How is the total pulling tension calculated for a complex underground cable pull with bends and slopes?

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How is the total pulling tension calculated for a complex underground cable pull with bends and slopes?

2025-08-16

Answer from Ningbo Changshi: The total pulling tension is the sum of the tension generated in each segment of the conduit run. Tension builds cumulatively, with each section (straight, bend, or slope) adding to the total. The most common formula for calculating tension in a straight or sloped section is:

$T_{o u t} = T_{in} + w L (cos θ \pm μ sin θ)$

Where:

$T_{o u t}$ = Tension leaving the section
$T_{in}$ = Tension entering the section
$w$ = Weight of the cable per unit length
$L$ = Length of the section
$θ$ = Angle of the slope (positive for uphill, negative for downhill)
$μ$ = Coefficient of friction between the cable and conduit

For bends, tension is not added, but multiplied exponentially. The tension leaving a bend is calculated as:

$T_{o u t} = T_{in} e^{μα}$

Where:

$e$ = The base of the natural logarithm (~2.718)
$μ$ = Coefficient of friction
$α$ = Angle of the bend in radians

By calculating the tension for each segment and adding them up, you can determine the total tension at the end of the pull. This calculation is a vital part of the planning process, and it is why we integrate real-time tension meters into all our pulling machines, ensuring the actual tension never exceeds the cable's specified limit.

What are the key differences in equipment required for overhead vs. underground utility cable pulling?What is sidewall pressure, and how is it calculated for bends in a conduit?

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