What is CMR cable?

CMR cable is Communications Riser cable. It is used in risers or shafts from floor to floor and only a riser or plenum (CMP) cable may be used for that purpose. Though CMP can be used in lieu of CMR, you cannot use CMR in a plenum space. CMR and CMP are fire resistance classifications. CM is for general purpose that may be used elsewhere not requiring special fire code considerations.