ICC G24 National Standard Master Plumber Exam — Questions and Answers

Question 1: What is the correct way to use Teflon tape (PTFE tape) on threaded pipe joints?

Wrap clockwise in the direction of the threads (2–3 wraps) (Correct answer)
Use on all types of pipe joints including solvent-welded
Apply only to female threads
Wrap counterclockwise against the thread direction

Correct answer: Wrap clockwise in the direction of the threads (2–3 wraps)

Teflon tape is wrapped clockwise in the direction of the threads (2 to 3 wraps) so that tightening the joint winds the tape tighter rather than unwinding it.

Question 2: Which appliance connection typically REQUIRES a flexible gas connector rather than rigid pipe?

Gas range/stove (Correct answer)
Gas-fired water heater
Gas fireplace insert with fixed framing
Gas furnace with fixed installation

Correct answer: Gas range/stove

A gas range requires a flexible connector because it is a movable appliance that must be pulled out periodically for cleaning and service, making rigid connections impractical and prone to damage.

Question 3: What is the function of the anode rod in a tank-type water heater?

To filter sediment
To regulate water pressure
To sacrifice itself to corrosion, protecting the tank lining (Correct answer)
To heat the water

Correct answer: To sacrifice itself to corrosion, protecting the tank lining

The anode rod (sacrificial anode) is made of magnesium or aluminum and corrodes preferentially to protect the steel tank lining from rust.

Question 4: What is the term for a fitting that connects a branch drain to a vertical stack?

Cleanout
Sanitary tee (Correct answer)
P-trap
Wye fitting

Correct answer: Sanitary tee

A sanitary tee is used to connect branch drain lines to a vertical stack, with its swept inlet directing flow downward to prevent turbulence.

Question 5: Where should plumber's putty NOT be used?

On marble, granite, or plastic fixtures (Correct answer)
Around faucet bases on porcelain sinks
Around the base of pop-up drains
Under drain basket strainers in stainless sinks

Correct answer: On marble, granite, or plastic fixtures

Plumber's putty can stain marble, granite, and plastic fixtures — silicone sealant should be used on these surfaces instead.

Question 6: What does 'Schedule' refer to in pipe specifications (e.g., Schedule 40)?

The pipe's wall thickness (Correct answer)
The pipe's diameter
The pipe's pressure rating
The pipe's installation timeline

Correct answer: The pipe's wall thickness

Schedule refers to the wall thickness of a pipe, with higher schedule numbers indicating thicker walls and greater pressure ratings.

Question 7: What type of wax ring alternative provides a better seal for uneven floors when installing a toilet?

Teflon tape wrap
Silicone caulk only
Double-stacked wax ring or foam gasket seal (Correct answer)
Plumber's putty

Correct answer: Double-stacked wax ring or foam gasket seal

For uneven floors or extra-thick flooring, a double-stacked wax ring or a foam gasket seal (like Fluidmaster) provides a better, adjustable seal than a single wax ring.

Question 8: What is the maximum allowed length for a flexible gas connector hose to a residential appliance?

6 feet (Correct answer)
12 feet
10 feet
3 feet

Correct answer: 6 feet

Most codes limit flexible gas connectors to 6 feet maximum to reduce the risk of mechanical damage, kinking, or accidental disconnection.

Question 9: What is the minimum water pressure required at a residential fixture per the IPC?

20 psi (Correct answer)
60 psi
40 psi
15 psi

Correct answer: 20 psi

The IPC requires a minimum static water pressure of 20 psi at every plumbing fixture to ensure adequate flow for proper operation.

Question 10: What does a pressure and temperature (P&T) relief valve on a water heater do?

Automatically releases water if pressure or temperature exceeds safe limits (Correct answer)
Regulates incoming water pressure
Prevents cold water from entering the tank
Controls the thermostat setting

Correct answer: Automatically releases water if pressure or temperature exceeds safe limits

The P&T relief valve is a critical safety device that automatically opens to release water and pressure if the tank exceeds safe temperature (210°F) or pressure (150 psi) limits.

Question 11: What is the purpose of insulating water supply pipes in unconditioned spaces?

To meet electrical code requirements
To prevent freezing and reduce heat loss from hot water lines (Correct answer)
To prevent water pressure loss
To reduce water noise in walls

Correct answer: To prevent freezing and reduce heat loss from hot water lines

Insulating pipes in unconditioned spaces (attics, crawl spaces, garages) prevents freezing in cold climates and reduces heat loss from hot water supply lines.

Question 12: What is the minimum burial depth required for a natural gas service line running underground to a residential building?

12 inches (Correct answer)
36 inches
6 inches
18 inches

Correct answer: 12 inches

Natural gas service lines must be buried at least 12 inches deep under normal conditions to protect them from surface disturbance and damage.

Question 13: What is the maximum typical low-pressure natural gas system operating pressure for residential appliances?

2 psi
10 psi
0.5 psi (14 in. WC) (Correct answer)
5 psi

Correct answer: 0.5 psi (14 in. WC)

Residential natural gas appliances typically operate at low pressure — commonly 7 in. WC for most appliances, with a maximum of about 14 in. WC (0.5 psi) at the appliance.

Question 14: What is the purpose of a manometer in plumbing work?

To detect pipe vibration
To measure gas or water pressure in a system (Correct answer)
To test drain flow rate
To measure pipe diameter

Correct answer: To measure gas or water pressure in a system

A manometer measures pressure in gas or water systems, helping verify that supply pressure is within the correct range for proper appliance operation.

Question 15: What personal protective equipment (PPE) is most important when soldering copper pipe?

Steel-toed boots
Safety glasses and heat-resistant gloves (Correct answer)
Dust mask only
Ear protection

Correct answer: Safety glasses and heat-resistant gloves

Safety glasses protect against flux splatter and hot solder, while heat-resistant gloves protect against burns when handling hot pipe and fittings during sweating operations.

Question 16: What is a backflow preventer and when is it required on a residential irrigation system?

A device preventing contaminated water from flowing back into the potable supply; required on all irrigation connections (Correct answer)
A filter for irrigation water; required in hard water areas
A flow meter; required for rebate programs
A pressure booster; required when pressure is below 30 psi

Correct answer: A device preventing contaminated water from flowing back into the potable supply; required on all irrigation connections

A backflow preventer stops potentially contaminated irrigation water (containing fertilizers, pesticides) from flowing back into the potable water supply, and is required on all residential irrigation connections.

Question 17: What type of pipe is most commonly used for natural gas distribution inside residential buildings?

PVC plastic pipe
Copper tubing
Black steel pipe (Correct answer)
CPVC pipe

Correct answer: Black steel pipe

Black steel pipe is the most widely approved material for interior natural gas distribution due to its strength, durability, and resistance to permeation.

Question 18: What should a plumber do before cutting into any wall or floor to run new pipe?

Check for existing utilities using a stud finder, pipe locator, or plans (Correct answer)
Turn off the main water supply
Notify the building owner only
Apply for a permit before any investigation

Correct answer: Check for existing utilities using a stud finder, pipe locator, or plans

Before cutting into any wall or floor, a plumber must verify the location of existing plumbing, electrical wiring, and structural members to avoid dangerous and costly damage.

Question 19: What is the purpose of applying joint compound (pipe dope) to threaded connections?

To mark pipe for cutting
To lubricate threads for easier assembly and create a leak-tight seal on threaded connections (Correct answer)
To permanently bond threaded fittings so they cannot be removed
To prevent corrosion only

Correct answer: To lubricate threads for easier assembly and create a leak-tight seal on threaded connections

Pipe dope (thread sealant compound) lubricates threads to prevent galling during assembly and seals the threaded connection against leaks, suitable for both water and gas.

Question 20: Which pipe joint method uses heat to melt and fuse thermoplastic pipes together?

Solvent welding
Compression fitting
Push-fit connection
Butt fusion (Correct answer)

Correct answer: Butt fusion

Butt fusion uses a heating plate to melt the ends of thermoplastic pipes, which are then pressed together to form a permanent fused joint.

Question 21: What is a flapper valve in a toilet and what does it do?

A check valve in the supply line
A rubber seal that opens during flushing to release tank water into the bowl (Correct answer)
A valve that controls water entering the tank
A float that controls water level

Correct answer: A rubber seal that opens during flushing to release tank water into the bowl

The flapper is a rubber seal at the bottom of the toilet tank that lifts when the toilet is flushed, allowing tank water to flow into the bowl, then reseals the tank.

Question 22: Which regulation requires plumbers working on lead service lines to follow specific work practice standards to protect workers and residents?

Uniform Plumbing Code Appendix D
EPA Lead and Copper Rule and OSHA Lead Standard (Correct answer)
Safe Drinking Water Act only
Clean Water Act

Correct answer: EPA Lead and Copper Rule and OSHA Lead Standard

The EPA Lead and Copper Rule governs lead service line replacement practices, while the OSHA Lead Standard sets worker protection requirements including PPE and air monitoring during lead pipe work.

Question 23: What type of trap is prohibited in most US plumbing codes?

Drum trap
P-trap
S-trap (Correct answer)
Running trap

Correct answer: S-trap

S-traps are prohibited because they are prone to self-siphonage, which can empty the water seal and allow sewer gases into the building.

Question 24: What tool is used to cut copper pipe cleanly without burrs?

Pipe cutter (tube cutter) (Correct answer)
Reciprocating saw
Hacksaw only
Angle grinder

Correct answer: Pipe cutter (tube cutter)

A pipe cutter (tube cutter) uses a hardened wheel to score and cut copper pipe cleanly with minimal burring, rotating around the pipe until it cuts through.

Question 25: What is 'potable water' and why is it important in plumbing codes?

Heated water above 120°F
Water treated with chlorine only
Recycled greywater
Water that is safe for human consumption and meets EPA standards (Correct answer)

Correct answer: Water that is safe for human consumption and meets EPA standards

Potable water is water that is safe for human consumption, cooking, and personal hygiene, and plumbing codes contain extensive provisions to protect it from contamination.

Question 26: What is a 'stack vent' in a plumbing system?

A vent that runs horizontally to outside air
The extension of a soil or waste stack above the highest fixture connection (Correct answer)
A mechanical vent device
A vent serving only one fixture

Correct answer: The extension of a soil or waste stack above the highest fixture connection

A stack vent is the upper portion of a soil or waste stack that extends above the highest fixture connection and terminates in open air to vent the system.

Question 27: What is the correct way to measure the length of pipe needed for a socket-type fitting connection?

Add the socket depth to each end of the face-to-face measurement (Correct answer)
Measure only the centerline distance
Subtract the socket depth from the total length
Face-to-face measurement only

Correct answer: Add the socket depth to each end of the face-to-face measurement

When calculating pipe length for socket fittings, you must add the socket depth for each fitting end to the face-to-face measurement to get the total cut length.

Question 28: Which model plumbing code is most widely adopted in the United States?

International Plumbing Code (IPC)
Uniform Plumbing Code (UPC)
National Standard Plumbing Code (NSPC)
Both UPC and IPC are widely adopted (Correct answer)

Correct answer: Both UPC and IPC are widely adopted

Both the Uniform Plumbing Code (UPC) and the International Plumbing Code (IPC) are widely adopted in the US, with western states generally using UPC and eastern states generally using IPC.

Question 29: What is the purpose of bonding a metal water pipe system to the electrical ground?

To equalize electrical potential and prevent electric shock from stray currents (Correct answer)
To improve water pressure
To prevent water hammer
To reduce pipe corrosion from chemical reactions

Correct answer: To equalize electrical potential and prevent electric shock from stray currents

Bonding metal pipes to the electrical grounding system equalizes electrical potential across the plumbing system, protecting occupants from electric shock due to stray currents or ground faults.

Question 30: Why must CSST (corrugated stainless steel tubing) gas piping be bonded to the electrical grounding system?

To meet color-coding identification requirements
To protect the thin stainless steel walls from damage caused by lightning-induced electrical arcing (Correct answer)
To increase gas flow capacity
To reduce operating gas pressure

Correct answer: To protect the thin stainless steel walls from damage caused by lightning-induced electrical arcing

CSST's thin corrugated stainless steel walls are vulnerable to arcing from indirect lightning strikes, which can burn through the material and cause gas leaks; bonding diverts this energy safely.

Question 31: What is the purpose of a check valve in a water supply system?

To allow water flow in only one direction (Correct answer)
To filter debris from water
To reduce water pressure
To measure water consumption

Correct answer: To allow water flow in only one direction

A check valve allows water to flow in only one direction, preventing backflow that could contaminate the supply system or damage equipment.

Question 32: What is hydrostatic testing in plumbing?

Testing water temperature at fixtures
Testing water quality for contaminants
Measuring water flow velocity
Pressure testing a plumbing system by filling it with water and applying specified pressure to check for leaks (Correct answer)

Correct answer: Pressure testing a plumbing system by filling it with water and applying specified pressure to check for leaks

Hydrostatic testing fills the plumbing system with water and pressurizes it to a specified level (typically 1.5 times working pressure) to detect any leaks before walls are closed.

Question 33: What is the minimum diameter for a building drain that receives discharge from a water closet (toilet)?

6 inches
2 inches
3 inches (Correct answer)
4 inches

Correct answer: 3 inches

The IPC requires a minimum 3-inch diameter for any drain pipe that receives waste from a water closet (toilet) to accommodate solid waste.

Question 34: Which type of fitting is required when changing direction from horizontal to vertical in a drain system?

Short-turn 90-degree elbow
Sanitary tee
Cross fitting
Long-sweep 90-degree elbow (Correct answer)

Correct answer: Long-sweep 90-degree elbow

A long-sweep 90-degree elbow is required for direction changes in drain lines because its gradual curve maintains flow velocity and prevents blockages.

Question 35: What is the maximum flow rate for a residential showerhead under current federal EPAct standards?

2.5 GPM (Correct answer)
2.0 GPM
3.0 GPM
1.5 GPM

Correct answer: 2.5 GPM

Federal EPAct standards set the maximum flow rate for residential showerheads at 2.5 gallons per minute (GPM) at 80 psi.

Question 36: What tool is used to make flared connections on soft copper or aluminum tubing?

Swage tool
Flaring tool (Correct answer)
Pipe bender
Pipe expander

Correct answer: Flaring tool

A flaring tool creates a cone-shaped flare at the end of soft copper or aluminum tubing, which creates a leak-tight mechanical seal when compressed by a flare nut fitting.

Question 37: What is the minimum required separation between a gas meter and electrical service equipment?

5 feet
3 feet (Correct answer)
No minimum separation required
10 feet

Correct answer: 3 feet

Most codes require at least 3 feet of clearance between a gas meter and electrical service equipment to reduce the risk of a spark igniting a gas leak.

Question 38: What is a pipe bender used for and when is it preferred over fittings?

Bending soft copper or conduit to change direction without fittings; preferred to reduce joint count and cost (Correct answer)
Straightening bent pipe; preferred for repairs
Flaring pipe ends; preferred for gas connections
Measuring pipe diameter; preferred on large-diameter pipe

Correct answer: Bending soft copper or conduit to change direction without fittings; preferred to reduce joint count and cost

A pipe bender creates smooth directional changes in soft copper or conduit without fittings, reducing the number of potential leak points and the cost of fittings.

Question 39: What does the term 'authority having jurisdiction' (AHJ) mean in plumbing codes?

The manufacturer of plumbing products
The local government body or official responsible for enforcing building and plumbing codes (Correct answer)
The national plumbing standards board
The plumber's licensing board

Correct answer: The local government body or official responsible for enforcing building and plumbing codes

The AHJ is the local organization, office, or individual responsible for enforcing the requirements of the applicable plumbing code in that jurisdiction.

Question 40: What is the standard color code for cold water supply lines using PEX tubing?

White
Green
Yellow
Blue (Correct answer)

Correct answer: Blue

Blue PEX tubing is the standard color code for cold water supply lines, while red is used for hot water.

Question 41: What is the minimum height above a roof surface for a vent terminal (vent through roof)?

6 inches
18 inches
12 inches (Correct answer)
2 inches

Correct answer: 12 inches

The IPC requires vent terminals to extend at least 6 inches above the roof surface to prevent blockage by debris, snow, or ice.

Question 42: What additive is mixed into natural gas to give it its distinctive warning odor?

Propane
Methane
Mercaptan (ethanethiol) (Correct answer)
Carbon monoxide

Correct answer: Mercaptan (ethanethiol)

Mercaptan (ethanethiol) is added to otherwise odorless natural gas so people can detect leaks by smell before concentrations reach dangerous levels.

Question 43: What is the ADA-required height range for a water closet (toilet) seat for accessible bathrooms?

17–19 inches AFF (Correct answer)
14–15 inches AFF
20–22 inches AFF
24–26 inches AFF

Correct answer: 17–19 inches AFF

ADA standards require accessible toilet seats to be between 17 and 19 inches above the finished floor to allow easier transfer for wheelchair users.

Question 44: What is 'rough-in plumbing'?

Temporary plumbing installed during construction
Plumbing installed without permits
The installation of supply and drain pipes before walls and floors are finished (Correct answer)
The initial flushing of new pipe systems

Correct answer: The installation of supply and drain pipes before walls and floors are finished

Rough-in plumbing refers to the installation of supply and drain/vent pipes during the framing stage, before walls, ceilings, and floors are closed in.

Question 45: Which pipe material is best suited for underground sewer lines due to its chemical resistance?

PEX
Schedule 40 PVC (Correct answer)
Copper
Galvanized steel

Correct answer: Schedule 40 PVC

Schedule 40 PVC is widely used for underground sewer lines because of its excellent chemical resistance and durability in soil environments.

Question 46: What is 'indirect waste' in plumbing?

Discharge from an appliance that drains into an open receptor rather than directly to the drainage system (Correct answer)
Waste that bypasses the main drain stack
Waste from outdoor fixtures
Greywater reused from sinks

Correct answer: Discharge from an appliance that drains into an open receptor rather than directly to the drainage system

Indirect waste is when an appliance (like a dishwasher or HVAC condensate line) drains into an open air gap receptor rather than connecting directly to the sanitary drainage system.

Question 47: What type of valve is used as the main shutoff valve for a residential water supply?

Ball valve or gate valve (Correct answer)
Needle valve
Butterfly valve
Globe valve

Correct answer: Ball valve or gate valve

Ball valves or gate valves are used as main shutoff valves because they provide full-bore flow when open and a complete shutoff when closed.

Question 48: What is the purpose of a lead-free requirement in US plumbing codes?

To protect potable water from lead contamination in fittings and solder (Correct answer)
To meet recycling standards
To reduce installation costs
To reduce pipe weight

Correct answer: To protect potable water from lead contamination in fittings and solder

Since 2014, the Safe Drinking Water Act requires all plumbing fittings, fixtures, and solder in contact with potable water to be lead-free (less than 0.25% weighted average lead content).

Question 49: What is a manifold system in residential plumbing?

A drain collection system under a slab
A manifold for gas distribution
A type of water softener
A multi-outlet distribution center that feeds individual supply lines to each fixture (Correct answer)

Correct answer: A multi-outlet distribution center that feeds individual supply lines to each fixture

A plumbing manifold is a central distribution hub, typically used with PEX, that feeds dedicated supply lines to each fixture for individual shutoff capability.

Question 50: Where must a manual gas shutoff valve be installed for a new gas appliance?

In the main electrical panel room
Within 6 feet of the appliance in the same room, in an accessible location (Correct answer)
At the gas meter only
Outside the building near the foundation

Correct answer: Within 6 feet of the appliance in the same room, in an accessible location

Code requires an accessible manual shutoff valve within 6 feet of each gas appliance in the same room so it can be quickly reached in an emergency.

Question 51: What is the purpose of a P-trap under a kitchen sink?

To filter food particles from drain water
To hold a water seal that blocks sewer gases from entering (Correct answer)
To connect hot and cold supply lines
To regulate water pressure to the faucet

Correct answer: To hold a water seal that blocks sewer gases from entering

The P-trap under a sink holds a water seal that physically blocks sewer gases from rising up through the drain opening into the living space.

Question 52: What safety feature is required on a tub/shower valve to prevent scalding?

Backflow preventer
Vacuum breaker
Pressure balancing valve or thermostatic mixing valve (Correct answer)
Check valve

Correct answer: Pressure balancing valve or thermostatic mixing valve

A pressure-balancing or thermostatic mixing valve is required on tub/shower controls to prevent scalding when a toilet is flushed or another fixture is used simultaneously.

Question 53: What type of faucet valve uses a rotating ceramic disc to control water flow?

Ceramic disc valve (Correct answer)
Ball valve faucet
Cartridge valve
Compression valve

Correct answer: Ceramic disc valve

A ceramic disc valve uses two precisely mated ceramic discs that rotate against each other to control flow and temperature, offering long life and precise control.

Question 54: What is the minimum burial depth for a residential water service line in a climate with a 36-inch frost depth?

At or below the local frost line (36 inches) (Correct answer)
24 inches below grade
12 inches below grade
48 inches below grade always

Correct answer: At or below the local frost line (36 inches)

Water service lines must be buried at or below the local frost line depth to prevent freezing; if the frost depth is 36 inches, the pipe must be buried at least 36 inches deep.

Question 55: What color jacket is standard on corrugated stainless steel tubing (CSST) used for gas piping?

Yellow (Correct answer)
Orange
Black
Red

Correct answer: Yellow

CSST gas piping is covered with a yellow plastic jacket, universally recognized as a gas-service identifier and providing physical protection.

Question 56: ABS pipe is typically used in which application?

Gas lines
High-pressure water mains
Drain, waste, and vent systems (Correct answer)
Hot water supply

Correct answer: Drain, waste, and vent systems

ABS (acrylonitrile butadiene styrene) pipe is primarily used in drain, waste, and vent (DWV) systems due to its impact resistance and affordability.

Question 57: What prevents sewer gases from entering a building through a floor drain that is rarely used?

The floor drain's check valve
Negative pressure in the drain
A trap primer or trap seal preservative (Correct answer)
The weight of the drain cover

Correct answer: A trap primer or trap seal preservative

A trap primer periodically adds water to the floor drain trap to replenish the water seal that evaporates in infrequently used drains.

Question 58: What chemical is used to test for gas leaks in a plumbing system?

Solvent cement
Soap solution or electronic leak detector (Correct answer)
Chlorine bleach
Pipe dope

Correct answer: Soap solution or electronic leak detector

A soap solution applied to gas fittings and joints will bubble at any leak point; electronic gas detectors are also used for more sensitive or hard-to-reach inspections.

Question 59: What is the maximum water pressure allowed at a residential service entrance without a pressure reducing valve (PRV)?

125 psi
60 psi
80 psi (Correct answer)
100 psi

Correct answer: 80 psi

Water pressure exceeding 80 psi at the service entrance requires a pressure reducing valve (PRV) to protect the plumbing system and appliances.

Question 60: What is a 'fixture unit' (DFU) used for in plumbing design?

A unit to calculate the drainage load that a fixture imposes on the drainage system (Correct answer)
A standard pipe length measurement
A measure of water supply pressure
A measurement of pipe wall thickness

Correct answer: A unit to calculate the drainage load that a fixture imposes on the drainage system

A drainage fixture unit (DFU) is a standardized measure of the probable discharge from plumbing fixtures, used to size drainage pipes and determine system capacity.

Question 61: What is the correct rough-in height for a bathroom lavatory (sink) drain?

12 inches AFF
16–20 inches AFF (Correct answer)
24 inches AFF
30 inches AFF

Correct answer: 16–20 inches AFF

Standard lavatory drain rough-in height is 16 to 20 inches above the finished floor (AFF), with 18 to 20 inches being most common for standard-height vanities.

Question 62: What tool is used to cut large-diameter cast iron pipe in the field?

Snap cutter (soil pipe cutter) or angle grinder with cutting disc (Correct answer)
Reciprocating saw only
Hacksaw
Pipe cutter wheel only

Correct answer: Snap cutter (soil pipe cutter) or angle grinder with cutting disc

A snap cutter (soil pipe cutter) uses hardened cutting wheels on a chain to score around large cast iron pipe and snap it cleanly, or an angle grinder with a cutting disc can be used.

Question 63: What is the purpose of a tempering valve (mixing valve) on a water heater?

To measure water flow rate
To prevent sediment buildup
To increase water pressure
To blend hot and cold water to deliver water at a safe temperature (Correct answer)

Correct answer: To blend hot and cold water to deliver water at a safe temperature

A tempering valve blends hot and cold water to deliver water at a pre-set safe temperature (typically 120°F) to prevent scalding.

Question 64: What unit is commonly used to measure low natural gas operating pressure in residential systems?

Millibars (mbar)
Pascals (Pa)
Pounds per square inch gauge (PSIG)
Inches of water column (in. WC) (Correct answer)

Correct answer: Inches of water column (in. WC)

Inches of water column (in. WC) is the standard unit for low residential gas pressures, where 27.7 in. WC equals 1 psi.

Question 65: Which fitting should be used when connecting a horizontal drain line to another horizontal drain line at the same elevation?

Sanitary tee
45-degree wye (Correct answer)
Long-sweep 90
Street elbow

Correct answer: 45-degree wye

A 45-degree wye fitting is used to connect horizontal drain branches because it promotes laminar flow and reduces the chance of blockages.

Question 66: Which type of water heater heats water only when it is needed, without a storage tank?

Tankless (on-demand) water heater (Correct answer)
Solar water heater
Heat pump water heater
Storage tank water heater

Correct answer: Tankless (on-demand) water heater

A tankless (on-demand) water heater heats water directly as it flows through the unit, eliminating standby heat loss associated with storage tanks.

Question 67: What is required when a new water heater is installed to protect the building from thermal expansion?

A pressure reducing valve only
A larger T&P valve
Additional pipe insulation
An expansion tank on the cold water supply side (Correct answer)

Correct answer: An expansion tank on the cold water supply side

When a check valve or backflow preventer creates a 'closed system,' an expansion tank must be installed on the cold water supply to water heater to accommodate thermal expansion.

Question 68: What type of vent connects a fixture's drain to a vent stack at a point above the fixture's flood level rim?

Wet vent
Individual vent (back vent) (Correct answer)
Common vent
Island vent

Correct answer: Individual vent (back vent)

An individual vent, also called a back vent or revent, connects directly from the fixture trap to the vent stack above the fixture's flood level rim.

Question 69: What is required before starting a major plumbing project in most US jurisdictions?

Insurance notification
Homeowner approval only
A plumbing permit from the local authority having jurisdiction (AHJ) (Correct answer)
Utility company approval

Correct answer: A plumbing permit from the local authority having jurisdiction (AHJ)

Most major plumbing work requires a permit from the local authority having jurisdiction (AHJ), ensuring the work is inspected and meets code requirements.

Question 70: What is the minimum clearance required in front of a toilet per the IPC?

21 inches (Correct answer)
12 inches
18 inches
30 inches

Correct answer: 21 inches

The IPC requires a minimum clearance of 21 inches in front of a water closet (toilet) to allow for use and maintenance.

Question 71: What is the recommended setting for a residential water heater thermostat to balance energy efficiency and safety?

120°F (Correct answer)
140°F
160°F
100°F

Correct answer: 120°F

120°F (49°C) is the EPA-recommended setting that balances energy efficiency, Legionella prevention, and scald protection for most households.

Question 72: What is the minimum rough-in distance from the back wall for a standard toilet rough-in?

14 inches
16 inches
10 inches
12 inches (Correct answer)

Correct answer: 12 inches

The standard toilet rough-in is 12 inches from the finished back wall to the center of the drain, with 10-inch and 14-inch sizes also available for non-standard applications.

Question 73: What does a 'rough inspection' verify in plumbing construction?

That all rough-in pipe installations are correct before walls are closed (Correct answer)
That finish fixtures are properly installed
That fixtures meet ADA requirements
That the water heater is functioning

Correct answer: That all rough-in pipe installations are correct before walls are closed

A rough inspection occurs after all supply and drain/vent pipes are installed but before walls are closed, verifying correct pipe sizing, slopes, and connections.

Question 74: Which type of copper pipe has the thinnest wall and is used for interior supply lines?

Type K
Type L
Type DWV
Type M (Correct answer)

Correct answer: Type M

Type M copper has the thinnest walls among the three pressure-rated copper types and is commonly used for interior supply lines in residential applications.

Question 75: What device is required to prevent backflow where a hose bib connects to a garden hose?

Pressure reducing valve
Check valve
Gate valve
Vacuum breaker (Correct answer)

Correct answer: Vacuum breaker

A vacuum breaker (anti-siphon device) is required at hose bibbs to prevent contaminated water from being siphoned back into the potable water supply.

Question 76: Which pipe is rated for both hot and cold water supply lines?

Cast iron
CPVC (Correct answer)
PVC
ABS

Correct answer: CPVC

CPVC (chlorinated polyvinyl chloride) is rated for both hot and cold water supply lines, unlike standard PVC which is only rated for cold water.

Question 77: What test method is required to verify gas piping integrity before placing the system in service?

Smoke test using theatrical fog
Pressure test with air or an inert gas (Correct answer)
Vacuum test at negative pressure
Hydrostatic (water) pressure test

Correct answer: Pressure test with air or an inert gas

Gas piping must be pressure tested with air or an inert gas (not the actual gas) to safely detect leaks before the system is charged.

Question 78: What is the purpose of the overflow tube in a toilet tank?

To add extra water capacity
To supply water to the bowl between flushes
To create siphon action during flushing
To prevent the tank from overflowing by routing excess water to the bowl (Correct answer)

Correct answer: To prevent the tank from overflowing by routing excess water to the bowl

The overflow tube prevents tank overflow by routing any excess water directly into the toilet bowl if the fill valve fails to shut off.

Question 79: What safety device is required on a gas water heater flue to prevent backdrafting?

A pressure relief valve
An expansion tank
A sediment trap
A barometric damper or draft hood (Correct answer)

Correct answer: A barometric damper or draft hood

A draft hood (barometric damper) is required on atmospherically vented gas water heaters to prevent flue gases from backdrafting into the living space.

Question 80: What is cross-connection in a plumbing system?

A physical link between potable water and a non-potable source (Correct answer)
Two pipes crossing each other in a wall
The connection point of supply and drain lines
A fitting joining two different pipe sizes

Correct answer: A physical link between potable water and a non-potable source

A cross-connection is any physical connection between potable (drinking) water and a non-potable source that could allow contamination of the drinking water supply.

Question 81: What is the required minimum distance between a water supply line and a drain line when running parallel in a wall?

6 inches
12 inches
No minimum required (Correct answer)
1 inch

Correct answer: No minimum required

The IPC does not specify a minimum horizontal separation distance between supply and drain lines running parallel, but they must not come into contact.

Question 82: What is the purpose of an air admittance valve (AAV)?

To add air to the water supply for pressure
To allow air into the drain system without a traditional vent pipe (Correct answer)
To prevent backflow in supply lines
To release excess air from hot water lines

Correct answer: To allow air into the drain system without a traditional vent pipe

An AAV (Studor valve) allows air into the drain system to equalize pressure, functioning as a vent without running pipe through the roof.

Question 83: What type of fitting connects two pipes of different materials, such as copper to CPVC?

Transition fitting (Correct answer)
Reducing coupling
Union fitting
Dielectric union

Correct answer: Transition fitting

A transition fitting is specifically designed to connect pipes made of different materials, ensuring a watertight seal between dissimilar pipe types.

Question 84: What is the maximum flush volume for a water closet (toilet) under federal standards?

1.6 GPF (Correct answer)
1.28 GPF
2.0 GPF
1.0 GPF

Correct answer: 1.6 GPF

Federal plumbing standards require water closets to use no more than 1.6 gallons per flush (GPF), with WaterSense certified models at 1.28 GPF.

Question 85: What is the purpose of a pipe reamer or deburring tool after cutting pipe?

To measure pipe diameter
To remove the interior burr left by cutting to restore full flow area (Correct answer)
To flare the pipe end
To clean the pipe exterior

Correct answer: To remove the interior burr left by cutting to restore full flow area

A reamer removes the interior burr created by a pipe cutter, restoring the full bore diameter and preventing the burr from causing turbulence or catching debris.

Question 86: What does a plumber use to solder (sweat) copper pipe joints?

Solvent cement and primer
Crimping tool and crimp rings
Propane or MAPP gas torch, solder, and flux (Correct answer)
Heat gun and thermoplastic welding rod

Correct answer: Propane or MAPP gas torch, solder, and flux

Sweating copper pipe requires a torch (propane or MAPP gas) to heat the fitting, flux to prevent oxidation and draw solder, and lead-free solder to fill the joint.

Question 87: Which gas has a specific gravity GREATER than air, causing it to sink and accumulate in low areas?

Natural gas (methane)
Carbon monoxide
Hydrogen
Propane (LP gas) (Correct answer)

Correct answer: Propane (LP gas)

Propane has a specific gravity of about 1.52 relative to air, so it sinks and can pool in basements, crawl spaces, and pits where it poses an explosion risk.

Question 88: What is the purpose of a sediment trap (dirt leg) on a gas line?

To measure gas flow
To prevent gas line freezing
To collect debris and moisture before it reaches the gas appliance valve (Correct answer)
To reduce gas pressure

Correct answer: To collect debris and moisture before it reaches the gas appliance valve

A sediment trap (dirt leg) is a downward-pointing nipple and cap installed near gas appliances that collects debris and condensate before they can clog or damage the appliance's gas valve.

Question 89: When sizing a natural gas pipe, which of the following factors is NOT used in the calculation?

Total BTU demand of the appliances
Total length of the pipe run
Allowable pressure drop
Color of the pipe material (Correct answer)

Correct answer: Color of the pipe material

Gas pipe sizing is based on BTU demand, pipe length, and allowable pressure drop — pipe color has no engineering significance in sizing calculations.

Question 90: What is 'water hammer' and what device prevents it?

Corrosion in pipes; prevented by a filter
Air in supply lines; prevented by a pressure regulator
Frozen pipe noise; prevented by insulation
Pressure spike from sudden valve closure; prevented by a water hammer arrestor (Correct answer)

Correct answer: Pressure spike from sudden valve closure; prevented by a water hammer arrestor

Water hammer is a pressure surge or shock wave caused by sudden valve closure, and a water hammer arrestor absorbs the shockwave to protect pipes and fittings.

Question 91: Which pipe material is most commonly used for residential water supply lines in the US?

Cast iron
Galvanized steel
PEX (Correct answer)
CPVC

Correct answer: PEX

PEX (cross-linked polyethylene) is the most widely used pipe for residential water supply due to its flexibility and ease of installation.

Question 92: What does 'wet venting' mean in a plumbing system?

A single pipe that serves as both a drain and a vent (Correct answer)
Venting through a plumbing appliance
Using water to flush vent pipes
Installing vent pipes in wet walls

Correct answer: A single pipe that serves as both a drain and a vent

Wet venting uses a single oversized pipe that serves simultaneously as a drain for one fixture and a vent for another downstream fixture.

Question 93: What type of sink mounting method sits on top of the countertop with the basin above the surface?

Vessel sink (Correct answer)
Integrated sink
Undermount sink
Drop-in (self-rimming) sink

Correct answer: Vessel sink

A vessel sink sits entirely on top of the countertop as a bowl, requiring a taller faucet and providing a design-forward appearance.

Question 94: What is the function of a fill valve in a toilet tank?

To control the flush volume
To regulate tank water temperature
To refill the tank with water after flushing (Correct answer)
To prevent water from entering the bowl between flushes

Correct answer: To refill the tank with water after flushing

The fill valve (ballcock) automatically refills the toilet tank with fresh water after each flush and shuts off when the water reaches the correct level.

Question 95: What is required to legally perform plumbing work for hire in most US states?

A general contractor license
A state-issued plumbing license (journeyman or master) (Correct answer)
Homeowner authorization only
A business license only

Correct answer: A state-issued plumbing license (journeyman or master)

Most US states require plumbers performing work for hire to hold a state-issued plumbing license, with journeyman and master plumber designations having different scopes of work.

Question 96: What is the purpose of a garbage disposal air gap on a dishwasher drain connection?

To allow air into the drain for faster drainage
To prevent dishwasher drain water from backflowing into the dishwasher (Correct answer)
To provide ventilation for the disposal motor
To measure water usage

Correct answer: To prevent dishwasher drain water from backflowing into the dishwasher

The dishwasher drain air gap (or high loop) prevents dirty drain water in the sink from backflowing into the dishwasher through the drain hose.

Question 97: What type of test is performed on a new DWV system to verify it is watertight?

Water test or air test at specified pressures per code (Correct answer)
Visual inspection only
Air pressure test at 100 psi
Dye test only

Correct answer: Water test or air test at specified pressures per code

New DWV systems are tested with either a water test (filled to the highest point) or an air test at pressures specified by the applicable plumbing code to verify no leaks.

Question 98: What fitting is typically installed at each gas appliance to allow individual shutoff without interrupting the entire system?

Ball check valve
Union fitting
Tee fitting
Appliance shutoff valve (gas cock) (Correct answer)

Correct answer: Appliance shutoff valve (gas cock)

An appliance shutoff valve (gas cock or stop valve) is required at each appliance connection to allow safe individual isolation for service or emergencies.

Question 99: What is a basin wrench used for?

Reaching and tightening faucet mounting nuts in tight spaces under sinks (Correct answer)
Tightening large pipe fittings under sinks
Tightening supply line connections
Removing drain basket strainers

Correct answer: Reaching and tightening faucet mounting nuts in tight spaces under sinks

A basin wrench has a long handle with a pivoting jaw that allows tightening or loosening the faucet mounting nuts in the cramped space between the sink basin and the wall.

Question 100: What is the purpose of a wax ring when installing a toilet?

To provide a gasket for the water supply connection
To anchor the toilet to the subfloor
To create a watertight seal between the toilet horn and the floor flange (Correct answer)
To level the toilet on uneven floors

Correct answer: To create a watertight seal between the toilet horn and the floor flange

The wax ring creates a watertight and airtight seal between the toilet's horn (outlet) and the floor flange, preventing waste leakage and sewer gas entry.

ICC G24 National Standard Master Plumber Exam

The ICC G24 National Standard Master Plumber exam tests knowledge of the International Plumbing Code (IPC), covering plumbing systems installation, safety regulations, drainage, venting, water supply, and fixture requirements for master plumber licensure.

100

Questions

240 min

Time Limit

70%

To Pass

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