Which tool is used to test for obstructions before pulling a cable through a raceway?

The tool primarily used to test for obstructions before pulling a cable through a raceway is the mandrel. A mandrel is a flexible device that can be inserted into the raceway to check for any blockages or bends that might impede the smooth passage of cables. By assessing the raceway in advance, a mandrel can help ensure that the path is clear, thus preventing potential issues during the actual cable installation process. Utilizing a mandrel allows electricians to gauge if the size and shape of the raceway are appropriate for the cable being installed.

Other tools listed, such as a vernier caliper, which measures dimensions, fish tape, which assists in routing wires and cables, and a cable puller, which helps with the actual pulling of cables, do not serve the specific purpose of testing for obstructions prior to cable installation. Each of these tools has its own function in the electrical process but does not evaluate raceway conditions before pulling cables through.