| Case | Span (m) | Vertical Load (kg/m) | Wind (N/m) | Tension (kN) | Max Vertical Sag (m) | Notes |
|---|---|---|---|---|---|---|
| A | 250 | 1.10 | 12 | 22 | 3.8 | Typical moderate span and tension. |
| B | 320 | 1.60 | 18 | 18 | 6.4 | Heavier loading increases sag. |
| C | 400 | 1.20 | 25 | 26 | 6.1 | Long span with strong wind effect. |
| D | 180 | 0.95 | 8 | 15 | 2.6 | Shorter span, lower sag. |
- Select units, then enter the span length and conductor unit weight.
- Add ice load and wind load if your load case requires them.
- Enter horizontal tension directly, or enable temperature adjustment.
- Set left and right support heights to model uneven supports.
- Enter required clearance to flag low-clearance outcomes.
- Press Calculate to view results above the form.
- Use the download buttons to share field-ready outputs.
Design intent and clearance planning
Transmission spans in construction corridors often target a minimum clearance band of 6–8 m, depending on local codes, terrain, and access roads. Use the clearance check to validate that the lowest point elevation stays above your required value under the selected loading case. Document inputs, assumptions, and crew conditions in daily reports consistently.
Load components used in sag checks
Vertical load combines conductor self-weight and optional ice load, while wind load acts transversely. The calculator resolves these into a resultant load per unit length to capture combined sag and lateral blowout. Typical preliminary wind inputs fall in the 10–30 N/m range for exposed spans, but project specifications should govern.
Method selection: parabolic versus catenary
The parabolic method is efficient when sag is small relative to span, providing quick screening for many field scenarios. The catenary method better represents the true curve when spans are long or loading is heavy. Compare both results to understand sensitivity before locking a stringing plan.
Temperature and tension behavior
Conductor tension can change with temperature due to thermal expansion and elastic stretch. When enabled, the calculator estimates an adjusted horizontal tension using elastic modulus, cross-sectional area, and thermal coefficient. For aluminum-based conductors, α commonly lies near 17–23 microstrain per °C, while elastic modulus is often 60–80 GPa.
Example data and output interpretation
Example case: span 300 m, vertical load 1.45 kg/m, wind 15 N/m, horizontal tension 20 kN, supports 18 m and 19 m, clearance requirement 7 m. A practical outcome might show maximum vertical sag near 5–6 m, small blowout, and a lowest-point clearance check that flags any shortfall.
Use the “lowest point from left support” to guide midspan survey marks, and use the approximate conductor length to plan pull and take-up allowances. Always confirm against project standards and permissible tension limits.
1) What is horizontal tension in this calculator?
It is the horizontal component of conductor tension used by the sag equations. Higher horizontal tension generally reduces sag, but it must remain within allowable limits for the conductor and hardware.
2) How do I choose wind load values?
Use project specifications or local design loads. If estimating early, start with a conservative transverse load per unit length for exposed spans, then refine using site category, height, and shielding effects.
3) What is blowout and why does it matter?
Blowout is the lateral displacement caused by wind. It affects clearance to structures and phase spacing. Combined with vertical sag, it helps identify the true worst-case conductor position.
4) When should I use the catenary method?
Use catenary for longer spans, heavier loading, or when you want a closer geometric representation. For quick screening where sag-to-span is small, the parabolic approximation is often adequate.
5) What does the temperature adjustment option change?
It estimates a new horizontal tension at the final temperature using thermal expansion and elastic stretch. This can noticeably change sag, especially with large temperature shifts or low stiffness conductors.
6) How are uneven support heights handled?
The calculator shifts the lowest point along the span using a common approximation. This helps estimate where maximum sag occurs and improves clearance checks when one support is higher than the other.
7) Why does the safety factor reduce effective tension?
A safety factor is applied as a conservative reduction of usable tension in calculations. It mimics design margins so the resulting sag is less optimistic when working near allowable limits.