Cable Pulling Tension Calculator
Enter a straight-bend-straight-bend-straight conduit route to compare the pull from each end. The calculator reports the lower-utilization direction, section tensions, sidewall pressure, and headroom against your entered limits.
Recommended pull directionReverse pull
- Forward ending tension (lbf)
- 113.5
- Reverse ending tension (lbf)
- 99.42
- Peak pulling tension (lbf)
- 99.42
- Maximum sidewall pressure (lbf/ft)
- 29.71
- Pulling-tension utilization
- 9.94%
- Sidewall-pressure utilization
- 5.94%
- Governing limit
- Pulling tension
- Remaining tension headroom (lbf)
- 900.58
Reverse pull section-by-section results
| Section | Entering tension (lbf) | Exiting tension (lbf) | Change or multiplier | Sidewall pressure (lbf/ft) | Status |
|---|---|---|---|---|---|
| Final straight | 10 | 20 | +10.00 lbf | 0 | Pass |
| Second bend | 20 | 23.4 | x1.170 | 11.7 | Pass |
| Second straight | 23.4 | 43.4 | +20.00 lbf | 0 | Pass |
| First bend | 43.4 | 59.42 | x1.369 | 29.71 | Pass |
| First straight | 59.42 | 99.42 | +40.00 lbf | 0 | Pass |
Bends are treated as horizontal capstan bends, and sidewall pressure is bend-exit tension divided by centerline radius.
How to use this calculator
- Choose US customary or metric units before entering the route.
- Enter total cable or bundle weight, friction coefficient, weight correction factor, and starting tension.
- Enter each straight length and slope, then each horizontal bend angle and centerline radius.
- Enter the manufacturer pulling-tension and sidewall-pressure limits for the cable and pulling method.
- Compare the recommended direction and review the section table for the governing location.
How the pull is calculated
This calculator models a route with three straight sections and up to two horizontal bends. It evaluates the route once in the forward direction and once from the opposite end. In the reverse direction, the section order is reversed and each straight-section slope changes sign. That is why a route with the same fittings can have a different result depending on which end is pulled.
For each inclined straight section, the calculator uses:
T_out = T_in + W * L * (sin(alpha) + w * mu * cos(alpha))
- T_in and T_out are entering and exiting tension.
- W is total cable or bundle weight per unit length.
- L is developed straight-section length.
- alpha is the signed slope angle from horizontal.
- mu is the coefficient of friction.
- w is the weight correction factor for the cable configuration.
For a level straight section, the sine term is zero and the equation reduces to T_out = T_in + W * L * w * mu. If a downhill section calculates at or below zero tension, the output is clamped to zero and the section is flagged because the taut-cable assumption no longer holds.
For each horizontal bend, the calculator uses the capstan equation:
T_out = T_in * exp(w * mu * theta)
theta is the bend angle in radians. Bend sidewall pressure is then estimated as P = T_out / R, where R is the conduit centerline bend radius. A zero-degree second bend is treated as inactive.
What moves the result
Friction coefficient, accumulated bend angle, cable weight, and weight correction factor usually move the result most. Bend effects compound because tension is multiplied through each bend, so an early bend can raise every later section. Pull direction matters when one end has more straight length, steeper uphill work, or a high-tension bend downstream of it.
What this leaves out
The model does not check conduit fill, jam ratio, minimum bending radius, conductor damage limits, pulling-grip capacity, rope or winch ratings, raceway strength, lubricant compatibility, or field condition changes. Vertical bends need orientation-specific equations rather than the horizontal bend equation used here. Use manufacturer data for the cable weight, allowable pulling tension, allowable sidewall pressure, and friction assumptions before relying on the result.
Worked example
With the default US inputs, the cable bundle weighs 2 lb/ft, the friction coefficient is 0.20, the weight correction factor is 1.00, and starting tension is 10 lbf. The route is 100 ft, a 90-degree bend with a 2 ft radius, 50 ft, a 45-degree bend with a 2 ft radius, and 25 ft.
The forward pull ends at about 113.50 lbf. Pulling in reverse ends at about 99.42 lbf, with a peak pulling tension of about 99.42 lbf and maximum sidewall pressure of about 29.71 lbf/ft. Against limits of 1,000 lbf and 500 lbf/ft, the reverse pull governs at about 9.94% pulling-tension utilization, so reverse is recommended.
Common questions
How is pulling tension calculated through a conduit bend?
A horizontal bend is modeled with the capstan equation: exit tension equals entering tension multiplied by exp(w * mu * theta). The bend angle must be in radians, and the weight correction factor and coefficient of friction are included in the exponent.
What coefficient of friction should I use?
Use a value supported by the cable, conduit, lubricant, and installation conditions. Published examples often show values around 0.10 to 0.35, but the correct value is project-specific and should come from tested or manufacturer data.
What is sidewall bearing pressure?
Sidewall bearing pressure is the force of the cable against the inside of a bend, expressed here as bend-exit tension divided by bend radius. A small radius or high exit tension can make sidewall pressure govern even when total pulling tension looks acceptable.
Why can pull direction change the answer?
Tension accumulates as the pull advances. Reversing the pull changes whether long straights, uphill sections, and high-angle bends occur early or late, so the peak tension and bend-exit pressure can change.
Where do the maximum limits come from?
The maximum pulling tension and maximum sidewall pressure should come from the cable manufacturer and the selected pulling attachment or method. The smaller practical limit may be set by the conductor, jacket, pulling eye, grip, rope, winch, or project specification.
Can this model vertical conduit bends?
Not directly. The bend equation here treats bends as horizontal capstan bends, while vertical bends need equations that account for gravity through the bend orientation.