EETC Wiring Methods 5 — Questions and Answers
Question 1: Which wiring method is specifically prohibited in ducts, plenums, or other air-handling spaces unless it is specifically listed for plenum use?
- Type MC cable with aluminum armor
- Type NM-B cable (Correct answer)
- Type CI (Circuit Integrity) cable
- Type CMP (Communications Plenum) cable
Correct answer: Type NM-B cable
NEC 300.22 prohibits Type NM-B cable in ducts or plenums because it is not listed for plenum use and produces toxic gases when burned.
Question 2: What is the maximum trade size for electrical nonmetallic tubing (ENT) permitted by the NEC?
- 1 inch
- 2 inches
- 3 inches (Correct answer)
- 4 inches
Correct answer: 3 inches
NEC 362.20 limits ENT to a maximum trade size of 2 inches; larger sizes are not listed or manufactured for ENT.
Question 3: In a concealed knob-and-tube wiring system found in older construction, what is prohibited from being done without special approval?
- Adding a new outlet
- Insulating over the wiring with thermal insulation (Correct answer)
- Connecting to a GFCI breaker
- Painting the ceramic knobs
Correct answer: Insulating over the wiring with thermal insulation
NEC 394.12 prohibits covering knob-and-tube wiring with thermal insulation because it depends on open-air cooling and insulation causes overheating.
Question 4: What is the purpose of an expansion fitting (expansion joint) in a conduit installation?
- To allow rotation of the conduit
- To compensate for thermal expansion and contraction (Correct answer)
- To increase the conduit fill capacity
- To transition between two different conduit types
Correct answer: To compensate for thermal expansion and contraction
Expansion fittings accommodate the linear expansion and contraction of conduit due to temperature changes, preventing stress on the system.
Question 5: When using surface metal raceways (Type 386), what is the primary NEC concern regarding splices?
- Splices are never permitted in surface raceways
- Splices must only be made at listed splice boxes or fittings (Correct answer)
- Splices require a minimum 12-inch straight section
- Splices must use crimp connectors only
Correct answer: Splices must only be made at listed splice boxes or fittings
NEC 386.56 permits splices in surface metal raceways only at listed junction boxes or fittings designed for that purpose.
Question 6: For a service entrance using rigid metal conduit, where must a conduit seal or plugged fitting be installed?
- At every coupling in the run
- At the service head and again at the meter socket
- Within 18 inches of the service entrance equipment (Correct answer)
- Only if the conduit is underground
Correct answer: Within 18 inches of the service entrance equipment
NEC 230.8 requires raceways to be arranged to drain and be sealed or plugged at the upper end to prevent moisture from entering the service equipment.
Question 7: Which statement is TRUE about using aluminum EMT?
- Aluminum EMT is not listed or manufactured
- Aluminum EMT cannot be buried in concrete
- Aluminum EMT is lighter and approved for most dry locations (Correct answer)
- Aluminum EMT requires a separate EGC always
Correct answer: Aluminum EMT is lighter and approved for most dry locations
Aluminum EMT is listed and permitted; it is lighter than steel EMT and is suitable for dry locations, though it cannot be buried in concrete or earth due to corrosion concerns.
EETC Wiring Methods 5
Which wiring method is specifically prohibited in ducts, plenums, or other air-handling spaces unless it is specifically listed for plenum use?