Five 1 AWG and five 3 AWG copper THW conductors in a 20-foot IMC raceway require a minimum trade size of what?

Five 1 AWG and five 3 AWG copper THW conductors in a 20-foot IMC raceway require a minimum trade size of what?

• A. 2 in.
• B. 3 in.
• C. 2 1/2 in.
• D. 11/2 in.

Answer: (C)

Raceway fill is all about space, not just how many wires you have. You determine how many conductors can run in a raceway by adding up each conductor’s cross‑sectional area and comparing that total to the interior cross‑sectional area of the raceway, with a maximum fill that limits how much of the raceway’s area can be occupied by conductors (the NEC uses a 40% fill limit for raceways). So for ten copper THW conductors (five of 1 AWG and five of 3 AWG), you first use the NEC tables to find each conductor’s cross‑sectional area and sum them. That total must fit within 40% of the interior area of the IMC raceway. When you check the IMC interior areas by trade size, the smallest size whose interior area is large enough to meet that 40% limit with ten conductors of these sizes is a 2 1/2 inch trade size. Hence, that is the minimum raceway size required.

Raceway fill is all about space, not just how many wires you have. You determine how many conductors can run in a raceway by adding up each conductor’s cross‑sectional area and comparing that total to the interior cross‑sectional area of the raceway, with a maximum fill that limits how much of the raceway’s area can be occupied by conductors (the NEC uses a 40% fill limit for raceways). So for ten copper THW conductors (five of 1 AWG and five of 3 AWG), you first use the NEC tables to find each conductor’s cross‑sectional area and sum them. That total must fit within 40% of the interior area of the IMC raceway. When you check the IMC interior areas by trade size, the smallest size whose interior area is large enough to meet that 40% limit with ten conductors of these sizes is a 2 1/2 inch trade size. Hence, that is the minimum raceway size required.