Advanced
Cable Pulling Tension Formula
Calculate cable pulling tension for conduit runs — weight, friction, and bend multiplier factors per NEC and manufacturer limits.
Formulas
T = W × L × f
Straight run pulling tension
T_bend = T_in × e^(f×θ)
Tension increase through a bend
Sidewall pressure = T / r
Sidewall bearing pressure at bends
Variable Definitions
T=Pulling tension(pounds (lbs))
W=Cable weight(pounds per foot (lbs/ft))
L=Straight run length(feet (ft))
f=Friction coefficient(dimensionless (typically 0.35-0.50))
θ=Bend angle(radians (90° = π/2 = 1.571))
r=Bend radius(feet (ft))
Worked Example
Pull 3× 500 kcmil copper cables (0.79 lbs/ft each) through 200 ft conduit with one 90° bend, f=0.35.
- Total weight: 3 × 0.79 = 2.37 lbs/ft
- Straight run: T = 2.37 × 200 × 0.35 = 165.9 lbs
- After 90° bend: T = 165.9 × e^(0.35 × 1.571) = 165.9 × 1.733 = 287.5 lbs
Answer: 287.5 lbs pulling tension (within typical 600 lb/kcmil limit)
When to Use
- •Planning cable pulls in long conduit runs
- •Verifying pulling tension won't exceed cable jacket damage threshold
- •Determining need for pulling lubricant
- •Designing conduit routes to minimize bends and total tension
Standards & References
- NEC 300.34 — Conductor Bending Radius
- IEEE 1185 — Cable Installation in Substations