Patent Application
20130267130
1. Field
The disclosed concept pertains generally to neutral bars and, more particularly, to such neutral bars for stranded conductors.
2. Background Information
It is known to employ a neutral bar to provide a common point for termination of a plurality of neutral conductors and one ground conductor in a panelboard or load center. Each of a plurality of screw terminals electrically and mechanically engages one end of a corresponding neutral or ground conductor.
Certain known neutral bars do not pass a UL486A-486B current cycling test for a 75° C. rating when using a #4 AWG stranded aluminum conductor. For example, the neutral bar screw breaks one or two strands of the #4 AWG stranded aluminum conductor at rated 35 lb-in. torque.
A glowing contact is a high resistance electrical connection, which can form, for example and without limitation, at the interface of a conductor (e.g., wire) and a screw terminal (e.g., line terminal; neutral terminal; ground terminal), for example, of a receptacle or a neutral bar. A glowing contact is known to produce substantial heat. It is very easy to create a high resistance or glowing contact at a screw terminal using copper wire. The hazards associated with glowing contacts, including contacts made with all combinations of copper, brass and iron are known. See, for example, U.S. Pat. Nos. 6,948,846; and 6,707,652.
There is room for improvement in neutral bars.
These needs and others are met by embodiments of the disclosed concept in which a neutral bar includes a plurality of neutral bar fasteners, each of the neutral bar fasteners comprising a first end, a rounded second end having a hemispherical surface opposite the first end, and a threaded shaft therebetween.
In accordance with an aspect of the disclosed concept, a neutral bar comprises: a plurality of neutral bar fasteners, each of the neutral bar fasteners comprising a first end, a rounded second end having a hemispherical surface opposite the first end, and a threaded shaft therebetween; and an elongated, generally rectangular member comprising a plurality of tapped openings and a plurality of cylindrical openings, each of the cylindrical openings being normal to a corresponding one of the tapped openings, wherein the threaded shaft of each of the neutral bar fasteners is threaded into a corresponding one of the tapped openings of the elongated, generally rectangular member, wherein each of the cylindrical openings is structured to receive a stranded conductor having a plurality of individual solid conductors, and wherein the hemispherical surface of each of the neutral bar fasteners is structured to engage the stranded conductor within a corresponding one of the cylindrical openings.
In accordance with another aspect of the disclosed concept, a neutral bar comprises: a plurality of neutral bar fasteners, each of the neutral bar fasteners comprising a first end, a rounded second end having a hemispherical surface opposite the first end, and a threaded shaft therebetween; and an elongated, generally rectangular member comprising a plurality of tapped openings and a plurality of cylindrical openings, each of the cylindrical openings being normal to a corresponding one of the tapped openings, wherein the threaded shaft of each of the neutral bar fasteners is threaded into a corresponding one of the tapped openings of the elongated, generally rectangular member, wherein each of the cylindrical openings is structured to receive a number of conductors, and wherein the hemispherical surface of each of the neutral bar fasteners is structured to engage the number of conductors within a corresponding one of the cylindrical openings.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.
As employed herein, the term “hemisphere” shall mean one of two half spheres formed by a plane through a sphere's center.
As employed herein, the term “hemispherical surface” shall mean all of the external surface of a hemisphere (e.g., without limitation, as shown as 6 in
Referring to
It is believed that the rounded end 14 of the disclosed neutral bar screw 10 works better than the flat end 4 of the flat end screw 2 (
Furthermore, a cooler running mating body of the neutral bar 30 is beneficial because it does not damage tin plating applied to the mating body of the neutral bar 30. The example neutral bar screw 10 is made of steel with zinc plating. On aluminum neutral bars, a layer of copper plating is applied before an optional layer of nickel plating and a top layer of tin plating. The copper plating acts as a primer for the tin plating. The tin plating does not stick to directly to the aluminum material. Other suitable neutral bar materials include copper bars with tin plating, copper bars without tin plating for use with copper conductors, and zinc bars with tin plating.
In the example embodiment, the aluminum elongated, generally rectangular member 30 includes a layer of copper plating applied thereto, an optional layer of nickel plating applied to the layer of copper plating, and a layer of tin plating applied to the optional layer of nickel plating or to the copper plating. The layer of copper plating acts as a primer for the layer of tin plating. Although examples of neutral bar and neutral bar screw materials and plating materials are disclosed, any suitable material and/or plating material (or no plating material) can be employed.
When the neutral bar temperatures run relatively hot, copper atoms can move into the tin plating. When the copper and tin atoms intermix, a high resistance alloy is created. This intermixing can cause the mating body of the neutral bar 30 to overheat and fail. Hence, a reliable electrical connection to the stranded conductor 38 (
The rounded end 14 of the neutral bar screw 10 does not pinch the outside of the solid conductors (strands) 40 (
Conversely, the prior flat end screw 2 of
In one embodiment, the hemispherical surface of the rounded end 14 of the neutral bar screw 10 has about a 0.188″ radius, although a larger or smaller radius on the neutral bar screw 10 can be employed. Preferably, the neutral bar screw radius that has the smallest gap to the neutral bar, such as 30, is the best radius.
The disclosed concept can be applied to a wide range of conductors (e.g., without limitation, #14, #12, #10, #8, #6 or #4 AWG wires, either solid or stranded, in copper or aluminum except for #14 AWG aluminum wire which is not listed in the UL test standard; a quantity or one, two or three #14, #12 or #10 AWG copper wires, solid or stranded; a quantity of one, two or three #12 or #10 AWG aluminum wires, solid or stranded).
The disclosed concept passes UL 486A-486B connector current cycling tests at a 75° C. rating. This UL Standard applies to single-polarity connectors for use with all alloys of copper or aluminum, or copper-clad aluminum conductors, or all three, for providing contacts between current-carrying parts of neutral bars. With #4 AWG aluminum conductor, UL requires 110 amperes for a 75° C. rating. For a 90° C. rating, the current is 140 amperes. The UL test consists of 500 cycles of 1 hour on/1 hour off current. The disclosed neutral bar screw 10 and neutral bar 30 pass the UL486A-486B current cycling test for a 75° C. rating when using a #4 AWG stranded aluminum conductor. Also, the neutral bar screw 10 does not break any strand of the #4 AWG stranded conductor at rated torque.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof
