Sag of Transmission Line Calculator

Sag of Transmission Line Calculator

Calculate the sag of a transmission line with supports at different heights using the approximate formula:
\[ f \approx \sqrt{\frac{3L\,(S-L)+(H_2-H_1)^2}{8}} – \frac{\left|H_2-H_1\right|}{2} \]

* Enter the horizontal span \( L \) (m), left support height \( H_1 \) (m), right support height \( H_2 \) (m), and cable length \( S \) (m).

Step 1: Enter Parameters

Example: 300 m

Example: 100 m

Example: 110 m

Example: 305 m (must be greater than L)

Derived Formula: \( f \approx \sqrt{\frac{3L\,(S-L)+(H_2-H_1)^2}{8}} – \frac{\left|H_2-H_1\right|}{2} \)


Practical Example:
For \( L = 300\,\text{m} \), \( H_1 = 100\,\text{m} \), \( H_2 = 110\,\text{m} \), and \( S = 305\,\text{m} \):
The calculator computes the sag of the cable (the vertical drop from the lower support to the cable’s lowest point).