There are several well known types of electrical raceway systems which are designed to be placed in a floor. There are, for example, "underfloor raceways" as defined in Article 354 of the National Electrical Code and "cellular metal floor raceways" as defined in Article 356 of the National Electrical Code. Raceway components designed for use in either of the two mentioned raceway systems, and conceivably in some other systems, can generally be referred to as raceway apparatus for placement in a floor.
As used herein, the simple term "raceway" or the phrase "raceway apparatus to be placed in a floor", or the like are intended to refer in a generic sense to raceway systems which may be used as part of an "underfloor raceway" or of a "cellular metal floor raceway" or both. Where the term "cellular metal floor raceway" is used, it is intended as a reference to the particular type of system defined in Article 356 of the National Electrical Code.
The raceway system disclosed in this application is designed primarily as a limited access feeder raceway for use in conjunction with a cellular metal floor raceway. It can conceivably, however, be utilized in other ways, and thus is generally referred to as a raceway apparatus to be placed in a floor.
The floors of buildings are commonly constructed with a corrugated metal floor decking over which a concrete floor is poured. The metal floor decking will typically have portions thereof provided with a bottom plate so that the corrugations of the metal decking along with the bottom plate define enclosed cells in which electrical wiring can be placed. Typically, three adjacent corrugations will be enclosed on the bottom to form three parallel cells which are referred to as a multi-cell cellular metal floor raceway.
Typically, such multi-cell cellular metal floor raceways will be placed at intervals of approximately six feet so that the cellular metal floor decking includes a system of parallel cellular metal floor raceways which extend across the width of the floor and are spaced at intervals of approximately six feet along the length of the floor.
The cellular metal floor raceways defined within the metal decking are typically used as the distribution ducts for the electrical supply system.
Additionally, a feeder raceway is typically laid across the top of the cellular metal flooring transversely to the direction of the cellular metal floor raceways. Generally, a raceway construction known as trench duct is utilized for the feeder raceway. A typical trench duct utilized with cellular metal flooring is shown in U.S. Pat. No. 3,886,702 to Fork. The trench duct lies across the top of the cellular metal flooring and it extends upward to the top floor level. A removable cover plate typically spans the trench duct and defines a portion of the floor. The trench duct is utilized to feed electrical cables to the various cellular metal floor raceways.
Trench duct typically has been provided with one of two basic designs. The trench duct can either be bottomless as shown in U.S. Pat. No. 3,886,702 to Fork, or the trench duct can include a bottom plate which has access openings which must be aligned with access openings in the cellular metal flooring.
A number of problems are inherent in the use of trench duct to feed cellular metal floor raceways. Trench duct is typically noisy to walk on and often gives an undesirable springy, spongy feeling under foot.
Additionally, the cover plate which spans the trench duct tends to bow from floor loading and often causes the floor finish to crack and break at the trim edges of the trench duct.
Additionally, since the trench duct extends vertically through the entire depth of the concrete slab, it prevents the use of structural wire mesh or other reinforcing to strengthen the slab at the location of the trench duct.
One alternative to conventional trench duct is the use of a limited access feeder duct. The limited access feeder ducts previously available have utilized a completely enclosed multi-cell duct having access openings in the bottom thereof for alignment with access openings in the cellular metal floor raceways. Access units mounted on the top of the limited access duct extend upward to the floor level to provide access to the feeder duct and the underlying cellular metal floor raceways at selected locations along the length of the feeder duct. One such system is that marketed as the Mac-Fab system of Mac-Fab Products of St. Louis, Mo.
The present invention provides an improved construction for such a limited access feeder raceway designed for use with cellular metal floor raceways.