Patent Publication Number: US-6906264-B1

Title: Color-coded armored cable

Description:
BACKGROUND OF INVENTION 
   The present invention relates to the general field of visually coded electrical conductors and cable, more particularly to the field of visually coded armored cable, and even more particularly to a new and improved version of color-coded armored cable. 
   Visual coding of electrical conductors and cable to distinguish their electrical properties, intended use, or other characteristics has been a long time practice. Such coding has typically used, for example, alpha-numeric stamping, varied marking patterns, or specific colors or color combinations, to respectively distinguish the electrical characteristics, application, or the like, of the conductors or cable. Such coding is represented by industry practices and documented in patents dating back at least as early as the 1900s. Examples of these patents are U.S. Pat. No. 951,147, issued Mar. 8, 1910; U.S. Pat. No. 2,106,048, issued Jan. 18, 1938; U.S. Pat. No. 3,720,747, issued Mar. 13, 1973; and U.S. Pat. No. 5,340,326 (FIG. 8), issued Aug. 23, 1994. 
   A particular type of cable known as armored cable has been in use for many decades. Metal clad armored cable comprises an elongated outer sheath of metal, primarily for the mechanical protection of the insulated conductors which extend through the inner passageway defined by the sheath. The metallic sheath is typically formed by a helically wound strip with adjacent convolutions overlapping and interlocking with one another to provide a flexible metal conduit that facilitates the electrical conductor installation process and the particular routing of conductors. 
   Given that visual coding of other type of cable had already become commonplace, it was then not surprising that visual coding, including color coding, of armored cable also became a common practice in the United States and elsewhere. This is reflected not only by industry adoption of color-coding of armored cable at least as early as the 1980s using, for example, paint applied to, or colored jackets surrounding, the cable sheath, but also by many disclosures of such approach in the patent literature. 
   For example, British patent specifications GB 194,419 (1923); U.S. Pat. No. 1,117,862 (1968); and U.S. Pat. No. 1,432,548 (1976) all disclose visual coding of armored cable. U.S. Pat. No. 4,875,871, issued Oct. 24, 1989, discloses color coding of various modular components of an electrical network including, significantly, color coding of flexible metal clad armored cable (FIG. 17 c ). A “family” of interrelated patents owned by WPFY Inc., namely U.S. Pat. Nos. 5,350,885; 5,468,914; 5,557,071; and 5,708,235 (re-issued as Re 38,345), all disclose various versions of color-coded armored cable, particularly those in which different patterns of visible indicia, i.e., predetermined arrangements of discrete markings, particularly color, have been selectively applied to the surface of the armored cable sheath. The selective application of the color pattern leaves exposed, as bare metal, preselected portions of the “crowns” and “valleys” of the cable sheath. The result is a difference of visual appearances, or duality of contrast, between the exposed metal portions and the pattern of colored indicia. 
   Unfortunately, prior color-coding techniques for armored cable, and the resulting color-coded armored cable, have substantial disadvantages associated with them. For example, use of color patterns or other types of visible indicia as the means for color-coding, like that described and claimed in the above-described family of WPFY patents, while admittedly artistic, can be distractions from the primary objective that the color-coding is intended to achieve—namely, the immediate and readily understood “decoding” or identification of the type and application of the particular coded armored cable. Additionally, the requirement that the color coating leave portions of the surface of the metal sheath exposed is not only unnecessary from an electrical standpoint, but results in a needless processing expense and could cause the sheath to be susceptible to corrosion. Furthermore, to the extent that industry has recognized these problems and adopted a solid, continuous, (rather than patterned) color-coding approach, the full benefits and advantages of this approach have not yet been achieved. For example, when using a continuous solid color coating applied to the cable sheath, unless the color coating has a high degree of retention to the surface of the sheath, the full benefit of this approach may not be realized. 
   It is therefore a principal object of the present invention to provide a new and improved version of color-coded armored cable substantially different from any prior approach, and one that provides an easily identifiable, efficient and durable identification system. It is another object of the present invention to provide an improved color-coded armored cable which avoids the disadvantages of one that has indicia or patterns applied to the outer surface of the metal sheath. It is another object to avoid the disadvantages associated with a color coding technique which requires exposed areas of bare metal on the surface of the cable sheath. It is a still further object of the invention to provide a new and improved version of solid color-coded armored cable, meeting the aforementioned objects. 
   SUMMARY OF THE INVENTION 
   In accordance with the above noted and other objects, the present invention provides an improved color-coded armored cable of a type in which the entire outside observable metallic surface of the cable sheath formed by a helically wound metal strip is covered with a solid, visually continuous non-patterned, preferably non-conductive, coating of material the coating being of a color which visually distinguishes the cable from others having different electrical properties, intended uses or applications, and/or other defined characteristics. 
   In accordance with important aspects of the invention, the longevity of retention of the non-patterned color coating to the observable outer surface of the metallic sheath is enhanced by incorporating the synergistic combination of features of an abraded metallic surface, a precise thickness of color coating, a polyethylene based lubricant of specific volumetric percentage incorporated into the color coating, and a specific profile shape and optimum number of convolutions of the helically wound metallic strip forming the cable sheath. An additional translucent coating is optionally disposed over the color coating. 
   In accordance with further aspects of the invention, the so-constructed color-coded armored cable is provided with a coating, preferably conductive, disposed over the interior surface of the cable sheath to facilitate fabrication of color-coated metal strips which form the sheath and to minimize damage to the color coating during handling of the metal strip. Moreover, the configuration and number of the sheath convolutions are such that the convolutions cooperate with one another in a way which provides good sealing contact between adjacent convolutions but will avoid undermining the retention of the color coating from the coated strips when the strip convolutions are moved relative to one another. The sheath also includes a maximum number of convolutions per unit length of the sheath to not only improve the bendability of the sheath, and to provide good electrical contact between the sheath and fittings to which the cable may be connected, but to be consistent with the overall objective of the invention—to enhance the longevity of retention of the color coating to the sheath surface by minimizing the degree of movement (and therefore potential scraping) of adjacent coated strip convolutions with respect to one another. 
   For a more complete understanding of the above mentioned and other features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying drawings, in which corresponding numerals in the different drawings refer to corresponding parts, in which the drawing figures are not necessarily to scale and may have certain portions exaggerated or shown in somewhat generalized or schematic form for purpose of clarity of description. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a longitudinal side elevation of a preferred embodiment of a color coded armored cable in accordance with the invention in which portions of the cable sheath are shown in section to illustrate its construction; 
       FIG. 2  is a perspective view of an untreated metal sheet to be formed into the desired cable sheath construction shown in  FIG. 1 ; 
       FIG. 3  is a detail perspective view in somewhat schematic form of an apparatus for coating the metal sheet of  FIG. 2 ; 
       FIG. 4A  is a perspective view of the coated metal sheet; 
       FIG. 4B  is a perspective view of a coated metal sheet showing an optional coating disposed over the color coating; 
       FIG. 5A  is a perspective view of the coated metal sheet before a slitting process; 
       FIG. 5B  is a perspective view showing strip segments formed from the coated metal sheet after the slitting process; 
       FIG. 6  is a perspective view on a larger scale of one of the coated metal strip segments of  FIG. 5B ; 
       FIG. 7  is a perspective view of the coated metal strip; showing its profile after formation in a roll forming apparatus 
       FIG. 8A  is a detail longitudinal section view showing the manner of interlocking adjacent convolutions of a prior art armored cable sheath; 
       FIG. 8B  is a detail longitudinal section view showing the manner of interlocking the convolutions of an armored cable sheath in accordance with the invention; 
       FIG. 8C  is a detail view of portions of adjacent convolutions showing tangential reference lines for the preferred convolution interlock of the present invention; and 
       FIG. 8D  is a detail view similar to  FIG. 8B  of the convolution interlock showing the relative positions of the convolution edges after bending of the flexible cable sheath. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring initially to  FIG. 1 , there is depicted a new and improved color-coded armored cable assembly  2  in accordance with the present invention. The cable assembly  2  comprises a color coded tubular metallic sheath  42  enclosing a set  38  of insulated conductors extending through the interior passageway defined by the sheath  42 . In the case of a Type AC armored cable, the conductor set  38  includes an uninsulated ground or bond wire  38   a  operable, if desired, to make contact with an inner wall surface of sheath  42 , particularly an electrically conductive contact when this surface is uncoated or coated with a conductive coating. However, the improvements of this invention are also applicable to other types of metal clad armored cable, including Type MC armored cable, in which the ground wire is an insulated conductor. The sheath  42  is formed of a helically wound, uniquely contoured metal strip  10 , preferably of aluminum, which has been color coated in a manner subsequently described herein. Each convolution  3  of the strip interlocks with its adjacent convolution at an overlap or interlock  50 , with uniformly spaced “crowns”  4  and “valleys”  5  defining the outer surface of the sheath  42 , as illustrated in FIG.  1 . 
   The metal strip  10  includes an outer surface  10   a  and an opposite inner surface  10   b , see  FIGS. 6 and 8B  also. A coating  14  of non-conductive material, preferably non-conductive paint, of a desired color, is applied over the entire outer surface  10   a  of the strip  10 , preferably to a dry film thickness (DFT) in the range of 0.3 mils to 0.4 mils DFT. As a consequence, the finally formed sheath  42  will essentially have the entirety of its outer or exterior observable surface of the chosen color. This color is chosen to uniquely identify the particular armored cable and distinguish it from others, for example by electrical properties, intended use, or other characteristics. The inner surface  10   b  of the metal strip  10  has a clear coating  18  applied thereto and which is, preferably, electrically conductive, but alternately may be non-conductive. Thus, the entirety of the inner or interior surface of the cable sheath  42  may be covered by this coating  18  which, if conductive, enables electrically conductive contact between coating  18  and wire  38   a , FIG.  1 . Notwithstanding the conductivity of coating  18 , this coating advantageously minimizes damage to the coating  14  when strip  10  is provided in coils and when uncoiled while being formed into the sheath  42 . Coating  18  may be formed of a non-pigmented polyester based paint, is preferably applied to a thickness of about 0.2 mils to 0.3 mils DFT, and also provides some lubricity during the strip forming process. 
   In accordance with an alternate embodiment of the invention, a translucent or transparent coating or layer  21 , is applied over the coating  14  to assist in the retention of the coating  14  to the sheath surface  10   a . This translucent layer or coating  21  may be paraffin, lanolin or water based. In accordance with a preferred embodiment, coating  21  is an acrylic wax. 
   There is now described a preferred method of producing the color-coded armored cable  2  of FIG.  1 . Referring initially to  FIG. 2 , there is depicted an untreated elongated sheet  1  of metal, preferably aluminum, but also optionally of any other suitable metal, such as low carbon steel. Metal sheet  1  preferably has a thickness of about 25.0 mils. An initial processing step involves abrading the surfaces of the sheet, particularly the surface  10   a  upon which color coating  14  is to be applied. Accordingly, for this purpose, the metal sheet  1  may be chemically abraded whereby, after an initial sequence of caustic baths and rinses, the sheet is subjected to an acidic solution or metal etching bath which results in the desired abrading of sheet surfaces  10   a  and  10   b . Alternatively, the surfaces  10   a  and  10   b  may be mechanically abraded. 
   Referring now to  FIG. 3 , the abraded metal sheet  1  is next passed through a coating application apparatus  12  comprising rotating rollers  16  and  20  which are adapted to respectively engage top surface  10   a  and opposed surface  10   b  of the sheet Roller  16  contains a non-conductive, colored coating material  14 , preferably paint or ink, which is transferred to the entire surface  10   a  of the metal sheet as this sheet passes through the rollers  16  and  20 , resulting in a coating  14  ( FIG. 4A ) of the desired color. As previously described, the color that is chosen for the coating  14  will be that color which is to identify the particular characteristic(s) of the armored cable  2 . For example, according to existing convention, for AC Type armored cable intended to be used in hospital installations, the color chosen would be green. However, other solid colors, such as red or blue, may be chosen, depending upon the application or other characteristic. 
   In accordance with a feature of this invention, the longevity of retention of the coating  14  to the metal surface  10   a  is found to be enhanced due to the abrading of this surface. In addition, it has been discovered that, particularly when using a substantially non-conductive polyester based paint, by maintaining the paint coating thickness in the range of 0.3 mils to 0.4 mils DFT, paint retention to the metal is optimized. 
   Roller  20  contains a conductive or non-conductive coating material which is transferred to the entire opposite surface  10   b  of the metal sheet  1  as the sheet passes through apparatus  12 , resulting in the coating  18  ( FIG. 4A ) preferably, as mentioned above, to a thickness in the range of 0.2 mils to 0.3 mils DFT. If coating  18  is conductive, it facilitates the grounding of AC Type armored cables in which a bare ground wire, such as wire  38   a , is extending through the sheath to conductively engage the inner sheath wall. Coating  18  also reduces friction between surface  10   b  and tooling for fabricating the strips  10  and protects coating  14  when the strips  10  are wound into coils and when the strips are uncoiled. 
   In accordance with another important feature of the invention, the material of the color coating  14  preferably contains a lubricant incorporated therein. This lubricant enables increased adherence of the color coating  14  to the surface  10   a  of the metal sheet  1  and ultimately to the entire outer observable surface of the sheath to be formed by an elongated strip of this metal. The lubricant is preferably a polyethylene based wax, with the amount of lubricant being critical. For example, if the amount of lubricant is insufficient, it does not assist in such adherence. On the other hand, if the amount is too great, it may interfere with cable structural integrity. Accordingly, it has been determined that the percentage of the polyethylene based wax lubricant per unit volume of paint of the type described herein should be within a range of from 0.45% to 0.55% with the optimum volume percentage of the lubricant being about 0.5%. 
     FIG. 4A  depicts the metal sheet  1  after emergence from the apparatus  12 . Accordingly, a coating  14  of non-conductive, colored material is disposed on surface  10   a  and a coating  18  of material, preferably conductive, is on the opposite surface  10   b . To further promote the durability of the final product and to further assist in retaining the color coating  14  over the entire surface  10   a , the metal sheet  1  may optionally have a translucent or transparent coating  21  disposed over the coating  14 , as depicted in FIG.  4 B. The clear or translucent coating  21  is shown in  FIGS. 1 and 4B  but not in the other drawing figures. 
   After an appropriate curing step, the coated metal sheet  1  next proceeds through a slitting process. Accordingly, utilizing a conventional slitting apparatus, not shown, the coated metal sheet  1  ( FIG. 5A ) is slit into a plurality of elongated coated metal strip segments  24  of desired width  22 , as depicted in FIG.  5 B.  FIG. 6  is an illustration of one of the coated metal strip segments  24 . While the width of each segment  24  will vary with the size of the sheath and number of conductors that the armored sheath is to enclose, it has been found that for most armored cable applications, the strip width  22  will normally be about 0.38 inches, 0.50 inches or 0.75 inches. Strip segments  24  are normally welded to each other end to end and formed into a coil, in a conventional manner, preparatory to use of the strip  10  in forming a sheath  42 . 
   Next in the construction of the color-coded armored cable  2  is the formation of the helically wound sheath  42 . Accordingly, utilizing conventional apparatus, not shown, but known to those skilled in the art, coiled and end to end connected elongated coated metal strip segments  24 , forming a continuous strip  10 , are uncoiled and contoured into a profile or shape generally as shown in FIG.  7 . The contoured strip  10  is formed in a continuous process which also includes forming the sheath  42 . Suitable so-called strip or roll armoring apparatus for forming the contoured strip  10  and the sheath  42  is commercially available from Roteq Machinery, Inc., Concord, Ontario, Canada, although other equipment may be used. The aforementioned apparatus forms a convex surface or “crown”  4  adjacent to a concave surface or “valley”  5  along the entire length of the metal strip  10 , thereby forming a contoured, coated metal strip including, for purposes of discussion herein, a so-called leading edge  56  and a so-called trailing edge  58 , FIG.  7 . 
   The strip or roll forming or armored cable forming apparatus, not shown, but of the type mentioned above, helically winds the contoured metal strip  10  around a conductor set  38  ( FIG. 1 ) to form the metallic sheath  42  and the color-coded armored cable  2 . Each successive convolution  3  winds over the previous convolution at a continuous overlap or interlock  50 , see  FIGS. 1 and 8B  through  8 D, the process continuing until the tubular metal sheath  42  is formed having the uniformly spaced crowns  4  and valleys  5 . 
   Referring now to  FIG. 8A , there is illustrated a detail longitudinal section view showing two overlapping and interlocked convolutions  53  of a prior art armored cable sheath  55 . The prior art sheath  55  shown is uncoated and is formed of a continuous metal strip  55   a . In the prior art sheath  55 , a leading edge  57  of one convolution of the strip  55   a  overlaps a trailing edge  59  of an adjacent convolution and provides area contact  51  between leading and trailing edges of the successive convolutions  53 , as illustrated. However, when prior art cable sheath  55  is bent during routing a cable from one point to another, sliding motion occurs between the adjacent convolutions which tends to scrape off any identifying coatings which might be applied to the outer surface  55   b  of the sheath. In other words, if the surface  55   b  were completely coated with an identifying colored paint or the like, as in the present invention, this paint would tend to be scraped off of the surface  55   b  in the area  51  of convolution overlap between the leading and trailing edges  57  and  59  as a consequence of relative movement between the adjacent convolutions, thus undermining the integrity of the color coating applied to surface  55   b  at the area of overlap, and thereby having the potential of changing the desired outer observable appearance of the sheath and exposing the sheath to possible corrosion. 
   However, in accordance with an important feature of the present invention, the contour of each of the convolutions  3  is configured such that the respective leading and trailing edges  56  and  58 , overlap, but the adjacent convolutions  3  engage one another at point  62  only, see FIG.  8 B. Contact point  62  also, of course, forms a continuous helical line along sheath strip  10  throughout the length of sheath  42 . This contact point  62  between convolutions  3  is maintained when adjacent convolutions are moved relative to each other when bending the sheath  42 , see  FIG. 8D , such that there is no tendency to scrape the color coating  14  off of the surface  10   a  and potentially change the appearance of the sheath. The arrow  33  in  FIG. 8D  indicates the direction of movement of one convolution  3  with respect to an adjacent convolution  3  during bending of the sheath  42 . In this way, the corner of the trailing edge  58  which forms the point or line contact  62  between convolutions at the conductive coating  18  remains as the only point of contact between adjacent convolutions as they are bent or rotated relative to each other about an axis, generally normal to the longitudinal axis of the sheath  42 . In this way, the leading edge  56  does not contact the color coating  14  during bending of the sheath  42  and the coating  14  remains intact at all times. Moreover, an area of overlap  30 ,  FIGS. 8B through 8D , is formed between adjacent convolutions  3  continuously, and between contact point or line  62  and corner  56   a  of leading edge  56 , see FIG.  8 C. However, area  30  may vary somewhat as one convolution is moved relative to the other, as shown in FIG.  8 D. The view of  FIGS. 8B through 8D  are taken from the longitudinal axis of the sheath  42  and correspond to the same portion of the sheath shown partially sectioned in FIG.  1 . 
   The improved relationship between interlocked convolutions  3  is realized by adjusting or modifying the aforementioned cable forming apparatus to provide a somewhat asymmetric convolution profile in a way such that, as shown in  FIG. 8C , a line  66  tangent to a surface of strip  10  at the leading edge  56  of a convolution  3  intersects a line  61  at an angle  70 , which angle is greater than an angle  72  between line  61  and a line  74  tangent to a surface of strip  10  at the trailing edge  58  the adjacent convolution, as shown. Reference line  61  is normal to the direction or path, indicated by arrow  63  in  FIG. 8C , that the strip  10  follows through the sheath and cable forming apparatus mentioned herein, which path is also, typically, parallel to the longitudinal central axis of sheath  42 . In this way, when sheath  42  is flexed or bent the contact point  62  moves along the inner surface of a convolution  3  toward the leading edge  56 . However, the comer  56   a , of leading edge  56 ,  FIG. 8C , does not contact the color coating  14  of the adjacent convolution when the convolutions are moved relative to each other. In the illustration of  FIG. 8C , the tangent lines  66  and  74  are shown tangent to the surfaces of the strip  10  at the respective leading and trailing edges  56  and  58 . However, these lines are also, essentially, tangent to the surfaces of the aforedescribed coatings on the strip  10 . 
   Still further, it has been recognized in accordance with the present invention that the number of convolutions per unit length of sheath  42  should, preferably, be adjusted to maximize the number of convolutions. A greater number of convolutions per unit length tends to reduce the resistance to bending of the sheath  42  and to minimize movement between adjacent convolutions, both of which are desirable. The number of convolutions per unit length of sheath which may be obtained is a function of the width of metal strip  10 . Analysis has shown that, for example, 48 convolutions per foot of length of sheath  42  is desirable for a sheath having a width of 0.38 inches of the strip  10  while 34 convolution per foot is desirable for a sheath having a 0.50 inch width of the strip  10 . Moreover,  24  convolutions per foot of sheath length is indicated to be desirable for a sheath having a strip width of about 0.75 inches. The above-mentioned numbers of convolutions per unit length of sheath is indicated to provide optimum results due to reducing movement between adjacent convolutions while retaining or enhancing sheath bendability, thus reducing the chance of the coating  14  being scraped off of the surface  10   a . Still further, closely spaced convolutions provide for better mechanical and electrical contact between sheath  42  and fittings to which the sheath may be connected, since such contact occurs at the crowns  4  of the convolutions  3 , for example. 
   Those skilled in the art will appreciate from the foregoing description that an improved color-coded armored cable assembly may be obtained with a sheath of the type described. It is believed that those skilled in the art will be able to practice the invention using otherwise known manufacturing and material selection processes known in the art of armored cable design and manufacturing. Advantageously, for the particular sheath  42  described hereinabove which may include the coating  18 , if such coating is conductive a continuous conductive path is provided along the interior surface of the sheath. This may be advantageous for use of a sheath of the type described herein for Type AC armored cables wherein regulations require the use an internal uninsulated bond or grounding wire, such as the wire  38   a , FIG.  1 . Moreover, while the color coating  14 , the coating  18  and the coating  21  have been described as being advantageously applied to the sheath forming metal strip before formation of the sheath convolutions, those skilled in the art will also recognize that these coatings may be applied during or even after formation of the sheath convolutions. Still further, the above-mentioned coatings may be applied using other types of application methods and coating materials, such as a powder coating. Moreover, other color-coding materials, such as ink, may be used instead of paint 
   Although preferred embodiments of the invention have been described in detail herein, those skilled in the art will also recognize that various substitutions and modifications may be made without departing from the scope and spirit of the appended claims.