CSLB C-36 Plumbing ContractorFixture and Appliance InstallationMedium
A plumber is installing a new utility sink in a laundry room. The drain line for the sink will connect to an existing 2-inch PVC drain pipe. The trap arm from the new P-trap will have a developed length of 48 inches. The local code specifies that a 1½-inch trap arm connecting to a 2-inch vertical drain must not exceed a certain developed length. What is the maximum developed length allowed for a 1½-inch trap arm connecting to a 2-inch vertical drain, according to typical plumbing codes (e.g., UPC)?
- A60 inches
- B30 inches
- C36 inches
- D42 inches
Show answer & explanationAnswer & explanation
Correct answer: C. 36 inches
According to the Uniform Plumbing Code (UPC) Table 1002.2 (Trap Arm Lengths), the maximum developed length for a 1½-inch trap arm connecting to a 2-inch vertical drain is 36 inches. The proposed 48-inch length exceeds this limit.
Why the other options are wrong
- A. 60 inches is typically the maximum for a 2-inch trap arm to a 3-inch or larger vertical drain.
- B. 30 inches is for a 1¼-inch trap arm to a 1½-inch vertical drain.
- D. 42 inches is not a standard maximum length for this configuration.
Trap Arm Maximum Developed Length (UPC)
The maximum developed length of a trap arm is the total length of the pipe from the trap weir to the vent fitting, which is regulated by plumbing codes (e.g., UPC Table 1002.2) based on trap and drain pipe size to ensure proper venting.
- Ensures proper trap seal protection.
- Prevents siphoning or back-pressure.
- Length varies by pipe diameter.
Memory trick: Trap arm length, size it right, or you'll have a venting fright.