Cable Sag-Tension

[Alaska60]

The parabolic equation for wire sag is S = W x L x L /(8 x T) where S=sag (ft), W=wire weight (lb/ft), L=Span (ft), and T =wire tension (lb).
Tension can be expressed by T = W x L x L /(8 x S).
The more accurate hyperbolic form for sag is S = (T/W) x {cosh[W x L/(2 x T)]-1}.
Does anyone know of a hyperbolic form for tension in terms of sag? You can't just switch T & S.

 

[7anoter4]

http://ieee-tpc.org/ieee_tutorials/IEEETPCTutorial_Sag-tensionCalcs.pdf

 

[7anoter4]

As w*S/(2*H) <<<1 the error between "correct" and "approximate" is less than 1 per 10000. Then the effort to find a "correct" relation between H=f(D) it is not significant.

 

[Alaska60]

Agreed. For slack spans the difference becomes more apparent. I was trying to be consistent in an Excel Sag-Tension app that uses the hyperbolic form for all calcs except finding an initial tension with a given sag.