Cable Pull Tension and Sidewall Pressure Calculator
Estimate pulling tension and bend sidewall pressure for horizontal conduit runs. For three equal-size single conductors, screen the conduit-to-conductor jam ratio.
Pull details
Three-conductor mode assumes equal-size single conductors.
For three conductors, enter their combined weight per foot.
The starting value is an example. Use a value supported by the cable, raceway, and lubricant data.
Enter the cable and pulling-equipment limit. Leave at 0 to skip this comparison.
Enter the cable manufacturer's limit. Leave at 0 to skip this comparison.
Route sequence
Calculated pulling forces
Jam ratio D/d: 5.00. Adjusted screening ratio: 5.25. Very small jamming probability
| Route segment | Tension in | Tension out | Sidewall pressure |
|---|---|---|---|
| 1: Straight run | 0.0 lb | 65.0 lb | — |
| 2: Bend | 65.0 lb | 128.4 lb | 26.8 lb/ft |
No maximum pull-tension limit was entered; this result is not compared with a cable or pulling-equipment rating.
No maximum sidewall-pressure limit was entered; this result is not compared with a cable rating.
About this calculator
Estimate cable tension through an ordered route of horizontal straight runs and horizontal bends. The calculator reports tension entering and leaving each segment, peak route tension, and sidewall pressure at each bend.
For three equal-size single conductors, it also estimates the jam ratio and screens the adjusted ratio against published jamming-probability ranges. The result is an engineering estimate, not a cable-pull approval.
Inputs and assumptions
Use the actual conduit inside diameter, cable or conductor outside diameter, total weight of the pulled group, incoming tension, and route dimensions. Enter friction and maximum allowable tension or sidewall pressure from the exact cable, raceway, lubricant, and pulling-equipment information.
A limit of 0 means no manufacturer limit was entered, so the calculator skips that comparison. It does not substitute a generic limit. The example values are provided to demonstrate the calculation and must be replaced with job data.
Method
For a horizontal straight run, the calculator adds the friction load to incoming tension: Tout = Tin + wμWL. Here, W is total cable-group weight per foot, μ is the friction coefficient, L is run length, and w is the cable-arrangement weight correction factor.
For a horizontal bend, it uses the cable-weight equation Tout = Tin cosh(wμφ) + sinh(wμφ) √(Tin² + (WR)²), where φ is bend angle in radians and R is bend centerline radius. Sidewall pressure is calculated from bend exit tension and radius, with the published arrangement correction for three-conductor pulls.
For three equal-size single conductors, D/d is conduit inside diameter divided by one conductor outside diameter. The calculator uses a cradled arrangement when D/d is at least 2.5 and a triangular arrangement below 2.5. The displayed adjusted screening ratio applies the guide’s 5% allowance for bend ovality before the probability-range lookup.
Example
With three 1/2 in. conductors weighing 1.5 lb/ft total in a conduit with a 2.5 in. inside diameter, D/d is 5.00 and the arrangement is cradled. At a friction coefficient of 0.40, a 100 ft horizontal run raises tension from 0 to 65.0 lb. A following 90-degree bend with a 2 ft centerline radius raises the estimated peak tension to about 128.4 lb and produces about 26.8 lb/ft of sidewall pressure. The adjusted jam screening ratio is 5.25.
This example does not establish a safe pulling limit. Replace every example value with verified product and job data, then compare results with the applicable manufacturer limits.
Interpret the results
Peak tension is the highest calculated tension along the entered route. Sidewall pressure is reported for each bend and as the maximum bend value. Limit messages compare those results only with limits you enter.
Jam probability is a geometric screen for three equal-size single conductors. It does not model the full cable path or guarantee a successful pull. Review the route, pull direction, cable construction, raceway condition, lubricant, pulling equipment, and installation method before work begins.
FAQs
Which cable arrangements does this calculator support?
It supports one cable or conductor, or three equal-size single conductors. Three-conductor mode uses the conduit-to-conductor diameter ratio to select a cradled or triangular arrangement. It does not model unequal conductors or complex cable groups.
Where do I get the friction coefficient and cable weight?
Use data from the cable manufacturer for the exact conductor or cable, raceway surface, and pulling lubricant. The starting values are an example only and may not match a job.
What does the jam ratio indicate?
For three equal-size single conductors, D/d is the conduit inside diameter divided by one conductor outside diameter. The calculator applies the guide’s 5% bend-ovality allowance when it screens the jamming-probability range. It does not prove that a pull will or will not jam.
Does this check pulling-equipment or cable limits?
Only when you enter the applicable maximum pull tension and sidewall-pressure limits from the cable and equipment manufacturers. A result below those entered values does not approve the pull or confirm that the entered limits apply to the job.
Can I use this for vertical or sloped runs?
No. This version covers horizontal straight runs and horizontal bends. It does not model vertical or sloped sections, vertical bends, reel setup, pulling-grip details, or a complete engineered pulling plan.
Sources
- Southwire Power Cable Installation Guide, Chapter 7 — pulling-tension equations, cable-arrangement factors, sidewall pressure, and jamming-probability screening. Verify cable-specific limits and current manufacturer guidance.