Cable Pulling Calculator

The cable pulling calculator determines the feasibility of installing cables through conduit, duct, cable tray, or direct burial routes. It models the physics of pulling tension accumulation through multi-segment routes with straight runs and bends.

For straight sections, the pulling tension increases according to T_out = T_in + w × L × μ × cos(θ) + w × L × sin(θ), where w is the cable weight force per unit length, L is the section length, μ is the coefficient of friction, and θ is the inclination angle from horizontal. Positive angles represent uphill runs where gravity opposes the pull.

At bends, the capstan equation applies: T_out = T_in × e^(μ × θ), where θ is the bend angle in radians. This exponential relationship means that tension increases dramatically at bends — a single 90° bend with μ=0.35 multiplies the tension by approximately 1.73.

Sidewall bearing pressure (SWBP) at each bend is calculated as SWBP = T / r, where T is the tension and r is the bend radius. IEEE 1185 recommends a limit of 5000 N/m to prevent cable jacket damage.

For conduit installations with 3 cables, the jam ratio (conduit ID / cable OD) is checked. Ratios between 2.5 and 3.0 present a risk of cables locking in a triangular formation per NEC Chapter 9, Table 1 Note 6. Conduit fill is verified against NEC Chapter 9 Table 1 limits (53% for 1 cable, 31% for 2, 40% for 3+).

The calculator performs bidirectional analysis, computing tension for both pull directions and recommending the direction with lower maximum tension. Maximum allowable tension is k × conductor area, where k = 70 N/mm² for copper and 40 N/mm² for aluminium per AEIC CS8.