Construction Electrician First Class (SCW), Retired

Tool 03 / Conduit fill

Know how much raceway is occupied.

Add up to three groups of THHN/THWN-2 conductors, then compare their total area with the Chapter 9 limit for the selected raceway.

Conductor group 1
Conductor group 2
Conductor group 3

Uses Chapter 9 Table 1 fill limits: 53% for one conductor, 31% for two, and 40% for three or more. Raceway areas come from Table 4; insulated conductor areas come from Table 5. This check does not determine ampacity adjustment or pulling difficulty.

Method reference: NEC Chapter 9 Tables 1, 4, and 5 walkthrough. Verify against the adopted code edition and manufacturer dimensions.