Overhead Line Tension Calculator

Calculator

Use this form to evaluate tension, sag, blowout, and reactions.

Unit system

Switch units without changing calculation logic.

Method

Pick the input mode that matches your workflow.

Safety factor

Applied to allowable support tension (minimum 1.0).

Span length m

Horizontal distance between supports.

Target vertical sag m

Midspan sag under selected loading.

Allowable support tension kN

Support hardware / structure limit (before safety factor).

Conductor mass per length kg/m

Bare conductor mass (without ice).

Conductor diameter mm

Used for wind and ice geometry.

Elastic modulus GPa

Typical aluminum is about 69–71 GPa.

Cross‑section area mm²

Used for elastic stretch in temperature mode.

Thermal expansion µm/m/°C

Typical aluminum ≈ 23 µm/m/°C.

Wind pressure Pa

Use 0 for no wind; pressure is N/m².

Ice thickness mm

Radial ice layer added around the conductor.

Ice density kg/m³

Common range: 850–950 kg/m³.

Initial temperature °C

Enter initial condition temperature.

Target temperature °C

Compute tension and sag at this temperature.

Initial horizontal tension kN

Horizontal component at initial temperature.

Example data

Use these sample values to sanity‑check your setup.

Span	Mass	Diameter	Wind	Ice	Method	Input	Support tension (approx.)	Vertical sag (approx.)
80 m	1.35 kg/m	18 mm	600 Pa	0 mm	Given sag	Sag = 2.0 m	≈ 22–28 kN*	≈ 2.0 m
120 m	1.60 kg/m	22 mm	800 Pa	3 mm	Allowable tension	Allowable = 35 kN	≈ 23 kN (design)**	≈ 3–5 m*

*Approximate because sag and tension depend on combined loading and chosen safety factor.
**Design allowable equals allowable divided by safety factor.

Formula used

Loads per unit length

w_v = (m + m_ice) g
w_h = P_wind · D_out
w = √(w_v² + w_h²)

Ice mass uses the annulus area between bare and iced diameters.

Parabolic sag‑tension

f_v = (w_v L²) / (8H)
f = (w L²) / (8H)
T = √(H² + (wL/2)²)

This approximation is widely used for practical spans with moderate sag.

Temperature adjustment (simplified)

The calculator uses a two‑state equation that balances geometric sag length and elastic stretch.

(w²L²)/(24H²) + H/(EA) − αT = constant

For high‑accuracy design, use utility standards, creep data, and full catenary methods.

Typical Field Inputs

Span length, conductor mass, and diameter drive most results. For example, an 80 m span with 1.35 kg/m and 18 mm diameter under 600 Pa wind yields 22–28 kN support tension when vertical sag is near 2.0 m and safety factor is 1.5. Doubling span can quadruple sag for the same horizontal tension.

Wind and Ice Loading

The tool converts wind pressure to a horizontal line load using projected outside diameter. At 600 Pa and 18 mm, wind load is about 10.8 N/m. Ice is modeled as a radial layer; a 3 mm layer on 22 mm conductor increases outside diameter to 28 mm, raises wind load to about 22.4 N/m at 800 Pa, and adds vertical weight based on ice density and gravity.

Reading Sag, Blowout, and Reactions

Vertical sag is reported at midspan from the vertical load component, while resultant sag reflects combined loading in the wind plane. Blowout is the midspan horizontal deflection, useful for checking phase spacing and clearance to structures. Support reactions equal half-span loads: Rv = wv·L/2 and Rh = wh·L/2, providing checks for crossarm and foundation demands.

Temperature Adjustment Mode

When temperature changes, tension shifts because the conductor expands and the sag geometry changes. The two-state equation combines a geometric term (w²L²/24H²) with elastic stretch (H/EA) and thermal strain (αT). Enter an initial horizontal tension at a known temperature (e.g., 18 kN at 15°C), then solve for the target condition (e.g., 45°C) to estimate final sag and support tension under the same loading set.

Construction Checks and Reporting

Use utilization to compare computed support tension against your allowable divided by the safety factor; values above 100% indicate the design allowance is exceeded. Review clearance by comparing vertical sag and blowout against site constraints. Export CSV for submittals and QA logs, and generate PDF summaries for reports and inspection packages quickly.

FAQs

1) What does support tension represent?
It is the tension magnitude at the support, combining horizontal tension and half-span loading. It helps verify hardware ratings, insulator strings, and structure capacity under the selected wind and ice conditions.

2) Why can wind increase tension even if sag is unchanged?
Wind adds a horizontal load component, increasing the resultant load per length. For a fixed sag, the required horizontal tension rises, which also raises the support tension and reactions.

3) When should I use the allowable tension method?
Use it when a hardware, structure, or stringing limit is known. The calculator applies your safety factor, then estimates the horizontal tension and sag that satisfy the design allowable under the current loads.

4) How should I choose wind pressure and ice thickness?
Use project or utility criteria and local design standards. Enter a representative pressure for the work site and an ice thickness for the governing weather case, then review how tension and blowout change.

5) What does utilization mean?
Utilization equals computed support tension divided by design allowable tension. Values below 100% indicate available margin. Values above 100% suggest revising span, sag, conductor, or allowable limits.

6) Is this suitable for final engineering design?
It is a planning and QA tool using practical approximations. For final design, confirm results with full catenary methods, creep data, and applicable standards, especially for long spans or extreme weather cases.

How to use

Pick a unit system and select a method.
Enter span length and conductor properties.
Add wind pressure and ice thickness if applicable.
Provide sag, allowable tension, or temperature inputs.
Press Calculate to see results above this form.
Download CSV or PDF for reporting and reviews.

Typical Field Inputs

Wind and Ice Loading

Reading Sag, Blowout, and Reactions

Temperature Adjustment Mode

Construction Checks and Reporting

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