# What is Sag in a Transmission Line?

**URL:** <https://forumautomation.com/t/what-is-sag-in-a-transmission-line/13600>\
**Category:** Electrical\
**Tags:** line\
**Created:** [October 3, 2025, 3:21pm UTC](https://forumautomation.com/t/what-is-sag-in-a-transmission-line/13600 "2025-10-03T15:21:49Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Rabert](https://forumautomation.com/user_avatar/forumautomation.com/rabert/32/6784_2.png) [@Rabert](https://forumautomation.com/u/Rabert)\
**Post date:** [October 3, 2025, 3:21pm UTC](https://forumautomation.com/t/what-is-sag-in-a-transmission-line/13600/1 "2025-10-03T15:21:49Z")

</div>

## What is Sag in a Transmission Line?

**[Sag in a transmission line](https://forumelectrical.com/sag-in-a-transmission-line/)** is the vertical distance across the highest point of support (such as a tower) & the lowest point of a conductor hung between two supports. This occurs when the conductor’s weight leads it to curve downward due to gravity resulting in a catenary curve (or a parabola in practical circumstances with low sag relative to span).

 ![image](https://cdn.forumautomation.com/original/2X/7/789d957834a4ebe8bb5297f41a13752cd5d46bb5.jpeg)

Sag is necessary for preventing mechanical stress on the conductor.

- Allows for thermal expansion as temperatures rise and fall.
- Provides protection against wind, ice load & swings.
- Provides mechanical strength & safe clearance from the ground.

Sag and tension are inversely proportionate, therefore there is a balance between the two.

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