Length of Cable with Sag

The length of a cable with sag is the effective length of a suspended cable (such as a fiber-optic or copper wire) when it is strung between two supports, and due to its weight, it sags rather than forming a straight line.

Factors to Consider

• Actual Length vs Horizontal Distance  -  The actual length of the cable is longer than the horizontal distance between the two supports because of the sag.
• Sag  -  The sag is the vertical distance between the lowest point of the cable and the straight line connecting the two supports.
• Catenary Curve  -  The shape of a hanging cable under its own weight forms a catenary curve.  The formula to calculate the actual length of the cable takes this curve into account.
• Cable Tension  -  Proper sag and tension are necessary to avoid excessive stress on the cable, which can affect the signal quality.
• Environmental Impact  -  Factors like wind, temperature, and load can influence sag, and engineers must account for this when designing cable installations.

This formula helps engineers calculate the appropriate cable length to maintain proper sag, tension, and signal integrity.

 

Length of a Cable with Sag formula
\( CL \;\approx\; L + ( 8 \; h^2 \;/\; 3 \; L ) \)
Symbol	English	Metric
\( CL \) = Cable Length	\(ft\)	\(m\)
\( L \) = Length of Span	\(ft\)	\(m\)
\( h \) = Height of Sag	\(ft\)	\(m\)