Journeyman Plumber ExamDrainage, Waste, and Venting (DWV) SystemsMedium
A plumber is installing a fixture trap for a commercial dishwasher in a restaurant. The dishwasher discharges indirectly into a floor sink. What is the minimum required trap arm size for this commercial dishwasher?
- A3 inches
- B1 1/2 inches
- C2 inches
- D1 1/4 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 2 inches
Commercial dishwashers generate a significant volume of hot, greasy water discharge. Plumbing codes typically require a minimum 2-inch trap and trap arm for commercial dishwashers to handle the flow and prevent clogging, even if discharging indirectly.
Why the other options are wrong
- A. 3 inches would be oversized for a commercial dishwasher trap arm and is not typically required.
- B. 1 1/2 inches is common for residential kitchen sinks, but usually insufficient for commercial dishwashers.
- D. 1 1/4 inches is generally too small for any dishwasher, especially commercial.
Commercial Dishwasher Trap Arm Size
The minimum diameter of the pipe connecting a commercial dishwasher's trap to the drainage system, designed to handle high volume and potential for grease.
- Commercial dishwashers discharge large volumes of water.
- Water is often hot and contains food particles/grease.
- Requires larger pipe to prevent blockages.
- Typically 2 inches minimum.
Memory trick: Trap Arm Size: Match the Flow, Watch it Grow.