Which device is essential for proving that a cable is de-energized?

The essential device for proving that a cable is de-energized is the cable spear. A cable spear is specifically designed to safely test and prove the absence of voltage in electrical cables before work is performed on them. By inserting a cable spear into the insulation of the cable, the device can determine whether the cable is energized or not, providing an essential confirmation for safety procedures.

While a voltage tester does measure the presence of voltage, it is not designed to provide the same level of safety and assurance when working directly with the cable. The measuring tape is used for measuring distances and does not play a role in determining the electrical status of a cable. An insulation tester is used to check the integrity of the insulation surrounding the conductors but does not specifically indicate whether the cable is energized or de-energized. Therefore, the cable spear is the most appropriate tool for ensuring safety when approaching electrical infrastructure.