Courtesy of www.MikeHolt.com
Q. What are the rules for the number of conductors permitted in a raceway?
See answer below.
A. As per Sec. 300.17 [Number and Size of Conductors in a Raceway], raceways must be large enough to permit the installation and removal of conductors without damaging their insulation.
When all conductors within a raceway are the same size and of the same insulation type, the number of conductors permitted or the raceway size can be determined using Annex C [Note (1) of Chapter 9].
When different size conductors are installed in a raceway, conductor fill is limited to the percentages in Table 1 and Note (6) of Chapter 9. Follow these steps for sizing raceways:
Step 1: When sizing a raceway, first determine the total area needed for the conductors (Chapter 9, Table 5 for insulated conductors and Chapter 9, Table 8 for bare conductors).
Step 2: Select the raceway from Chapter 9, Table 4 in accordance with the percent fill listed in Chapter 9, Table 1.
Here’s an example that helps illustrate the use of this rule.
Question: What size Schedule 40 PVC conduit is required for the following conductors?
- 3—500kcmil THWN-2
- 1—250kcmil THWN-2
- 1—3 AWG THWN-2
Solution:
Step 1: Determine the total area needed for the conductors [Chapter 9, Table 5].
500kcmil THWN-2 0.7073 in2 × 3 = 2.1219 in.2
250kcmil THWN-2 0.3970 in2 × 1 = 0.3970 in.2
3 AWG THWN-2 0.0973 in2 × 1 = +0.0973 in.2
Total Area of Conductors = 2.6162 in.2
Step 2: Select the raceway at 40% fill [Chapter 9, Table 1 and Table Note (6), and Table 4].
Use 3 in. Schedule 40 PVC because there is 2.907 sq in. of conductor fill at 40%.
These materials are provided to us by Mike Holt Enterprises in Leesburg, Fla. To view Code training materials offered by this company, visit www.mikeholt.com/code.
