NC Plumbing, Heating & Fire Sprinkler
Contractors Board – Plumbing Contractor
Examination (Limited) Questions and Correct
Answers (Verified Answers) Plus Rationale
2027 Q&A| Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent water hammer
C. To prevent sewer gases from entering a building
D. To increase drainage velocity
Rationale: A plumbing trap maintains a water seal between the
drainage system and the occupied space. This water seal helps prevent
sewer gases and odors from entering the building while still allowing
wastewater to drain.
2. Which fitting is generally used to change the direction of a drainage
pipe while providing a relatively smooth flow path?
,A. Tee
B. Wye
C. Coupling
D. Cap
Rationale: A wye fitting is designed to introduce a branch into a
drainage system at an angle that promotes smoother wastewater flow.
Standard tees are generally not preferred for horizontal drainage-flow
changes because they can create turbulence and resistance.
3. What is the main function of a plumbing vent system?
A. Increase water pressure
B. Supply drinking water
C. Protect trap seals and allow air into the drainage system
D. Increase the temperature of wastewater
Rationale: Drainage systems require air movement to maintain proper
pressure relationships. Venting helps prevent siphonage and
backpressure that could otherwise remove water from fixture traps.
4. A trap seal is most directly threatened by which condition?
A. Properly sized water piping
B. Siphonage
,C. Adequate venting
D. Correct fixture installation
Rationale: Siphonage can draw the water out of a trap when
wastewater flows through connected piping. Proper venting helps
equalize pressure and protect the trap seal.
5. Which material is commonly used for residential cold-water
distribution piping?
A. Cast iron soil pipe
B. PEX
C. Clay sewer pipe
D. Vitrified tile
Rationale: PEX is widely used for potable-water distribution because it is
flexible, corrosion-resistant, and suitable for hot- and cold-water
applications when properly listed and installed.
6. What is the purpose of a cleanout in a drainage system?
A. To increase water pressure
B. To measure water temperature
C. To provide access for cleaning and removing obstructions
D. To prevent freezing of water lines
, Rationale: Cleanouts provide access to drainage piping so that
blockages can be located and removed using appropriate equipment.
7. Which condition can contribute to excessive pressure loss in a
water-distribution system?
A. Oversized piping
B. Short pipe runs
C. Undersized piping
D. Reduced number of fittings
Rationale: Undersized piping increases frictional resistance and can
produce excessive pressure loss, especially when several fixtures
operate simultaneously.
8. What device is commonly used to prevent contaminated water
from flowing backward into the potable-water supply?
A. Pressure gauge
B. Expansion tank
C. Backflow preventer
D. Cleanout
Rationale: Backflow-prevention devices protect potable-water systems
from contamination caused by reverse flow. The appropriate device
depends on the degree and type of hazard.
Contractors Board – Plumbing Contractor
Examination (Limited) Questions and Correct
Answers (Verified Answers) Plus Rationale
2027 Q&A| Instant Download Pdf
1. What is the primary purpose of a plumbing trap?
A. To increase water pressure
B. To prevent water hammer
C. To prevent sewer gases from entering a building
D. To increase drainage velocity
Rationale: A plumbing trap maintains a water seal between the
drainage system and the occupied space. This water seal helps prevent
sewer gases and odors from entering the building while still allowing
wastewater to drain.
2. Which fitting is generally used to change the direction of a drainage
pipe while providing a relatively smooth flow path?
,A. Tee
B. Wye
C. Coupling
D. Cap
Rationale: A wye fitting is designed to introduce a branch into a
drainage system at an angle that promotes smoother wastewater flow.
Standard tees are generally not preferred for horizontal drainage-flow
changes because they can create turbulence and resistance.
3. What is the main function of a plumbing vent system?
A. Increase water pressure
B. Supply drinking water
C. Protect trap seals and allow air into the drainage system
D. Increase the temperature of wastewater
Rationale: Drainage systems require air movement to maintain proper
pressure relationships. Venting helps prevent siphonage and
backpressure that could otherwise remove water from fixture traps.
4. A trap seal is most directly threatened by which condition?
A. Properly sized water piping
B. Siphonage
,C. Adequate venting
D. Correct fixture installation
Rationale: Siphonage can draw the water out of a trap when
wastewater flows through connected piping. Proper venting helps
equalize pressure and protect the trap seal.
5. Which material is commonly used for residential cold-water
distribution piping?
A. Cast iron soil pipe
B. PEX
C. Clay sewer pipe
D. Vitrified tile
Rationale: PEX is widely used for potable-water distribution because it is
flexible, corrosion-resistant, and suitable for hot- and cold-water
applications when properly listed and installed.
6. What is the purpose of a cleanout in a drainage system?
A. To increase water pressure
B. To measure water temperature
C. To provide access for cleaning and removing obstructions
D. To prevent freezing of water lines
, Rationale: Cleanouts provide access to drainage piping so that
blockages can be located and removed using appropriate equipment.
7. Which condition can contribute to excessive pressure loss in a
water-distribution system?
A. Oversized piping
B. Short pipe runs
C. Undersized piping
D. Reduced number of fittings
Rationale: Undersized piping increases frictional resistance and can
produce excessive pressure loss, especially when several fixtures
operate simultaneously.
8. What device is commonly used to prevent contaminated water
from flowing backward into the potable-water supply?
A. Pressure gauge
B. Expansion tank
C. Backflow preventer
D. Cleanout
Rationale: Backflow-prevention devices protect potable-water systems
from contamination caused by reverse flow. The appropriate device
depends on the degree and type of hazard.
