Patent Application
20080110660
1. Field of the Application
This application relates generally to expansion couplings for coupling electrical conduits. More particularly, the application relates to an expansion coupling internally maintaining an electrical ground across the electrical conduits.
2. Description of the Related Art
Electrical conduit is often used to enclose electrical wiring. These conduits may be metallic, and in certain instances are required to be grounded. Conduits enclosing such electrical wiring may be interconnected with electrical couplings. Some of these couplings allow for thermal expansion of the electrical conduits, permitting relative longitudinal movement between the conduits in response to temperature changes. These couplings must not only allow for thermal expansion of the conduits, but also must maintain ground continuity across the conduits during such expansion and longitudinal movement.
When applicable, it is well known to use expansion couplings to connect conduits. Some expansion couplings use an external bonding jumper to provide ground continuity. However, external bonding jumpers may become loose and are susceptible to tampering and theft. Accordingly, some expansion couplings have been designed with internal grounding mechanisms. Examples of expansion couplings with internal grounding can be found in U.S. Pat. Nos. 3,783,178 and 4,250,350. One problem associated with expansion couplings with internal grounding mechanisms is that electrical inspectors cannot always tell if the expansion coupling is properly grounded, and oftentimes redundant external bonding jumpers are installed to allow the expansion coupling to pass inspection. Thus, there is a need to design an expansion coupling that can be readily disassembled in the field to allow electrical inspectors to verify proper grounding is in place.
In addition, expansion couplings that allow for thermal expansion typically must allow for relative longitudinal movement of a conduit end to move within the expansion coupling housing. As a result, a seal may be used to prevent moisture and contaminants from entering the expansion coupling. Thus, there is a need to provide a seal to allow relative longitudinal movement of a conduit end within the expansion coupling that is effective at preventing moisture and contaminants from entering the expansion coupling.
These as well as other aspects and advantages will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. Further, it should be understood that the embodiments described in this summary and elsewhere are intended to illustrate the invention by way of example only.
The present application provides an electrical expansion coupling comprising a housing having a first end and a second end, with a first end cap secured to the first end with a first sealing gland positioned therein, and a second end cap secured to the second end with a second sealing gland positioned therein, with an axial sliding ground plate adapted to receive an electrical conduit positioned within the first end of the housing, and a stationary ground plate adapted to receive an electrical conduit positioned within the second end of the housing, a grounding member electrically connecting the axial sliding ground plate and the stationary ground plate, and an anti-rotation mechanism adapted for preventing relative rotation of the sliding ground plate and the stationary ground plate when a conduit is threaded into the sliding ground plate or the stationary ground plate. The expansion coupling may also include a sealing gland having outer circumferential troughs on its outer diameter, such that when the sealing gland is compressed by the end cap, an inner circumferential trough is formed on the inner diameter of the sealing gland that serves to trap lubricant within the inner circumferential trough to provide for improved lubrication. Additionally, an expansion coupling providing for easy field inspection of grounding components is also provided.
Exemplary embodiments of the invention are described herein with reference to the drawings, in which:
Referring to
Although not shown, rather than having end caps 38 and 38′ attached directly to housing 16, internal or external threaded couplers could be used to indirectly attach the end caps to the housing 16. Alternatively, a number of other fastening means may be used to secure the end caps 38, 38′ to the housing 16.
The expansion coupling 10 may further include ground components comprising a sliding ground plate 24, a stationary ground plate 28, and a ground cable 26 extending therebetween. The ground cable 26 connects the sliding ground plate 24 to the stationary ground plate 28. The ground cable may be a flexible cable as shown or even a rigid rod that slides through the sliding ground plate 24 during axial movement of the sliding ground plate 24. Alternatively a sweeper ring could also be used maintain grounding during axial moving of the sliding ground plate 24. The ground components serve to provide an electrical ground between the two pieces of conduit 12 and 14 (shown in
The sliding ground plate 24 is axially moveable within the housing 16 and the stationary ground plate 28 is positioned generally within the second end 17′ of housing 16. As shown in
The expansion coupling 10 may further include a sealing gland positioned at the first end 17 of the housing 16. The expansion coupling may include a first sealing gland 32 with a first backup washer 30 positioned between the first sealing gland 32 and the sliding ground plate 24 and a first friction washer 36 positioned between the first sealing gland 32 and a first end cap 38. The opposite end of the housing 16 may include another sealing gland positioned at the second end 17′ of the housing 16. Thus, the expansion coupling may include a second sealing gland 32′ with a second friction washer 36′ positioned between the second sealing gland 32′ and second end cap 38′. Preferably, the first backup washer 30 is comprised of commercial quality steel, and the first and second friction washers 36 and 36′ are comprised of nylon.
The first and second sealing glands 32 and 32′ are preferably comprised of neoprene and as shown in
The first end cap 38 may be threadingly secured to the first end 17 of the housing 16 for ease of removal to allow access to the interior of the expansion coupling 10. The first end cap 38 may further include a plurality of flat surfaces 42 on an outer perimeter to facilitate installation and removal of the first end cap 38 by a user.
The second end cap 38′ may be threadingly secured to the second end 17′ of the housing 16 for ease of removal to allow access to the interior of the expansion coupling 10. The second end cap 38′ may also further include a plurality of flat surfaces 42′ on an outer perimeter to facilitate installation and removal of the second end cap 38′ by a user.
Once assembled as shown in
The expansion coupling 10 preferably includes an anti-rotation mechanism to prevent relative rotational movement of the sliding ground plate 24 and the stationary ground plate 28 when the conduits 12 and 14 are threaded into the respective ground plates. The anti-rotation mechanism may comprise, as best shown in
Other anti-rotation mechanisms may also be used to prevent the relative rotation of ground plates 24 and 28 during the threading of the conduits 12 and 14 into the respective ground plates 24 and 28. For example, as shown in
Alternately, an aperture may be constructed in the surface of the sliding ground plate 24, and a rod may be attached to the stationary ground plate such that the rod passes through the aperture in the sliding ground plate during axial movement of the sliding ground plate 24, and serves to prevent relative rotation of the ground plates 24 and 28 during threading of the conduits 12 and 14. Any other known type of anti-rotation mechanism may also be used.
Referring to
As shown in
As best seen in
The present design provides further advantages as well. In operation, the expansion coupling 10 may be disassembled without disconnecting the conduits 12 and 14 from the respective ground plates 24 and 28. The internal components of the expansion coupling 10 may be easily inspected in the field to insure proper grounding is present. As depicted in
While certain features and embodiments of the present application have been described in detail herein, it is to be understood that the application encompasses all modifications and enhancements within the scope and spirit of the following claims.
