What is the maximum distance from the branch to the fixture?

What is the maximum distance from the branch to the fixture?

• A. 12 inches
• B. 24 inches
• C. 30 inches
• D. 36 inches

Answer: (C)

Trap arms must be vented within a limited distance to prevent the drain from siphoning the fixture’s trap. The allowed distance between the trap outlet and the vent (the branch) depends on the size of the trap. For a common fixture with a 1-1/4 inch trap, the maximum trap-arm length to the vent is 30 inches. That’s why 30 inches is the best choice here: it represents the furthest distance you can run the branch to the fixture while still providing proper venting and preventing siphonage. Shorter distances, like 12 or 24 inches, are within the limit but not the maximum, and a 36-inch distance would apply to larger trap sizes, not the typical 1-1/4 inch scenario.

Trap arms must be vented within a limited distance to prevent the drain from siphoning the fixture’s trap. The allowed distance between the trap outlet and the vent (the branch) depends on the size of the trap. For a common fixture with a 1-1/4 inch trap, the maximum trap-arm length to the vent is 30 inches. That’s why 30 inches is the best choice here: it represents the furthest distance you can run the branch to the fixture while still providing proper venting and preventing siphonage. Shorter distances, like 12 or 24 inches, are within the limit but not the maximum, and a 36-inch distance would apply to larger trap sizes, not the typical 1-1/4 inch scenario.