What type of easement benefits a person or corporation, such as an electrical company installing lines?

The correct choice is the easement in gross, which is designed specifically to benefit a person or entity rather than a particular parcel of land. In the scenario of an electrical company installing lines, the easement in gross allows the utility company to access and maintain their infrastructure across property that they do not own. This type of easement is not tied to any specific tract of land but is instead associated directly with the company itself, providing them the rights necessary to carry out their operations.

In contrast, other types of easements do not serve this purpose. An easement by necessity is typically granted when a parcel of land is landlocked and requires access to a roadway. A prescriptive easement arises when a party uses someone else's land continuously and openly for a statutory period, leading to a right to continue that use. Finally, a conservation easement is aimed at limiting the use of land to protect its conservation value, which does not directly pertain to the utilities' needs for installation of lines. Thus, the easement in gross is clearly the most suitable in providing the necessary access for the electrical company’s operations.