Fiber Optic Cable Fire Resistance Ratings

This article describes the fire resistance ratings code from NEC for fiber optic cables. We carry a large inventory of all types of fiber optic cables, you can get them here or by clicking on the following picture.

:: Why Do We Need Fire Rating on Fiber Cables?

The National Electrical Code (NEC) has classification system for optical fiber cables. These requirements specify how the fiber cables will perform under fire conditions. These requirements concentrate on how the fiber cables will add a dangerous amount of fuel and transmit fire from one place to another.

Article 770 of the NEC, also known as NFPA 70, covers requirements for optical fiber cables. NEC requires that cables used in premises, both commercial and residential, be “listed for the purpose” by a Nationally Recognized Test Laboratory.

UL (Underwriters Laboratories Inc.) is the most recognized listing agency in the US. UL 444 is the overall specification used to identify the requirements for listed communication cables.

:: Fiber Optical Cable Jacket Material Ratings

Insulation/jacketing material types are almost the same for fiber optic cables as for metallic cables, but the rating codes are different. The ratings include plenum use, general purpose, and conductive cable types. You can refer to section 770 of NEC code for more information.

From the flame resistance point, the requirements for fiber optic cables are the same as for conventional cables. Only plenum rated fiber cables can be used in air plenums and only riser rated fiber cables can be used in vertical riser shafts.

Plenum rated fiber cables may be substituted for riser use or general purpose use. Likewise, riser rated fiber cables may be substituted for general purpose use. In addition to that, ports and pathways for fiber cables also must meet the appropriate flammability and fire-stop requirements as with metallic cables.

What is Plenum Area?

A plenum is a building space, compartment,, duct or chamber used for air flow or to form part of an air distribution system. A plenum is a space used to move air to workspaces for the purpose of ventilation, heating or cooling. The informal words for plenums are “air duct” and “air return”.

What is Riser Area?

A riser is a floor opening, shaft, or duct that runs vertically through one or more floors. Riser cable is intended for use in vertical shafts that run between floors. Many buildings have a series of equipment rooms that are placed vertically in a reinforced shaft for the purpose of enclosing power distribution equipment, HVAC units, telephone distribution and other utility services throughout the building.

What is General Purpose Area?

A general purpose area is all other area that is not plenum or riser, which is on the same floor.

:: Fire Rating Levels

Four levels of fire resistance are specified for both nonconductive and conductive fiber cables. These 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.

1. OFNP and OFCP Fiber Cable

OFNP stands for Optical Fiber Nonconductive Plenum Cable and OFCP stands for 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 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.

The is 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).

2. OFNR and OFCR Fiber Cable

OFNR stands for Optical Fiber Nonconductive Riser Cable and OFCR stands for Optical Fiber Conductive Riser Cable. These cables must not transmit flame from one floor to another when placed vertically in a building shaft.

It can not be installed in plenums. This cable has fire-resistance characteristics tested to UL-1666 “Standard Test for Flame Propagation Height of Electrical and Optical Fiber Cable Installed Vertically in Shafts”. OFNP and OFCP cables can be used as substitutes for OFNR and OFCR cables respectively.

3. OFNG and OFCG Fiber Cable

OFNG stands for Optical Fiber Nonconductive General-Purpose Cable and OFCG stands for Optical Fiber Conductive General-Purpose Cable.  These cables may not transmit flame for more than 4 feet, 11 inch. They shall not penetrate floors or ceilings, i.e., may only be used within a single floor.

OFNG and OFCG cables can be installed in typical horizontal, single floor installations. They can not be installed in plenums or risers. The equivalent in CSA standard is “FT-4’ cable type. OFNP, OFNR and OFCP, OFCP cables can be used as substitutes for OFNG and OFCG respectively.

4. OFN and OFC Fiber Cable

OFN stands for Optical Fiber Nonconductive and OFC stands for 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.

OFN and OFC cables do not have equivalent in CSA rating.

:: Other Cables

Outside Plant and Unmarked Cables

NEC allows outside plant cables or other unmarked cables to be installed indoors as long as they are completely installed in metal conduit or electrical metallic tubing.