Cable Sag
Cable Sag
For a given tension a cable sags by an amount set by its span and load — important for clearance under power lines.
The sag is d = w·L²/(8·T). where w is the load per unit length, L the span and T the horizontal tension.
Inputs
w := 15 N/m=15 kg/s^2
L := 100 m=100 m
T := 20000 N=20000 N
Apply the parabolic-cable sag formula.
d := w·L^2/(8·T)=937.5 mm
Results
Higher tension reduces sag but raises the load on the towers. Sag also grows as conductors heat and lengthen, which sets clearance limits.
Assumptions & limitations
- Parabolic (uniform horizontal load) cable.
- Small sag-to-span.
- Constant tension.