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CA C-36 Plumbing study materials
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CA C-36 Plumbing practice questions

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Question 1Plumbing codes, regulations, and standards

The California Plumbing Code (Title 24, Part 5) is based primarily on which model code?

  1. The Uniform Plumbing Code Correct answer.
  2. The National Standard Plumbing Code
  3. The International Plumbing Code
  4. The International Residential Code

Explanation

California adopts the Uniform Plumbing Code, published by the International Association of Plumbing and Mechanical Officials (IAPMO), as the model document for Title 24, Part 5. The state then amends that model code with California-specific provisions covering water conservation, seismic protection, and materials.

Question 2Plumbing codes, regulations, and standards

Which of the following plumbing jobs is generally exempt from a plumbing permit under the California Plumbing Code?

  1. Replacing a lavatory faucet Correct answer.
  2. Adding a new exterior hose bibb
  3. Installing a new gas-fired water heater
  4. Replacing a section of building drain

Explanation

The code exempts minor repair and replacement work, such as stopping leaks and replacing fixture trim including faucets, from the permit process. New installations, new piping, and replacement of drainage piping or water heaters require a permit and inspection.

Question 3Plumbing codes, regulations, and standards

The discharge pipe from a temperature and pressure relief valve on a residential water heater must terminate:

  1. Not more than 6 inches above the floor with an unthreaded end Correct answer.
  2. At any convenient point inside the garage
  3. Not less than 12 inches above the floor with a threaded cap
  4. Directly into the drainage system with a solid connection

Explanation

Relief valve discharge must terminate not more than 6 inches above the floor or an approved receptor, with an unthreaded end so that no cap or plug can be added. The pipe must be full size, must not be trapped, and must not be directly connected to the drainage system.

Question 4Plumbing codes, regulations, and standards

Under the California Plumbing Code, the minimum permitted slope for horizontal drainage pipe of 3-inch nominal size is:

  1. 1/8 inch per foot
  2. 1/2 inch per foot
  3. 1/16 inch per foot
  4. 1/4 inch per foot Correct answer.

Explanation

The Uniform Plumbing Code as adopted in California requires 1/4 inch per foot for pipe 3 inches and smaller and permits 1/8 inch per foot only for pipe 4 inches and larger. This threshold differs from the IPC, which allows 1/8 inch per foot starting at 3 inches.

Question 5Plumbing codes, regulations, and standards

The liquid seal of a fixture trap must be maintained at a depth of:

  1. Not less than 4 inches and not more than 12 inches
  2. Not less than 3 inches and not more than 6 inches
  3. Not less than 1 inch and not more than 3 inches
  4. Not less than 2 inches and not more than 4 inches Correct answer.

Explanation

Trap seals are limited to a 2-inch minimum so the seal is deep enough to resist evaporation and pressure fluctuation, and a 4-inch maximum so the trap does not become excessively deep. Deeper seals increase the risk of excessive back pressure and are harder to clean.

Question 6Plumbing codes, regulations, and standards

A water closet must be installed so that its centerline is not less than how many inches from a side wall or partition?

  1. 24 inches
  2. 12 inches
  3. 15 inches Correct answer.
  4. 18 inches

Explanation

The code requires at least 15 inches of clear space from the centerline of a water closet to any side wall or partition, and at least 15 inches of clearance in front of the bowl. This provides shoulder room for the user and access for cleaning.

Question 7Plumbing codes, regulations, and standards

Which method provides the highest degree of backflow protection at a plumbing fixture or receptor?

  1. A double check valve assembly
  2. An air gap Correct answer.
  3. An atmospheric vacuum breaker
  4. A hose bibb vacuum breaker

Explanation

An air gap is a physical separation between the supply outlet and the flood level rim of the receptor, so backflow is impossible even if a valve fails. Mechanical devices such as check valves and vacuum breakers depend on moving parts and are rated lower than an air gap.

Question 8Plumbing codes, regulations, and standards

A commercial restaurant with a kitchen sink, pre-rinse sprayer, and dishwasher must have which of the following installed on the kitchen drainage?

  1. A grease interceptor sized to the fixture load Correct answer.
  2. A lint interceptor
  3. A sewage ejector pump
  4. A sand and oil separator

Explanation

Commercial food-service establishments must route kitchen waste through an approved grease interceptor so fats, oils, and grease do not congeal in the building sewer. The interceptor must be sized in accordance with the code and the number and type of fixtures served.

Question 9Plumbing codes, regulations, and standards

The maximum permitted spacing between cleanouts in horizontal drainage piping is:

  1. 50 feet
  2. 75 feet
  3. 150 feet
  4. 100 feet Correct answer.

Explanation

The code requires a cleanout at intervals not exceeding 100 feet in horizontal drainage piping, plus cleanouts at the end of each building drain, at aggregate changes of direction greater than 135 degrees, and at the base of stacks. This keeps every rodding run reachable.

Question 10Plumbing codes, regulations, and standards

The minimum required horizontal distance from a roof-mounted vent terminal to a door, openable window, or outdoor air intake is:

  1. 10 feet Correct answer.
  2. 25 feet
  3. 3 feet
  4. 5 feet

Explanation

Vent terminals must be at least 10 feet horizontally from any door, openable window, or air intake of the building, and at least 6 inches above the roof surface. These clearances keep sewer gas out of occupied spaces and above snow or ponding water.

Question 11Plumbing codes, regulations, and standards

How must a water heater be secured for seismic protection in California?

  1. With one strap at mid-height of the tank
  2. With two straps, one in the upper third and one in the lower third of the tank Correct answer.
  3. With two straps placed at the very top and very bottom of the tank
  4. With three straps evenly spaced over the tank height

Explanation

California requires two straps, one located in the upper third and one in the lower third of the tank. The lower strap must be at least 4 inches above the controls and the upper strap at least 6 inches below the top of the heater so the tank cannot tip or slide during an earthquake.

Question 12Plumbing codes, regulations, and standards

Under the California Plumbing Code, the maximum weighted average lead content permitted in the wetted surface of pipes, fittings, and fixtures is:

  1. 0.25 percent Correct answer.
  2. 4 percent
  3. 0.5 percent
  4. 8 percent

Explanation

The code defines lead free as not more than 0.25 percent weighted average lead content of the wetted surface for pipes, fittings, and fixtures. This aligns California law with the federal Reduction of Lead in Drinking Water Act.

Question 13Plumbing codes, regulations, and standards

The maximum flush volume for a water closet installed new in California is:

  1. 1.28 gallons per flush Correct answer.
  2. 0.8 gallons per flush
  3. 1.6 gallons per flush
  4. 2.0 gallons per flush

Explanation

California limits new water closets to 1.28 gallons per flush, which is stricter than the federal 1.6 gallon standard. The reduced volume is set by the California Energy Commission and carried into the state plumbing and green building standards.

Question 14Plumbing codes, regulations, and standards

A drainage and vent system is water tested by filling it to a depth of at least 10 feet at the lowest point. The minimum required holding time is:

  1. 15 minutes Correct answer.
  2. 5 minutes
  3. 30 minutes
  4. 60 minutes

Explanation

The water test requires the system to be filled to a depth of at least 10 feet at the lowest point and held for at least 15 minutes before inspection. An air test at 5 psi for 15 minutes is an alternative where water testing is impractical.

Question 15Plumbing codes, regulations, and standards

In a commercial food preparation area, the handwashing lavatory must be:

  1. Separate from and not used for food preparation or utensil washing Correct answer.
  2. Omitted when a utility sink is installed in the same room
  3. The same sink used for food preparation when it is kept clean
  4. The mop sink when the mop sink is within 20 feet

Explanation

Food facilities must provide a handwashing lavatory that is separate from food preparation, utensil washing, and janitorial sinks, supplied with hot and cold water, soap, and towels. This separation prevents contamination of food and clean utensils.

Question 16Plumbing codes, regulations, and standards

A thermal expansion control device is required on a water heater when:

  1. The heater is gas-fired rather than electric
  2. The water supply is closed by a check valve, pressure-reducing valve, or backflow preventer Correct answer.
  3. The heater is installed outdoors
  4. The heater is equipped with a temperature and pressure relief valve

Explanation

A check valve, pressure-reducing valve, or backflow preventer creates a closed system, so heated water has nowhere to expand and pressure rises until the relief valve opens. An expansion tank or other approved device absorbs that volume and protects the piping and the relief valve.

Question 17Plumbing codes, regulations, and standards

A building has a boiler treatment chemical injection system connected to the potable water supply with a direct connection. Which backflow preventer is required for this high-hazard application?

  1. A reduced-pressure principle assembly Correct answer.
  2. A hose connection vacuum breaker
  3. A pressure vacuum breaker
  4. A double check valve assembly

Explanation

Chemical injection creates a high hazard because a toxic substance could enter the potable supply. A reduced-pressure principle assembly protects against both backsiphonage and backpressure and discharges to atmosphere if a check fails, so it is required for high-hazard connections.

Question 18Plumbing codes, regulations, and standards

The maximum permitted support spacing for horizontal runs of 2-inch PVC Schedule 40 drainage pipe is:

  1. 6 feet
  2. 12 feet
  3. 10 feet
  4. 4 feet Correct answer.

Explanation

PVC Schedule 40 requires shorter support intervals than metal pipe because the plastic is less rigid and sags when heated. The code support table sets a maximum horizontal spacing of 4 feet for PVC Schedule 40, with vertical support at 10-foot intervals.

Question 19Plumbing codes, regulations, and standards

The developed length of a fixture trap arm between the trap weir and its vent connection is limited primarily to prevent:

  1. Excessive noise in the drainage system
  2. Backpressure from the building drain into the fixture
  3. Clogging of the trap arm with debris
  4. Self-siphonage of the trap seal from an excessive drop Correct answer.

Explanation

The trap arm may slope only enough for drainage before it is vented; if the arm is too long, the drop between the trap weir and the vent lets the arm act as a drain and siphon the trap dry. The code therefore limits trap arm length by pipe size and slope.

Question 20Plumbing codes, regulations, and standards

A gas water heater installed in a private garage must have its ignition source elevated at least 18 inches above the floor unless:

  1. The unit is equipped with a temperature and pressure relief valve
  2. The garage is detached from the dwelling
  3. The unit is listed as flammable vapor ignition resistant (FVIR) Correct answer.
  4. A drain pan is installed beneath the heater

Explanation

The 18-inch elevation protects the burner or pilot from gasoline vapors that collect near the garage floor. A water heater listed as flammable vapor ignition resistant is designed and tested to resist ignition of those vapors, so the elevation requirement does not apply to it.

Question 21Plumbing codes, regulations, and standards

A water service pipe is to be installed in the same trench as a building sewer. Which condition does the code require?

  1. No separation is required when both pipes are listed plastic
  2. The water service is placed below the sewer so both drain in the same direction
  3. The water service is at least 12 inches above the sewer and rests on a solid shelf at one side of the trench Correct answer.
  4. The water service is bedded directly on the sewer pipe with a 2-inch sand cushion

Explanation

Where a water service and building sewer share a trench, the water service must be at least 12 inches above the sewer and supported on a solid shelf at one side of the trench. Otherwise the two pipes must be separated by at least 5 feet of undisturbed or compacted earth so contamination cannot reach the potable line.

Question 22Plumbing codes, regulations, and standards

Where corrugated stainless steel tubing (CSST) is installed for gas piping in a dwelling, California requirements call for:

  1. No bonding if the tubing is listed and labeled
  2. Using the tubing as the grounding electrode for the electrical service
  3. Bonding to the grounding electrode system with a conductor not smaller than 6 AWG copper Correct answer.
  4. A dielectric union at the gas meter and at each appliance

Explanation

CSST is thin-walled and can be damaged by lightning-induced arcing, so the listing and the electrical code require it to be bonded to the grounding electrode system with a conductor sized 6 AWG copper or equivalent. Bonding equalizes potential and reduces the chance of a pinhole puncture.

Question 23Plumbing codes, regulations, and standards

A C-36 Plumbing contractor license issued by the California Contractors State License Board authorizes the holder to:

  1. Certify and test backflow prevention assemblies
  2. Design plumbing systems in place of a licensed engineer
  3. Install, alter, and repair plumbing systems and contract for that work Correct answer.
  4. Perform electrical panel and service work

Explanation

The C-36 classification covers the plumbing trade, allowing the licensee to install, alter, and repair plumbing systems and to contract for that work. Backflow assembly testing, electrical work, and engineering design each require separate certification or licensure.

Question 24Plumbing codes, regulations, and standards

Where a building drain is below the level of the next upstream manhole and fixtures are subject to sewage backup, the code requires:

  1. A second trap installed in series
  2. An approved backwater valve on the affected drain or branch Correct answer.
  3. An air admittance valve on each fixture drain
  4. A vent cap installed at the cleanout

Explanation

When a drainage outlet is lower than the upstream public manhole, sewage can reverse flow into the building during surcharging. An approved backwater valve installed on the affected drain or branch closes automatically against reverse flow while allowing normal discharge.

Question 25Drainage, waste, and vent (DWV) systems

What is the minimum water seal depth required for a plumbing fixture trap under the California Plumbing Code?

  1. 4 inches
  2. 2 inches Correct answer.
  3. 1 inch
  4. 3 inches

Explanation

A fixture trap must maintain a liquid seal of at least 2 inches and not more than 4 inches. The seal blocks sewer gas from entering the building, while an excessive seal can be difficult to maintain and may trap debris.

Question 26Drainage, waste, and vent (DWV) systems

A 2-inch horizontal drainage pipe is being installed. What is the minimum slope required by the California Plumbing Code?

  1. 1/4 inch per foot Correct answer.
  2. 1/2 inch per foot
  3. 1/16 inch per foot
  4. 1/8 inch per foot

Explanation

The code requires 1/4 inch per foot for drainage pipe 2 1/2 inches and smaller, and 1/8 inch per foot is allowed only for 3-inch through 6-inch pipe. The steeper slope helps small lines carry solids without settling.

Question 27Drainage, waste, and vent (DWV) systems

What minimum height must a vent pipe terminate above a flat roof that is not used for any purpose other than weather protection?

  1. 2 inches
  2. 6 inches Correct answer.
  3. 4 inches
  4. 12 inches

Explanation

Vent terminals must extend at least 6 inches above a roof used only for weather protection. A roof used for other purposes requires a higher vent terminal because people may be on the roof.

Question 28Drainage, waste, and vent (DWV) systems

Which of the following fixture traps is prohibited by the California Plumbing Code?

  1. A P-trap
  2. A trap with a 4-inch water seal
  3. A trap with a removable cleanout plug
  4. An S-trap Correct answer.

Explanation

S-traps are prohibited because they can self-siphon and lose their seal under normal flow. P-traps, traps with cleanout plugs, and traps with seals within the 2-to-4-inch range are permitted.

Question 29Drainage, waste, and vent (DWV) systems

Using standard drainage fixture unit values in the California Plumbing Code, what is the DFU rating of a water closet?

  1. 3 Correct answer.
  2. 4
  3. 2
  4. 1

Explanation

A water closet is rated at 3 drainage fixture units. For comparison, a lavatory is typically 1 DFU and a bathtub or shower is typically 2 DFU.

Question 30Drainage, waste, and vent (DWV) systems

What is the minimum diameter permitted for a vent pipe under the California Plumbing Code?

  1. 1 1/4 inches Correct answer.
  2. 1 1/2 inches
  3. 1 inch
  4. 2 inches

Explanation

A vent pipe must be at least 1 1/4 inches in diameter, and it must also be at least half the diameter of the drain it serves. A smaller vent can restrict airflow and cause trap siphonage.

Question 31Drainage, waste, and vent (DWV) systems

What is the primary purpose of venting a plumbing fixture trap?

  1. To filter grease from waste
  2. To support the fixture drain
  3. To increase drainage velocity
  4. To protect the trap seal Correct answer.

Explanation

Venting equalizes pressure on both sides of the trap seal so flowing waste does not siphon the seal out. It also allows sewer gases to escape outdoors instead of entering the building.

Question 32Drainage, waste, and vent (DWV) systems

What device is required where a plumbing fixture is installed below the level of the next upstream manhole in the building sewer?

  1. Pressure-reducing valve
  2. Vacuum breaker
  3. Backwater valve Correct answer.
  4. Thermostatic mixing valve

Explanation

A backwater valve prevents sewage from reversing into fixtures that are below the upstream manhole level. It must be installed where it remains accessible for maintenance and testing.

Question 33Drainage, waste, and vent (DWV) systems

What is the minimum size fixture drain permitted for a water closet?

  1. 2 inches
  2. 3 inches Correct answer.
  3. 4 inches
  4. 1 1/2 inches

Explanation

A water closet requires a minimum 3-inch fixture drain because of its 3-DFU rating and the need to carry solids. Smaller drains would be prone to clogging, while larger drains are permitted but are not the minimum.

Question 34Drainage, waste, and vent (DWV) systems

A 3-inch horizontal building drain requires a cleanout. What is the minimum cleanout size that may be installed?

  1. 3 inches Correct answer.
  2. 2 inches
  3. 1 1/2 inches
  4. 2 1/2 inches

Explanation

A cleanout must be the same size as the pipe it serves, up to a maximum of 4 inches. Therefore, a 3-inch drain requires a 3-inch cleanout, not a reduced-size fitting.

Question 35Drainage, waste, and vent (DWV) systems

In DWV terminology, what is a wet vent?

  1. A vent that also serves as a drain Correct answer.
  2. A vent installed below the fixture trap
  3. A vent that carries only rainwater
  4. A vent that terminates in the attic

Explanation

A wet vent is a pipe that functions as both a drain and a vent for fixtures. It is permitted only for limited fixture combinations and must be sized and installed according to the code.

Question 36Drainage, waste, and vent (DWV) systems

What is an air gap in a plumbing drainage system?

  1. The horizontal distance from a vent terminal to a property line
  2. A vacuum-breaking fitting installed on a trap
  3. The vertical gap between a drain outlet and a flood rim Correct answer.
  4. The horizontal distance from a vent terminal to an operable window

Explanation

An air gap is the unobstructed vertical separation between the lowest point of an indirect waste outlet and the flood level rim of the receiving receptor. It is the most reliable form of backflow protection for indirect waste.

Question 37Drainage, waste, and vent (DWV) systems

How often must horizontal PVC drainage pipe be supported?

  1. Every 6 feet
  2. Every 2 feet
  3. Every 4 feet Correct answer.
  4. Every 3 feet

Explanation

Horizontal PVC drainage pipe must be supported at intervals not exceeding 4 feet, with additional support at changes in direction. Proper support prevents sagging, joint stress, and slope loss.

Question 38Drainage, waste, and vent (DWV) systems

Which fitting is used to connect a vertical drain to a horizontal drain in the direction of flow?

  1. A double sanitary wye
  2. A sanitary tee Correct answer.
  3. A drum trap
  4. A 1/8 bend

Explanation

A sanitary tee has a curved branch that directs flow from a vertical drain into a horizontal drain without a sharp turn. Wyed fittings are used for horizontal-to-horizontal drainage connections.

Question 39Drainage, waste, and vent (DWV) systems

Why is a trap primer installed for a floor drain?

  1. To maintain the trap seal by adding water Correct answer.
  2. To prevent grease from entering the drain
  3. To increase the trap seal to 4 inches
  4. To vent sewer gas from the drain

Explanation

Floor drains that see little use can lose their seal by evaporation. A trap primer automatically adds a small amount of water to keep the trap seal intact and prevent sewer gas from entering.

Question 40Drainage, waste, and vent (DWV) systems

A grease interceptor is required for which type of establishment?

  1. A car wash
  2. A dental clinic
  3. A commercial kitchen Correct answer.
  4. A residential laundry room

Explanation

Grease interceptors are required where fats, oils, and grease are discharged in quantities that could clog the building sewer, typically commercial kitchens. They must be sized and maintained according to the code.

Question 41Drainage, waste, and vent (DWV) systems

A horizontal drainage pipe runs 30 feet at the minimum slope required for a 2-inch pipe. What is the total fall?

  1. 5 inches
  2. 3 3/4 inches
  3. 10 inches
  4. 7 1/2 inches Correct answer.

Explanation

The minimum slope for 2-inch drainage pipe is 1/4 inch per foot. Multiplying 30 feet by 1/4 inch per foot gives 7 1/2 inches of total fall, which provides adequate scouring velocity.

Question 42Drainage, waste, and vent (DWV) systems

What is the minimum vent size for a 4-inch drainage pipe?

  1. 2 1/2 inches
  2. 2 inches Correct answer.
  3. 3 inches
  4. 1 1/2 inches

Explanation

A vent must be at least half the diameter of the drain it serves, and never less than 1 1/4 inches. For a 4-inch drain, half the diameter is 2 inches, so 2 inches is the minimum vent size.

Question 43Drainage, waste, and vent (DWV) systems

Where must an individual fixture vent connect to the fixture drain?

  1. At the crown of the trap
  2. At the building sewer
  3. Downstream of the trap, within the permitted trap-arm length Correct answer.
  4. Upstream of the trap, at the fixture outlet

Explanation

The vent must connect downstream of the trap so it protects the trap seal without connecting directly to the fixture outlet. It must also be within the trap-arm length allowed for the drain size.

Question 44Drainage, waste, and vent (DWV) systems

A basement bathroom is installed below the level of the building sewer. What system is required to lift the sewage to the sewer?

  1. A backwater valve on the sewer
  2. A sump pump for clear water
  3. A grease interceptor for kitchen waste
  4. A sewage ejector pump Correct answer.

Explanation

Fixtures installed below the building sewer require a sewage ejector pump to lift wastewater to the sewer. A sump pump is intended for clear groundwater, not sewage.

Question 45Drainage, waste, and vent (DWV) systems

How must a horizontal vent pipe be graded?

  1. Perfectly level for its entire length
  2. Back to the drain at 1/4 inch per foot Correct answer.
  3. Away from the drain at 1/8 inch per foot
  4. Toward the vent terminal at 1/2 inch per foot

Explanation

Horizontal vents must slope back to the drainage pipe they serve so condensation and rainwater can drain into the sewer. The required grade is not less than 1/4 inch per foot.

Question 46Drainage, waste, and vent (DWV) systems

A cleanout installed below a floor must be provided with what feature?

  1. An accessible gas-tight plug Correct answer.
  2. A permanent sealed cover with no access
  3. A concrete cap
  4. A cover at least 4 inches above the floor

Explanation

Cleanouts must remain accessible for maintenance. A below-floor cleanout needs a gas-tight plug and an accessible cover so it can be opened without breaking the floor.

Question 47Drainage, waste, and vent (DWV) systems

What is the drainage fixture unit value for a bathroom group consisting of a water closet, a lavatory, and a bathtub or shower?

  1. 4 DFU
  2. 6 DFU Correct answer.
  3. 3 DFU
  4. 8 DFU

Explanation

The code assigns 6 DFU to a standard bathroom group containing a water closet, lavatory, and bathtub or shower. The individual values are 3 DFU, 1 DFU, and 2 DFU respectively.

Question 48Drainage, waste, and vent (DWV) systems

Which fitting is required where a horizontal drainage branch connects to another horizontal drain in the direction of flow?

  1. A wye Correct answer.
  2. A sanitary tee
  3. A 90-degree elbow
  4. A double sanitary tee

Explanation

Horizontal-to-horizontal drainage connections must be made with a wye or a combination wye and 1/8 bend. A sanitary tee is limited to vertical-to-horizontal connections and is not approved for this horizontal junction.

Question 49Drainage, waste, and vent (DWV) systems

What minimum height must a vent pipe terminate above a roof that is used as an outdoor patio?

  1. 7 feet Correct answer.
  2. 12 inches
  3. 10 feet
  4. 6 inches

Explanation

Where a roof is used for purposes other than weather protection, such as a patio, the vent terminal must extend at least 7 feet above the roof. The ordinary 6-inch height applies only where the roof is not used for other purposes.

Question 50Drainage, waste, and vent (DWV) systems

What range of liquid seal depth is required for a plumbing trap serving a fixture?

  1. 4 to 6 inches
  2. 1 to 2 inches
  3. 6 to 12 inches
  4. 2 to 4 inches Correct answer.

Explanation

The plumbing code adopted in California requires a liquid trap seal of at least 2 inches and no more than 4 inches. A seal shallower than 2 inches is lost too readily to evaporation and siphonage, while a deeper seal is prohibited because the larger slug of water is more easily pulled out of the trap by the discharge of the fixture.