Raceways, Conductors, and Cable Systems
Raceway fundamentals
Expect questions on conduit types (rigid metal, intermediate metal, electrical metallic tubing, rigid nonmetallic, flexible), their permitted uses, and fill limits. Understand that raceway fill is based on conductor count and size, that bends are limited in number between pull points, and that supports and expansion fittings matter. Know how to calculate conduit fill from Chapter 9 tables and how to apply the jam ratio concept in general terms.
Conductor sizing and derating
Know ampacity tables, ambient temperature correction, and adjustment for more than three current-carrying conductors in a raceway. Understand that the equipment grounding conductor is sized by rule, not by ampacity, and that neutral conductors count as current-carrying only in defined circumstances. Recognize termination temperature limitations, which can cap the usable ampacity below the insulation rating.
Traps in questions
Frequent errors: applying derating before temperature correction or vice versa without following the required sequence, forgetting that the 90-degree column is often used only for derating calculations, and ignoring the weakest link at terminations. Another trap is confusing conduit fill with box fill.
Worked example
Six current-carrying conductors in a raceway require adjustment. Rule of thumb: apply the adjustment factor for the count, then the ambient correction, then compare to the termination rating and take the lowest value. Always state the sequence in your reasoning so partial credit is clear.
Practice approach
Work numerical problems with the tables open, then repeat closed-book, and write the sequence of steps from memory each time.