Chapter 18, Problem 20R

1. a. When more than three current-carrying conductors are installed in one raceway, their allowable ampacities must be reduced according to NEC __________.
2. b. The following is a project. We need four 15-ampere branch circuits. We will use two 3-wire multiwire branch circuits and 14 AWG THHN conductors. We will install the conductors in EMT. The room temperature will not exceed 86°F (30°C). The connected load is nonmotor and is noncontinuous.
   1. 1. What is the minimum trade size EMT? __________
   2. 2. What is the ampacity of the conductors before derating? __________
   3. 3. What is the ampacity of the conductors after derating? __________
   4. 4. What is the maximum overcurrent protection permitted for these conductors? __________
3. c. Let’s increase the conductor size to 12 AWG THHN for the same installation to see what happens.
   1. 1. What is the minimum trade size EMT? __________
   2. 2. What is the ampacity of the conductors before derating? __________
   3. 3. What is the ampacity of the conductors after derating? __________
   4. 4. What is the maximum overcurrent protection permitted for these conductors? __________
4. d. It (is) (is not) necessary to count equipment grounding conductors, a neutral conductor that carries the unbalanced current from other conductors of the same circuit, and/or “travelers” when installing 3-way and 4-way switches for the purposes of derating the ampacity of these conductors. Circle the correct answer. Explain.