Code Quiz

Aug 14, 2006 5:21 PM, By Steven Owen

Q. What is the maximum number of 12 AWG THHN insulated conductors permitted in a strut-type channel raceway that is 1½ inches by 1½ inches and of unlimited length? The channel location is defined as indoors and dry. The ambient temperature does not exceed 30°C. The raceway sections of this strut-type channel are joined with external joiners.

A) 54
B) 55
C) 34
D) 35

Answer: A

Explanation: The number of conductors permitted in a strut-type channel raceway shall not exceed the percentage fill noted in Table 384.22. When using external joiners, Table 384.22 permits a 40% fill. Therefore, for a 1½ inch by 1½ inch strut-type channel, the allowable fill according to Table 384.22 is 0.731 square inches.

From Chapter 9, Table 5, the approximate area of a 12 AWG THHN insulated conductor is 0.0133 square inches. 0.731 ÷ 0.0133 = 54.96. However, we must round down to 54, so as not to exceed the 40% fill requirement.

Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at necexpert@aol.com.