CA C36 Plumbing Contractor Exam

CA C36 Plumbing Contractor Exam Questions And Correct Answers (Verified Answers) Plus Rationale2026 Q&A| Instant Download Pdf

• Which of the following is the standard minimum slope for a 2-inch

diameter horizontal drain pipe?

• 1/8 inch per foot
• 1/4 inch per foot
• 1/2 inch per foot
• 1 inch per foot

Rationale: A 1/4 inch per foot slope ensures proper drainage and

prevents solids from settling in a 2-inch pipe.

• What is the primary purpose of a vent in a plumbing system?
• To increase water pressure
• To allow air into the drainage system and prevent siphoning of

traps

• To filter water
• To heat water

Rationale: Vents maintain atmospheric pressure in the pipes and

prevent traps from losing their water seal.

• Which type of pipe is commonly used for underground water supply?

A. CPVC

B. PVC

• Ductile iron
• Galvanized steel

Rationale: Ductile iron is durable and resistant to underground

corrosion, making it ideal for buried water mains. 1 / 3

• The maximum allowable distance between supports for a horizontal

PVC pipe of 3 inches in diameter is:

• 4 feet
• 6 feet
• 8 feet
• 10 feet

Rationale: PVC pipes must be supported at intervals specified by code

to prevent sagging; 3-inch pipes typically require 8-foot spacing.

• What is the function of a trap in a plumbing fixture?
• To increase water flow
• To prevent sewer gases from entering the building
• To regulate water pressure
• To filter debris

Rationale: Traps hold water that blocks sewer gases from rising into

occupied spaces.

• A plumber is installing a water heater. Which of the following is

required to prevent backflow?

• Globe valve
• Gate valve
• Check valve
• Angle valve

Rationale: Check valves allow water to flow in one direction,

preventing contamination of the potable water supply.

• In a residential building, what is the minimum pipe diameter for a main

sewer line?

• 2 inches
• 4 inches
• 6 inches
• 8 inches

Rationale: 4-inch diameter is the minimum standard for residential

building sewer mains to handle expected waste flow.

• Which of the following materials is suitable for hot water distribution?

A. PVC

B. CPVC

• Galvanized iron
• Polyethylene 2 / 3

Rationale: CPVC is rated for hot water use, unlike standard PVC,

which may deform at high temperatures.

• What type of joint is typically used to connect cast-iron soil pipes?
• Solvent cement
• Threaded
• Hub-and-spigot with lead and oakum
• Compression fitting

Rationale: Hub-and-spigot joints with lead and oakum create

watertight seals for cast-iron soil pipes.

• What is the purpose of an expansion tank in a closed water

heating system?

• To heat water faster
• To absorb pressure changes and prevent pipe damage
• To filter water
• To store extra water

Rationale: Expansion tanks prevent excessive pressure buildup when

water expands due to heating.

11. The water hammer in a plumbing system is caused by:

• Low water temperature
• Sudden closure of a valve
• Leaking pipes
• Incorrect pipe slope

Rationale: Rapidly closing valves cause pressure surges known as

water hammer.

• What is the correct order of operations for joining copper pipes

using soldering?

• Heat, clean, apply flux, solder
• Clean, apply flux, heat, solder
• Apply flux, solder, heat, clean
• Heat, solder, clean, flux

Rationale: Cleaning removes oxidation, flux prevents oxidation during

heating, and solder is applied to a heated joint for bonding.

• For a proper plumbing system, the minimum size of a vent pipe

serving a single fixture is:

• 3/4 inch
• 1 inch
• 1 1/4 inch
• / 3