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Southwire Wire Pulling Equation:
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The Southwire Wire Pulling Equation calculates the output tension (T_out) required when pulling wire 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 electrical installations to ensure proper wire pulling without damage.
The calculator uses the Southwire equation:
Where:
Explanation: The equation accounts for the exponential increase in tension due to friction as the wire is pulled around bends in the conduit.
Details: Accurate tension calculation is crucial for preventing wire damage during installation, ensuring proper conductor integrity, and complying with electrical code requirements for maximum pulling tensions.
Tips: Enter input tension in lb or N, coefficient of friction (typically 0.15-0.5 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 pulls, μ typically ranges from 0.15 to 0.5. Dry pulls have higher coefficients, usually between 0.5 and 1.0.
Q2: How do I convert degrees to radians?
A: Multiply degrees by π/180. For example, 90° = 90 × π/180 = π/2 ≈ 1.57 radians.
Q3: What is the maximum recommended pulling tension?
A: Generally, 0.008 lb per circular mil for copper and 0.006 lb per circular mil for aluminum, but consult specific wire manufacturer recommendations.
Q4: Does this equation account for multiple bends?
A: For multiple bends, calculate sequentially: the output tension from one bend becomes the input tension for the next bend.
Q5: When should I use this calculation?
A: Use for all wire pulling operations through conduit, especially when dealing with bends, to ensure you don't exceed maximum allowable pulling tensions.