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Polywater Calculator

American Polywater's
Duct Winding Factor Calculation Page

Calculate the Effect of Duct Memory and Displacement on Pulling Tensions

Introduction: This page will calculate tensions on fiber optic or other lightweight cable when it is pulled into "straight" sections of innerduct that have regular displacements due to reel memory and placement technique. The program determines the bend in degrees that the displacement produces and develops a duct factor that is used for the tension calculations for the "straight" section total length.  Seemingly small, but regular, displacements in continuous duct can produce high duct factors and exponential increases in tension. For a more detailed technical discussion of the effect of duct displacement on pulling tensions, link to TeleTopics 13 .

Data Entry: Data entry views duct displacement as a two dimensional wave with an amplitude and period that you specify. The line diagram below helps clarify this. The amplitude of an innerduct pulled into a 4" conduit would presumably be much less than innerduct dropped into a 12" trench. The entry data is restricted to "reasonable" values. For detailed definitions and specific restrictions on entry data, use the Definitions and Restrictions link.

To use the calculator, first choose the system of units you wish to use. All fields must be filled in. The Calculate Button sends your data to Polywater's web server for calculation. The results are returned and shown in the box below the entry fields. The Demonstrate Button quick fills all fields and sends the information out for calculation. The Polywater® F COF Button inserts a typical lubricated coefficient of friction for Polywater® Lubricant with MDPE cable jacket and HDPE innerduct. The calculator will be easier to see and use if you expand this page to full screen size.

Definitions and Restrictions


Run Length
Cable Weight
Incoming Tension 
Friction Coefficient

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Calculations Explanation

Duct Factor: This is a measure of the "straightness" of the duct. An absolutely straight duct has a duct factor of zero(0). Duct factors less than 3 are generally needed for long fiber optic pulls into continuous duct (innerduct), and duct factors less than 1 are the most desirable. With more field experience to establish validity, the duct factor may be included in American Polywater's Pull Planner™ for Windows™ Software for use in calculating fiber optic tension in long innerduct runs. Please note that a duct factor calculation feature is not active in the software at this time.

Effective Angle: This is the calculated bend (in degrees) per unit of length (ft or M).

Total Bend in Run: The effective angle times the total run length.

Pulling Tension if Straight Run: Offered for comparative purposes. Represents the tension if there was no bend (a zero duct factor).

Pulling Tension with Bends: Tension calculated based on the duct factor above. With significant bend (> 1000 degrees), this estimated tension can be thousands of times higher than the straight run estimate.

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