Shield Wire Sag Calculator

Plan overhead protection with reliable sag predictions. Switch between parabolic and catenary, with load options. Save results for crews, checks, and final documentation today.

Inputs

Enter span, loading, and tension to compute sag.
Example table Formula used How to use
Switches labels and conversions at submit time.
Catenary improves accuracy for larger sags.
Horizontal distance between supports (level span).
Use horizontal component at the support.
Weight per length, excluding ice and wind.
Used for wind projection and ice geometry.
Radial ice thickness around the wire.
Typical glaze ice is 800–917 kg/m³.
Use design wind pressure at conductor height.
Round cylinder Cd often ranges 0.9–1.2.

Thermal estimate (optional)

Adjusts tension using a simplified linear approach.
Temperature at which tension is specified.
Higher temperature reduces tension and increases sag.
Steel is often near 190–210 GPa.
Cross-sectional metal area, excluding air gaps.
Use 11–13 for many steel-based wires.
After calculating, results appear above this form.

Example data table

These example values illustrate typical inputs and outputs for a level span.
Case Span Tension Unit weight Diameter Ice Wind pressure Method Vertical sag Resultant sag
A 300 m 25 kN 12 N/m 12.5 mm 0 mm 600 Pa Parabolic ~5.4 m ~5.4 m
B 450 m 30 kN 15 N/m 14 mm 5 mm 800 Pa Catenary Higher Higher
Replace examples with your design basis and site conditions.

Formula used

  • Vertical load per length: wv = wself + wice
  • Ice load per length: wice = ρice g · π[(r+t)2 − r2]
  • Wind load per length: wwind = p · Dproj · Cd, where Dproj = D + 2t
  • Resultant load per length: wr = √(wv2 + wwind2)
  • Parabolic sag (midspan): s = w L2 / (8H)
  • Catenary sag (midspan): s = (H/w) [cosh(wL/(2H)) − 1]
  • Wire length (catenary): S = (2H/w) sinh(wL/(2H))
  • Midspan tension estimate: T ≈ √(H2 + (wL/2)2)
Thermal estimate: Hadj = Href − (E·A·α·ΔT). This is a simplified linear adjustment intended for screening-level checks.

How to use this calculator

  1. Select your unit system and sag method.
  2. Enter span length, horizontal tension, and unit weight.
  3. Add diameter, ice thickness, wind pressure, and Cd if needed.
  4. Enable thermal adjustment when tension is temperature-specific.
  5. Click Calculate to show results above the form.
  6. Download CSV or PDF for reporting and field review.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.