherein at least one of the second
are plates is proximate the first end of the movable contact in the second position of
the movable arm, wherein a portion of at least one of the second are plates is disposed
distal from the fixed contact and beyond the side opposite the contact portion of the
movable contact, wherein the insulative housing is generally disposed between the are
chute and the operating mechanism, wherein the insulative housing includes a first
portion proximate the second end of the first are plates, wherein the insulative housing
includes a second portion proximate the second end of the second are plates, and
wherein the second portion is smaller than the first portion of the insulative housing.
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:
Figure 1 is a vertical elevation view of a circuit breaker in accordance
with an embodiment of the invention.
Figure 2 is an isometric view of the operating mechanism and three poles
of the circuit breaker of Figure 1.
Figure 3 is an isometric view of a slot motor housing.
Figure 4 is an isometric view of the slot motor housing of the circuit
breaker of Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As employed herein, the term "number" shall mean one or an integer
greater than one (i.e., a plurality).
The invention is disclosed in association with a three-pole circuit
breaker, although the invention is applicable to a wide range of circuit breakers
having any number of poles.

Referring to Figure 1, a circuit breaker 2 includes a fixed contact 4, a
movable contact 6, an operating mechanism 8, an are chute 10 and a slot motor 12.
The operating mechanism 8 includes a movable arm 14 carrying the movable contaci
6. The movable arm 8, which is pivotally mounted with respect to molded housing
16, has a first closed position wherein the fixed and movable contacts 4,6 are closed
and a second open position (shown in phantom line drawing) wherein the fixed and
movable contacts 4,6 are open. The are chute 10 includes a plurality of spaced apart
are plates 18 including a number of first are plates 20 and a number of second are plates 22.
The fixed contact 4 includes a first end 24 disposed toward the are chute 10, a contact portion 26 and a second end 28 disposed toward the operating
mechanism 8. The movable contact 6 includes a first end 30, a contact portion 32
electrically contacting the contact portion 26 of the fixed contact 4 in the first closed
position of the movable arm 14, a second end 34 and a side 36 opposite the contact
portion 32 of the movable contact 6.
Also referring to Figure 4, the slot motor 12 (Figure 1) includes a slot
motor structure 38 (e.g., made of steel; made of steel laminations) (shown in phantom
line drawing in Figure 4) disposed about the fixed and movable contacts 4,6 and a
portion of the movable arm 14, and an insulative housing 40 (as best shown in Figure
4). The insulative housing 40 at least substantially covers the slot motor structure 38 .
and insulates the slot motor structure from the movable arm 14 and the fixed and
movable contacts 4,6. Preferably, any exposed areas of the slot motor structure 38 are
covered by a suitable insulative tape 41 as shown in Figure 2. Alternatively, the
insulative housing 40 may be molded to cover (not shown) the arms 86 (Figure 4) of
the slot motor structure 38. The insulative housing 40 includes a base 42 and a pair of
arms 44,46 disposed from the base. Each of the arms 44,46 includes a first portion 48
disposed proximate a number of the first are plates 20 and a second portion 50
disposed proximate a number of the second are plates 22. The second portion 50 is
smaller than the first portion 48. A space 52 (shown in phantom line drawing
extended from the first portion 48 of the arm 46) extending from the first portion 48
of the arms 44,46, which is not occupied by the second portion 50 thereof, is generally
occupied by a side wall 55 (Figure 2) of the are chute 10 and a portion 54 of the

second are plates 22. The second portion 50 of the arms 44,46 forms a debris shield
56 between the second are plates 22 and the operating mechanism 14.
The first are plates 20 include a first end 58 distal from the operating
mechanism 14 and a second end 60 facing the operating mechanism. The second are plates 22 include a first end 62 distal from the operating mechanism 14 and a second
end 64 facing the operating mechanism. The second ends 60,64 of the first and
second are plates 20,22 form a generally arcuate path 66. The first end 30 of the
movable contact 6 generally follows the generally arcuate path 66 from a position
intermediate the first closed position (as shown in Figure 1) and the second open
position (as shown in phantom line drawing in Figure 1) toward the second open
position. At least one of the first are plates 20, such as are plate 68, is; disposed
proximate the first end 24 of the fixed contact 4 and the first end 30 of the movable
contact 6 in the first closed position of the movable arm 14. At least one of the
second are plates 22, such as are plate 70, is proximate the first end 30 of the movable
contact 6 in the second open position of the movable arm 14. A portion 72 of at least
one of the second are plates 22 is disposed distal from the fixed contact 4 and beyond
the side 36 opposite the contact portion 32 of the movable contact 6. In other words,
in the example of Figure 1, the portion 72 of at least one of the second are plates 22 is
disposed above (with respect to Figure 1) the fixed contact 4.
Figure 2 shows the operating mechanism 8 and three poles 74,76,78 of
the circuit breaker 2 of Figure 1. Each of these poles, as shown with pole 74, includes
corresponding ones of the are chute 10, the slot motor 12, the movable arm 14 and the
separable contacts 4,6 (Figure 1).
Figure 3 shows a low-profile insulative slot motor housing 80 and the
steel laminations 38 (shown in phantom line drawing) therefor. Unlike the insulative
housing 40 (as best shown in Figure 4), the insulative housing 80 does not include the
second portion 50 which forms the debris shield 56 between the second are plates 22
and the operating mechanism 14.
As shown in Figure 4, the insulative slot motor housing 40 at least
substantially covers the U-shaped slot motor laminations 38 (shown in phantom line
drawing), thereby insulating the same from the fixed and movable contacts 4,6 and
from the movable arm 14 of Figure I. As shown in Figure 1, the bottoms 82 of the

generally U-shaped laminations 38 are under the fixed contact 4, which is carried by
the reverse loop conductor 83. As is well known, the laminations 38 are disposed
about the fixed contact 4, the movable contact 6 and a portion of the movable arm 14.
The steel laminations 38 form a slot motor structure including a base 84 and two arms
86, with the base 84 being disposed opposite the contact portion 26 of the fixed
contact 4 and with the arms 86 extending toward the second end 64 of the second are plates 22.
As shown in Figures 1 and 2, the insulative slot motor housing 40 is
generally disposed between the are chute 10 and the operating mechanism 8, with the
first portion 48 being proximate the second end 60 of the first are plates 20 and the
second portion 50 being proximate the second end 64 of the second are plates 22.
As best shown in Figure 4, the slot motor housing 40 includes a
generally U-shape, as formed by the base 42 and arms 44,46, corresponding to the U-
shaped laminations 38. The insulative housing second portion 50 includes for each of
the arms 44,46 a triangular-shaped structure 88 forming a portion of the debris shield
56, which obstructs debris from the second are plates 22 from entering the operating
mechanism 8. The edges 90 of the triangular-shaped structure 88 approximate the
generally arcuate path 66 (Figure 2) and the second ends 64 of the second are plates
22.
Example
A non-limiting example of the insulation material of the slot motor
housing 40 is a suitable glass filled polyester. One example is Rosite® 3550D, which
is marketed by Industrial Dielectrics, Inc. of Noblesville, Indiana. This material
preferably provides some out-gassing responsive to an arcing event.
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.

What is Claimed is:
1. A circuit breaker (2) comprising:
a fixed contaci (4);
a movable contact (6);
an operating mechanism (8) comprising a movable arm (14)
carrying said movable contact;
an are chute (10) comprising a plurality of spaced apart arc
plates (20,22) including a number of first are plates (20) and a number of second are
plates (22); and
a slot motor (12) comprising:
a slot motor structure (38) disposed about said fixed and
movable contacts and a portion of said movable arm, and
an insulativc housing (40) at least substantially covering
said slot motor structure and insulating said slot motor structure from said movable
arm and said fixed and movable contacts, said insulative housing comprising a base
(42) and a pair of arms (44,46) disposed from said base,
wherein each of said arms includes a first portion (48) disposed
proximate said first are plates and a second portion (50) disposed proximate said
second are plates,
wherein a space (52) extending from said first portion of said
arms, which is not occupied by said second portion of said arms, is generally occupied
by part of said are chute (10) including a portion (54) of said second are plates, and
wherein said second portion of said insulative housing forms a
debris shield (56) between said second are plates and said operating mechanism.
2. The circuit breaker (2) of Claim 1 wherein the base (42) and
arms (44,46) of said insulative housing (40) have a generally U-shape; and wherein
the second portion (50) of said insulative housing includes for each of said arms a
triangular-shaped structure (88) forming a portion of said debris shield (56).
3. The circuit breaker (2) of Claim 1 wherein said first and second
are plates include ends (60,64) forming a generally arcuate path; wherein said
movable arm has a first position wherein said fixed and movable contacts are closed
and a second position wherein said fixed and movable contacts are open; wherein said

movable contact generally follows said generally arcuate path from a position
intermediate said first and second positions toward said second position; and wherein
the second portion of said insulative housing includes an edge (90) which
approximates said generally arcuate path.
4. The circuit breaker (2) of Claim 3 wherein the second portion
(50) of said insulative housing (40) obstructs debris from said second are plates (22)
from entering said operating mechanism (8).
5. The circuit breaker (2) of Claim 3 wherein the second portion
(50) of said insulative housing (40) comprises two triangular-shaped structures (88)
structured to form said debris shield (56).
6. The circuit breaker (2) of Claim 1 wherein said slot motor
structure (38) comprises a plurality of steel laminations (38).
7. The circuit breaker (2) of Claim I wherein said insulative
housing (40) is made of a glass filled polyester.
8. A slot motor (12) comprising:
a slot motor structure (38) structured to be disposed about a
fixed contact (4), a movable contact (6) and a portion of a movable arm (14) carrying
said movable contact, and
an insulative housing (40) at least substantially covering said
slot motor structure, said insulative housing being structured to insulate said slot
motor structure from said movable arm and said fixed and movable contacts, said
insulative housing comprising a base (42) and a pair of arms (44,46) disposed from
said base,
wherein each of said arms includes a first portion (48)
structured to be disposed proximate a number of first are plates (20) and a second
portion (50) structured to be disposed proximate a number of second are plates (22),
and
wherein a space (52) extending from said first portion of said
arms, which is not occupied by said second portion of said arms, is structured to be
generally occupied by part of an are chute (10) including a portion (54) of said second
are plates.

9. The slot motor (12) of Claim 8 wherein said insulative housing
(40) includes a generally U-shape having said base (42) and said pair of arms (44,46);
and wherein the second portion (50) of said insulative housing includes for each of
said arms a triangular-shaped structure (88) structured to form a portion of a debris
shield (56).
10. The slot motor (12) of Claim 8 wherein said slot motor
structure comprises a plurality of generally U-shaped laminations (38); and wherein
said insulative housing (40) includes a general U-shape corresponding to said U-
shaped laminations.
11. The slot motor (12) of Claim 8 wherein the second portion (50)
of said insulative housing includes an edge (90) which approximates a generally
arcuate path (66).
12. The slot motor (12) of Claim 8 wherein the second portion (50)
of said insulative housing comprises two triangular-shaped structures (88) forming a
debris shield (56).
13. The slot motor (12) of Claim 8 wherein said insulative housing
(40) includes a generally U-shape having said base (42) and said pair of arms (44,46);
and wherein the second portion (50) of said insulative housing includes for each of
said arms a structure (88) which forms a portion of a debris shield (56) and which has
an edge (90) that approximates a generally arcuate path (66).
14. The slot motor (12) of Claim 8 wherein said insulative housing
(40) is made of a glass filled polyester structured to out-gas responsive to an arcing
event.
15. A circuit breaker (2) comprising:
a housing (16);
a fixed contact (4);
a movable contact (6);
an operating mechanism (8) comprising a movable arm (14)
carrying said movable contact, said movable arm being pivotally mounted with
respect to said housing, said movable arm having a first position wherein said fixed
and movable contacts are closed and a second position wherein said fixed and
movable contacts are open;

an are chute (10) comprising a plurality of spaced apart are
plates (20,22) including a number of first are plates (20) and a number of second are
plates (22); and
a slot motor (12) comprising:
a slot motor structure (88) disposed about said fixed and
movable contacts and a portion of said movable arm, and
an insulativc housing (40) at least substantially covering
said slot motor structure and insulating said slot motor structure from said movable
arm and said fixed and movable contacts,
wherein said fixed contact includes a first end (24) disposed
toward said are chute, a contact portion (26) and a second end (28) disposed toward
said operating mechanism,
wherein said movable contact includes a first end (30), a
contact portion (32) electrically contacting the contact portion of said fixed contact in
the first position of said movable arm, a second end (34) and a side (36) opposite the
contact portion of said movable contact,
wherein said first are plates (20) include a first end (58) distal
from said operating mechanism and a second end (60) facing said operating
mechanism,
wherein said second are plates (22) include a first end (62)
distal from said operating mechanism and a second end (64) facing said operating
mechanism,
wherein at least one (68) of said first are plates (20) is disposed
proximate the first end of said fixed and movable contacts in the first position of said
movable arm,
wherein at least one (70) of said second are plates (22) is
proximate the first end of said movable contact in the second position of said movable
arm,
wherein a portion (62) of at least one of said second are plates
(22) is disposed distal from said fixed contact and beyond the side opposite the
contact portion of said movable contact,

wherein said insulative housing (40) is generally disposed
between said are chute (10) and said operating mechanism (8),
wherein said insulative housing (40) includes a first portion
(48) proximate the second end (60) of said first are plates (20),
wherein said insulative housing (40) includes a second portion
(50) proximate the second end (64) of said second are plates (22), and
wherein said second portion is smaller than said first portion of
said insulative housing.
16. The circuit breaker (2) of Claim 15 wherein said insulative
housing (40) includes a generally U-shape having a base (42) and two arms (44,46);
and wherein the second portion (50) of said insulative housing includes for each of
said arms (44,46) a triangular-shaped structure (88) structured to provide a portion of
a debris shield (56) between said second are plates (22) and said operating mechanism
(8).
17. The circuit breaker (2) of Claim 15 wherein said slot motor
structure comprises a plurality of generally U-shaped laminations (38); and wherein
said insulative housing (40) includes a general U-shape corresponding to said U-
shaped laminations.
18. The circuit breaker (2) of Claim 17 wherein said U-shaped
laminations include a base (84) and (wo arms (86), said base being disposed opposite
the contact portion (26) of said fixed contact (4), said arms (86) extending toward the
second end (64) of said second are plates (22).
19. The circuit breaker (2) of Claim 15 wherein the second ends
(60,64) of said first and second are plates (20,22) form a generally arcuate path (66);
wherein the first end (30) of said movable contact (6) generally follows said generally
arcuate path (66) from a position intermediate said first and second positions toward
said second position; and wherein the second portion (50) of said insulative housing
(40) includes an edge (90) which approximates said generally arcuate path (66).
20. The circuit breaker (2) of Claim 15 wherein the second portion
(50) of said insulative housing (40) obstructs debris from said second are plates (22)
from entering said operating mechanism (8).

21. The circuit breaker (2) of Claim 15 wherein the second portion
(50) of said insulative housing (40) comprises two triangular-shaped structures (88)
structured to provide a debris shield (56) between said second are plates (22) and said
operating mechanism (8).
22. The circuit breaker (2) of Claim. 15 wherein said insulative
housing (40) includes a generally U-shape having a base (42) and two arms (44,46);
wherein the second ends (60,64) of said first and second are plates (20,22) form a
generally arcuate path (66); wherein the first end (30) of said movable contact (6)
generally follows said generally arcuate path from a position intermediate said first
and second positions toward said second position; and wherein the second portion
(50) of said insulative housing (40) includes for each of said arms (44,46) a structure
(88) which includes an edge (90) that approximates said generally arcuate path, in
order to provide a debris shield (56) between said second are plates (22) and said
operating mechanism (8).

A circuit breaker (2) includes fixed and movable contacts (4,6), an
operating mechanism (8) including a movable arm (14) carrying the movable contact,
an are chute (10) including a plurality of spaced apart first and second are plates
(20,22), and a slot motor (12). A slot motor structure (38) is disposed about the
contacts and a portion of the movable arm. An insulative housing (40) at least
substantially covers and insulates the slot motor structure from the movable arm and
contacts. The insulative housing includes a base (42) and a pair of arms (44,46)
disposed therefrom. Each of the arms includes a first portion (48) disposed proximate
the first are plates (20) and a second smaller portion (50) disposed proximate the
second are plates (22). A space (52) extending from the first portion (48), not
occupied by the second portion (50), is generally occupied by a portion (54) of the
second are plates (22). The second portion (50) forms a debris shield (56) between
the second are plates (22) and the operating mechanism (80).