306A Fixture Installation 3 — Questions and Answers
Question 1: What is the minimum size of a trap required for a residential bathtub?
- 1¼ inch
- 1½ inch (Correct answer)
- 2 inch
- 3 inch
Correct answer: 1½ inch
A residential bathtub requires a minimum 1½-inch trap to handle the drainage flow rate from the bathtub without causing excessive backup or slow drainage.
Question 2: When installing a bidet, what backflow prevention device is required?
- No backflow prevention is needed
- A vacuum breaker on the hot and cold supplies (Correct answer)
- An air gap on the drain only
- A check valve on the cold supply only
Correct answer: A vacuum breaker on the hot and cold supplies
A vacuum breaker is required on the bidet's hot and cold water supplies because the spray nozzle can be submerged below the flood level rim, creating a potential cross-connection with the potable water supply.
Question 3: What is the purpose of an 'overflow' on a lavatory basin?
- To allow air into the drain system
- To prevent the basin from overflowing if the drain is closed and the faucet is left running (Correct answer)
- To connect to the vent system
- To provide a secondary drain connection
Correct answer: To prevent the basin from overflowing if the drain is closed and the faucet is left running
The overflow opening near the top of the lavatory basin allows water to drain into the waste pipe if the basin is plugged and the faucet is left running, preventing water from spilling onto the floor.
Question 4: What is the correct sequence for roughing in a shower installation?
- Install the drain, then the valve body, then the framing
- Install the framing, set the drain to the correct height, install the valve body at the correct depth, and connect supply and drainage (Correct answer)
- Install the tile first, then cut openings for the valve and drain
- Install the showerhead first and work downward
Correct answer: Install the framing, set the drain to the correct height, install the valve body at the correct depth, and connect supply and drainage
The correct sequence is: frame the shower stall, set the drain at the correct height relative to the finished floor, install the valve body at the correct depth behind the finished wall surface, and connect all supply and drainage piping.
Question 5: What type of trap is required under a kitchen sink with a food waste disposer?
- S-trap for direct gravity flow
- P-trap connected to a properly vented drain (Correct answer)
- Running trap installed downstream
- No trap is needed because the disposer acts as one
Correct answer: P-trap connected to a properly vented drain
A P-trap connected to a properly vented drain is required under a kitchen sink with a food waste disposer. The disposer does not replace the need for a trap and vent to prevent sewer gas entry.
Question 6: When installing an accessible (barrier-free) water closet, what is the required seat height?
- 330 mm to 380 mm (13 to 15 inches)
- 380 mm to 430 mm (15 to 17 inches)
- 430 mm to 480 mm (17 to 19 inches) (Correct answer)
- 500 mm to 550 mm (20 to 22 inches)
Correct answer: 430 mm to 480 mm (17 to 19 inches)
Accessible water closets must have a seat height of 430 to 480 mm (17 to 19 inches) to facilitate easier transfer from a wheelchair and provide a more comfortable height for people with mobility limitations.
306A Fixture Installation 3
What is the minimum size of a trap required for a residential bathtub?