EETC Wiring Methods 3 — Questions and Answers
Question 1: In a cable tray installation, what is the minimum width of a ladder-type cable tray for a 600V power cable with an outside diameter of 3.5 inches?
- 6 inches
- 9 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
NEC 392.22 requires single-conductor cables in ladder trays to maintain spacing and the tray width must accommodate the cable diameter; 12-inch trays accommodate most standard power cables.
Question 2: What NEC article governs the installation of electrical metallic tubing (EMT)?
- Article 342
- Article 344
- Article 348
- Article 358 (Correct answer)
Correct answer: Article 358
NEC Article 358 specifically covers the installation and use of electrical metallic tubing (EMT).
Question 3: A 'wet location' as defined by the NEC includes all of the following EXCEPT:
- Underground installations
- Locations subject to saturation with water
- Exposed to weather
- Indoor locations with controlled humidity below 50% (Correct answer)
Correct answer: Indoor locations with controlled humidity below 50%
The NEC defines wet locations as those subject to weather, saturation, or underground exposure; controlled indoor humidity does not qualify as a wet location.
Question 4: When installing conduit through a fire-rated wall, what is required?
- A conduit seal fitting only
- A firestop system listed for the opening (Correct answer)
- A junction box on each side
- Metal conduit must be used
Correct answer: A firestop system listed for the opening
NEC 300.21 requires that penetrations of fire-rated walls be firestopped using approved materials or methods to maintain the fire rating.
Question 5: What is the maximum allowable fill percentage for a conduit containing three current-carrying conductors?
- 31% (Correct answer)
- 40%
- 53%
- 60%
Correct answer: 31%
NEC Table 1, Chapter 9 limits conduit fill to 40% for two conductors and 40% maximum, but with three or more conductors the fill is 40%; however, for conductors over 2, fill is limited to 40% per NEC—specifically 40% for 2 conductors and 40% for 3+, the standard answer for 3+ conductors is 40%.
Question 6: Liquidtight flexible nonmetallic conduit (LFNC) is identified by which NEC article?
- Article 350
- Article 356 (Correct answer)
- Article 360
- Article 362
Correct answer: Article 356
NEC Article 356 covers liquidtight flexible nonmetallic conduit (LFNC) installation and use requirements.
Question 7: Which wiring method requires a bushing where conductors enter a box or enclosure to protect conductors from the sharp edges of conduit?
- Type NM cable only
- All rigid conduit types (Correct answer)
- Flexible metal conduit only
- All metallic wiring methods
Correct answer: All rigid conduit types
NEC 300.4(G) and 344.46 require insulating bushings where rigid conduit enters enclosures to protect conductors from abrasion.
EETC Wiring Methods 3
In a cable tray installation, what is the minimum width of a ladder-type cable tray for a 600V power cable with an outside diameter of 3.5 inches?