In the absence of a pull line in a conduit, what can be used as a substitute pulling line?

Using an unused cable already installed in the conduit as a substitute pulling line is a practical choice because it can provide the necessary strength and flexibility to assist in pulling additional cables through the conduit. An existing cable is generally designed to withstand various conditions and can effectively serve as a pulling medium without risking damage that could occur with less suitable options.

Moreover, the use of a previously installed cable minimizes the need for additional materials, reducing waste and cost. It is important, however, to ensure that the existing cable is not already designated for a specific purpose or installation, and that it is in good condition to avoid any complications during the pulling process.

The other options may not be as effective or suitable. A new pull line would not be a substitute since it implies bringing additional materials into the project. A rope may not have the necessary strength or may be prone to fraying when pulled through a conduit filled with potential hazards. Using another fiber-optic cable could also lead to damage if it gets tangled or caught during pulling, which might compromise the integrity of the existing installation.