Master Plumber Exam Gas Piping Systems 4 — Questions and Answers
Question 1: Propane (LP gas) differs from natural gas in a critical safety way because propane:
- Burns at a lower temperature
- Is lighter than air and dissipates upward
- Is heavier than air and can accumulate in low areas (Correct answer)
- Cannot be stored in tanks
Correct answer: Is heavier than air and can accumulate in low areas
Propane has a specific gravity of about 1.5, meaning it is heavier than air and will settle in basements, pits, and low spots creating explosion hazards.
Question 2: What is the required BTU content used to size natural gas piping when the specific BTU rating of appliances is unknown?
- 800 BTU per cubic foot
- 1,000 BTU per cubic foot (Correct answer)
- 1,100 BTU per cubic foot
- 1,200 BTU per cubic foot
Correct answer: 1,000 BTU per cubic foot
Natural gas is typically rated at approximately 1,000 BTU per cubic foot for standard piping sizing calculations.
Question 3: Which type of fitting is NOT approved for use in a gas piping system?
- Malleable iron fittings
- Steel weld fittings
- Cast iron fittings (Correct answer)
- Forged steel fittings
Correct answer: Cast iron fittings
Cast iron fittings are not approved for gas piping because they are brittle and can crack under pressure or mechanical stress.
Question 4: When installing a gas meter, what is the minimum required clearance from an electrical meter?
- 1 foot
- 2 feet
- 3 feet (Correct answer)
- 5 feet
Correct answer: 3 feet
Gas meters must be installed at least 3 feet away from electrical meters to reduce ignition risk from electrical sparks.
Question 5: A gas appliance connector (flexible connector) used to connect a range to the gas supply line may be a maximum of:
- 2 feet
- 3 feet
- 4 feet (Correct answer)
- 6 feet
Correct answer: 4 feet
Flexible gas appliance connectors are limited to a maximum length of 6 feet to prevent kinking, stress, and concealed installation.
Question 6: What is the minimum test pressure required for a medium-pressure gas system (above 0.5 psi) under NFPA 54?
- 1.5 times the working pressure, minimum 3 psi (Correct answer)
- 2 times the working pressure
- 50 psi regardless of working pressure
- The same as working pressure
Correct answer: 1.5 times the working pressure, minimum 3 psi
For systems above 0.5 psi, the test pressure must be at least 1.5 times the working pressure with a minimum of 3 psi.
Question 7: Which valve type is required as the main shutoff at the gas meter on a residential service?
- Globe valve
- Ball valve or plug (cock) valve (Correct answer)
- Gate valve
- Butterfly valve
Correct answer: Ball valve or plug (cock) valve
Ball valves and plug/cock valves are required at meter shutoffs because they provide a positive, quick quarter-turn shutoff and clear open/closed indication.
Master Plumber Exam Gas Piping Systems 4
Propane (LP gas) differs from natural gas in a critical safety way because propane: