Training Radius, Pulling Radius and Sidewall pressure.
Training Radius, Pulling Radius and Sidewall pressure.
Training radius is what you can bend a cable to after you have pulled. As it's called it's to get it into equipment and terminated. Usually less that pulling ridius in 600 volt cable.
Pulling radius is the minimum radius you can bend a cable to while pulling it. If you bend it more you can damage the insulation and/or shielding. As pulling tension increases the potential for damaging the cable goes up due to sidewall pressure. Sidewall pressure is the cable tension divided by the radius (in feet ) of the bend it's being pulled around.
A 2,000 lb pulled over a 2' radius sheave is a is a sidewall pressure of 1,000 lbs. Thats the simple answer, it's less when you pulling triplex or multiconductor. Maximum side wall pressure runs between 3-600 lbs + or - depending on the manufacturer.
More cable is dammaged by excessive sidewall pressure than overtensioning.
If your pulling MV cable get to know your manufactures rep. Some will help you set up your pull and even walk it down with you.
Polywaters "Pull Planner" program is good and cheap ( about $100 the last time I bought one). It calculates tension and sidewall pressure.
Quiz:
Your pulling 250 kCmil cable with a minimum bending radius of 12" in an underground run. You pull it out of vault with a 36" round opening. The vault in near the end of the pull. You plan on pulling the last 60' back into the vault and into a building.
Question- how much trouble are you in?
