Which per-phase ampacity value is correct for six parallel No.3/0 THHN conductors in the same conduit?

Which per-phase ampacity value is correct for six parallel No.3/0 THHN conductors in the same conduit?

• A. 340 A
• B. 360 A
• C. 320 A
• D. 380 A

Answer: (B)

For conductors run in parallel, the current-carrying capacity adds across all the parallel paths. Six No. 3/0 THHN conductors in the same conduit share the load, so the per-phase ampacity is six times the ampacity of a single No. 3/0 THHN conductor at the chosen temperature rating. In the problem’s data, a single No. 3/0 THHN conductor has an ampacity of 60 A, so six in parallel give 6 × 60 A = 360 A per phase. This is why the per-phase ampacity value is 360 A.

For conductors run in parallel, the current-carrying capacity adds across all the parallel paths. Six No. 3/0 THHN conductors in the same conduit share the load, so the per-phase ampacity is six times the ampacity of a single No. 3/0 THHN conductor at the chosen temperature rating. In the problem’s data, a single No. 3/0 THHN conductor has an ampacity of 60 A, so six in parallel give 6 × 60 A = 360 A per phase. This is why the per-phase ampacity value is 360 A.