Article 770 of the NEC (National Electrical Code), also known as NFPA 70, covers requirements that specify cables used in premises, both commercial and residential to be “listed for the purpose” by a NRTL (National Recognized Test Laboratory). Besides, NEC has also specified the flame-retardant and fire-resistant rating codes for optical fiber cables, which includes plenum, riser and general purpose.
Typically, there are four levels of fire resistance for both non-conductive and conductive cables. The fire resistance levels are outlined below from most stringent to least. The ratings are hierarchical, i.e., from a fire resistance standpoint, a higher rating can be substituted for any lower rating, but not vice versa (OFNG and OFN are interchangeable for NEC purposes). Also, non-conductive may be substituted for conductive, but not vice versa.
|NEC Marking||CSA Equivalent||Common Term|
|OFNP/OFCP||FT6||Non-conductive/conductive optical fiber plenum cable|
|OFNR/OFCR||n/a||Non-conductive/conductive optical fiber riser cable|
|OFNG/OFCG||FT4||Non-conductive/conductive optical fiber general-purpose cable|
|OFN/OFC||n/a||Non-conductive/conductive optical fiber general-purpose cable|
OFNP/OFCP – OFNP refers to Optical Fiber Non-conductive Plenum Cable and OFCP refers to Optical Fiber Conductive Plenum Cable. OFNP and OFCP cables must have resistance to flame spread and reduced smoke generating properties. These cables are approved for placement in air handling ducts and chambers (Plenums) without the use of fireproof conduit. The purpose of the rating is to lessen the transmission of fire and visible smoke to unaffected parts of the building. Toxic or corrosive elements of the smoke are not measured. OFNP/OFCP Plenum cables are held to the most stringent testing of any of the cables rated by NEC, rated for both flammability and smoke generation. And they have the highest cable fire rating and no other cable types can be used as substitutes. This cable type can be marked as “FT-6” by Canadian Standards Association (CSA).
OFNR/OFCR – OFNR refers to Optical Fiber Non-conductive Riser Cable and OFCR refers to Optical Fiber Conductive Riser Cable. These cables must not transmit flame from one floor to another when placed vertically in a building shaft (riser). OFNR/OFCR Riser cables are subjected to flame tests only, and are not held to as high of a standard as Plenum rated cables. Plenum cables may be substituted for Riser.
OFNG/OFCG – OFNG refers to Optical Fiber Non-conductive General-Purpose Cable and OFCG refers to Optical Fiber Conductive General-Purpose Cable. These cables may not transmit flame for more than 4 ft, 11 in. They shall not penetrate floors or ceilings, i.e., may only be used within a single floor. OFNG/OFCG cables can be used anywhere in commercial buildings other than areas where Plenum or Riser cables are required. They are flame tested and held to a lower standard than either Plenum or Riser cables. Both Plenum and Riser rated cables are acceptable substitutes for General Purpose rated cables.
OFN/OFC – OFN refers to Optical Fiber Non-conductive and OFC refers to Optical Fiber Conductive. These cables may not transmit flame to the top of the tray. They shall not penetrate floors or ceilings, i.e., may only be used within a single floor.
Note: Apart from the four flame resistance levels specified by NEC, there is another commonly used cable—LSZH. Required in many situations by European standards (RoHS), LSZH cables have been developed to eliminate toxic gasses produced when water interacts with substances released when a cable’s jacket burns. They are recommended for use in enclosed areas with little ventilation or in areas where sensitive equipment could be damaged. In addition to designated as LSZH, it may be rated Riser or General Purpose.
From the comparison above, we can see that OFNP plenum cables have the most excellent capacity for fire resistance. FS provides various types of OFNP plenum cables including patch cables, MTP plenum trunk cables and MTP-LC plenum harness cables, among which the MTP plenum cables are the most desirable product for addressing the problems of unfortunate fire incident and high bandwidth demands in a restricted data center space. As they not only meet the high density cabling with higher port density MTP connector, but also protect equipment and people during a fire.
In addition, our MTP cables provide highest performance and lowest insertion loss. MTP fiber connectors are directly sourced from U.S. Conec® and are tested and guaranteed by 3D interferometer. Moreover, the insertion loss of MTP connectors is kept at no more than 0.35 dB ensuring good physical connection and clean signal. They are genuine MTP high quality cables made of Corning® fibers. For the details, please visit www.fs.com.