What does CMX mean?Updated 2 minutes ago

CMX (Communications, Residential) is the lowest UL cETLus fire rating for communication cables, determined by flame and smoke testing. 

It is critical to note that CMX does NOT mean "outdoor" or "direct burial cable".  All cable meant for outdoor/direct burial usage is considered to be OSP or Outside Plant cable, and often is completely unlisted with no fire rating at all.  

While outdoor/direct burial CMX fire rated cables do exist and are technically "Listed," they still have significant restrictions as to where, legally, they can be used indoors. In commercial settings, CMX is generally treated as unlisted indoors, permitted only for the first 50 feet when entering from outside. 

In residential single or duplex structures, CMX can be used indoors in limited, necessity-driven situations, but should be confined to as few cable drops as possible even when legally permitted. Always consult NEC/NFPA 70 and local codes for specific usage requirements.