Cable pulling tension calculator
Estimate the pulling tension on a straight run with a bend, plus the sidewall pressure at that bend, and check both against the cable's ratings before you set the winch.
Friction drag on the straight run is weight times length times the coefficient of friction; the bend multiplies that by e to the power of friction times the bend angle (the capstan effect), and sidewall pressure is the tension out of the bend divided by the radius. Pull from the end that keeps the biggest bends near the start, where tension is lowest.
One straight section with one bend. A run with several bends, slope or back-to-back sweeps compounds tension through every bend and needs a full pull plan, not this estimate. Always use the cable maker's rated maximum tension and sidewall pressure.
Common questions
On a straight, flat run the tension is the cable weight per foot times the length times the coefficient of friction. Add any tension already on the cable coming in. When the cable goes through a bend, the tension coming out is the tension going in multiplied by e raised to the coefficient of friction times the bend angle in radians. That capstan effect is why a bend early in a pull is far cheaper than the same bend at the end.
A dry duct is commonly taken at about 0.5. A good pulling lubricant brings it down to roughly 0.35, and a low-friction duct or a generous lube job can reach about 0.2. Lube is the cheapest tension reducer you have, and it also cuts the heat that can damage a jacket on a long pull.
Sidewall pressure is the crushing force a cable feels as it is dragged around a bend, equal to the tension coming out of the bend divided by the bend radius in feet. Even when the straight-line tension is fine, a tight radius can generate enough sidewall pressure to flatten or damage the cable. A larger sweep radius lowers it directly.
It comes from the cable maker, not a rule of thumb. Power cables are often figured from the conductor area, while fiber and communications cables carry a fixed installation rating, commonly a few hundred pounds. Enter the rated maximum tension and sidewall pressure for your specific cable; the calculator checks your pull against them.
Not directly. This tool models one straight section with a single bend at its end, which is a good sanity check for a simple pull. A run with multiple bends compounds tension through each one, and the order and direction of the pull change the answer, so a multi-bend or sloped run needs a full pull plan rather than a single calculation.
TrackOver's FiberOps logs reels and pulls, tracks daily footage and 811 mark-outs, and turns your KMZ design into a crew-readable route map with the as-built the prime asks for.