For a conductor strung between two supports at the same level, the relationship between sag and tension can be approximated using the parabolic formula. This approximation is accurate for most power lines where the sag is small relative to the span length.

Sag Formula:

The sag (S) is calculated as:

S=8TwL2

Where:

• S = Sag (in meters)

• w = Weight of the conductor per unit length (in N/m or kg/m)

• L = Span length (in meters)

• T = Horizontal tension in the conductor (in N or kgf)

Conversely, if you know the sag, you can calculate the tension:

Tension Formula:

T=8SwL2