NC Plumbing, Heating & Fire Sprinkler
Contractors Board – Plumbing
Contractor Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf.
1. A North Carolina plumbing contractor is preparing to install a
complete plumbing system in a newly constructed commercial
building containing multiple toilet groups, lavatories, service sinks, a
commercial kitchen, and several mechanical rooms. The contractor
must determine the appropriate licensing classification before
entering into the contract. Which classification is intended for
plumbing work in commercial, industrial, institutional, and other non-
single-family-detached applications?
A. Plumbing Class II Contractor
B. Restricted Limited Plumbing Contractor
,C. Plumbing Class I Contractor
D. Plumbing Technician, Class II
Rationale: Plumbing Class I is the classification associated with plumbing
contracting for commercial, industrial, institutional, and other buildings
beyond the Class II single-family-detached residential scope.
2. During installation of a new sanitary drainage system, a contractor
must maintain proper slope on a horizontal drainage pipe. The
purpose of providing the required slope is primarily to:
A. Increase the pressure available at fixtures
B. Maintain adequate gravity flow and promote self-scouring of the
drainage pipe
C. Prevent water from entering the vent system
D. Eliminate the need for cleanouts
Rationale: Proper drainage slope allows wastewater and solids to move by
gravity while reducing the likelihood of sediment accumulation and
blockages within the piping.
3. A plumbing contractor installs a water closet using a drainage
connection that does not provide adequate venting. Several fixtures
subsequently exhibit slow drainage and trap siphonage. Which
plumbing principle has most likely been violated?
,A. Fixture-unit sizing
B. Water hammer protection
C. Protection of the trap seal through proper venting
D. Thermal expansion control
Rationale: Proper venting protects trap seals by limiting pressure
fluctuations that can siphon or blow the water out of fixture traps.
4. A contractor is sizing a building's water service and determines that
several fixtures may operate simultaneously. Which factor is most
important when applying a fixture-unit method for sizing the water
distribution system?
A. The total number of cleanouts
B. The total length of the sanitary vent system
C. The probable simultaneous demand represented by the assigned water-
supply fixture units
D. The number of roof drains
Rationale: Water-supply fixture units are used to estimate probable
demand rather than simply adding the maximum flow rate of every fixture
as though all fixtures operated simultaneously.
5. A building contains a group of plumbing fixtures located below the
level at which the public sewer can accept gravity discharge. What is
, generally required to move wastewater from this area into the
building sewer?
A. A pressure-reducing valve
B. A vacuum breaker
C. A thermal expansion tank
D. A sump or sewage ejector system designed for the application
Rationale: Where gravity drainage cannot discharge to the sewer, a
properly designed sump or sewage ejector system can collect and pump
wastewater to an acceptable discharge point.
6. A plumber installs a potable-water connection to equipment that
contains chemicals capable of contaminating the building's water
supply. Which principle requires protection against this potential
contamination?
A. Hydraulic balancing
B. Backflow prevention
C. Drainage fixture loading
D. Pipe insulation
Rationale: Backflow prevention protects potable water from
contamination caused by backsiphonage or backpressure from a connected
nonpotable system.
Contractors Board – Plumbing
Contractor Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationale 2027 Q&A| Instant
Download Pdf.
1. A North Carolina plumbing contractor is preparing to install a
complete plumbing system in a newly constructed commercial
building containing multiple toilet groups, lavatories, service sinks, a
commercial kitchen, and several mechanical rooms. The contractor
must determine the appropriate licensing classification before
entering into the contract. Which classification is intended for
plumbing work in commercial, industrial, institutional, and other non-
single-family-detached applications?
A. Plumbing Class II Contractor
B. Restricted Limited Plumbing Contractor
,C. Plumbing Class I Contractor
D. Plumbing Technician, Class II
Rationale: Plumbing Class I is the classification associated with plumbing
contracting for commercial, industrial, institutional, and other buildings
beyond the Class II single-family-detached residential scope.
2. During installation of a new sanitary drainage system, a contractor
must maintain proper slope on a horizontal drainage pipe. The
purpose of providing the required slope is primarily to:
A. Increase the pressure available at fixtures
B. Maintain adequate gravity flow and promote self-scouring of the
drainage pipe
C. Prevent water from entering the vent system
D. Eliminate the need for cleanouts
Rationale: Proper drainage slope allows wastewater and solids to move by
gravity while reducing the likelihood of sediment accumulation and
blockages within the piping.
3. A plumbing contractor installs a water closet using a drainage
connection that does not provide adequate venting. Several fixtures
subsequently exhibit slow drainage and trap siphonage. Which
plumbing principle has most likely been violated?
,A. Fixture-unit sizing
B. Water hammer protection
C. Protection of the trap seal through proper venting
D. Thermal expansion control
Rationale: Proper venting protects trap seals by limiting pressure
fluctuations that can siphon or blow the water out of fixture traps.
4. A contractor is sizing a building's water service and determines that
several fixtures may operate simultaneously. Which factor is most
important when applying a fixture-unit method for sizing the water
distribution system?
A. The total number of cleanouts
B. The total length of the sanitary vent system
C. The probable simultaneous demand represented by the assigned water-
supply fixture units
D. The number of roof drains
Rationale: Water-supply fixture units are used to estimate probable
demand rather than simply adding the maximum flow rate of every fixture
as though all fixtures operated simultaneously.
5. A building contains a group of plumbing fixtures located below the
level at which the public sewer can accept gravity discharge. What is
, generally required to move wastewater from this area into the
building sewer?
A. A pressure-reducing valve
B. A vacuum breaker
C. A thermal expansion tank
D. A sump or sewage ejector system designed for the application
Rationale: Where gravity drainage cannot discharge to the sewer, a
properly designed sump or sewage ejector system can collect and pump
wastewater to an acceptable discharge point.
6. A plumber installs a potable-water connection to equipment that
contains chemicals capable of contaminating the building's water
supply. Which principle requires protection against this potential
contamination?
A. Hydraulic balancing
B. Backflow prevention
C. Drainage fixture loading
D. Pipe insulation
Rationale: Backflow prevention protects potable water from
contamination caused by backsiphonage or backpressure from a connected
nonpotable system.
