NEVADA CONTRACTOR C-1 PLUMBING EXAM | ALL
QUESTIONS AND ANSWERS (VERIFIED ANSWERS) PLUS
DETAILED RATIONALES | COMPLETE STUDY GUIDE |
DOWNLOAD INSTANT PDF 2027-2028
1. What is the primary function of a building trap in a commercial sanitary drainage
system when required by local plumbing codes?
A. To increase wastewater velocity through main building drains
B. To prevent the circulation of sewer gases from the municipal main into the building drainage
piping
C. To filter suspended solid waste before it enters public sewer mains
D. To regulate internal pipe pressure during high-volume discharge surges
Answer: B
A building trap provides a liquid seal barrier that blocks sewer gases and vermin from
traveling backward from the public sewer system into the private building drain network.
2. According to standard plumbing codes, what is the minimum required vertical drop for
a horizontal drainage pipe with a 2-inch diameter to maintain proper self-cleansing
velocity?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Answer: C
Horizontal drainage piping measuring 2 inches or less in diameter must be installed with a
minimum slope of 1/4 inch per foot to ensure wastewater flows fast enough to prevent solid
accumulation.
3. Which type of backflow prevention assembly is approved for high-hazard cross-
connections where there is a potential risk of health hazards or chemical contamination?
A. Dual check valve assembly
,B. Atmospheric vacuum breaker
C. Reduced pressure principle backflow preventer
D. Standard swing check valve
Answer: C
The reduced pressure principle assembly utilizes two independently operating check valves
and a relief valve, making it the premier choice for high-hazard cross-connections.
4. When sizing a copper water supply distribution system for a multi-story commercial
building, which factor is primarily used to determine main supply pipe diameters?
A. Total building square footage
B. Total number of plumbing fixtures expressed in Water Supply Fixture Units (WSFU)
C. Maximum outdoor ambient temperature fluctuations
D. Linear footage of vertical risers
Answer: B
Water supply piping is sized using Water Supply Fixture Units (WSFU), which quantify the
probable simultaneous hydraulic demand of all connected fixtures.
5. What is the minimum required depth below finished grade for installing exterior
building sewer piping to prevent freezing in moderate winter climates, unless otherwise
specified by local code?
A. 6 inches
B. 12 inches
C. 18 inches to 24 inches
D. 48 inches
Answer: C
Exterior building sewers must typically be buried at least 18 to 24 inches deep—or below the
local frost line—to protect the piping infrastructure from freezing and mechanical damage.
,6. Which joining method is standard for connecting rigid Type L copper water tubing
underground beneath a concrete slab foundation?
A. Soldered joints using 50/50 tin-lead solder
B. Brazed joints using high-temperature silver alloy filler metal
C. Flared mechanical compression fittings only
D. Push-fit plastic fittings without clamps
Answer: B
Underground copper water piping connections must be brazed using a filler metal melting
above 1,000 degrees Fahrenheit to withstand soil stress and corrosion.
7. What is the primary purpose of installing a thermal expansion tank in a closed domestic
water heating system?
A. To increase total hot water storage capacity during peak morning hours
B. To absorb increased water volume created during heating cycles and prevent dangerous
pressure relief valve discharges
C. To filter calcium and magnesium ions out of incoming municipal water
D. To boost water delivery pressure on upper residential stories
Answer: B
When water is heated in a closed system with a backflow preventer, it expands; an expansion
tank provides an air-cushion chamber to absorb this volume change safely.
8. Which code-approved test is required for verifying the gas tightness of a newly installed
fuel gas distribution piping system before initial operation?
A. Water column vacuum test at 1 psi
B. Air pressure test using a gauge showing a pressure not less than 1.5 times the proposed
working pressure
C. Dynamic flow test running all appliances simultaneously
D. Visual inspection without pressure application
Answer: B
, Fuel gas piping must pass a pneumatic pressure test using air, nitrogen, or inert gas at a
specified test pressure for a designated duration to confirm complete integrity.
9. What is the minimum trap seal depth required for standard plumbing fixtures under
model codes?
A. 1 inch
B. 2 inches (with a maximum of 4 inches)
C. 6 inches
D. 12 inches
Answer: B
Model plumbing codes mandate a trap seal depth between 2 and 4 inches to ensure adequate
water barrier retention against sewer gas migration despite normal evaporation.
10. When installing a commercial grease interceptor for a restaurant kitchen, where should
the flow control fitting be installed relative to the interceptor unit?
A. Downstream of the interceptor outlet
B. Upstream of the interceptor, as close as possible to the fixture being served
C. Directly inside the grease interceptor chamber
D. On the vent stack extending through the roof
Answer: B
A flow control fitting must be installed upstream of the grease interceptor to regulate
incoming wastewater velocity and air intake, ensuring proper grease separation efficiency.
11. Which type of plastic pipe is approved for interior hot and water distribution systems,
offering flexibility and resistance to freeze-burst damage?
A. PVC (Polyvinyl Chloride)
B. ABS (Acrylonitrile Butadiene Styrene)
C. PEX (Cross-linked Polyethylene)
D. DWV Cellular Core PVC
QUESTIONS AND ANSWERS (VERIFIED ANSWERS) PLUS
DETAILED RATIONALES | COMPLETE STUDY GUIDE |
DOWNLOAD INSTANT PDF 2027-2028
1. What is the primary function of a building trap in a commercial sanitary drainage
system when required by local plumbing codes?
A. To increase wastewater velocity through main building drains
B. To prevent the circulation of sewer gases from the municipal main into the building drainage
piping
C. To filter suspended solid waste before it enters public sewer mains
D. To regulate internal pipe pressure during high-volume discharge surges
Answer: B
A building trap provides a liquid seal barrier that blocks sewer gases and vermin from
traveling backward from the public sewer system into the private building drain network.
2. According to standard plumbing codes, what is the minimum required vertical drop for
a horizontal drainage pipe with a 2-inch diameter to maintain proper self-cleansing
velocity?
A. 1/16 inch per foot
B. 1/8 inch per foot
C. 1/4 inch per foot
D. 1/2 inch per foot
Answer: C
Horizontal drainage piping measuring 2 inches or less in diameter must be installed with a
minimum slope of 1/4 inch per foot to ensure wastewater flows fast enough to prevent solid
accumulation.
3. Which type of backflow prevention assembly is approved for high-hazard cross-
connections where there is a potential risk of health hazards or chemical contamination?
A. Dual check valve assembly
,B. Atmospheric vacuum breaker
C. Reduced pressure principle backflow preventer
D. Standard swing check valve
Answer: C
The reduced pressure principle assembly utilizes two independently operating check valves
and a relief valve, making it the premier choice for high-hazard cross-connections.
4. When sizing a copper water supply distribution system for a multi-story commercial
building, which factor is primarily used to determine main supply pipe diameters?
A. Total building square footage
B. Total number of plumbing fixtures expressed in Water Supply Fixture Units (WSFU)
C. Maximum outdoor ambient temperature fluctuations
D. Linear footage of vertical risers
Answer: B
Water supply piping is sized using Water Supply Fixture Units (WSFU), which quantify the
probable simultaneous hydraulic demand of all connected fixtures.
5. What is the minimum required depth below finished grade for installing exterior
building sewer piping to prevent freezing in moderate winter climates, unless otherwise
specified by local code?
A. 6 inches
B. 12 inches
C. 18 inches to 24 inches
D. 48 inches
Answer: C
Exterior building sewers must typically be buried at least 18 to 24 inches deep—or below the
local frost line—to protect the piping infrastructure from freezing and mechanical damage.
,6. Which joining method is standard for connecting rigid Type L copper water tubing
underground beneath a concrete slab foundation?
A. Soldered joints using 50/50 tin-lead solder
B. Brazed joints using high-temperature silver alloy filler metal
C. Flared mechanical compression fittings only
D. Push-fit plastic fittings without clamps
Answer: B
Underground copper water piping connections must be brazed using a filler metal melting
above 1,000 degrees Fahrenheit to withstand soil stress and corrosion.
7. What is the primary purpose of installing a thermal expansion tank in a closed domestic
water heating system?
A. To increase total hot water storage capacity during peak morning hours
B. To absorb increased water volume created during heating cycles and prevent dangerous
pressure relief valve discharges
C. To filter calcium and magnesium ions out of incoming municipal water
D. To boost water delivery pressure on upper residential stories
Answer: B
When water is heated in a closed system with a backflow preventer, it expands; an expansion
tank provides an air-cushion chamber to absorb this volume change safely.
8. Which code-approved test is required for verifying the gas tightness of a newly installed
fuel gas distribution piping system before initial operation?
A. Water column vacuum test at 1 psi
B. Air pressure test using a gauge showing a pressure not less than 1.5 times the proposed
working pressure
C. Dynamic flow test running all appliances simultaneously
D. Visual inspection without pressure application
Answer: B
, Fuel gas piping must pass a pneumatic pressure test using air, nitrogen, or inert gas at a
specified test pressure for a designated duration to confirm complete integrity.
9. What is the minimum trap seal depth required for standard plumbing fixtures under
model codes?
A. 1 inch
B. 2 inches (with a maximum of 4 inches)
C. 6 inches
D. 12 inches
Answer: B
Model plumbing codes mandate a trap seal depth between 2 and 4 inches to ensure adequate
water barrier retention against sewer gas migration despite normal evaporation.
10. When installing a commercial grease interceptor for a restaurant kitchen, where should
the flow control fitting be installed relative to the interceptor unit?
A. Downstream of the interceptor outlet
B. Upstream of the interceptor, as close as possible to the fixture being served
C. Directly inside the grease interceptor chamber
D. On the vent stack extending through the roof
Answer: B
A flow control fitting must be installed upstream of the grease interceptor to regulate
incoming wastewater velocity and air intake, ensuring proper grease separation efficiency.
11. Which type of plastic pipe is approved for interior hot and water distribution systems,
offering flexibility and resistance to freeze-burst damage?
A. PVC (Polyvinyl Chloride)
B. ABS (Acrylonitrile Butadiene Styrene)
C. PEX (Cross-linked Polyethylene)
D. DWV Cellular Core PVC
