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Minneapolis Journeyman Plumber with
Gas - 498 - MN-MI Contractor Exam
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1. What is the minimum depth for underground water service piping in
Minneapolis to prevent freezing?
A. 12 inches B. 24 inches C. 42 inches D. 60 inches D. 60 inches [ANSWER] Rationale: Minneapolis experiences severe frost penetration. Minnesota plumbing code requires water service piping to be buried below frost line, typically 60 inches or deeper, to prevent freezing and pipe rupture.
2. What is the minimum slope required for horizontal drainage piping 3 inches
and smaller?
A. 1/8 inch per foot B. 1/4 inch per foot C. 1/2 inch per foot D. 1 inch per foot B. 1/4 inch per foot [ANSWER] Rationale: Minnesota Plumbing Code (based on IPC with amendments) requires 1/4" per foot slope for pipes 3 inches or less to ensure proper scouring velocity and prevent solids accumulation.
3. What is the minimum trap seal depth?
A. 1 inch B. 2 inches C. 3 inches D. 4 inches B. 2 inches [ANSWER] Rationale: A trap seal must be at least 2 inches and not more than 4 inches to prevent sewer gas from entering while avoiding self-siphonage issues.
4. What device prevents backflow due to backsiphonage only?
A. Double check valve assembly B. Reduced pressure principle assembly C. Atmospheric vacuum breaker D. Pressure vacuum breaker C. Atmospheric vacuum breaker [ANSWER] Rationale: An AVB protects only against backsiphonage, not backpressure. It must be installed downstream of the last shutoff valve.
5. Gas piping must be pressure tested at what minimum pressure for low-
pressure systems?
A. 3 psi B. 5 psi C. 10 psi D. Working pressure only C. 10 psi [ANSWER] Rationale: Minnesota fuel gas code requires a minimum 10 psi test for residential gas piping systems to ensure leak integrity prior to operation.
6. What is the maximum developed length for a 2-inch trap arm without
additional venting?
A. 4 feet B. 5 feet
C. 6 inches [ANSWER] Rationale: Single-wall vent connectors require 6 inches clearance to combustibles to prevent fire hazards.
10. What is the minimum water service pipe size for a single-family dwelling?
A. 1/2 inch B. 3/4 inch C. 1 inch D. 1-1/4 inch B. 3/4 inch [ANSWER] Rationale: A 3/4-inch minimum ensures adequate flow and pressure for residential fixture demand.
11. A water heater T&P relief valve discharge pipe must terminate:
A. Into a floor drain B. Outdoors above grade C. Within 6 inches of floor D. Into a sump pit C. Within 6 inches of floor [ANSWER] Rationale: Discharge must be visible and within 6 inches of the floor, not threaded or capped, to prevent scalding and allow observation.
12. What is the maximum allowable pressure drop in a low-pressure gas system?
A. 0.3 inch w.c. B. 0.5 inch w.c. C. 1.0 inch w.c. D. 2.0 inch w.c. B. 0.5 inch w.c. [ANSWER] Rationale: Gas pipe sizing tables are based on 0.5 inch water column pressure drop to maintain appliance performance.
13. What is required when installing PEX through studs?
A. Insulation only B. Nail plates C. Tape wrap D. Sleeve only B. Nail plates [ANSWER] Rationale: Nail plates protect piping from puncture by fasteners within 1-1/4 inches of framing face.
14. What is the minimum vent size for a water closet?
A. 1-1/4 inch B. 1-1/2 inch C. 2 inch D. 3 inch C. 2 inch [ANSWER] Rationale: A water closet requires a minimum 2-inch vent to properly protect the trap seal.
15. What is the required minimum separation between water and sewer service
lines horizontally?
A. 5 feet B. 10 feet C. 15 feet D. 20 feet B. 10 feet [ANSWER] Rationale: Minnesota code requires 10 feet horizontal separation to prevent contamination risk.
16. A backwater valve is required when:
B. 120°F [ANSWER]
Rationale: 120°F prevents scalding while providing sufficient hot water.
20. What fitting must be used for vent connections in horizontal position?
A. Sanitary tee B. Wye C. Long sweep elbow D. Double tee B. Wye [ANSWER] Rationale: Sanitary tees are prohibited on their back; wyes maintain proper flow. (Questions 21–50 continue in same structured format below.)
21. Minimum slope for 4-inch building sewer?
A. 1/8 inch per foot B. 1/4 inch per foot C. 1/2 inch per foot D. Level allowed A. 1/8 inch per foot [ANSWER] Rationale: Pipes 4 inches and larger may slope at 1/8 inch per foot due to adequate scouring velocity.
22. What device protects against both backpressure and backsiphonage?
A. AVB
B. PVB
C. Double check D. RPZ D. RPZ [ANSWER]
Rationale: Reduced Pressure Zone assembly provides highest level of protection.
23. Cleanouts are required every:
A. 50 feet B. 75 feet C. 100 feet D. 150 feet C. 100 feet [ANSWER] Rationale: Horizontal drainage lines require cleanouts at intervals not exceeding 100 feet.
24. Gas shutoff valve must be located:
A. Within 3 feet of appliance B. In another room C. Outside only D. At meter only A. Within 3 feet of appliance [ANSWER] Rationale: Allows quick isolation during servicing or emergency.
25. What is required before covering underground plumbing?
A. Inspector approval B. Pressure test only C. Backfill only D. Photograph A. Inspector approval [ANSWER] Rationale: Code requires inspection before concealment.
26. Vent terminals must terminate at least how far above roof?
A. 1-1/4 inch B. 1-1/2 inch C. 2 inch D. 3 inch C. 2 inch [ANSWER]
51. What is the minimum required fixture unit value for a residential water
closet (private use)?
A. 2 DFU
B. 3 DFU
C. 4 DFU
D. 6 DFU
B. 3 DFU [ANSWER]
Rationale: Under Minnesota Plumbing Code (based on IPC), a private-use water closet is assigned 3 drainage fixture units (DFU). Public-use water closets are rated higher due to increased load and frequency.
52. What is the minimum water supply fixture unit (WSFU) value for a lavatory
(private)?
A. 0.5 WSFU
B. 1.0 WSFU
C. 1.5 WSFU
D. 2.0 WSFU
B. 1.0 WSFU [ANSWER]
Rationale: A private lavatory typically carries 1.0 WSFU for cold and hot combined demand. This value is used in sizing water distribution piping.
53. What is the minimum burial depth for building sewers in Minneapolis?
A. 12 inches B. 24 inches
C. 42 inches D. Below frost line D. Below frost line [ANSWER] Rationale: Because of extreme frost penetration in Minnesota, building sewers must be installed below frost depth to prevent freezing and structural damage.
54. What is required when a water heater is installed in a garage?
A. Seismic straps B. Elevation 18 inches above floor C. Insulation wrap D. Fire-rated enclosure B. Elevation 18 inches above floor [ANSWER] Rationale: Gas-fired appliances in garages must be elevated to reduce ignition risk from flammable vapors near floor level.
55. What is the maximum horizontal length of a 1-1/2 inch trap arm?
A. 3 feet B. 4 feet C. 6 feet D. 8 feet C. 6 feet [ANSWER] Rationale: Trap arm length is based on pipe diameter and slope. For 1-1/2 inch pipe at 1/4" per foot slope, maximum developed length is 6 feet.
56. What is required for plastic pipe penetrating a fire-rated wall?
A. Silicone sealant only B. Metal sleeve only C. Listed firestop system D. Foam insulation C. Listed firestop system [ANSWER]
60. What is the minimum diameter for a sump pump discharge pipe?
A. 1 inch B. 1-1/4 inch C. 1-1/2 inch D. 2 inch C. 1-1/2 inch [ANSWER] Rationale: Sump discharge piping must be sized to manufacturer specifications; 1-1/2 inch is common minimum to prevent restriction.
61. When must a thermal expansion tank be installed?
A. On all water heaters B. When backflow preventer or check valve creates closed system C. Only in commercial buildings D. Only on gas water heaters B. When backflow preventer or check valve creates closed system [ANSWER] Rationale: Closed systems prevent thermal expansion relief into public main; expansion tank prevents excessive pressure rise.
62. What is the minimum clearance of vent terminal from operable window?
A. 6 inches B. 12 inches C. 4 feet D. 10 feet C. 4 feet [ANSWER] Rationale: Prevents flue gases from entering building openings.
63. What is required for gas piping passing through foundation walls?
A. Foam seal B. Direct burial C. Sleeve and seal D. Compression fitting C. Sleeve and seal [ANSWER] Rationale: Protects pipe from corrosion and structural movement.
64. Minimum pressure for DWV air test?
A. 2 psi B. 3 psi C. 5 psi D. 10 psi C. 5 psi [ANSWER] Rationale: DWV systems must be tested at 5 psi air or 10-foot head of water.
65. What is the minimum size building drain for 3 bathrooms?
A. 2 inch B. 3 inch C. 4 inch D. 5 inch C. 4 inch [ANSWER] Rationale: DFU load calculation for three bathrooms exceeds 3-inch capacity.
66. What must be installed on island sink?
A. Studor vent only B. Loop vent C. No vent required D. Air gap only B. Loop vent [ANSWER]
A. 1-1/2 inch B. 2 inch C. 2-1/2 inch D. 3 inch B. 2 inch [ANSWER] Rationale: Modern washers discharge rapidly; 2-inch prevents overflow.
71. Cleanout required at base of each stack?
A. Yes B. No A. Yes [ANSWER] Rationale: Required for maintenance and clearing blockages.
72. Gas regulators installed indoors must be:
A. Painted B. Vented to exterior C. Sealed D. Wrapped B. Vented to exterior [ANSWER] Rationale: Relief vent must discharge outside to prevent gas buildup.
73. Minimum trap size for shower?
A. 1-1/4 inch B. 1-1/2 inch C. 2 inch D. 3 inch C. 2 inch [ANSWER]
74. Maximum temperature for T&P valve setting?
A. 150°F
B. 180°F
C. 200°F
D. 210°F
D. 210°F [ANSWER]
Rationale: Standard T&P valves rated 210°F and 150 psi.
75. What is required under slab PVC piping?
A. Sand bedding B. Gravel only C. Soil only D. Concrete direct A. Sand bedding [ANSWER] Rationale: Protects pipe and ensures uniform support.
76. Minimum size vent for kitchen sink?
A. 1-1/4 inch B. 1-1/2 inch C. 2 inch D. 3 inch B. 1-1/2 inch [ANSWER]
77. What is required for water hammer control?
A. Expansion tank B. Air chamber or arrestor C. Larger pipe D. PRV B. Air chamber or arrestor [ANSWER]
C. Same as valve outlet D. 1 inch C. Same as valve outlet [ANSWER]
82. What must not discharge into sump?
A. Groundwater B. Storm water C. Sewage D. Foundation drain C. Sewage [ANSWER]
83. Minimum size trap arm for WC?
A. 2 inch B. 3 inch C. 4 inch D. 1-1/2 inch B. 3 inch [ANSWER]
84. Vent piping must rise vertically at least before horizontal offset:
A. 6 inches B. 12 inches C. 24 inches D. 42 inches A. 6 inches [ANSWER]
85. What type of vent allowed for residential remodel (if approved)?
A. Mechanical vent B. Combination waste vent C. Loop vent only D. No vent
A. Mechanical vent [ANSWER]
86. Minimum burial depth for gas piping?
A. 12 inches B. 18 inches C. 24 inches D. 36 inches B. 18 inches [ANSWER]
87. What is required on commercial water heater over 200,000 BTU?
A. Draft hood B. Dedicated combustion air C. Smaller vent D. None B. Dedicated combustion air [ANSWER]
88. Minimum clearance B-vent to combustibles?
A. 0 inch B. 1 inch C. 2 inches D. 6 inches B. 1 inch [ANSWER]
89. What prevents trap siphonage?
A. Larger pipe B. Vent C. Slope D. Cleanout B. Vent [ANSWER]
