Type CMR communication riser cables are primarily permitted for which application?

Type CMR (Communications Riser) cables are specifically designed and rated for use in vertical spaces, often referred to as risers, in a building. These are areas where cables run between floors, typically in conduits or other vertical shafts. The construction of CMR cables includes materials that limit the spread of flames and the generation of smoke, making them suitable for these environments where fire safety is a significant concern.

The application of CMR cables is critical in preventing fire from traveling up into the higher sections of a building through the riser spaces, which could potentially connect multiple floors. This application requires cables that not only provide good electrical performance but also adhere to strict safety regulations in terms of fire resistance.

The other options denote applications that do not fall under the specific use case for CMR cables. In-wall installations may require different ratings, such as CMP (Communications Multimedia Power) for in-wall spaces, while outdoor and underwater applications typically require cables specifically designed for those environments due to exposure to elements and moisture, which CMR cables are not engineered to withstand.