ARIZONA REGISTRAR OF CONTRACTORS (AZ
ROC) |C-37 PLUMBING CONTRACTOR
(COMMERCIAL PLUMBING) PRACTICE EXAM
– 250 QUESTIONS WITH VERIFIED ANSWERS
& RATIONALES 2026/2027 EDITION
1. Minimum size of a water service for a small commercial building is usually:
A) 1/2 in
B) *3/4 in
C) 2 in
D) 4 in
Answer: B
Rationale: 3/4 in is commonly the minimum service size for small commercial
occupancy, subject to code and demand.
2. A backflow prevention device used on a commercial boiler feed line is
typically:
A) Air gap
B) *Reduced pressure zone assembly
C) Vacuum breaker
D) Check valve only
Answer: B
,Rationale: RPZ provides high hazard protection for boiler feed and cross-
connections.
3. The minimum slope for a 4-inch horizontal drainage pipe is:
A) 1/16 in per ft
B) *1/8 in per ft
C) 1/4 in per ft
D) 1/2 in per ft
Answer: B
Rationale: 4-inch and larger horizontal drainage often uses 1/8 in/ft minimum
where allowed.
4. A plumbing vent that serves only one fixture is a:
A) Circuit vent
B) *Individual vent
C) Relief vent
D) Yoke vent
Answer: B
Rationale: Individual vent connects one fixture trap to the vent system.
5. The minimum air gap for a water supply outlet is:
A) 1/4 in
,B) *1 in or twice the effective opening
C) 2 in always
D) 6 in
Answer: B
Rationale: Air gap must be at least twice the effective opening, with a minimum
of 1 inch.
6. A commercial kitchen sink requires what type of backflow protection if
directly connected?
A) Vacuum breaker
B) *Air gap
C) Check valve
D) RPZ only
Answer: B
Rationale: Food-handling sinks require an air gap for highest protection.
7. Cleanouts are required at the base of a vertical stack when the stack is
longer than:
A) 25 ft
B) *50 ft
C) 75 ft
D) 100 ft
Answer: B
, Rationale: Base cleanouts are required for stacks exceeding 50 ft unless otherwise
approved.
8. The minimum size of a building drain is typically:
A) 2 in
B) *3 in
C) 4 in
D) 6 in
Answer: B
Rationale: Building drains are commonly minimum 3 inches for commercial, but
code may require larger.
9. A grease interceptor is required for:
A) Toilet waste
B) *Commercial kitchen grease-laden waste
C) Storm drainage
D) Urinal waste
Answer: B
Rationale: Grease interceptors prevent fats, oils, and grease from entering
drainage.
10. Water hammer is best controlled by:
ROC) |C-37 PLUMBING CONTRACTOR
(COMMERCIAL PLUMBING) PRACTICE EXAM
– 250 QUESTIONS WITH VERIFIED ANSWERS
& RATIONALES 2026/2027 EDITION
1. Minimum size of a water service for a small commercial building is usually:
A) 1/2 in
B) *3/4 in
C) 2 in
D) 4 in
Answer: B
Rationale: 3/4 in is commonly the minimum service size for small commercial
occupancy, subject to code and demand.
2. A backflow prevention device used on a commercial boiler feed line is
typically:
A) Air gap
B) *Reduced pressure zone assembly
C) Vacuum breaker
D) Check valve only
Answer: B
,Rationale: RPZ provides high hazard protection for boiler feed and cross-
connections.
3. The minimum slope for a 4-inch horizontal drainage pipe is:
A) 1/16 in per ft
B) *1/8 in per ft
C) 1/4 in per ft
D) 1/2 in per ft
Answer: B
Rationale: 4-inch and larger horizontal drainage often uses 1/8 in/ft minimum
where allowed.
4. A plumbing vent that serves only one fixture is a:
A) Circuit vent
B) *Individual vent
C) Relief vent
D) Yoke vent
Answer: B
Rationale: Individual vent connects one fixture trap to the vent system.
5. The minimum air gap for a water supply outlet is:
A) 1/4 in
,B) *1 in or twice the effective opening
C) 2 in always
D) 6 in
Answer: B
Rationale: Air gap must be at least twice the effective opening, with a minimum
of 1 inch.
6. A commercial kitchen sink requires what type of backflow protection if
directly connected?
A) Vacuum breaker
B) *Air gap
C) Check valve
D) RPZ only
Answer: B
Rationale: Food-handling sinks require an air gap for highest protection.
7. Cleanouts are required at the base of a vertical stack when the stack is
longer than:
A) 25 ft
B) *50 ft
C) 75 ft
D) 100 ft
Answer: B
, Rationale: Base cleanouts are required for stacks exceeding 50 ft unless otherwise
approved.
8. The minimum size of a building drain is typically:
A) 2 in
B) *3 in
C) 4 in
D) 6 in
Answer: B
Rationale: Building drains are commonly minimum 3 inches for commercial, but
code may require larger.
9. A grease interceptor is required for:
A) Toilet waste
B) *Commercial kitchen grease-laden waste
C) Storm drainage
D) Urinal waste
Answer: B
Rationale: Grease interceptors prevent fats, oils, and grease from entering
drainage.
10. Water hammer is best controlled by:
