Circuit breaker terminal cover with integrated arc chamber vents

A multi-phase circuit breaker assembly 10 includes a circuit breaker 12 having a housing 13 containing circuit breaker operating components and having a gas venting chamber 22 associated with each phase of the circuit breaker. The circuit breaker has a plurality of line wiring terminals 26 at a first end 14 of the housing. Each line wiring terminal corresponds to a phase of the circuit breaker. A terminal cover 30 is removably coupled to the first end of the housing so as to cover the line wiring terminals and prevent access to the line wiring terminals when coupled to the first end of the housing, and to gain access to the line wiring terminals only when removed from the first end of the housing. The terminal cover 30 includes a plurality of vent structures 38 integrally formed therewith. Each vent structure is in communication with an associated gas venting chamber and each vent structure is isolated from each other such that arc gases generated in each phase of the circuit breaker are exhausted through an associated vent structure with arc gases from one phase being prevented 1) from coming into contact with arc gases or line wiring terminals of a different phase, and 2) from coming into contact with wiring terminals of the same phase, thereby preventing a short circuit.

FIELD OF THE INVENTION
 This invention relates to circuit breakers and more particularly to a
 terminal cover which enables exhaust gases to vent from the circuit
 breaker during a circuit interrupt condition.
 BACKGROUND OF THE INVENTION
 Many industrial molded case circuit breakers have terminals and provisions
 for wiring connectors at each end of the circuit breaker. Frequently in
 the design of circuit breakers, a removable terminal cover is provided.
 With the terminal cover removed, the electrician has easy access to the
 breaker terminals for assembling, tightening, or inspecting the electrical
 connections. When the terminal cover is replaced, the cover helps prevent
 accidental contact with the live terminals from the front of the circuit
 breaker. A second function of a terminal cover is to prevent hot, ionized
 gases caused by short circuit interruption from exiting from the front of
 the circuit breaker. Such gases could strike grounded metal on the front
 of the equipment enclosure and cause an electrical ground fault.
 Typically, hot, ionized gases from short circuit interruption are exhausted
 from an arc chamber of the circuit breaker. Often, the design of the
 circuit breaker is such that the hot gases flow against the terminal
 connections before exiting the circuit breaker. After the gases exit the
 circuit breaker, the exhaust from the different poles of the breaker,
 which are at different electrical potentials, mix together. This mixing
 can result in a phase-to-phase arcing fault across the terminals of the
 circuit breaker. Additionally, there exists the potential for shorting the
 electrical path through the circuit breaker arc stack by arcing from the
 open moving blade directly to the lug, thereby eliminating the arc stack
 from the current path. This may result in the circuit breaker being unable
 to perform its primary function of interrupting the short circuit current.
 The problem of phase-to-phase arcing in a circuit breaker has been
 addressed. One solution is to lengthen the walls of the molded case so
 that the walls extend further beyond the wiring lugs. This lengthens the
 path required for a phase-to-phase arc and thus reduces the likelihood
 that a phase-to phase arc will occur. However, this solution has the
 disadvantage of increasing the overall size of the circuit breaker.
 Another solution is to guide the gases so that they exit the breaker
 without coming into contact with the breaker terminals and wiring lugs.
 U.S. Pat. No. 5,811,749 provides a terminal cover having chamber vents.
 Access holes for receiving a tool are provided to reach through the cover
 to tighten the terminal screws. The access holes are tubular in shape and
 extend through the arc chamber vents. Thus, the access holes
 disadvantageously reduce the cross-sectional area of the vents and
 restrict the flow of gases. In addition, the tubular access holes require
 a complicated and costly mold which requires cross-slides from opposite
 directions.
 Accordingly, there is a need to provide an improved terminal cover for a
 circuit breaker which effectively permits arc gases to be vented from the
 circuit breaker while preventing access to the line terminals.
 SUMMARY OF THE INVENTION
 An object of the present invention is to fulfill the need referred to
 above. In accordance with the principles of the present invention, this
 objective is obtained by providing a multi-phase circuit breaker assembly
 including a circuit breaker having a housing containing circuit breaker
 operating components and having a gas venting chamber associated with each
 phase of the circuit breaker. The circuit breaker has a plurality of line
 wiring terminals at a first end of the housing. Each line wiring terminal
 corresponds to a phase of the circuit breaker. A terminal cover is
 removably coupled to the first end of the housing so as to cover the line
 wiring terminals and prevent access to the line wiring terminals when
 coupled to the first end of the housing, and to gain access to the line
 wiring terminals only when removed from the first end of the housing. The
 terminal cover includes a plurality of vent structures integrally formed
 therewith. Each vent structure is in communication with an associated gas
 venting chamber and each vent structure is isolated from each other such
 that arc gases generated in each phase of the circuit breaker are
 exhausted through an associated vent structure with arc gases from one
 phase being prevented 1) from coming into contact with arc gases or line
 wiring terminals of different phases, and 2) from coming into contact with
 a line wiring terminal of the same phase, thereby preventing a short
 circuit.
 A method of venting gases from a multi-phase circuit breaker assembly
 during a circuit interrupt condition is also provided.
 Other objects, features and characteristics of the present invention, as
 well as the methods of operation and the functions of the related elements
 of the structure, the combination of parts and economics of manufacture
 will become more apparent upon consideration of the following detailed
 description and appended claims with reference to the accompanying
 drawings, all of which form a part of this specification.

DETAILED DESCRIPTION OF THE INVENTION
 Referring to FIG. 1, a circuit breaker assembly having terminal covers in
 accordance with the principles of the present invention is shown generally
 indicated at 10.
 The circuit breaker assembly 10 comprises an industrial rated multiphase
 circuit breaker 12. In the illustrated embodiment, the circuit breaker 12
 includes a molded plastic housing 13 having a first end 14 and an opposing
 second end 16.
 In the illustrated embodiment, the circuit breaker 12 is a three phase
 circuit breaker and thus comprises three separate line terminal
 compartments within the housing 13. As shown in FIG. 1, each line terminal
 compartment 17 contains the circuit breaker operating components including
 a moving contact 18 and a stationary contact 20. A gas venting chamber 22
 surrounds and guides the arc that occurs upon separation of the stationary
 and movable contacts. The arc gases that are generated during intense
 circuit interruption are dispersed through a plurality of arc plates 24 to
 rapidly cool and de-ionize the electrically charged arc gases. The arc
 gases are indicated by the arrows A in FIG. 1.
 A line wiring terminal 26 is associated with each line terminal compartment
 and thus each phase of the circuit breaker 12. The circuit breaker 12 also
 includes a load wiring terminal 28 at the second end 16 of the housing 13
 associated with each phase of the circuit breaker 12.
 The arc gases exiting from the gas venting chamber 22 of one line terminal
 compartment 17 must be prevented from contacting a line wiring terminal
 within the same and/or an adjacent line terminal compartment to prevent a
 so-called "phase-to-phase" fault.
 Thus, in accordance with the principles of the present invention, a
 terminal cover, generally indicated at 30, is provided and is removably
 coupled to the first end 14 of the housing 13. As best shown in FIGS. 2
 and 3, the terminal cover 30 includes a generally plate-like main body 31
 having a pair of fastener apertures 32 therethrough. Each fastener
 aperture aligns with a housing aperture 34 defined in a front face of the
 housing 13 (FIG. 1). A threaded fastener 36 extends through each fastener
 aperture 32 and engages the associated housing aperture 34 in the housing
 13 to couple the terminal cover 30 to the circuit breaker 12. When the
 terminal cover 30 is secured to the housing 13, finger and tool access to
 the wiring terminals is prevented. Thus, a greater degree of protection
 against ingress of solid foreign bodies is provided by the terminal cover
 of the invention, as compared to terminal covers which permit tool and or
 finger access to the terminals. Only when the terminal cover 30 is removed
 from the housing 13, upon removing the fasteners 36, is access to the
 wiring terminals 26 or 28 achieved. The terminal cover 30 also includes a
 pair of access apertures 35 therethrough which provide access to fasteners
 which are employed to secure the circuit breaker 12 to a panel (not
 shown).
 The terminal cover 30 includes a plurality of vent structures, generally
 indicated at 38, formed integrally therewith. Preferably, the terminal
 cover 30 with vent structures 38 is molded from plastic in a single
 process. However, the terminal cover 30 may be produced as separate pieces
 then joined by one of several methods, for example, with the use of
 adhesive, snap fits, heat staking, etc. Each vent structure 38 is formed
 so as to extend from a surface 39 of the main body 31 and is generally
 U-shaped defining an open passageway 40 between an inlet opening 42 and an
 exit opening 44. In the illustrated embodiment, each vent structure 38 has
 a flange 46 near the inlet opening 42 which abuts surface 48 of the first
 end 14 of the circuit breaker 12. The flange 46 is not required, but aids
 in coupling the vent structure 38 to the circuit breaker 12. In addition,
 the housing 13 of the circuit breaker 12 includes a protruding portion 50
 associated with each vent structure 38. Thus, as shown in FIG. 1, a
 protruding portion 50 is received in the inlet opening 42 and abuts an
 interior surface 52 of the associated vent structure 38. Each inlet
 opening 42 is in open communication with respect to an associated gas
 venting chamber 22 and each vent structure 38 is isolated from each other
 such that arc gases generated in each phase of the circuit breaker 12 are
 exhausted through an associated vent structure 38 with arc gases from one
 phase being prevented from coming into contact with arc gases or line
 wiring terminals 26 of different phases, or with a line wiring terminal 26
 of the same phase. Thus, a short circuit is prevented.
 In addition, the vent structures 38 are constructed and arranged to guide
 arc gases outwardly from the circuit breaker 12 in a direction of long
 axis B of the circuit breaker 12. Surface 52 of end 54 of each vent
 structure 38 is tapered to directed gases away from the front of the
 circuit breaker 12. Thus, the gases are directed away from grounded metal
 on the front of the equipment enclosure to prevent an electrical ground
 fault.
 In the illustrated embodiment, the circuit breaker 12 has three phases.
 Thus, three vent structures 38 are provided. It can be appreciated that
 the terminal cover 30 can be used with circuit breakers having phases
 other than three by modifying the terminal cover to have the same amount
 of vent structures as circuit breaker phases.
 As shown in FIG. 1, a terminal cover 30 is provided over the load wiring
 terminals 28 as well. Thus at the load end of the circuit breaker 12, the
 terminal cover 30 merely functions as a protective cover. Alternatively, a
 terminal cover having no vent structures can be employed at the load end
 of the circuit breaker 12.
 As can be appreciated from the drawings, the access apertures 35 and
 fastener apertures 32 do not interfere with the vent structures 38. Since
 there are no access holes through the vent structures as in prior art
 structures, the vent structures 38 of the invention are not restricted and
 the gases can flow more freely. This facilitates arc interruption by
 blowing the arc into the arc plates more quickly. Further, the vent
 structures are useful in a large circuit breaker because a large vent area
 is needed due to increased gas flow. The terminal cover 30 is easy to
 manufacture since the mold requires a cross slide from only one direction.
 The foregoing preferred embodiments have been shown and described for the
 purposes of illustrating the structural and functional principles of the
 present invention, as well as illustrating the methods of employing the
 preferred embodiments and are subject to change without departing from
 such principles. Therefore, this invention includes all modifications
 encompassed within the spirit of the following claims.