How to Use the Cable Pulling Tension Calculator
Pulling conductors into conduit or tray with too much tension stretches the copper and damages insulation, which usually shows up later as a failed insulation resistance test. This calculator adds the straight-run friction load to the exponential rise that happens at every bend, then compares the result with the allowable pulling tension.
Straight-run tension is T = cable weight × length × coefficient of friction. Each bend multiplies the tension by T₂ = T₁ × e(fθ), so a single 90° bend at f = 0.5 raises tension about 2.19 times. Because bends near the pulling end are the worst case, this tool conservatively assumes every bend is passed at the end of the run.
The common NEC/ICEA rule limits conductor tension to 0.008 lb per circular mil, which is 8 lb per kcmil per conductor, with a practical ceiling of about 5,000 lb on a bolted pulling eye and 1,000 lb on a basket grip over the jacket. Sidewall bearing pressure is tension divided by bend radius in feet and is normally held to about 500 lb/ft for power cable. Always confirm the limits printed in the cable manufacturer data sheet, and have the final pull plan reviewed by the engineer of record.
Frequently Asked Questions
At a bend the cable presses against the raceway wall, so friction compounds and tension grows multiplicatively as e^(fθ). Two 90° bends multiply tension by roughly 4.8, which is why bends are best placed near the feed end or broken up with a pull box.
Total tension can be within limits while a tight radius concentrates force at one bend and crushes the cable. Tension and SWBP are independent checks, and the usual fix for high SWBP is a larger bend radius.
Dropping the coefficient of friction from 0.75 to 0.35 cuts straight-run tension by more than half and also reduces the multiplier at each bend. Use only a lubricant listed as compatible with the cable jacket.