The calculation, without hidden assumptions
Screen a cable pull before rigging by keeping route order visible. Straight sections add friction linearly; a bend multiplies the tension already present, so putting the same bend near the feed or pulling end can materially change final tension and sidewall pressure.
How to use this calculator
Enter total cable/bundle weight per route length from manufacturer data, not conductor metal weight alone.
Enter straight length before and after the bend, friction coefficient and weight-correction factor appropriate to the pull.
For a bend, enter total sweep angle and centerline radius. Zero bend angle models a straight-only pull.
Optionally enter manufacturer/project maximum pulling tension and sidewall-pressure limits; the calculator compares rather than invents them.
Compare forward and reverse results before choosing reel and pulling-equipment placement; model complex multi-bend routes with a full pull-planning method.
Where people use it
- •Screen a feeder pull with one dominant conduit bend.
- •See whether reversing an asymmetric route reduces tension.
- •Estimate sidewall pressure at a sweep elbow.
- •Compare lubrication/friction assumptions without hiding them.
- •Check an estimate against cable-manufacturer pulling and sidewall limits.
Example: 200 ft + 90° bend + 50 ft
For a 1.5 lb/ft cable bundle, μ=0.30, weight factor 1.0 and 2 ft bend radius, forward tension is about 166.68 lbf while reversing the route gives about 126.04 lbf. The forward bend sidewall pressure is about 72.09 lbf/ft. The bend position matters because it multiplies the tension already accumulated.
What the result does not assume
- •This owner models horizontal straight sections and one equivalent horizontal bend. Complex routes, vertical rises, multiple bends, rollers and transitions require segment-by-segment pull planning.
- •Coefficient of friction depends on cable jacket, raceway, lubricant, temperature, cleanliness and installation practice. Use project/manufacturer or validated test data where available.
- •Weight-correction factor is explicit because multiple-cable configurations can increase effective friction; do not assume 1.0 is universally correct.
- •Sidewall pressure here uses T/R for a single cable or multiple conductors under a common jacket. Other cable configurations use different correction equations.
- •Manufacturer cable pulling tension, sidewall pressure, bend radius, pulling attachment and equipment ratings govern the final installation.
- •This does not check conduit fill, jamming, clearance, ampacity, pull-box rules, lubricant compatibility or pulling-equipment capacity.
Frequently asked questions
How is cable pulling tension calculated in a straight conduit?+
For a horizontal straight section, the added friction tension is weight-correction factor × coefficient of friction × cable weight per length × section length, added to incoming tension.
Why do bends increase pulling tension so much?+
A bend approximately multiplies incoming tension by e raised to weight factor × friction coefficient × bend angle in radians. Because the multiplier acts on incoming tension, route order matters.
What is cable sidewall pressure?+
It is the radial force per route length where cable bears against a bend. For a single cable or common jacket, a basic screen is bend-exit tension divided by bend radius.
Should I use the default friction coefficient as a standard?+
No. It is only a realistic editable example. Jacket, conduit, lubricant and field conditions can change friction substantially; use validated project data when available.
Why compare the reverse pull?+
On an asymmetric route, placing the bend earlier can make its exponential multiplier act on less accumulated straight-run tension. Reversing can therefore reduce final tension and sidewall pressure.
Does a PASS mean the pull is approved?+
No. It only means the modeled value is within the limit you entered. Final pull planning must use manufacturer limits and account for the complete route, equipment, bend radius, fill, jamming and field conditions.
Semantic next steps
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