Pulling Tensions

Given the amount of tension on cables going into a section of conduit (T1), the following equations determine the amount of tension on cables coming out of the conduit section (T2).

TIP: T1 of the conduit's first section only is the reelback or initial tension.

In subsequent sections of conduit, T, of a preceding section of conduit is T1 of the next section of conduit.

  • T2 = Outgoing tension (lb)
  • T1 = Incoming tension (lb)
  • L = Length of conduit section (ft)
  • K = Effective coefficient of friction (dimensionless)
  • W = Total weight of cables (lb/ft)
  • T = Offset angle (degrees)
  • e = Base of natural logs (2.718)
  • a = Bend angle (radians) (see table below)

Degrees

Radians*

11.25°

.196

22.50°

.393

30°

.524

45°

.785

60°

1.047

90°

1.571

* 1 radian = 57.30°

A. For straight horizontal pulls:

T2 = T1 + LWK

B. For straight upward pulls:

T2 = T1 + LW (sin T + K cos T)

C. For straight downward pulls:

T2 = T1 - LW (sin T - K cos T)

D. For horizontal, upward, or downward pulls around bends:

T2 = T1 eKa

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