When alarm conductors are installed between floors of a building, the cable must be _____ rated.

The correct choice is that the cable must be Riser or Plenum rated when alarm conductors are installed between floors of a building. Riser-rated cables are specifically designed to be used in vertical spaces, like between floors, and are engineered to limit the spread of fire and the emission of smoke in vertical shafts. This is important in maintaining safety and compliance with building codes, which often require such specifications for any cable that runs between floors to prevent fire hazards.

Plenum-rated cables, meanwhile, are intended for use in spaces that facilitate air circulation for heating and air conditioning systems. While they are also fire-resistant, they are typically used in ceiling spaces where air flows are prominent.

Understanding these ratings is crucial for ensuring that security installations adhere to local codes and safety regulations, thereby preventing possible fire hazards while providing effective security solutions. Low voltage and shielded ratings are relevant for different applications, but do not specifically address the requirements for vertical installations in a way that ensures minimal fire risk.