Knowledge of the calculation of pulling tension during the installation of a fiber optic cable is a must for an OSP engineer. Before installation, a detailed plan for pulling shall be prepared according to the terrain conditions. The number of curves, ups, and downs in the terrain through which the fiber optic cable pass-through must be estimated and a detailed plan shall be outlined in order to ensure a safe installation of fiber optic cable.
Some of our readers suggested us to provide the formula for calculating the pulling tension for optical fiber cable during installation.
Today let us discuss the equation to calculate the tension during pulling a fiber optic cable. Friction between the fiber optic cable and duct surface is also an important parameter. The tension on fiber optic cable while pulling horizontally shall not exceed 9.8W of the cable if international standards for cable pulling are followed. Bellcore specification is 2670N maximum. Some installers specify 2.5W, where W is the weight of 1 km cable.
The optical fiber cable is coiled in the figure of eight (Figure-8) shape and one end is connected with Cable pulling stock. When the cable is pulled vertically, or in angle and when the duct route is not horizontal, the cable pulling tension changes. The formula to calculate the fiber optic cable pulling tension is given below:
T1 = 9.8W x L (Sina1 + uCosa1) + T0
Where,
u is the Coefficient of friction between the duct inner surface and the cable. Generally, a value of 0.5 shall be considered for calculation)
a1 is the duct route inclination angle. For horizontal pulling, the angle is taken as 0. For vertical pulling, the angle is 90 degrees.
Thus for vertical pulling, The Tension T1 becomes 9.8WL + T0 and for horizontal pulling, the tension becomes 9.8uWL + T0
T1 is the tension when the cable is pulled in angle
T0 is the tension before inclination.
W is the weight of 1 km of cable
L is the installation length
When the duct passes through a horizontally curved area, the Tension after the curve while pulling the fiber optic cable will be
T1 = KT0
Where,
T1 is the tension after the curve
T0 is the tension before the curve
K is expressed as exp (0.0175ua2)
a2 is the degree of angle of Curve
For example, if the coefficient of friction between cable and duct inner surface is 0.5, and the angle of curve in 90 degrees, K will be 2.19 and if a roller is used, the friction will be zero and the K will be 1.
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