Wiring Methods and Materials
Matching the Method to the Environment
Wiring-method questions hinge on suitability: is the method permitted in the location, and is it supported and secured correctly? Know the difference between flexible cords (not permitted as permanent wiring), raceways, cable assemblies, and conductors. Each Chapter 3 article gives permitted uses, prohibited uses, and installation requirements-focus on the prohibited uses, which drive most exam traps.
Support and Securing
Memorize the pattern rather than every number: Type NM cable is secured within 12 in. of boxes and supported every 4.5 ft; ENT and RMC have their own intervals; flexible connections have length limits. A frequent trap is a distance given in inches when the Code uses feet, or a support rule confused with a securing rule.
Boxes and Fill
Box fill is heavily tested. Count conductors, add for devices, clamps, and equipment grounding conductors per the tables, then compare to the box volume. Another trap: conductor ampacity vs. termination temperature rating-you may not always use the 90°C column for the final answer.
Raceway Fill and Bending
Raceway fill limits (typically 40% for three or more conductors) and bend radius rules appear often. Rule of thumb: no more than 360° of bends between pull points.
Worked Example
A question asks how far from a box Type NM cable must be secured. Answer: within 12 in. of the box and every 4.5 ft thereafter. If an answer says "within 8 in.," it is a distractor.