CEP Installation & Maintenance Practices 4 — Questions and Answers
Question 1: What is the maximum voltage drop recommended by NEC 210.19(A) Informational Note for branch circuits to minimize energy waste?
- 2% for branch circuits
- 3% for branch circuits (Correct answer)
- 5% for branch circuits
- 10% for branch circuits
Correct answer: 3% for branch circuits
NEC 210.19(A) Informational Note No. 4 recommends a maximum 3% voltage drop for branch circuits, with 5% total for feeders and branch circuits combined.
Question 2: When installing liquidtight flexible metal conduit (LFMC) in a wet location, what additional fitting requirement applies?
- Standard compression fittings may be used
- Only listed liquidtight fittings rated for wet locations are permitted (Correct answer)
- The conduit must be sealed with silicone at both ends
- LFMC is not permitted in wet locations
Correct answer: Only listed liquidtight fittings rated for wet locations are permitted
NEC 350.42 requires listed fittings specifically designed for use with LFMC, and when used in wet locations, those fittings must be listed for wet locations.
Question 3: A maintenance worker discovers that the equipment grounding conductor (EGC) in a 20A, 120V circuit has been disconnected at the receptacle. What is the immediate hazard?
- The circuit will not function without the EGC
- A ground fault will cause immediate tripping of the breaker
- Fault current may energize metal enclosures, creating a shock hazard (Correct answer)
- The neutral will carry doubled current, overheating the wire
Correct answer: Fault current may energize metal enclosures, creating a shock hazard
Without the EGC, a fault in the equipment will energize the metal casing, creating a lethal shock hazard since there is no low-impedance return path to trip the breaker.
Question 4: What does NEC Article 410 require regarding the clearance between a recessed luminaire and thermal insulation?
- No clearance is required if the insulation is fiberglass
- At least 3 inches of clearance unless the luminaire is IC-rated (Correct answer)
- At least 6 inches of clearance for all recessed luminaires
- Thermal insulation must never be within 12 inches of any luminaire
Correct answer: At least 3 inches of clearance unless the luminaire is IC-rated
NEC 410.116(B) requires at least 3 inches of clearance between recessed luminaires and thermal insulation unless the luminaire is listed and marked as suitable for direct contact with insulation (IC-rated).
Question 5: When testing a newly installed grounding electrode system, what is the maximum acceptable ground resistance for a single electrode per NEC 250.56?
- 5 ohms
- 10 ohms
- 25 ohms (Correct answer)
- 50 ohms
Correct answer: 25 ohms
NEC 250.56 states that if a single ground rod, pipe, or plate electrode has a resistance to ground exceeding 25 ohms, a supplemental electrode must be added.
Question 6: What is the purpose of applying anti-oxidant compound when terminating aluminum conductors on lugs?
- To improve the aesthetics of the termination
- To prevent the oxide layer from increasing resistance at the connection (Correct answer)
- To lubricate the conductor for easier insertion
- To meet NEC color-coding requirements for aluminum
Correct answer: To prevent the oxide layer from increasing resistance at the connection
Aluminum rapidly forms a high-resistance oxide layer when exposed to air; anti-oxidant compound penetrates and prevents oxidation, maintaining low contact resistance at the termination.
Question 7: Per NEC 300.5, what is the minimum burial depth for a 120/240V residential service lateral using direct-buried cable (USE-2 or URD)?
- 6 inches
- 12 inches
- 18 inches
- 24 inches (Correct answer)
Correct answer: 24 inches
NEC Table 300.5 requires a minimum burial depth of 24 inches for direct-buried service lateral conductors at 0–600V residential circuits.
CEP Installation & Maintenance Practices 4
What is the maximum voltage drop recommended by NEC 210.19(A) Informational Note for branch circuits to minimize energy waste?