Electricity: conductors and insulators – Overhead – Towers – poles or posts
Reexamination Certificate
2003-04-28
2004-09-28
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Overhead
Towers, poles or posts
C174S068300, C174S068100, C138S177000
Reexamination Certificate
active
06797877
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to the field of tubing. More particularly, the invention relates to the field of electrical metallic tubing (“EMT”) apparatus including tubing, connectors and couplings, methods of coupling sections of EMT, and methods of connecting EMT to other apparatus such as junction boxes or transition fittings.
BACKGROUND ART
Currently EMT is connected by using one of two methods, either a set screw coupling or a compression coupling. The connectors are made from either electroplated steel or from die cast zinc. Set screw EMT couplings are sleeves which slip over the outside diameter of two opposing EMTs. Set screw EMT couplings typically have an inner ridge to make sure that the two pieces of EMT butt up properly to the center of the coupling. The coupling has set screw(s) that penetrate the wall of the coupling and when tightened create both a ground path and a tight fit.
Compression couplings are made of three “body parts” plus a split gland ring. The inner body is threaded on each end and then the split gland ring is slipped on and then the “outer body” on each end is threaded onto the inner body. By tightening the outer body ends, the split gland ring is tightened around the EMT, providing a tight fit and a good ground path.
In the installation of EMT, provisions have to be made to address the need for a good ground path. Concerns have frequently been raised by inspectors and regulators about the integrity of the ground path of steel EMT. The integrity of the ground path may be degraded if the set screws or compression sleeves are not tightened fully because electrical continuity relies on good, tight connections at each connection or coupling point.
Traditional set screw connectors are basically the same as couplings except one end is threaded or has some other type of attaching mechanism so that the EMT can be attached to an enclosure, such as a junction box or some other piece of equipment that has a knock out hole of the correct size for the connector to fit. Connectors are usually held in place with locknuts that lock the connector into place and provide a continued ground path.
Existing EMT couplings and connectors require the installer to either turn a set screw or turn an “outer body.” The need to “tighten” a set screw or “turn” an outer body not only requires additional work space but is also subject to human error, such as inadequate tightening. If threaded connections are subject to vibration, the screws and/or outer bodies can loosen over time, compromising the ground path. Moreover, “twist tightening” increases the time and effort it takes for mechanics to install EMT. Thus, a need exists for an EMT coupling and connector system and method that does not require set screw or other means of twist tightening while still providing a proper ground path.
Currently available snap fit connectors and couplings are expensive to manufacture and provide a less than optimal ground path.
DISCLOSURE OF THE INVENTION
It is an object of the present invention is to provide EMT, connector, coupling, method for connecting, and method for coupling which are quick and efficient to install.
It is a further object of the present invention is to provide an EMT, a connector for an EMT, and a coupling for an EMT that provides a safe and reliable ground path which does not depend on set screws being tightened and remaining tightened.
A still further object of the present invention is to provide an EMT, a connector for an EMT, and a coupling for an EMT that is efficient to manufacture.
Yet another object is provide an EMT, a connector for an EMT, and a coupling for an EMT that is easy to use and capable of being used in existing systems and equipment.
These and other objects are achieved by the present invention which in one aspect comprises an electrical metallic tube (“EMT”) comprising an inner surface forming an EMT cavity; an EMT outer surface; an EMT first end; and at least one indentation in the EMT outer surface at or near the EMT first end, the indentation adapted to receive a corresponding barb from a sleeve device. The EMT is preferably manufactured with a number of dimples that are pressed or punched into the EMT outer surface close to the EMT first end around its circumference. The number of dimples and the distance from the EMT first end depend on the size required to meet the necessary pull out tests and other criteria. The dimples are preferably shaped like a capital D with the flat side facing the EMT first end and the rounded side facing the center. The indentation can also be a linearly-shaped dimple or roll groove around the entire EMT outer surface so there is a continuous area for the barbs of the sleeve device to snap into. The indentation is preferably a minimal depth so as to not cause a loss in wiring capacity through the EMT cavity.
It is further preferable that the inventive EMT have an EMT second end having a mirror image indentation arrangement as the EMT first end. Preferably, each length of EMT will have four indentations at or near each of its ends. Moreover, because the indentation would not be raised above the EMT outside surface, the inventive EMT can be used with traditional connectors/couplings available in the market place, which typically slip over the outside diameter of the EMT if the inventive couplings/connectors are not available.
In another aspect, the invention is a sleeve device for connecting EMT comprising: a sleeve inner surface forming a sleeve cavity adapted to receive an end of an EMT; a sleeve outer surface; a first sleeve end; and at least one barb on the sleeve inner surface at or near the first sleeve end. The barb is adapted to engage a corresponding indentation on the EMT described above. Depending on design needs in the field, the sleeve device can be adapted to be either a coupling or a connector by appropriately designing the opposing end of the sleeve device.
The sleeve device is preferably designed to have a C-shaped cross sectional profile and is constructed of spring steel. When the sleeve device is used to directly receive an EMT, the sleeve cavity preferably has a diameter that is slightly larger than the diameter of the EMT outer surface. When the sleeve device is used in conjunction with a linking device, as discussed below, the sleeve cavity will preferably have a diameter that is slightly larger than the diameter of the outer surface of the linking device. The barbs are designed to slide over the EMT outer surface and “snap” into the corresponding indentations (or the roll groove) on the EMT. Preferably, the barb would point down and slightly back and will “capture” or “contact” the flat part of the D-shaped dimple or linearly-shaped dimple. If the sleeve device needs to be removed from the inventive EMT, the sleeve device could be spun or twisted and the barbs would free up as the spinning would result in the barb sliding over the rounded part of the (D) or slotted depression. It is preferred that the sleeve device have four barbs at or near its first sleeve end for engaging four corresponding indentations on the EMT. The barbs help provide a ground path for the EMT by increasing the area of contact.
It further preferable that the sleeve device further comprise at least one ground tab formed by a slot in the sleeve device. The ground tab can be bent downward so that the ground tab would scrape the outer surface of the EMT, resulting in additional contact area. This helps to enhance the current carrying capability and helps to maintain electrical continuity throughout the system.
In order to be able to use the sleeve device on cut EMT or EMT manufactured without indentations at its ends, the sleeve device preferably includes a set screw locking mechanism similar to traditional EMT set screw fittings. This allows maximum flexibility and eliminates the need for the field mechanic to carry two types of couplings/connectors. In this embodiment, the sleeve device will comprise a set screw hole extending through the sleeve outer surface and the sleeve inner surface for threadi
Belles Brian L.
Estrada Angel R.
Fein Michael B.
Jonn Maneely Company
O'Connor P.C. Cozen
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