Wire-pulling lubricant is an important part of the professional electrician's tool kit. When a bundle of wires are being pulled (usually with a fish tape or rope through a long span of electrical conduit, the friction between the wire's jacket (usually PVC) and the metal inside of the pipe becomes far too great. At this point, human or even mechanically powered wire pullers cannot overcome the force of friction. What is done to make the job easier? That's right, lubricate the wire.
There exist many industrial wire-pulling lubricants that will satisfy the job. These compounds are designed to provide a large amount of slippery, while adhering to the wire so it will remain lubricated the farther it is pulled into the conduit. These compounds must also be absolutely non-flammable, as well as their residues, as they will dry and remain coating the current carrying wire, which presents a potential fire hazard.
The size of the cables being run, the size, length, and number of bends in the conduit depends on the amount of lubricant needed. Sometimes getting the first ten feet of the bundle itself coated will be enough; larger pulls, with lots of bends and so on, may require pulling a lubricant coated sponge through the conduit a few times before passing the wire through.
American Polywater Corporation makes Polywater, a very popular line of wire lubricants. I am most acquainted with Ideal Yellow 77, an almost banana pudding-looking lubricant useful for industrial wire-pulling applications. And yes, a part of being an electrician's helper is to be the wire lube guy. Every wonder what it's like to be covered in lube?