This disclosure generally relates to technology for connecting an electrical cable to an electrical device.
Electrical cable lugs are often used to connect an electrical cable to an electrical device. Examples of electrical devices include an electrical panel, bus bar, a junction box, and so on. Lugs are typically made from electrically conductive materials (e.g., copper). The electrical cable can be connected to the electrical device via one or more connection points in the lug. An insulated casing of the cable is removed and the exposed electrical cable is fastened to the connection point(s) in the lug (e.g., using mechanical fasteners such as a bolt assembly). The lug is then fastened to the electrical device (e.g., using mechanical fasteners).
Safety and durability of the electrical connection between the electrical cable and the electrical device often depend on various properties of the lug. It is often the case that material with high electrical conductivity does not have sufficient mechanical strength for a durable electrical connection. Repetitive thermal fatigue can lead to poor electrical contact and result in the exposed electrical cable losing mechanical connection with the connection point. Poor electrical contact and lack of sufficient mechanical strength of the lug can lead to lack of compliance with electrical safety standards and create safety hazards due to exposed electrical cables. On the other hand, many materials with sufficient strength and durability are not suitable for serving as a mechanical lug because they lack sufficient electrical conductivity.
Examples described in this disclosure provide a mechanical lug with physical and material features that enhance the mechanical and electrical connection between an electrical cable and an electrical device. In one aspect, this disclosure teaches a mechanical lug for electrically connecting an electrical cable and an electrical device. In some examples, the mechanical lug can include a body portion, a connection point, an electrical cable fastener, a shoulder portion, a neck portion, and an electrical device fastener. The body portion can have a longitudinal axis. The connection point can be defined in the body portion transversely to the longitudinal axis. In many examples, the connection point can include grooves. The electrical cable fastener can be configured to press the electrical cable into contact with the grooves when the electrical cable is inserted into the connection point. The shoulder portion can be coupled to the body portion. The shoulder portion can have a shoulder surface that is oriented transversely to the longitudinal axis. The shoulder surface can be configured to contact a first surface of the electrical device. The neck portion can be coupled to the shoulder portion. The neck portion can be configured to extend through a hole in the electrical device. The electrical device fastener can be configured to fasten the mechanical lug to the electrical device.
In one aspect, a method can connect a cable to an electrical device via a mechanical lug such as those discussed herein. The method can include inserting an uncovered portion of an electrical cable into the mechanical lug's connection point. The method can include pressing that uncovered portion into contact with the connection point's grooves by the mechanical lug's electrical cable fastener. The method can include extending the mechanical lug's neck portion through a hole in an electrical device. The method can include bringing the mechanical lug's shoulder portion into contact with a first surface of the electrical device. The method can include fastening the mechanical lug to the electrical device with the mechanical lug's electrical device fastener.
Certain mechanical lugs in accordance with embodiments of the present invention may have one or more advantages. For example, mechanical lug like those described herein can improve the safety of electrical connections and can make it easier to comply with electrical safety standards. Embodiments of the mechanical lug with grooves at the connection point can improve electrical conduction and result in greater heat dissipation at the connection point. Many such embodiments can enhance the integrity of the mechanical connection between the electrical cable and the lug, thereby significantly reducing the likelihood of the electrical cable being disconnected due to repetitive thermal fatigue at the connection point. Embodiments of the mechanical lug can provide improved material hardness and tensile strength, thereby providing a rugged, safe and durable electrical connection. Some mechanical lug embodiments discussed in this disclosure provide greater electrical conductivity between the mechanical lug and the electrical device. For example, some embodiments provide significantly more surface contact between the lug and the electrical device than conventional lug/component configurations.
The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.
The following detailed description is exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides some practical illustrations for implementing examples of the present invention. Examples of constructions, materials, dimensions, and manufacturing processes are provided for selected elements, and all other elements employ that which is known to those of ordinary skill in the field of the invention. Those skilled in the art will recognize that many of the noted examples have a variety of suitable alternatives.
Embodiments of the invention include a mechanical lug 100 for electrically connecting an electrical cable and an electrical device. The electrical cable can include many conducting filaments of an electrically conductive material (e.g., copper, aluminum) housed in an insulating sheath. The electrical cable can include finely stranded wire, types B, C, and K wire, and the like. Often, the insulating sheath of the electrical cable can be stripped to expose the conducting filaments so that the exposed electrical cable can be electrically connected to the mechanical lug 100. The electrical cable can be rated to a high current rating (e.g., 125 amperes, 150 amperes, 400 amperes, etc.) suitable for use in power generation equipment. Electrical cables of various sizes can be accommodated by the mechanical lug 100. The electrical device 200 can be a bus bar, an electrical power distribution panel, a transformer and similar electrical components. Such electrical devices can be found in domestic and industrial electrical panels, enclosures, or devices.
Reference is now made to
The connection point 130 can be defined in the body portion 110 transversely to the longitudinal axis LA. In some preferred embodiments, the connection point 130 can be defined in the body portion 110 perpendicularly to the longitudinal axis LA. The connection point 130 can be adapted to receive the electrical cable. The connection point 130 can be an opening defined in the body portion 110 transversely to the longitudinal axis LA, as best seen in
In some embodiments, the connection point 130 can include grooves 132. When the electrical cable is inserted into the connection point and pressed by the electrical cable fastener 140, the grooves 132 can increase the surface area of contact between the electrical cable and the mechanical lug 100. The individual conductors of the electrical cable are brought into conformity with the surfaces of the grooves 132, resulting in greater surface area contact than if the connection point had a smooth connection surface. This increased surface contact can enhance the electrical connection between the electrical cable and the connection point 130. In some embodiments, the mechanical lug 100 can include indentations, flutes, projections, slots and the like for enhancing connection between the electrical cable and the connection point 130. Some such embodiments can be useful for providing better electrical connection because of higher surface area of contact between the electrical cable and the mechanical lug 100. Some such embodiments can make inadvertent disconnection of the electrical cable from the connection point 130—a potentially hazardous situation—significantly less likely. In some such embodiments, the grooves 132 can act as grippers, thereby increasing frictional force on the electrical cable and preventing it from slipping out of the connection point. Some such embodiments can make it less likely that individual conductors of the electrical cable are broken because of the load applied by the electrical cable fastener 140. The grooves 132 can distribute that load, lessening the chances of breaking any individual conductors. In many instances, the electrical cable's electrical conductivity can be significantly compromised if even a very low percentage (e.g., 1%) of the individual conductors are damaged or broken. In some embodiments, the grooves 132 can be threaded (right-hand or left-hand threads). In some embodiments, the grooves 132 can be a series of closed grooves rather than threads.
The electrical cable fastener 140 can be configured to press the electrical cable into contact with the grooves 132 once the electrical cable is inserted into the connection point 130. In the illustrated embodiment shown in
The shoulder portion 150 can be coupled to the body portion 110 and can press against the electrical device when engaged. In some embodiments, the shoulder portion 150 can be integrally formed with the body portion 110 by fabrication techniques such as casting or undercutting. The shoulder portion 150 can have a shoulder surface 152 that is oriented transversely to the longitudinal axis LA. As best seen in
In some embodiments, the mechanical lug 100 can include a turn prevent 180. In some embodiments, the turn prevent 180 can extend from the shoulder portion 150 generally parallel to the longitudinal axis LA. As seen in
The first and second turn prevents 180, 190 when engaged with the first and second receptacles can inhibit inadvertently high torques on the mechanical lug 100 (e.g., torques exceeding 400 inch-pounds applied on the electrical cable fastener 140), thereby preventing damages to finely stranded electrical cable. Such embodiments can facilitate better mechanical connection between the mechanical lug 100 and the electrical device by preventing the electrical cable and the electrical device from being damaged during installation due to inadvertent application of high torques to the mechanical lug 100.
The neck portion 160 can be coupled to the shoulder portion 150 and can be configured to extend through a hole in the electrical device 200. The neck portion 160 can be integrally formed with the body portion 110 and the shoulder portion 150 by fabrication techniques such as casting, or metal forming (e.g., turning and undercutting). In some preferred embodiments, the neck portion 160 can include a neck surface 162 configured to contact a surface defining the hole in the electrical device 200. Such embodiments can be useful for increasing the surface area of contact between the mechanical lug 100 and the electrical device 200. In some embodiments, the entire (or nearly entire) surface of the neck portion 160 can contact the corresponding surface of the hole in the electrical device. In some embodiments, the neck surface 162 can be roughened to create a plurality of contact points between the neck surface 162 and the electrical device hole. Many such embodiments can offer a variety of advantages, such as enhanced electrical conductivity and better heat dissipation characteristics of the electrical connection. Such embodiments can allow the mechanical lug to be operable to very high temperatures, often on the order of 105 degrees Celsius.
Referring again to
Embodiments of the mechanical lug 100 can have a variety of material properties. In some embodiments, the mechanical lug 100 can have an electrical conductivity of at least 80% IACS. In some embodiments, the mechanical lug 100 can have an electrical conductivity of at least 85% IACS. In many instances, an electrical conductivity in the range of approximately 80% to approximately 85% can enhance the electrical contact between the electrical cable and the electrical device. In some embodiments, the mechanical lug 100 can have a material hardness of at least B70. In some embodiments, the mechanical lug 100 can have a material hardness of at least B83. In many instances, a material hardness in the range of B70-B83 can facilitate a durable and mechanically rugged construction of the mechanical lug 100, ensuring that the mechanical lug 100 does not deform over time. In some preferred embodiments, the mechanical lug 100 can have an electrical conductivity of at least 80% IACS and a material hardness of at least B70. In some preferred embodiments, the mechanical lug 100 can have an electrical conductivity of at least 80% IACS and a material hardness of at least B83. In some preferred embodiments, the mechanical lug 100 can have an electrical conductivity of at least 85% IACS and a material hardness of at least B70. In some preferred embodiments, the mechanical lug 100 can have an electrical conductivity of at least 85% IACS and a material hardness of at least B83.
Embodiments of the mechanical lug can be made of a variety of alloys. In some embodiments, the mechanical lug 100 can be made of 18150 class 2 copper zirconium. In some embodiments, the mechanical lug 100 can be made of an alloy comprising between approximately 98.25% and approximately 99.45% copper, between approximately 0.5% and approximately 1.5% chromium and between approximately 0.05% and approximately 0.25% zirconium. Some such embodiments can be useful for superior electrical conductivity and material durability, because of the combination of high electrical conductivity of copper relative to other metals (e.g. nickel, steel, and the like) and the high material hardness of the alloy that includes chromium and zirconium in comparison to pure copper. An alloy of composition similar to those listed can be used for fabricating the mechanical lug 100 without loss of functionality.
Embodiments of the invention can include a method for connecting a cable to an electrical device. The method may include providing a mechanical lug (e.g., like those discussed elsewhere herein). In some embodiments, the method can include uncovering (e.g., stripping) a portion of an electrical cable. The method can include inserting an uncovered portion of the electrical cable into a connection point of the mechanical lug and pressing the uncovered portion of the electrical cable into contact with the grooves by the electrical cable fastener. In some embodiments, the method can include extending the neck portion of the mechanical lug through a hole in the electrical device and bringing the shoulder portion into contact with a first surface of the electrical device. In some instances, the method can include fastening the mechanical lug to the electrical device with the electrical device fastener. The mechanical lug such as those described herein can be useful for connecting an electrical cable with an electrical device, such as a bus bar or a power distribution panel in household power supply lines or industrial power transmission facilities.
Some embodiments can include various safety features for preventing tampering with the mechanical lug when connected to an electrical cable and an electrical device. For example, some embodiments can include outside insulation over the mechanical lug, electrical cable, and electrical device. Some embodiments may provide a tamper-resistant enclosure. In some embodiments, when the mechanical lug is connected to an electrical cable and an electrical device, the assembly can be considered finger safe.
Various examples of the invention have been described. Although the present invention has been described in considerable detail with reference to certain disclosed embodiments, the embodiments are presented for purposes of illustration and not limitation. Other embodiments incorporating the invention are possible. One skilled in the art will appreciate that various changes, adaptations, and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.