Pulling tensions for cables

Pulling During Installation

Tension is developed in the cable when pulled due to the friction between the outer surface of the cable and the surface over which it is pulled. Excessive lengths can lead to high tensions during pulling, creating the risk of cable damage, particularly at bends.

Some simple rules and precautions are suggested when pulling cables during installation.

1) Pull on the conductor, using a pulling eye wherever possible.

2) Do not pull directly on interlocked armour. If basket weave types of grip are used, make them as long as possible to distribute the force on the insulation, and apply a heat shrinkable tube over the armour and/or jacket to prevent damage.

3) Provide generous radii for bends. This will decrease the pulling tensions and the risk of armour and jacket damage.

4) Pull in the direction of the end with the lowest elevation, to reduce pulling forces.

5) Avoid sharp bends near the pulling end, as they increase the total pulling tension exponentially in the inverse of the radius of the bend. Try to line up the pull with the straightest section at the pulling end.

6) Provide rollers at bends wherever conditions permit, to reduce the pulling tensions due to friction.

7) Use approved pulling lubricants wherever possible, particularly in cramped spaces and in underground raceway.

The following formulae, extracted from the Aluminum Electrical Conductor Handbook, published by the Aluminum Association, may be used for calculation.

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