We were asked for some advice on a 1500MCM electrical cable being installed last week. It wasn’t a long pull but the pulling tension was higher than expected, and the cable jacket was experiencing some damage coming out of the vault. Overall, there wasn’t anything wrong but we suggested a few incremental changes to reduce the pulling tension.
 

Cables have design allowables from the factory: minimum bend radius and sidewall bearing pressure are the concern here. Minimum bend radius is self-explanatory: try to bend a cable too hard, and it will ‘kink’ – at the least, the outside layers will risk delaminating. Minimum bend radius will define the sheave or quadrant that must be used when turning corners under tension.
Sidewall bearing pressure is similar, but it relates the pulling tension to the bend radius. This limit can be even more restrictive, and knowing your cable specifications are a necessity when designing your pull.
Sidewall bearing pressure is measured in pounds per feet: you can allow more tension (pounds) only if you have a larger radius (feet). If a single sheave isn’t big enough, then an assembly of sheaves or a quadrant become necessary.
Gentle bends maybe acceptable for a cable, but a 90 degree underground sweep at the end of the pull – where the tension is greatest – could damage the jacket or insulation without your knowledge.
Since the length and geometry of the pull cannot be changed in most cases, the remaining option is to reduce the pulling tension. DCD Design has the Tube-Lube 326 sprayable lubricant that thoroughly wets the cable jacket and reduces friction with less mess, reduced consumption, and no environmental concerns. And all our Manhole Tools have quick-connect spray outlets built-in for easy application.
Reducing tension will allow more freedom for directing the cable at the pulling end. A cable puller like DCD’s Tuf-Lugger has an on-board meter for measuring pulling tension, allowing you to monitor the load and make changes to the pull if needed. The calibrated Load Monitor System is an optional accessory to provide more accurate data (for fiber optic pulls, for example) but it’s not typically required for electrical cable.