PC Wiring Methods and Protection 3 — Questions and Answers
Question 1: When conductors of different systems share a raceway, what is the primary NEC requirement per 300.3(C)?
- All conductors must be the same gauge
- All conductors must be insulated for the highest voltage present (Correct answer)
- Low-voltage conductors must occupy a separate compartment
- AC and DC conductors may not share the same raceway
Correct answer: All conductors must be insulated for the highest voltage present
NEC 300.3(C)(1) requires that all conductors share insulation rated for the highest voltage present when they occupy the same raceway.
Question 2: What is the minimum radius of the inner edge of a bend in ¾-inch EMT per NEC Table 344.24?
- 4 inches
- 4½ inches
- 6 inches
- 10 inches (Correct answer)
Correct answer: 10 inches
NEC Table 344.24 specifies a 10-inch minimum bend radius for ¾-inch EMT to prevent conductor insulation damage.
Question 3: Which of the following wiring methods is approved for use in a Class I, Division 1 hazardous location?
- Type MC-HL cable (Correct answer)
- Type NM cable
- Electrical metallic tubing (EMT)
- Liquidtight flexible nonmetallic conduit
Correct answer: Type MC-HL cable
Type MC-HL (Hazardous Location) cable is specifically listed for Class I, Division 1 locations per NEC 501.10.
Question 4: Per NEC 358.30, EMT must be securely fastened within how many inches of each outlet box, junction box, or cabinet?
- 18 inches
- 24 inches (Correct answer)
- 36 inches
- 48 inches
Correct answer: 24 inches
NEC 358.30(A) requires EMT to be secured within 24 inches of each outlet box, junction box, cabinet, or fitting.
Question 5: What protection is required for NM cable passing through a 2×4 stud less than 1¼ inches from the edge of the stud?
- No protection required at that depth
- A listed steel plate at least 1/16 inch thick (Correct answer)
- A conduit sleeve at least 2 inches long
- An insulating bushing
Correct answer: A listed steel plate at least 1/16 inch thick
NEC 300.4(A)(1) requires a steel plate at least 1/16 inch thick when NM cable is within 1¼ inches of the edge of framing members.
Question 6: Liquidtight flexible metallic conduit (LFMC) is permitted for outdoor use in which scenario?
- Any outdoor application without restriction
- Only when listed for outdoor use and protected from sunlight (Correct answer)
- Only when buried at least 6 inches deep
- It is never permitted outdoors
Correct answer: Only when listed for outdoor use and protected from sunlight
LFMC is permitted outdoors when listed for that use, but must be protected from direct sunlight unless listed as sunlight-resistant per NEC 350.12.
Question 7: What is the NEC requirement for sealing conduits entering a service entrance panel from underground?
- No sealing is required if the conduit is Schedule 80
- The conduit must be sealed to prevent entry of gases or moisture (Correct answer)
- A bushing is sufficient without sealing
- Sealing is required only if the conduit exceeds 2 inches in diameter
Correct answer: The conduit must be sealed to prevent entry of gases or moisture
NEC 230.8 requires raceways entering buildings from underground to be sealed or plugged to prevent gas or moisture from entering the service equipment.
PC Wiring Methods and Protection 3
When conductors of different systems share a raceway, what is the primary NEC requirement per 300.3(C)?