US1995407A - Armored cable - Google Patents

Description

March 26, 1935. s, WALKER 1,995,407

ARMORED CABLE Filed Aug. 7, 1934 ATTORNEYS Patented Mar. 26, 1935 UNITED STATES PATENT OFFICE 11 Claims.

This invention relates to armored cable of the flexible type and is concerned more particularly with a novel cable, which includes a new helically woundmetallic strip armor, formed to permit easy severance thereof, and also includes means for protecting the conductors and their insulation against injury from the cut edges of the armor, and with a new method of preparing the cable for attachment to an outlet box or other element of the distributing system in such manner that injury to the conductors or their insulation is prevented, this method involving the use of the protectin means referred to.

Flexible armored cable is now widely used in wiring buildings and such cable includes an armor commonly consisting of a properly formed steel strip wound to form a helix in which the convolutions overlap and interlock. The armor encloses the usual rubber insulated conductors and these conductors are further insulated by an additional wrapping of insulating material, such as paper wound helically or cotton braided about the conductors.

When a piece of armored cable is to be put in service, the installer cuts the cable to the desired length and then must remove a portion the armor to expose the conductors in order to complete his operation. As a rule, the armor must terminate at and connect with a metallic portion of the distributing system in order to provide the necessary ground connection, while the con ductors continue on to the device installed therein. One method of connecting the armor to a part of the distributing system is to run it into a connector of the type ordinarily used with a panel box or an outlet box. Another method is to run the armor into a box provided with special means for clamping the armor. In severing the armor so that a portion of it can be removed to expose the conductors, a hacksaw is usually employed and if the saw is allowed to out too deeply, it will injure the conductors lying beneath the armor. Unless the operator is expert in making this out and unless he is careful to do it properly, he will produce a rough pointed end and also a rough burred edge on the armor which eventually may puncture the conductors and render them unfit to perform their service. It is, therefore, apparent that any method which guides and aids the operator in making a safe cut is highly desirable.

Various expedients have been proposed to protect insulation of the conductors against damage from the rough and pointed edge of the armor produced by ordinary cutting methods commonly practiced. One method that is used involves inserting a bushing of insulating material into the end of the armor to lie between the armor and the conductors. While such bushings serve the purpose more or less satisfactorily, they are 5 necessarily supplied separate from the cable and in quantities which may or may not be sufficient for the purpose. As a matter of fact, it is a trade practice to furnish a specified number of bushings for a standard coil of armored conductor, and if the number supplied is not sufficient, the installer must of necessity secure additional bushings or omit the bushings so necessary to a proper installation. Also, bushings may be lost or workmen who are careless may not be willing to go to the trouble to install them. A bushing has the further disadvantage that space must be provided to a sufficient depth between the armor and the conductors for the insertion of the bushing, and this space is ordinarily made available by the removal of a portion of the wrapping about the conductors by the installer. A careless workman may, accordingly, forget or ntentionally omit the operations necessary for the proper protection of the conductors by the use of the bushing and this leaves a weak spot in the distributing system. Investigation of field conditions indicates the seriousness of this weakness in this particular method of installation.

The cable of the present invention differs from ordinary cable in numerous respects, and it includes armor so formed that severance of the armor is a simple operation and bushings are not required in connection with the cable to protect the insulated conductors. The new armor also reduces the probability of improper use of a cutting tool resulting in rough pointed edges on and distortion of the armor at the cut, and for these purposes, the metallic strip of which the armor is made is provided with cutting lines made by impression or otherwise, and permitting complete severance of the armor without the necessity of cutting through it entirely across a convolution. The treatment given the strip, as mentioned, preferably obviates the necessity of any cutting whatever through those portions of the armor lying against the conductors, and this substantially prevents injury to the conductors even by an inexpert workman. As another feature, the r cable contains means by which the conductors may be protected from injury by the rough cut edge or pointed end of the armor and this means is present throughout the length of the cable and is therefore available at any point along the armor for its intended purpose. Preferably, this means takes the form of an additional tape extending lengthwise of the cable and lying between the armor and the conductors, the tape being available for wrapping about the conductors in such manner as to reinforce and increase their protection at a point where the possibility of injury is greatest.

To make it possible to form the metallic strip with the cutting lines into the finished armor without causing the strip to part at the lines, and also to enable the installer to sever the armor without cutting it entirely through and to guide him in making the cut so that an edge is left which permits efiicient use of the tape, the cutting lines on the metallic strip lie on the outside thereof and at an oblique angle to the length of the strip. Preferably, although not necessarily, the cutting lines extend entirely across the strip and they are of greater depth at one end than at the other. When the strip with the cutting lines or impressions, as described, is formed into armor, the operation is carried on in such manner that the deeper portions of the impressions lie in the overlapped portion of each convolution, and when the armor is to be severed along an impression, it is necessary to cut the armor only through the overlapping part of a convolution, the deeper impression in the overlapped part permitting this portion of the strip to be ruptured by bending. When the severance is completed, the edge of the end convolution of the strip lies at such an angle to the axis of the cable as practically to insure that the tape will be so employed as to afford the maximum protection.

When a piece of the new armored cable is to be put in service, it is cut to the proper length, and the surplus armor removed by severing the armor at the proper point where there is an impression. The protective tape left free by reason of the armor having been removed, is then wound around the conductors, the edge of the tape is inserted under the end of the armor, the tape is folded back over the cut edge of the armor, and the cable so prepared inserted into the proper open- .ing, which may be an opening in a box in the distributing system or in a connector to be inserted in an opening in a box.

I prefer to use a tape of paper or fibre or similar material as the protective element and to lay this tape lengthwise of the cable and between the conductors and the armor. A metallic tape, however, may also be used for the purpose, the metal not being objectionable since it is insulated from the wires and will be grounded through the usual clamping device. A metallic tape has the advantage of grounding more adequately the two metallic containers or boxes interconnected by means of the armored conductor, but for ordinary purposes, the tape used will be paper with sufiiclent toughness to accomplish the desired purpose.

For a better understanding of the invention, reference may be had to the accompanying drawing, in which Figure 1 is a view in elevation of the new cable with the connector in place, parts of the armor being broken away to illustrate the construction;

Figures 2 and 3 are sectional views on the lines 2--2 and 3-3, respectively, of Figure 1;

Figures 4 to 8, inclusive, illustrate different steps in the method of employing the protective strip, and

Figure 9 is a partial sectional view, illustrating the manner of cutting the armor.

The drawing illustrates the new cable as including the usual rubber insulated wires 10 enclosed in an insulating wrapping 11, which may be a paper strip wound helically about the wires or cotton braided over them. The wires with their wrapping or braid are enclosed in an armor 12, which is made of the usual steel strip wound helically and with the convolutions overlapping, as illustrated in Figure 2. The cross-section of each convolution has a reverse curve so that each convolution has a hump 13, and the overlapped convolutions are interlocked. Between the armor and the wrapped wires is a protective tape 14 extending throughout the length of the cable and preferably of relatively heavy paper. As illustrated, the tape has a width somewhat less than the diameter of the wrapped wires so that it may lie at one side of the wire, and while paper is the preferred material for the tape, thin metal may be employed in some instances.

In order to facilitate severance of the armor and also to assist the installer in using the tape most effectively as a protection for the insulation on the conductors against abrasion by the edge of the armor at the point of severance, the metal strip of which the armor is made is provided with predetermined cutting lines on the outer surface thereof lying at a relatively short spacing, so that one of these lines is likely to be available at any place where the armor is to be severed. In practice, it has been found that a spacing between the lines of about 2 inches or slightly less is generally satisfactory and the lines may be produced, for example, by impressing or indenting the metal strip or by cutting partly through it.

When the cutting lines are formed on the outside of the strip and at an oblique angle to the length of the strip and also at a similar angle to the longitudinal axis of the finished armor, they do not weaken the metal of the strip to such an extent as to interfere with the strip being shaped into final helical form. In the operation of forming the strip with angular lines into armor, the application of force to coil the strip is not applied simultaneously throughout the entire length of any line, but, as the bending operation proceeds, the coiling force acts only on a point on any line at any instant. If the lines lay transverse to the length of the strip and on the outer surface thereof, the coiling of the strip into armor would open up each line and wouldcause the strip to part, un-

less the lines were so shallow as to be useless for their intended purpose.

The lines lying at the specified angle may have a depth so chosen that upon cutting through the overlapped portion only of a convolution, severance of the armor may be completed by bending it manually, this bending operation resulting in the rupture of the overlapped and uncut portion of the strip at the line. Thus with the lines formed in the manner described, the armor can be severed at a desired point by a combination of cutting and bending operations and it is not necessary actually to cut through the metal strip across its entire width. Preferably, each cutting line is not of the same depth from end to end, but is made deeper in that part of the strip which is to constitute the overlapped portion of a strip. With the lines thus formed, that part of the convolution which is accessible to the cutting tool has the shallower portion of the cutting line, and this gives the armor the necessary strength to withstand the forces to which it is subjected during installation, while the overlapped portion being more deeply impressed, can be easily ruptured manually and without causing distortion of the armor.

The cutting lines spaced along the strip, as described, serve the further purpose of assisting the installer in the actual operations of severing the armor in that the angularly disposed lines serve as a guide for the cutting instrument so that a straight tool, such as a file or hacksaw, can be be applied to the armor to cut through the necessary portion of a convolution without the tool coming into contact with the overlapping portions of adjacent convolutions. The lines thus enable a workman to sever a particular convolution without damaging those lying on either side of it, and when the armor is cut along a cutting line, the severed edge of the armor lies at an oblique angle to the axis of the armor and this facilitates use of the tape to protect the installation of the wires against abrasion by the out edge. Preferably, each cutting line lies at an angle of approximately 45 to the longitudinal axis of the armor, as a severed edge lying at this angle permits the best use of the tape.

In making a connection of the new cable of the construction illustrated in the drawing to a box or the like, the workman removes a portion of the armor to expose the conductors and protective strip. This cut is made by means of a file or hacksaw, and the cutting tool is applied along an impression, which serves as a guide. When the tool is so used, it contacts only with the outer or overlapping portion of the convolution of the armor which lies at a distance from the conductors, as indicated in Fig. 9, and only this portion of the armor need be cut through, since the inner or overlapped convolution is more deeply impressed and may be broken by bending. When the weakened overlapped portion of the armor is ruptured by bending, the metal has a clean edge and there is substantially no distortion of the armor remaining on the cable. In cutting along an impression, as described, the underlying portion 26 of the next adjacent convolution acts as a stop which tends to prevent the cutting tool from striking the conductors and injuring the insulation thereon. The line 27 in Figure 9 indicates the position of the cutting edge of the tool at the completion of the cut. The cut edge 17 of the armor may then be protected by the tape and for this purpose, the tape is first folded under along a diagonal line 18 so that the free end of the tape extends at right angles to the cable and in the same general direction as the convolutions of the armor. The tape is then wrapped around the cable one or more times, as indicated in Figure 5, and the edge 19 of the tape is forced under the end of the armor so that the tape assumes the position shown in Figure 7, with the tape lying under the point 20 at the outer end of the cut edge. The tape is then folded over with another diagonal fold along the line 21 so that the end portion 22 of the tape passes over the cut edge 17 of the armor and the end of the tape is then laid against the outer surface of the armor. With the tape arranged in this manner, it will be evident from Figure 8 that the conductors and their wrapping 11 are fully protected from abrasion by the cut edge of the armor by means of the tape.

Any standard means of connection may then be used at the end of the armor, as for example, the standard connector is illustrated at 23. This connector has a tubular portion into which the end of the armor is received, and also has a threaded portion carrying a lock nut 24. When the connector is mounted in place, it overlies the end portion 22 of the tape which lies against the outside of the armor and serves to hold the tape in position to cover the edge of the armor. The connector has the usual grounding screw 25 which is tightened up to engage the armor when the connector is in position.

With the arrangement described, it will be apparent that the tape 14 may be used to provide full protection for the conductors against injury from the rough cut edge of the end convolution of the armor, and since the tape is present throughout the length of the cable, it is always available for use and the additional required protection of the conductors is not likely to be overlooked by the workman. The wrapping of the tape about the conductors so as to provide the additional required protection is a simple operation when the armor has been properly cut, and the proper cutting of the armor for the use of the tape is facilitated by the provision of the cutting lines.

While I have explained the use of the new cable with a standard connector, it is to be understood that the utility of the new cable is not limited to the use of any particular connecting means. When connected to a box provided with an internal clamp, the armor is severed and the protective tape is used in the same manner as has been described, the exposed being then held in place over the cut edge and against the outside of the armor by the clamp. In all cases, the tape provides the desired protection, regardless of whether the cable is connected to the box by a clamp or a connector, and the use of the tape does not require that space between the armor and conductors be provided by removal of a portion of the insulating wrapping on the conductors.

In the foregoing, I have described the new armor with the cutting lines as an integral part of a cable in which the armor is formed about the conductors during the process of manufacture. It is to be understood, however, that the new armor may be formed apart from the conductors, and the latter subsequently installed. In both cases, the cutting lines afford the same advantages of easy severance.

What I claim is:

1. An armored cable which comprises a hollow metallic armor, insulated conductors within the armor, and a non-metallic protective tape at one side of the conductors and lying between the conductors and armor, said tape extending lengthwise throughout the cable and having an end portion projecting out of the armor and available for protecting the conductors against injury from the end portions of the armor.

2. An armor cable which comprises a hollow metallic armor made up of a. helically wound metal strip, said strip having cutting lines at predetermined intervals on the outer surface thereof and facilitating the severance of said strip, insulated conductors within the armor, and a protective tape at one side of the conductors and lying between the conductors and the armor, said tape extending lengthwise throughout the cable and having an end portion projecting out of the armor and available for protecting the conducportion of the tape tors against injury from the end portions of the armor.

3. An armored cable which comprises a metallic armor made up of a metallic strip Wound helically and having cutting lines facilitating the severance thereof at predetermined intervals thereon, said cutting lines lying at a. predetermined angle to the axis of the cable, insulated conductors within the armor, and a protective tape at one side of the conductors and between the conductors and armor, said tape extending lengthwise throughout the length of the cable and having an end portion projecting out of the armor and available for protecting the conductors against injury from the portions of the armor.

4. An armored cable which comprises a hollow metallic armor made up of a strip wound helically with the convolutions overlapped and interlocking, said strip having predetermined cutting lines at intervals along its length and lying at a predetermined angle to the axis of the cable and to the longitudinal axis of the strip, insulated conductors within the armor, and a protective tape at one side of the conductors and between the conductors and armor, said tape extending throughout the length of the cable and having a portion projecting out of the armor and available for protecting the conductors against injury i'rom end portions of the armor.

5. An armored cable containing conductors and a connector for securing the cable to a boxpr the like, in combination with a protective tape lying within the armor and having a portion projecting out of the armor and led around the conductors and back over the cut edge of the armor, the end of said tape lying between the outside of the armor and a portion of said connector.

6. An armored cable containing conductors and a connector for securing the cable to a box, in combination with a protective tape which lies within the armor and has a portion which projects out of the armor, is folded around the conductors with said folded portion partially lying under the end edge of the armor, and is led back over the cut edge of the armor and against the outer surface of the armor, the end of said protective tape lying between the armor and a portion of said connector.

7. An armored cable which comprises the combination of insulated conductors enclosed in armor formed of a metal strip wound helically with the convolutions overlapped and interlocking, said strip having predetermined cutting lines at relatively short intervals along its length; a connector mounted to enclose the end of the armor, and a tape running lengthwise throughout the length or" the cable and having an end portion projecting out of the armor, wrapped around the wires and lying under the edge of the end convolution of the armor, and led back over the cut edge of the armor with the end of the tape extending lengthwise of the cable and lying between the outside of the armor and a portion of said connector.

8. A hollow metallic armor for enclosing insulated conductors, which comprises a metallic strip wound helically and having predetermined cutting lines on the outer surface thereof at relatively short intervals, said lines lying at such an angle to the axis of the strip that one convolution or" the strip may be cut through by a straight cutting instrument applied along one of said lines wlhout said instrument doing damage to adjacent convolutions of said armor.

9. A hollow metallic armor for enclosing insulated conductors, which comprises a metallic strip wound helically with adjacent convolutions overlapping, said strip having predetermined cutting lines on the outer surface thereof lying at an oblique angle to the longitudinal axis of the strip.

10. A hollow metallic armor for enclosing insulated conductors, which comprises a metallic strip wound helically with adjacent convolutions overlapping, said strip having weakened lines on its outer surface lying at an oblique angle to the longitudinal axis of the strip, the lines being of sufficient depth in the overlapped portions of the convolutions to permit said portions to be ruptured along the lines by manual bending of the armor.

11. A hollow metallic armor for enclosing insulated conductors, which comprises a metallic strip wound helically with adjacent convolutions overlapping, said strip having weakened lines on its outer surface lying at an oblique angle to the longitudinal axis of the strip, the lines being of insufiicient depth in the overlapping portions of the convolutions to permit said portions to be parted along the lines except by use of a cutting instrument.

HERVEY S. WALKER.

Images