Abstract:
A flexible electric coupling having a conductive bonding jumper for connecting two pieces of equipment in a harsh environment. The flexible electric coupling comprises a corrugated conduit having a raceway for electrical cables to pass therethrough. The flexible electric coupling provides flexibility, structural support, resistance to corrosion, as well as adequate current carrying capabilities provided by an interiorly located bonding jumper.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a flexible electrical coupling and, more specifically, to a flexible electrical coupling having a conductive bonding jumper for use in industrial, corrosive environments.  
           [0002]    This application claims priority to U.S. Provisional Application No. 60/311,161, filed Aug. 8, 2001.  
         BACKGROUND OF THE INVENTION  
         [0003]    It is often required in industrial applications to make electrical connections between pieces of equipment and/or motors for running such equipment. Such industrial environments are typically quite harsh, often including conditions that are quite corrosive and which result in vibratory movement of the equipment and motors. Accordingly, to establish the required electrical connections, as well as to protect the connections from the harsh environments, flexible electrical conduits have been used.  
           [0004]    Such known flexible conduits typically comprise an internal solid, corrugated stainless steel conduit that is terminated at each end, typically by a threaded steel fitting. A braid of external stainless steel is typically provided on the exterior of the corrugated conduit to provide additional strength, as well as protection against corrosive environments, since stainless steel has relatively high resistance to corrosion. Under the National Electrical Code (NEC), such flexible electrical conduit must meet the minimum standard of carrying electrical current so that if a motor or other piece of electrical equipment shorts, current can be transferred through the coupling to an appropriate ground. While stainless steel is advantageous because of its high corrosive resistance, its electrical conductivity property is relatively low. Accordingly, users frequently attach a bonding strap of higher conductivity material, such as bronze or brass, between the metal fittings attached to both ends of the coupling, so as to increase the electrical conductivity across the coupling and hence meet the NEC requirements for current-carrying capability. Disadvantageously, such additionally attached jumpers of bronze or brass add more cost to the coupling and do not provide the same benefit of high corrosive resistance as stainless steel. Furthermore, the additional strap tends to be relatively loose and often serves as an undesirable handle for users or workers to grasp during operation.  
           [0005]    Accordingly, it is desirable to provide a flexible electrical coupling for use in industrial, corrosive environments that provides necessary electrical conductivity and resistance to corrosion, as well as being cost effective.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention is directed to a flexible electrical coupling member. The electrical coupling member is formed of a first tubular member comprising a flexible corrugated conduit having a raceway for passage of electrical cables, or wires, therethrough. First and second fittings terminate first and second ends respectively of the first tubular member. Each fitting has a housing with an interior in communication with the conduit raceway. A second tubular member is disposed circumferentially exterior of the first tubular member, and is used for structural support for providing strength to the first tubular member. A conductive member is secured circumferentially interior of the second tubular member, and is conductively attached to the first and second fittings.  
           [0007]    In another embodiment, the present invention is a flexible electrical coupling member which has a first tubular member formed of a stainless steel corrugated conduit having a raceway for passage of electrical wires therethrough. First and second fittings terminate first and second ends respectively of the first tubular member. Each fitting has a housing with an interior in communication with the conduit raceway. A second tubular member is also in the electrical coupling member, the second tubular member being placed circumferentially exterior of the first tubular member and being formed of a braided stainless steel support member. A third tubular member is also included in the coupling member, the third tubular member being formed of a braided bonding jumper positioned between the first and second tubular members, and is conductively attached to the first and second fittings.  
           [0008]    In a further embodiment, the present invention is a flexible electrical coupling member with a first tubular member comprising a flexible corrugated conduit having a raceway for passage of electrical wires therethrough. First and second fittings terminate first and second ends respectively of the first tubular member. Each of the fittings is formed of a housing with an interior in communication with the conduit raceway. A second tubular member circumferentially exterior of the first tubular member is formed from a braided mesh of at least two materials. One of the at least two materials possesses a higher electrical conductivity than the other material. The other material possesses a higher strength than the first material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a schematic representation of an electrical connection between two pieces of equipment protected by the flexible electrical coupling of the present invention.  
         [0010]    [0010]FIG. 2 is a partially cross-sectioned longitudinal view of the flexible electrical coupling of FIG. 1, fragmented for clarity and to show details thereof.  
         [0011]    [0011]FIG. 3 is a partially cross-sectioned longitudinal view of the flexible electrical coupling of FIGS. 1 and 2, fragmented for clarity and with a section cut away to show further details thereof.  
         [0012]    [0012]FIG. 4 is a side elevational view of the bonding jumper of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    Turning now to the drawing figures, there is shown in FIG. 1 a  flexible electrical coupling  10  interconnecting two pieces of electrical equipment  12  and  14 . The electrical equipment  12  and  14  may be electrical motors, machinery or the like which are electrically powered and which are required to be electrically interconnected for operation. Such pieces of equipment  12  and  14  interconnected by flexible electrical coupling  10  are commonly used in industrial and construction applications where the environmental conditions are typically harsh with the equipment being subjected to corrosive elements and vibratory movements. Electrical current carrying cables (not shown) electrically interconnect equipment  12  and  14  through the flexible electrical coupling  10 , with coupling  10  thereby protecting such electrical cables and the interconnections between the equipment  12  and  14 . Because pieces of equipment  12  and  14  may move relative to each other, coupling  10  is required to have sufficient flexibility to accommodate such movement. In addition, it is required by the National Electrical Code that the coupling  10  have the capability for carrying a minimum current so that if there is a short in either piece of equipment  12  or  14 , current can be suitably transferred through the coupling  10  to ground, thereby reducing the risk of personal injury or electrocution.  
         [0014]    Referring now to FIG. 2, the details of the coupling  10  are described. Coupling  10  comprises an internal corrugated conduit  16  terminated on each end by a metallic electrical fitting  18 . Corrugated conduit  16  is preferably formed of stainless steel and is of generally solid tubular construction having an internal raceway  16   a  running throughout its length for receipt therethrough of electrical cables. Conduit  16  being corrugated is generally relatively flexible and is preferably formed of stainless steel because of its generally high resistance to corrosion.  
         [0015]    Each fitting  18  terminating the conduit  16  at each end is formed of metal, preferably stainless steel, and is suitably attached to the conduit  16  by welding, brazing or other appropriate securement techniques. In the embodiment shown, fitting  18  includes an exterior threaded portion  18   a  by which the terminated conduit  16  may be attached to each piece of electrical equipment  12  and  14 , respectively. Each fitting  18  further comprises an interior opening  18   b  that communicates with the conduit raceway  16   a  for receipt therethrough of electrical cables. It should be appreciated that fitting  18  may also be provided with an internal threaded portion for attachment thereof to pieces of equipment  12  and  14 .  
         [0016]    Coupling  10  also comprises an external, flexible strength member  20  that is preferably resistive to corrosion. In the preferred form, strength member  20  is a stainless steel wire braid that is supported externally of the conduit  16  and is suitably secured thereto with its longitudinal ends respectively extending beneath the fittings  18 . Braiding  20  provides additional strength to the coupling  10  and, due to braiding, is sufficiently flexible to accommodate required vibratory and other operational movements.  
         [0017]    In accordance with the invention, a bonding jumper  22 , formed of relatively high electrical conductivity material, is supported by the conduit  16  and electrically connected to each fitting  18 . Accordingly, a relatively good electrical path is established over the length of the coupling  10  between each fitting  18  by the jumper  22 .  
         [0018]    Jumper  22  in one arrangement is disposed externally of the conduit  16  and internally of the external braiding  20 . Jumper  22  may be a braided tubular structure as shown in FIG. 4, or a solid strap or ribbon, formed of bronze, brass or copper, with tin plating, and preferably braided for flexibility and strength. Jumper  22  may be attached to each fitting by a pressure fit or crimped to a standard electrical lug and welded to each fitting  18 . In disposition internally of the external braiding  20 , jumper  22  is not directly exposed to corrosive environments and, as such, need not necessarily be formed of material having high resistance to corrosion. In addition, disposition of the jumper  22  internally of the braiding  20  provides for a neater coupling  10  without loose parts that may be used by workers to grab during operation.  
         [0019]    In an alternative arrangement shown in FIG. 3, bonding jumper  22  may be disposed internally within the conduit  16  within the raceway  16   a  and suitably secured internally of each fitting  18 .  
         [0020]    In a further arrangement, a bonding jumper may be integrally woven (not shown) into the external braiding  20 , whereby the braiding may comprise both stainless steel and higher conductivity wires, such as bronze, brass or copper, which may also be tin plated.  
         [0021]    Having described the preferred embodiments herein, it should be appreciated that the flexible electrical coupling described herein provides various improvements over the known flexible couplings. It should be appreciated, however, that the preferred embodiments are intended to be illustrative rather than limiting and that variations may be made thereto without departing from the contemplated scope of the invention.