US3657513A - Electrical heating cables - Google Patents

Abstract

An improved junction between the cold section of an electrical heating cable and the input leads, the cold or non-heating section being disposed between the hot section and the input leads. The disclosure relates to a mechanically reliable, electrically-safe splice utilizing a stranded conductor for the input lead.

Description

United States Patent Howard ELECTRICAL HEATING CABLES Inventor: Lawrence Howard, Wauconda, 111.

Assignees: Jack Hille; Avrum N. Andalman, trustee; Arnold L. Cohen; Avrum N. Andalman, Chicago, 111. part interest to each Filed: July 22, 1970 Appl. No.: 57,230

U.S. Cl ..219/200, 174/90 Int. Cl ..B60l l/02 Field of Search ..219/200, 209, 528, 541, 544;

174/86 RR, 88 R, 40, 76, 77; 338/273, 274, 332

References Cited UNITED STATES PATENTS Josephine ..174/76 X [151 3,657,513 [4 1 Apr. 18, 1972 1,241,809 10/ 1917 Beardsley et al ..174/88 X 3,127,291 3/1964 Betz et al. ..174/84 R 2,009,980 7/1935 Abbott ...338/274 X 3,071,748 1/1963 Lucia ..338/268 355,611 1/1887 Howson ..174/84 R 324,413 8/1885 Patterson ..174/84 R 2,780,704 2/ 1957 Charbonneau ..338/274 X Primary Examiner-C. L. Albritton Attorney-Leonard S. Knox [57] ABSTRACT An improved junction between the cold section of an electrical heating cable and the input leads, the cold or non-heating section being disposed between the hot section and the input leads. The disclosure relates to a mechanically reliable, electrically-safe splice utilizing a stranded conductor for the input lead.

4 Claims, 7 Drawing Figures 1 ELECTRICAL HEATING CABLES BACKGROUND OF THE INVENTION It is known to provide electrically heated cables for a great many purposes, some of which are the heating of sidewalks to melt snow, pipes to prevent freezing, tanks to improve the flowability of liquids therein, gutters and downspouts.

In those cases where the cable is embedded, for example, in a sidewalk area, it is expected that the installation have the utmost reliability for, if open or short circuits develop, locating the trouble and its repair may involve the expensive removal and replacement of a large area of the concrete and the installation of new cable.

One widely-used form of cable utilizes a heating section (hot section) comprising one or more wires of proper electrical resistance, e.g. Nichrome, contained ina metallic sheath together with densely compacted pulverulent, refractory, insulating material, e.g. magnesium oxide. The sheath is generally of non-rusting metal, e.g. copper or stainless steel.

A so-called cold section is interposed between the hot section and the terminal leads in order to isolate the terminals and junction box from the effects of heat. Heretofore the leads, sometimes termed pigtails, were a solid conductor so that manipulation thereof during installation, e.g. splicing the leads of several cables in a common junction box, would often cold-work the lead to the point of potential or actual rupture. Replacement of the pigtail necessarily led to considerable expense, as pointed out above.

SUMMARY OF THE INVENTION The invention comprehends a terminal lead for a heating cable of the type mentioned which constitutes a strong, reliable transition from the cold section to the terminals to which the cable is connected. In what follows reference will be made primarily to a single conductor serving as the resistance of the hot section. However an example of a plural-conductor device will be described, the principles of the invention being equally applicable thereto.

In a preferred form the end face of a terminal lead of stranded wire is butted to the end face of the wire of the cold section and soldered. To add mechanical strength a sleeve is located over the splice and the wires and sleeve sweated together to form a homogeneous mass. Desirably the outer diameter of the stranded lead is greater than that of the abutted wire in order that substantially equal cross-sectional areas are opposed at the joint. The sleeve may be crimped to implement the strength of the splice. Moreover the crimping may be performed in a manner such that the wall of the sleeve is punctured. In this way it is assured that the voids within the sleeve receive a full complement of solder.

A second outer sleeve is positioned over the splice as described and an epoxy resin or equivalent electrically insulating substance is used to till the space between the outer and inner sleeves and those portions of the conductors not enclosed by the inner sleeve. Thus mechanical strength is enhanced and the splice hermetically sealed. If desired the inner sleeve may be wrapped with a dielectric tape or otherwise insulated from the outer sleeve to preclude grounding.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation of a section of heating cable connected to a conduit fitting, the resistance wire being connected to the source at both ends;

FIG. 2 is a similar view in which two resistance wires are contained in a common sheath, and connected to the source at one end of the sheath;

FIG. 3 shows details of a preferred mode of splicing the stranded pigtail directly to the cold section;

FIG. 4 shows a splice between the resistance wire and cold section;

FIG. 5 is a splice incorporating the features of FIG. 3 but consisting of two conductors;

FIG. 6 shows the splice from thehot section to the cold section, in the case of plural conductors; and

DESCRIPTION OF THE PREFERRED EMBODIMENTS A heater cable 10 is shown in FIG. 1. The portion 11, termed the hot section, comprising a resistance wire 13 of Nichrome or equivalent, contained centrally of a metallic sheath 15, usually of non-corrosive metal, such as stainless steel, although, for many applications, copper is used. The space intermediate the wire 13 and sheath 15 is filled with a tightly compacted refractory 16, such as magnesium oxide. The portion of the cable just described is conventional.

The hot section 11 may be of any length required for the application, e. g. a section of sidewalk. In this case the hot section may be several hundred feet in length and bent in zig-zag form, as is known. In the interests of good practice and to comply with local ordinances, each end of the section 11 is terminated in so-called cold sections 21-21, referred to above. This expedient isolates the hot section from the leads or insulated pigtails and thus avoids the detrimental efiect of abnormal temperature on the insulated stranded wires.

Although the mode of connecting the ends of the hot and cold sections does not form a part of the invention the same will be described in the interests of completeness and clarity. The splice 27 connecting the hot and cold sections is shown in FIG. 4. The end of the resistance wire 13 is brazed at 28 in abutting relation with a copper wire 29, this latter being of a length coextensive with the distance calculated to minimize excessive transfer of heat to the terminal leads and the components directly associated therewith, as will be shortly described. The wire 29 is protected by a sheath 32 of some non-corrosive material e.g. copper. A dense mass 33 of refractory material, such as compacted magnesium oxide, insulates the wire 29 from the sheath 32 and assures their relative coaxial position.

Following joining of the wires 13 and 29 a sleeve 36 of rigid, non-corrosive material, e.g. brass, is placed over the ends of the sheaths l5 and 32 and soldered in place. In the event one of these sheaths is less in diameter than the other, a tubular shim 37 may be interposed. It will be noted that the joints at the ends of the sleeve 36 are sweated.

FIG. 6 illustrates a splice 27a of the fonn of FIG. 4, but applied to the multiple conductor cable 10a of FIG. 2, similar reference numerals have been employed. It is believed that the assembly will be clear from the description of FIG. 4.

Referring to FIG. 3, the other end of the cold section 21 has the sheath 32 and refractor material 33 cut back to expose the conductor 29 for a short distance and the end is desirably squared off as at 51. The pigtail 53 of stranded wire and the conductor 29 are inserted one from each end into the sleeve 58 and held rigidly. Heat and solder are applied with solder entering the sleeve through perforations in the sleeve and filling the voids between the wire 29, pigtail 53 and sleeve 58 to integrate these components.

As an additional safety feature the sleeve 58 and adjacent portions of the spliced wires may be wrapped with insulating tape 63.

A sleeve 60 of brass is placed over the assembly just described and sweated at 62 to the sheath 32. Since, for the same current-carrying capacity, the pigtail 53 will be larger than the wire 29, it may become necessary to insert a shim 24 and to sweat the same to the sheath 32 and sleeve 60.

While maintaining the pigtail 53 centrally of the sleeve 60 an epoxy resin 67 or equivalent is poured into the sleeve 60 and cured. It will be seen that the pigtail 53 includes insulation 68 which may be part of the stranded conductor as supplied or placed thereover following the splicing operation.

FIG. 5 shows the same details as in FIG. 3 but in connection with plural conductors Similar reference numerals have been used. In this example it will be obvious that suitable insulation will be used between and around the conductors to preclude short circuit or grounding.

FIG. 2 shows a cable a employing a pair of resistance wires 75-75 (FIG. 7) which are terminated at the remote end of the cable in a weld 77 or other form of joint. A cap 78 soldered at 79 to the obvious 21a encloses the joint 77.

The sleeve 60 or 600 is attached to a fitting 25 or 25a by means of a compression coupling 81 or 81a while the pigtails are carried through conduit to a junction box, all as is understood. It will be obvious that the sleeves 60 or 600 may be coupled directly to the box.

From the foregoing it will have become apparent that the termination of the heater in a stranded conductor and the reinforcement of the splice between that conductor and the thereto-joined solid conductor, results in a splice of maximum durability. Flexure applied to the pigtail cannot be transmitted to the abutted ends of the splice because of the rigid nature of the components constituting the same. Bending force are absorbed wholly in the stranded wire beyond the splice. Similar considerations apply to twisting and tension forces.

Where, herein, reference is made to a stranded conductor it is intended to include a braided conductor also.

We claim:

1. In an electrical heating cable to be connected to a source of supply at terminals in a junction box and having a hot section and a cold section intermediate the hot section and junction box, the cold section having a solid conductor within a sheath and dielectric material between the conductor and sheath, a terminal lead construction comprising: a stranded conductor to be connected to the terminal butted end-to-end with the solid conductor, a first, rigid, electrically conducting sleeve surrounding the butted ends, the conductors and sleeve being united by a non-compressive, sweat-soldered joint integrating the conductors and sleeve, said sleeve being crimped to said conductors, a second, rigid, metallic sleeve surrounding and spaced from said first sleeve, said second sleeve being telescoped over the sheath and joined thereto, said stranded conductor, except for the portion within said first sleeve having insulation thereover, said second sleeve overlapping a por tion of said insulation, and dielectric material within the second sleeve embracing said insulation and anchoring the stranded conductor.

' 2. An electrical junction comprising a solid conductor, a stranded conductor having insulation thereover, said conductors being positioned in abutting end-to-end relation, a first, rigid, metallic sleeve positioned over and spaced from the abutted ends, fusible, non-compressive material in the space between the conductors and sleeve integrating said conductors and sleeve, a second, rigid, metallic sleeve surrounding and spaced from said first sleeve, dielectric material between said sleeves, said material embedding the insulation and restraining movement thereof.

3. An electrical junction a solid conductor, a stranded conductor said conductors being positioned in end-to-end abutting relation, a first, rigid sleeve snugly positioned over, spaced from, and crimped on the ends of the conductors, fusible material filling the voids between the conductors and sleeve, and integrating the conductors and sleeve, the solid conductor being housed in a sheath and insulated therefrom, the stranded conductor having insulation thereover terminating closely adjacent said first sleeve, a second, rigid sleeve surrounding a portion of the insulation of the stranded conductor and a portion of the sheath, and a rigid matrix of dielectric material filling the voids between the second sleeve and the elements surrounded thereby.

4. The combination in accordance with claim 3 in which said second sleeve is telescoped over the adjacent end portion of the sheath.

Claims (4)

1. In an electrical heating cable to be connected to a source of supply at terminals in a junction box and having a hot section and a cold section intermediate the hot section and junction box, the cold section having a solid conductor within a sheath and dielectric material between the conductor and sheath, a terminal lead construction comprising: a stranded conductor to be connected to the terminal butted end-to-end with the solid conductor, a first, rigid, electrically conducting sleeve surrounding the butted ends, the conductors and sleeve being united by a non-compressive, sweat-soldered joint integrating the conductors and sleeve, said sleeve being crimped to said conductors, a second, rigid, metallic sleeve surrounding and spaced from said first sleeve, said second sleeve being telescoped over the sheath and joined thereto, said stranded conductor, except for the portion within said first sleeve having insulation thereover, said second sleeve overlapping a portion of said insulation, and dielectric material within the second sleeve embracing said insulation and anchoring the stranded conductor.

2. An electrical junction comprising a solid conductor, a stranded conductor having insulation thereover, said conductors being positioned in abutting end-to-end relation, a first, rigid, metallic sleeve positioned over and spaced from the abutted ends, fusible, non-compressive material in the space between the conductors and sleeve integrating said conductors and sleeve, a second, rigid, metallic sleeve surrounding and spaced from said first sleeve, dielectric material betweEn said sleeves, said material embedding the insulation and restraining movement thereof.

3. An electrical junction a solid conductor, a stranded conductor, said conductors being positioned in end-to-end abutting relation, a first, rigid sleeve snugly positioned over, spaced from, and crimped on the ends of the conductors, fusible material filling the voids between the conductors and sleeve, and integrating the conductors and sleeve, the solid conductor being housed in a sheath and insulated therefrom, the stranded conductor having insulation thereover terminating closely adjacent said first sleeve, a second, rigid sleeve surrounding a portion of the insulation of the stranded conductor and a portion of the sheath, and a rigid matrix of dielectric material filling the voids between the second sleeve and the elements surrounded thereby.

4. The combination in accordance with claim 3 in which said second sleeve is telescoped over the adjacent end portion of the sheath.

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