Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsHard
A plumber is installing a new drainage system in a residential bathroom. The shower stall requires a 2-inch trap. What is the maximum developed length permitted for the trap arm connecting this shower trap to the horizontal branch drain?
- A3 feet 6 inches
- B2 feet 6 inches
- C5 feet
- D8 feet
Show answer & explanationAnswer & explanation
Correct answer: C. 5 feet
The maximum developed length of a trap arm is determined by its diameter. For a 2-inch trap arm, the maximum developed length permitted by most plumbing codes is 5 feet. This ensures proper venting and prevents trap seal loss.
Why the other options are wrong
- A. 3 feet 6 inches (42 inches) is typically the maximum for a 1 1/2-inch trap arm.
- B. 2 feet 6 inches (30 inches) is typically the maximum for a 1 1/4-inch trap arm.
- D. 8 feet is too long for a 2-inch trap arm and would likely lead to trap seal siphoning.
Trap Arm Developed Length
The total length of the drain pipe from the trap weir to the vent fitting, measured along the centerline of the pipe.
- Critical for preventing trap seal loss.
- Maximum length is dependent on trap arm diameter.
- Ensures proper air circulation to the trap.
Memory trick: Lengthy Limits, Lessen Loss.