Final answer:
Grounded distribution wiring was introduced in residential electric systems in the late 1900s, specifically becoming widespread in the 1960s as a standard safety feature to prevent electric shock and fire hazards.
Step-by-step explanation:
The introduction of grounded distribution wiring in residential electric systems was a significant development in the history of electrical engineering and safety. The correct answer to when grounded distribution wiring was first introduced is in the late 1900s. Grounding provides a safe path for electrical current to follow back to the ground in the case of a fault, which helps to prevent electric shock and fire hazards. The practice of grounding in residential wiring began to become widespread in the 1960s, and it has been a standard safety feature in electrical systems ever since.