Conduit Fill Practice for the California Electrician Exam

One worked example

Five 12 AWG THHN run in 1-inch EMT. Are you under the fill limit?

1. 1

   Name the problem

   This is a conduit fill. Bundle too many wires and they cannot shed heat, so code caps how much of the pipe the conductors can take up.

2. 2

   Add up the conductor area

   Each conductor takes a fixed area from Chapter 9 Table 5. Add them all together.

   5 × 12 AWG THHN = 0.0665 sq in

   Subtotal: 0.0665 sq in (5 conductors)

3. 3

   Find the allowed fill

   Table 1 sets the cap by how many conductors are in the pipe. One conductor 53%, two 31%, three or more 40%.

   5 conductors → 40% allowed

   Raceway area (Table 4): 0.864 sq in

   Allowed = 0.864 × 0.40 = 0.3456 sq in

4. 4

   Compare

   Your conductors fill 7.70% of the pipe. The raceway has room. You are under the limit.

   0.0665 sq in vs 0.3456 sq in allowed

Now try one

Your turn. Nine 12 AWG THHN in 1/2-inch EMT.

What percent of the pipe do they fill?

1. 1

   Compare

   Your conductors fill 39.38% of the pipe. The raceway has room. You are under the limit.

   0.1197 sq in vs 0.1216 sq in allowed

Train it on the platform