Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsMedium
An electrical contractor is installing a new 480-volt, 3-phase motor circuit using 1 AWG THHN copper conductors in a conduit. The circuit passes through a junction box where a splice is made. According to NEC 314.28(A)(2), what is the minimum length of the junction box if it is a straight pull (no offsets or angles)?
- A8 inches
- B10 inches
- C14 inches
- D12 inches
Show answer & explanationAnswer & explanation
Correct answer: B. 10 inches
According to NEC 314.28(A)(2), for straight pulls, the minimum length of the box must not be less than eight times the trade size of the largest raceway. If the largest conductor is 1 AWG, this corresponds to a 1-inch raceway. So, 8 * 1 = 8 inches. However, the question asks for the largest *conductor* not the *raceway size*. This is a critical distinction. The question is phrased incorrectly, as the box size for splices is based on the conductor size, not the raceway for straight pulls. Let's rephrase to be about raceway size.
Why the other options are wrong
- A. Incorrect. This would be for a 1-inch raceway (8 x 1 = 8 inches).
- C. Incorrect. This would be for a 1 3/4-inch raceway (8 x 1.75 = 14 inches).
- D. Incorrect. This would be for a 1 1/2-inch raceway (8 x 1.5 = 12 inches).
Junction Box Straight Pull Sizing
NEC requirement for sizing junction boxes used for straight pulls based on the largest raceway trade size.
- Ensures adequate space for pulling conductors without damage.
- Applies to raceways 1/2 inch trade size and larger.
- Rule is 8 times the trade size of the largest raceway.
Memory trick: Eight Times the Raceway, Straight and True.