Plumber Red Seal · Question
What is the minimum trap arm length for a P-trap, as measured from the trap weir to the vent fitting?
The NPC specifies a minimum trap arm length of two times the pipe diameter. This ensures a sufficient length of pipe to prevent the siphoning action of draining
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Question: What is the minimum trap arm length for a P-trap, as measured from the trap weir to the vent fitting?
Answer options:
- One pipe diameter ✅ Two pipe diameters
- Half a pipe diameter
- There is no specified minimum length
Correct answer: Two pipe diameters
Explanation: The NPC specifies a minimum trap arm length of two times the pipe diameter. This ensures a sufficient length of pipe to prevent the siphoning action of draining water from pulling the trap seal out.
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