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Southwire Cable Pulling Formula:
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The Southwire cable pulling formula calculates the output tension (T_out) required when pulling cable through conduit based on input tension (T_in), coefficient of friction (μ), and the angle of bend (θ) in radians. This equation is essential for determining proper cable pulling forces and preventing damage during installation.
The calculator uses the Southwire cable pulling formula:
Where:
Explanation: The formula accounts for the exponential increase in tension due to friction as the cable passes through bends in the conduit.
Details: Accurate cable pulling tension calculation is crucial for preventing cable damage, ensuring proper installation, and maintaining electrical system integrity. Excessive tension can damage cable insulation or conductors.
Tips: Enter input tension in lb or N, coefficient of friction (typically 0.2-0.5 for lubricated pulls), and bend angle in radians. All values must be valid (tension > 0, μ ≥ 0, θ ≥ 0).
Q1: What are typical coefficient of friction values?
A: For lubricated cable pulls, μ typically ranges from 0.2 to 0.5. Dry pulls may have higher coefficients up to 0.8 or more.
Q2: How do I convert degrees to radians?
A: Multiply degrees by π/180 (approximately 0.0174533). For example, 90° = 90 × π/180 = π/2 ≈ 1.5708 radians.
Q3: What is the maximum recommended pulling tension?
A: Maximum tension varies by cable type but is typically limited to 0.008 lb/circ mil for copper and 0.006 lb/circ mil for aluminum.
Q4: Does this formula account for multiple bends?
A: For multiple bends, calculate sequentially: T_out from first bend becomes T_in for second bend, and so on.
Q5: When should I use this calculation?
A: Use for all cable pulling operations through conduit, particularly when dealing with bends, to ensure safe installation practices.