Wiring Methods and Installation Practices
This domain tests wiring-method selection: cable or raceway, support, fill, separation, plenum and riser ratings, and firestopping. Questions usually give a field condition and ask which article controls it.
Core rules
- Class 1 circuits use Chapter 3 methods such as EMT, FMC, MC, or NM cable where permitted. Class 2 and Class 3 circuits use Article 725 Part III methods and must be separated by at least 2 in (50 mm) from power and Class 1 conductors unless a barrier or listed exception applies (725.136).
- In a plenum, 300.22(C) limits wiring to metal raceways and to cables specifically listed for plenum use, such as CMP, CL2P, and FPLP. Riser cable (CMR, CL2R, FPLR) may be used in risers but not in plenums. General-purpose cable is for other spaces.
- Support cables per 300.11. Do not hang them from ceiling grid, sprinkler pipe, or duct hangers. Firestop penetrations per 300.21.
- Box fill is governed by 314.16; conduit fill by Chapter 9, with 40 percent fill for three or more conductors. Bending radius follows 300.34.
Worked example
A CL2 cable runs above a suspended ceiling that is used as a return-air plenum. Because 300.22(C) applies, the cable must be CL2P. A CL2R would be acceptable only if the space were a riser and not a plenum. The cable also needs independent support and 2 in separation from luminaire wiring unless a barrier is used.
Traps
Using CL2R in a plenum; supporting from ceiling grid; exceeding 40 percent conduit fill; running fire alarm and Class 2 in one raceway without a barrier; failing to firestop; using NM cable in a wet location.