A commercial electrician is installing a new 480-volt, 3-phase motor feeder in a wet location. The feeder consists of 3/0 AWG THWN-2 copper conductors. What is the minimum allowable bend radius for 1-1/2 inch Rigid Metal Conduit (RMC) with these conductors, assuming a field bend without a one-shot bender?
- A12 inches
- B7 1/2 inches
- C6 inches
- D9 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 9 inches
According to NEC Table 2, for a 1-1/2 inch trade size RMC, the minimum radius of the bend is 6 times the conduit diameter for conductors without lead sheath. The outside diameter of 1-1/2 inch RMC is approximately 1.9 inches. Therefore, 6 * 1.9 inches = 11.4 inches. However, NEC 344.24, 'Bends - How Made', refers to Table 2. Table 2 actually lists the minimum bend radius as a multiple of the nominal trade size for different conduit types. For RMC without a lead sheath, if the conductors are 1 AWG or larger, or using a one-shot bender for 2-inch and larger, it's 8 times the trade size. Otherwise, it's 6 times. For 1-1/2 inch RMC, 6 times 1.5 inches is 9 inches. This is the correct calculation.
Why the other options are wrong
- A. Incorrect. This would be for a 2-inch RMC (6 x 2 = 12 inches).
- B. Incorrect. This would be for a 1 1/4-inch RMC (6 x 1.25 = 7.5 inches).
- C. Incorrect. This would be for a 1-inch RMC (6 x 1 = 6 inches).
RMC Bend Radius (Field Bend)
The minimum radius allowed for a bend in Rigid Metal Conduit (RMC) when made in the field, as specified by NEC Table 2.
- Prevents damage to conductors during pulling.
- Sized as a multiple of the conduit's trade size.
- Differs based on conductor type and bending method (e.g., one-shot bender).
Memory trick: Bending Rules Reduce Wire Woes.