In vertical runs within a shaft, communications cables must be what type?

In vertical runs within a shaft, communications cables must be rated as CMR (Communications Riser). The CMR rating is specifically designed for cables that are installed in vertical spaces, such as riser shafts, where they could be exposed to fire or other hazards. CMR-rated cables are constructed to prevent flames from traveling vertically between floors, which is critical for maintaining safety in building infrastructure.

Using CMR cables in these applications helps to ensure compliance with fire safety codes and standards, reducing the risk of fire spreading through riser ducts. The other cable ratings, such as CMX and CMU, do not provide the same level of protection required for vertical installations. CMX is intended for outdoor use but not for vertical runs, while CMU is for general use in non-plenum areas but isn’t suitable for riser applications. Therefore, the use of CMR-rated cables for vertical runs within a shaft is essential for safety and code compliance.