Torque limiting socket for twist-on wire connectors

Details Torque limiting socket for twist-on wire connectors Torque limiting socket for twist-on wire connectors

1995-12-12

2001-03-06

Kincaid, Kristine (Department: 2831)

Electricity: conductors and insulators

Conduits, cables or conductors

Combined

C007S107000, C081S121100, C081S124300

Reexamination Certificate

active

06198049

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to connecting electrical wires with twist-on type connectors; and more particularly, to tools for fastening such connectors.
The ends of two or more wires of an electrical circuit are often connected together using a twist-on type wire connector. These connectors are available in a variety of sizes and shapes and commonly have a conical shaped body of insulating material, such as plastic, with an opening at the larger end. The opening communicates with a tapered aperture which has helical threads cut in the interior surface of the body. The fastening operation is performed by inserting the stripped ends of two or more wires into the open end and rotating the connector so that the threads screw onto and twist the wires together to form an electrical coupling. An improved connector has a tapered metal spring inserted into the aperture of the insulating body. The spring engages the bare wires and aids in providing a conductive path there between.
Twist-on type wire connectors frequently are used by electricians to connect two or more wires in a junction box within a building. In this application, electricians typically twist on the connectors by hand, although manual tools, such as a hexagonal socket wrench or a nut driver, can be used. These connectors also are employed in a variety of electrical appliances. For example, connections between the wires of a ballast in a fluorescent lighting fixture and the electrical supply cord are made in this manner. In a factory, the wire connectors often are attached using a pneumatically or electrically powered nut driver because of the high volume assembly at a fixed location. These power tools have a socket specifically designed to engage the body of the connector.
A fastening tool, especially an power-driven one, easily can apply an excessive amount of torque to the connector, thus damaging either the wires or the connector. If cracks in the connector are undetected, a short circuit could occur at the connection.
One solution to this problem was to limit the torque with a clutch mechanism between the tool motor and the socket. However, torque limiting devices add additional expense, size and weight to the tool, and require adjustment to the optimum level for each specific wiring application.
SUMMARY OF THE INVENTION
A general object of the present invention is to provide a manual or power driven fastening tool for a twist-on wire connector.
Another object is to provide a wire connector fastening tool which self-limits the amount of torque that can be applied to the connector during the fastening operation.
These and other objectives are fulfilled by a system for joining ends of electrical wires to a predefined torque level, which comprises a twist-on connector and a tool socket specifically designed to cooperate in limiting the amount of torque that the socket is able to apply to the connector. The connector includes a hollow body with an open end in which to receive the wires, a closed end and an outer surface extending between the open and closed ends. At least a portion of the outer surface has elements which form a cross section with a polygonal shape. For example, that portion of the body has side surfaces meeting at outside corners to form a hexagonal cross section.
The tool socket includes a coupling by which torque is applied to the tool socket by a driver. An aperture is provided in the tool socket to removably receive the closed end of the connector with side walls of the aperture engaging the portion of the connector's outer surface. The aperture is significantly larger in cross section than the connector so that a gap exists between the side walls and the outer surface. For example, the aperture may have a polygonal cross section with portions of the side walls between the polygon corners being directed away from the connector to form the gap. The gap results in the transfer of torque between the socket and the connector being concentrated at the outside corners of the connector. This torque concentration causes the elements of the connector, such as the outside corners of the polygon, to deform when the tool socket applies greater than the predefined torque level to the connector. After that deformation, the socket turns freely about the connector inhibiting additional torque from being applied.


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patent: 5476024 (1995-12-01), Hsieh

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