Choosing the Right Cable1. The first thing to consider in choosing the right cable is the kind of load to which the cable might be subjected. Once this is determined, it is time to make an evaluation of what kind of safety factor will be desired. In some extreme cases the suggested safety factors are as high as 10:1. Normally, the safety factors are 4:1 or 5:1 of the minimum breaking strength of the cable being used. EXAMPLE: Let's say that you are going to hang something that weighs 55 pounds from the ceiling of a public building. If this item were to fall onto someone below, it would certainly cause harm, or worse. The minimum safety factor that you would want to consider would be 5:1. Therefore 55 x 5 = 275. The minimum breaking strength of the cable that you would select would be in excess of 275 pounds.
You must also consider other factors to which the cable might be subjected, such as the possibility of a shock load in an earthquake or exposure to winds or blowing air from ventilation systems. Cable is not recommended, nor is it rated for shock loads. Unknown loads must be determined by testing prior to determining which cable to use. Determining the load that the cable will be exposed to, and under what conditions, will enable us to choose an appropriate diameter of cable.
2. The next step is to select a construction of cable. Is the cable going to go over pulleys? If so, consult the table regarding minimum recommended pulley groove diameters to determine the construction of cable most compatible to the pulley diameter being used. If the cable is not going over pulleys, it may still need to be somewhat flexible. If moderate flexibility is required (such as with a door retaining lanyard) a 7 x 7 construction will probably be adequate.
Maybe the cable is for guying purposes or being used on a railing. In such cases a 1 x 19 construction is normally preferred. Our sales staff will be happy to help you determine the proper construction of cable for your applications. Sample assemblies are available at a nominal or no cost in many cases. The tables in the Strand and Cable page show breakaway strengths for readily available types of strand and cable.
3. The third step is choosing the correct cable composition. The primary considerations in choosing the composition of the cable are service life, environment, and cost.
Just because the cable is going to be exposed to the elements outdoors does not mean that it should necessarily be galvanized such as wire rope used on tow trucks. The service life of the cable is probably a year or two at best. Unless you are in a severe environment, the cable will not have an opportunity to significantly deteriorate within the cable's service life. There is no need to use galvanized in this circumstance. Also, most special purpose hoisting ropes, such as compacted ropes and spin resistant ropes, are not available in galvanized. (Although some sizes of spin resistant wire rope are available in stainless steel.) Non-galvanized wire rope is referred to as bright and is usually coated with a petroleum based lube. Galvanized aircraft cable is almost always used in smaller diameter assemblies when stainless steel is not specified (smaller being under 1/4 inch diameter).
Galvanized cable is normally adequate corrosion protection for most conditions. Exceptions to this statement include the following conditions or situations.
- Applications close to a salt water or salt air environment. This would include applications that are exposed to winter salting of roads.
- Environments of corrosive chemical exposure.
- Applications such as food preparation and medical products or any other that has a frequent wash down.
- Applications where an aesthetic consideration with a preference for shine exists.
- Stainless steel is the preferred choice when the exceptions listed above apply.
4. The final consideration will be whether or not the cable needs to be coated. Some of the most common reasons to choose coated cable are:
- To increase the appearance of the size of the cable.
- To protect the cable from undesired substances.
- To offer the cable in a certain color for aesthetic reasons.
- To protect the cable and/or the pulleys that the cables are running over from abrasion.
- To reduce friction
If the answer is yes, it should be coated, please refer to the few paragraphs concerning different types of coatings in our construction and components of strand and cable page.