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Using Software to Simplify Cable Pulling

PULL-PLANNER™ 2000 SOFTWARE FOR ESTIMATING
CABLE PULLING TENSION

American Polywater's Pull-Planner™ 2000 is a menu-driven, user-friendly program for calculating cable pulling tension. It combines the accepted "cable pulling equations" with an internal data base of friction data from Polywater's laboratory. To understand the benefits of the software, we must first review the theory of tension calculation.

One key parameter in tension calculation is the "coefficient of friction." What is coefficient of friction and where does it come from? Let's use an old physics class example . . . a wooden block (say, 10 lbs. in weight) on a horizontal steel plate. Say it takes 5 lbs. force (lbf.) to pull (drag) the block across the plate. The coefficient of friction (wood block to steel plate) is defined as the ratio of the "dragging force" (5 lbf.) to the normal force (weight or 10 lbf.). In this case, the friction coefficient would be .5 (dimensionless number).

Experience tells us that if we replace the wooden block with a 10 lb. rubber block, it will take a greater force to drag the rubber block (say, 12 lbf.). The measured coefficient of friction (rubber/steel) would be 1.2. It's important to note that the friction coefficient is specific to both the rubbing surfaces.

In the experiment above, we would also find that it took a somewhat higher force to start the block moving than to keep it moving. There would actually be two coefficients of friction, one called static (or standing) and one called dynamic (or moving).

Replace the block with cable and the plate with conduit, and we have cable pulling . . . with a few complications. Neither the cable nor the conduit is flat. There may be more than one cable which gives multiple rubbing surfaces. Pulls are not straight, so forces other than gravitational weight occur at conduit bends. Finally, pulling compounds (lubricants) are commonly used to lower the friction coefficient.

However, in cable pulling, the friction coefficient still depends on the jacket type, conduit type, and the lubricant type. "Generalized" coefficients of friction don't mean much. We see the usefulness of the internal data base in the Pull Planner™ 2000 Software, which includes friction coefficient data for a variety of common conduit and jacket types.

Simplified forms of the tension calculation equations are:

Note that these equations have a different form for bends than straight sections. The equation for a straight section is consistent with the previous example, i.e.:, the tension added is the cable weight times the coefficient of friction. However, the non-gravitational forces in bends move the coefficient of friction to the exponent and multiply this factor by the tension coming into the bend.

There are several implications to this. First, cable pulling calculations must be approached in segments. In other words, the tension add on from a straight section becomes the incoming tension multiplying in a bend section. There is no simple solution for multiple bend pulls, and software is often the easiest way to do the calculations, especially when "what if" scenarios are desired.

Note how relatively small changes in "µ" (friction coefficient) in conduit bends can result in significant differences in pulling tension. The importance of a quality lubricant becomes obvious, as the savvy marketers at American Polywater know!

The full pulling equations are much more complex then the simplified forms above. They contain weight correction factors for multiple cable pulls and gravitational corrections for non-horizontal conduit sections and bends.

American Polywater's Pull-Planner™ 2000 Software is a Windows™ based program that can be run on 16 or 32 bit systems. The software has many neat features including:

1. Calculates and recalculates tension and sidewall pressure with fast changes of friction coefficient, incoming tension, and direction of pull.
   
   
2. Enables a custom "cable.dat" file with end user entered cable weight and OD info. This data is available whenever the program is run.
   
   
3. Prints hard copy of all pull details and calculations, or saves copy to a text file for import into a word processing document.
   
   
4. Enables entry or calculation of "maximum allowable" cable tension and sidewall pressure and "flags" screen or printer output when maximum is surpassed.
   
   
5. Determines conduit fill, cable configuration, jam ratio, and clearance for any combination of wires and cables in a pull.
   
   
6. Enables easy addition, subtraction, or insertion of conduit segments while analyzing a pull.
   
   
7. Enables saving and reuse of specific pull data.
   
   
8. Calculates the amount of Polywater® Lubricant appropriate for the pull.
   
   
9. Has an internal friction coefficient data base that includes a broad range of common cable jackets and conduits.
   
   
10. Enables the use of "dual" friction coefficients if desired, one at high and one at low sidewall bearing pressure.
    
    
11. Enables "back-calculation" of an effective friction coefficient from field measured tensions. Useful for determining effectiveness of field operations or for additional calculations in a similar environment.
    

Call American Polywater toll-free at 1-800-328-9384 for more information or to
place an order over the phone. Visa, MasterCard, or AMEX accepted

P.O. Box 53 | Stillwater, MN 55082 USA
1-(651) 430-2270 (Voice) | 1-(651) 430-3634 (Fax)
1-(800) 328-9384 (Toll-Free US/Canada Only)

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