CMR stands for Communications Riser Cable, a type of communication cable rated for use in vertical spaces, such as between floors in commercial or industrial buildings.
CMR-rated cables are specifically designed to prevent the spread of flames between building floors through vertical shafts or riser spaces. These areas are used to route communication cables between floors, often alongside other mechanical or electrical systems. To meet riser rating requirements, CMR cables are constructed with flame-retardant materials that help confine fire to its point of origin. This makes them a vital part of building safety design, particularly in large facilities where vertical cable pathways are common.
Unlike CMP cables, which are plenum-rated and provide the highest level of flame resistance, CMR cables are intended for use in non-plenum vertical risers where air-handling systems are not present. They balance fire protection with flexibility and cost efficiency, making them a popular choice for structured cabling systems used in data, security, access control, and audiovisual applications. CMR cables are typically jacketed with flame-retardant PVC and tested under specific burn conditions to ensure compliance with national standards.
CMR cables are regulated by the National Electrical Code (NEC) under Article 800 and are tested according to Underwriters Laboratories (UL) 1666, which measures vertical flame spread performance in riser applications. These regulations ensure the cable’s safety and suitability for use in multi-story commercial buildings.
Riser-rated cables emerged as building codes evolved to address fire propagation in vertical cable runs. The rating system, established by the NEC and UL, standardized how cables are classified for safety, distinguishing between general-purpose, riser, and plenum applications. Over time, advancements in jacket compounds and flame-retardant materials have improved both performance and reliability in CMR-rated products.