Is CMX Rated Ethernet Cable automatically meant for outdoor use? Is this what is meant by "Outdoor/Direct Burial" cable?Updated 6 months ago
No. The terms "CMX" and "outdoor Ethernet" cable address completely different things. The terms are often misapplied and confused with each other. The CMX term is now widely misunderstood as a result.
OSP = Stands for "Outside Plant" and means cable that is designed for installation outside and is resistant to water, ice, sunlight, and snow to varying degrees depending on the specific cable. This term is applied to above ground outdoor and direct burial Ethernet cable. OSP communications cable need not be marked at all, and may or may not have a low level CMX fire rating.
CMX = Stands for "Communications, Residential" and is a cETLus or UL fire rating. This means the cable passed (very minimal) vertical flame testing in a laboratory. A CMX fire rating is often seen stamped on certain outdoor and direct burial cables but must be tested per regulation otherwise it is counterfeit. Any CMX rated Ethernet cable needs to be backed up by the appropriate regulatory agency Certificate if installed in certain ways as outlined below.
What is the Law?
Commercial structures are treated the same regardless of circumstances. Any Outside Plant cable, including CMX fire rated, is considered not fire rated at all and may not be installed inside a commercial structure EXCEPT the cable may come into the structure up to 50 feet before termination or transition to an approved indoor fire rated cable like CM, CMR, or CMP. An exception is made where the cable may go further into the structure but the entire run coming in must be sealed in intermediate weight (IMC) threaded metallic conduit. The threads of the conduit sections must also be sealed.
Residential structures have the same restrictions as commercial structures except CMX fire rated outdoor cable may be used without restriction but for two caveats:
- The CMX fire rated outdoor cable must be 0.25" or thinner in overall diameter
- The structure may only be a single or duplex residential dwelling
What about apartments? Multi-unit dwellings like apartments are treated the same as commercial structures and all commercial rules apply.
Local Code dictates the Law in your jurisdiction, but the NEC/NFPA 70 National Guidelines are often accurate for your locale. It is always best to check first, especially in a commercial installation.
Learn more about outdoor cables in our Cable Academy blogs:
- Selecting the Correct Outdoor Ethernet Cable
- Running Outdoor Ethernet Cable: Tips, Techniques and Best Practices
Check out our outdoor and direct burial Ethernet cables below: