Construction Electrical Systems in Construction 1 — Questions and Answers
Question 1: What is the standard voltage for most residential electrical service in the United States?
- 120/208V three-phase
- 120/240V single-phase (Correct answer)
- 277/480V three-phase
- 240/480V single-phase
Correct answer: 120/240V single-phase
Standard US residential service is 120/240V single-phase, providing 120V for outlets and 240V for large appliances.
Question 2: Which wire color is used for the grounding conductor in standard US residential wiring?
- White
- Black
- Red
- Green or bare copper (Correct answer)
Correct answer: Green or bare copper
Green insulated wire or bare copper conductor is the NEC-standard color code for equipment grounding conductors.
Question 3: What does GFCI stand for in electrical construction?
- Ground Fault Circuit Interrupter (Correct answer)
- General Fault Current Indicator
- Ground Fault Current Insulator
- General Fault Circuit Isolator
Correct answer: Ground Fault Circuit Interrupter
GFCI stands for Ground Fault Circuit Interrupter, a device that detects current leakage to ground and trips within milliseconds to prevent electrocution.
Question 4: According to the NEC, what is the maximum number of current-carrying conductors in a conduit before derating is required?
- 2
- 3 (Correct answer)
- 4
- 6
Correct answer: 3
NEC requires derating of conductor ampacity when more than 3 current-carrying conductors are bundled together in a raceway or cable.
Question 5: What type of conduit is most commonly used outdoors and in wet locations for commercial construction?
- EMT (Electrical Metallic Tubing)
- PVC (Rigid Nonmetallic Conduit) (Correct answer)
- FMC (Flexible Metal Conduit)
- ENT (Electrical Nonmetallic Tubing)
Correct answer: PVC (Rigid Nonmetallic Conduit)
PVC rigid nonmetallic conduit resists moisture and corrosion, making it the preferred choice for outdoor and wet-location installations.
Question 6: What is the minimum depth required for direct-burial electrical cable (UF cable) under a residential driveway?
- 6 inches
- 12 inches
- 18 inches
- 24 inches (Correct answer)
Correct answer: 24 inches
NEC Table 300.5 requires UF cable buried under residential driveways to be at a minimum depth of 24 inches to protect against damage from vehicle loads.
Question 7: Which document serves as the primary standard for electrical installations in construction in the United States?
- OSHA 1926 Subpart K
- NFPA 70 (National Electrical Code) (Correct answer)
- IEEE Standard 141
- ANSI C2 (NESC)
Correct answer: NFPA 70 (National Electrical Code)
NFPA 70, the National Electrical Code (NEC), is the primary standard adopted by most US jurisdictions governing safe electrical installations in buildings.
Construction Electrical Systems in Construction 1
What is the standard voltage for most residential electrical service in the United States?