Enjoy this plenum rated Single-Pair Fire Alarm Cable from West Penn is suitable for use indoor, it is plenum rated to run through indoor ducts and other spaces that allow for environmental airflow to connect audio, control, initiating, and notification circuits. The conductors feature black and red insulation within a Plenum-rated PVC jacket, so it is easy to maintain polarity at each end. Shielding helps prevent RF interference of your audio signals.