306A National Plumbing Code of Canada 1 — Questions and Answers
Question 1: What is the minimum size of a building drain serving a single water closet according to the National Plumbing Code of Canada?
- 2 inch
- 3 inch (Correct answer)
- 4 inch
- 6 inch
Correct answer: 3 inch
The National Plumbing Code of Canada specifies a minimum 3-inch diameter for a building drain serving a water closet to ensure adequate flow and prevent blockages.
Question 2: According to the Code, what is the maximum distance a P-trap can be from the vent connection?
- 1.2 m for 1¼ inch trap (Correct answer)
- 1.5 m for 1¼ inch trap
- 2.0 m for 1¼ inch trap
- 3.0 m for 1¼ inch trap
Correct answer: 1.2 m for 1¼ inch trap
The Code limits the trap-to-vent distance to 1.2 m for a 1¼-inch trap arm to maintain the trap seal and prevent siphonage.
Question 3: What minimum slope is required for a 4-inch horizontal drainage pipe in the National Plumbing Code of Canada?
- 1 in 25 (1%)
- 1 in 50 (2%) (Correct answer)
- 1 in 100 (1%)
- 1 in 10 (10%)
Correct answer: 1 in 50 (2%)
A 4-inch horizontal drain requires a minimum slope of 1 in 50 (approximately 2%) to maintain self-cleansing velocity and prevent solid deposits.
Question 4: How many fixture units does a standard bathtub have according to the National Plumbing Code of Canada?
- 1 fixture unit
- 2 fixture units (Correct answer)
- 3 fixture units
- 4 fixture units
Correct answer: 2 fixture units
A bathtub is rated at 2 fixture units in the National Plumbing Code of Canada, reflecting its moderate water demand and drainage load.
Question 5: What is the minimum depth of a trap seal required by the National Plumbing Code of Canada?
- 25 mm
- 50 mm (Correct answer)
- 75 mm
- 100 mm
Correct answer: 50 mm
The Code requires a minimum trap seal depth of 50 mm (approximately 2 inches) to prevent sewer gases from entering occupied spaces.
Question 6: According to the Code, when is a backwater valve required on a building drain?
- On all building drains
- When fixtures are below the level of the street or the manhole cover (Correct answer)
- Only on commercial buildings
- Only when required by the building owner
Correct answer: When fixtures are below the level of the street or the manhole cover
A backwater valve is required when fixtures are installed below the level of the adjacent street or manhole cover to prevent sewage backup during surcharge conditions.
306A National Plumbing Code of Canada 1
What is the minimum size of a building drain serving a single water closet according to the National Plumbing Code of Canada?