A protective system for an electric unit operated by an installable battery pack includes: a control device configured to activate the electric unit in the case of the installed battery pack by operating a main switch; a contact device of the electric unit and a contact device of the battery pack including mutually complementary contact elements, which in each case form a first and a second interface for producing a first and a second electrical connection between the electric unit and the battery pack. In this instance, the contact devices are configured, during the installing of the battery pack, to produce the first electrical connection before the second electrical connection in time.