Why Cable?

Cable, otherwise commonly known as wire rope or aircraft cable, is a good choice where the architect wants to minimize the obstruction of the view through the railing (either towards the structure or away from) or where a high tech look is desired.

Cable also has memory, which glass, mesh, or rod does not. As long as the shock load is not sharp, the cable will return to original configuration.

Typical applications include office buildings, shopping centers, sports complexes, warehouse conversions, residential interiors, mezzanines, decks, and viewing platforms. Cable is also a popular choice for trellises (refer to Trellis-Works section).

Cable Material

Generally, Cables for railings are manufactured from type 316 stainless steel. Galvanized steel cable is also used but is not nearly as popular as stainless steel. Seldom is bright steel cable used, because of rusting (unless you want that look or effect).

The effect on the price, of a cable-railing job, by skimping on the quality of the cable is negligible. It is best to specify the best product, type 316 stainless steel.

Cable Construction

Cable is very strong in tensile strength and is suitable material for pedestrian railings. Most cable is flexible for going over pulleys or lifting/moving heavy loads. For use in railings, one wants rigidity, not flexibility, because the cable needs to be as tight (rigid) as possible to minimize deflection and meet the 4" code requirement when a load is applied.

As little stretch as possible under tension is also important. The longer the cable run, the more a cable will stretch, which could present installation problems.

The following are common cable constructions. Note the characteristics of each:

Cable Sizes

1/8" - Can be used on horizontal railings where there is little or no public pedestrian traffic or where railing does not need to meet code requirements (such as where there is little or no drop off). 1/8" diameter cable can be vulnerable to failure under shack loads caused by abuse, such as a heavy person applying a downward load on the cable. Can be used on vertical railings, which are not as susceptible to heavy loads as horizontal railings.

3/16" - Quite satisfactory for pedestrian railings. 3/16" and larger cable diameters have significantly higher load ratings than 1/8" and are, therefore, not as susceptable to failure. Relatively small diameter minimizes visual obstruction.

1/4", 5/16", 3/8" - Diameters larger than 3/16" can be used where a larger diameter is desirable from a visual/aesthetics standpoint.

Cable Coatings

Cables can be coated using Poly-Vinyl-Chloride (PVC) which has excellant resistance to the ultra violet rays of the sun in clear or in colors. Normally, the cable diameter is increased by 1/16" when coated.

Also stainless steel can go through a process called "Black Oxide", which turns the metal black and also enhances its stainless qualities. Refer to: The Basics of Black Oxide

Cable Lay

The lay of the cable is the direction that the cable is wound during manufacturing. The tensioning device being used should be turned in the sane direction as the lay of the cable to prevent unwinding ("birdcaging") of the cable. Therefore, right or left hand lay should be specified, depending on the tensioning hardware used. If in doubt about the direction the tensioning device is turned, check with the manufacturer of the hardware.

Cable Spacing

To meet the 4" code requirement, cable generally needs to be spaced less than 4" apart on end posts, intermediate posts and cable braces. Post holes must be centered less than 4" apart, so that under load the cable will not flex and exceed 4" in open space at any point in the railing. How far to center the holes depends upon two factors:

1) Cable construction and diameter.
2) The length of cable run between intermediate posts or support braces.

The smaller the diameter of cable, the closer the holes need to be centered and the closer the intermediate posts or support braces need to be placed.

Following are suitable Maximum spacings using 3/16" (unjacketed/uncoated) diameter 1x19 cable:

Center-to-center hole spacing on posts and braces - 3.25"
Length of unsupported run between posts and braces - 42"

Rail Frame Construction

It is important that cables must be tensioned when they are installed to prevent flxing or sag. Properly tensioned, each cable will exert between 300 and 500 pounds of tension on each post. If there are ten cables being strung on the railing, a total of between 3,000 and 5,000 pounds of tension will be applied to each end post. A properly constructed cable railing frame is extremely important, to prevent the end posts from deflecting when the cables are properly tightened/tensioned.

While cable runs between terminating end posts can be quite long, the cable must be supported with intermediate posts and/or cable braces frequently to prevent cable flexing. Also, intermediate posts (through which cables may be strung) are required, to insure the structural integrity of the frame under load. For structural purposes, the distance between posts/intermediate posts will depend upon the construction of the frame and the frame material used.

There are three recommended frame styles for horizontal railings. Round pipe, Rectangular tube, and Square tube. Carbon steel (powder coated or painted) or stainless steel can be used.

With any of these frame styles, 1/4" x 1" braces (attached to the top rail and to the bottom rail or mounting surface) can be used between intermediate posts, if desired, to reduce costa and minimize visual obstruction. Bottom rail supports may be required, depending upon the distance between end and intermediate posts.

Round Pipe Construction
End posts should be constructed from schedule 80 pipe. Top rails, bottom rails (if applicable), and intermediate posts can beconstructed from schedule 40 pipe.

Rectangular Tube Construction
End posts can be constructed from 3"x1" or 2"x1" tube, using a dounle end post construction with round spacers between the tubes, as illustrated below.