The trap for a residential automatic washing machine shall be placed ______ inches above the floor.

The correct placement of the trap for a residential automatic washing machine is 12 inches above the floor. This height is specified to ensure proper drainage and prevent any backflow of wastewater into the appliance. A trap positioned too low could lead to issues such as siphoning of wastewater or inadequate drainage, which can create problems like flooding or foul odors in the laundry area.

Maintaining the trap at this height also helps in accommodating the gravity flow of water and optimizing the performance of the drainage system. Additionally, positioning the trap too high or too low could cause complications with code compliance and effective operation of the plumbing system. Hence, the requirement for a 12-inch height is standardized to foster reliability and functionality in residential plumbing setups.