General Contractor License Mechanical, Electrical, and Plumbing Systems 1 — Questions and Answers
Question 1: Under the National Electrical Code (NEC), what is the minimum burial depth for a residential underground feeder (UF) cable installed without conduit?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
NEC requires UF cable to be buried at least 24 inches deep in most residential applications, but 18 inches when the circuit is GFCI-protected and limited to 120V/20A.
Question 2: Which type of pipe is most commonly required by code for natural gas supply lines inside a residential structure?
- PVC schedule 40
- Black steel pipe (Correct answer)
- CPVC
- PEX tubing
Correct answer: Black steel pipe
Black steel pipe is the standard code-approved material for interior natural gas supply lines because it is durable and does not corrode from gas contact.
Question 3: According to the IRC, what is the required minimum headroom clearance for a residential stairway?
- 6 feet 4 inches
- 6 feet 6 inches
- 6 feet 8 inches (Correct answer)
- 7 feet 0 inches
Correct answer: 6 feet 8 inches
The IRC requires a minimum headroom clearance of 6 feet 8 inches measured vertically from the stair nosing to any overhead obstruction.
Question 4: When sizing a residential water heater, which factor is the MOST important determinant of required capacity?
- Tank color and insulation rating
- First Hour Rating (FHR) (Correct answer)
- BTU input rating only
- Tank diameter
Correct answer: First Hour Rating (FHR)
The First Hour Rating (FHR) indicates how many gallons a water heater can supply in the first hour of use, making it the primary sizing factor for residential demand.
Question 5: In a residential electrical panel, a double-pole 240V breaker that trips on only one leg is an indication of what condition?
- Overload on the neutral wire
- A failed breaker requiring replacement (Correct answer)
- Proper load balancing
- A ground fault only
Correct answer: A failed breaker requiring replacement
A double-pole breaker that trips on only one side indicates the breaker mechanism has failed internally and the entire breaker must be replaced.
Question 6: Which plumbing fitting is required at the base of a soil stack where it transitions from vertical to horizontal?
- 90-degree elbow
- Sanitary tee
- Long-sweep 1/4 bend (Correct answer)
- Coupling
Correct answer: Long-sweep 1/4 bend
A long-sweep 1/4 bend (long-turn 90) is required at the base of a soil stack to allow waste flow to transition smoothly from vertical to horizontal without clogging.
General Contractor License Mechanical, Electrical, and Plumbing Systems 1
Under the National Electrical Code (NEC), what is the minimum burial depth for a residential underground feeder (UF) cable installed without conduit?