Supports: cabinet structure – Knockdown or setup type – Adjacent walls rigidly interlocked
Reexamination Certificate
2000-12-22
2003-04-15
Mai, Lanna (Department: 3636)
Supports: cabinet structure
Knockdown or setup type
Adjacent walls rigidly interlocked
C312S265500, C312S223100
Reexamination Certificate
active
06547348
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to electrical panelboards and, in particular, power panels and switchboards. The invention further relates to trim plates used with power panels and switchboards, and the removal of multiple trim plates for group mounted power panels and switchboards.
BACKGROUND OF THE INVENTION
Electrical panelboards are enclosures used in electrical distribution systems to provide a common distribution and protection point for electrical circuits. Panelboards can include electrical distribution components such as switches, metering, instrumentation, protective devices and the like. Panelboards are installed in industrial, commercial and residential facilities. Panelboards vary in their size and electrical rating depending upon the specific application. Manufacturer's design considerations include ease of manufacture, ease of use and compliance with Underwriters Laboratory (“UL”) standards.
Generally, a power circuit input is connected to at least one common power bus within the panelboard via a switch, circuit breaker or lugs located within the panelboard. Electrical branch circuits are connected to the power bus via circuit breakers or other protective devices. Wiring interconnects the branch circuit protective devices to at least one remote electrical load.
Switchboard and power panels are two types of electrical panelboards. Generally, modern switchboards are identified by the characteristics of: a high amperage rating of between 200 Amps to 2000 Amps; floor mounting; a wide range of electrical distribution components capable of being installed within the switchboard; and interior accessibility from any one of the four sides, front, rear, left, or right. Generally, power panels are characterized by features including: a lower maximum ampacity; smaller physical size; wall mounting; and only front access to the interior.
UL standards provide equipment design criteria that insure the safe operation of electrical panelboards. The standards reduce the shock hazard posed to operating personnel and the likelihood of equipment failure. UL standards restrict the size of external openings located in fully assembled power panels and switchboards. Specifically, UL Standard No. 67 (“UL 67”) restricts the dimension to 0.125 inches.
The front of a four-piece front style switchboard or power panel includes two side plates, a top plate and a bottom plate. A central opening is formed between the four plates. Multiple trim plates span central opening of the power panel or switchboard and prevent accidental contact with energized components within the switchboard or power panel. The trim plate edges abut the edge of the adjacent trim plates. However, a gap is created at each abutment.
Today, manufacturers comply with UL 67 using more difficult and costly designs and manufacturing methods. First, closer manufacturing tolerances must be maintained to avoid gaps larger than allowed by UL 67. Second, the power panel or switchboard design must insure that any gap adjustments occurring during shipping and installation do not result in a violation of UL 67.
Modern trim plates are secured to the switchboard or power panel via fasteners and plastic clips. The clips are not durable and have a tendency to break when trim plates are installed or removed. Also, trim plate removal is difficult because trim plates must be held in place when being installed or removed. Otherwise, the trim plate will drop to the ground with all of the fasteners removed.
Finally, the four piece front style switchboards and power panels present additional problems in removing and installing trim plates. State of the art designs require that the side plates of the switchboard or power panel be removed any time a trim plate is removed or installed. Side plate removal is time consuming and reduces personnel safety because internal panelboard wiring is exposed when the side plates are removed.
Electrical enclosures also use a dead-front style wherein the dead front is constructed from a top, a bottom and two sidewalls. A dead-front electrical panelboard includes a central opening between sidewall flanges similar to the opening found in a four-piece front style panelboard. Trim plates are used to span the central opening formed between the flanges of a dead front power panel or switchboard. The dead front does not fully span the front opening of the body. Instead a hinged door with integral flanges is secured to the dead front. The combination door and dead-front are secured to the front of the electrical enclosure. The door flanges cover the space between the outer edge of the dead front and the outer edge of the electrical enclosure. The trim plates used in modern dead front style switchboards and power panels suffer from the preceding problems described for four-piece front style switchboards and panelboards.
SUMMARY OF THE INVENTION
It is therefore advantageous to design an electrical enclosure that includes trim plates providing a gap-free installation. It is also desirable to incorporate the preceding feature in a more rigid trim plate installation. Further, it is desirable to incorporate the preceding features in trim panel design that eliminates the need to grasp the trim panel when removing and installing the mounting fasteners. Additional benefits are provided by an electrical enclosure designed to allow individual trim panel removal without the need to remove other enclosure plates or panels. Further, it is desirable to provide a enclosure design that allows group removal of all trim panels. Additionally, it is desirable to design an electrical panelboard, in particular a switchboard or power panel, incorporating the preceding features. According to the present invention, an electrical enclosure including an enclosure body and a plurality of trim plates with a first flange having a first flange shape cooperatively engaging a second flange having a second flange shape providing a gap free installation attains the foregoing and other objects and advantages.
Additionally, a method of gap-free trim plate installation requiring no external restraint during installation is provided. The method uses the interlocking trim panel flanges to restrain the trim panel while the trim panel mounting fasteners are installed.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of instrumentalities and combinations particularly pointed out in the appended claims.
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Craft Hamon Leroy
Hilgendorf Robert Lee
Lafond Michael Paul
Cantor & Colburn LLP
General Electric Company
Mai Lanna
Tran Hanh V.
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