What sizes are plenum cable?

• A. 30 and 32
• B. 26 and 28
• C. 22 and 24
• D. 18 and 20

Answer: (C)

Plenum cable is rated for use in air‑handling spaces, like ceilings, where the insulation must limit flame spread and smoke. For alarm and security wiring in those spaces, the standard conductor sizes are 22 and 24 AWG. These gauges strike a practical balance: they’re thin enough to be flexible and fit through tight spaces, yet thick enough to carry the small signaling currents used by sensors, panels, and similar devices without excessive resistance. Larger gauges (18–20) are heavier and used where more current is needed, while smaller gauges (30–32) are fragile and not typical for everyday plenum low‑voltage runs. So the common plenum cable sizes are 22 and 24 AWG.