High-voltage switches with arc preventing or extinguishing devic – Arc preventing or extinguishing devices – Housing structure
Reexamination Certificate
1999-11-05
2001-03-06
Scott, J. R. (Department: 2832)
High-voltage switches with arc preventing or extinguishing devic
Arc preventing or extinguishing devices
Housing structure
C200S306000
Reexamination Certificate
active
06198063
ABSTRACT:
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.
REFERENCES:
patent: 5194840 (1993-03-01), Frutuoso et al.
patent: 5241289 (1993-08-01), Markowski et al.
patent: 5278531 (1994-01-01), Link et al.
patent: 5304761 (1994-04-01), Rosen et al.
patent: 5811749 (1998-09-01), Bausch et al.
Scott J. R.
Siemens Energy & Automation Inc.
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