What Are OFNP, OFNR, OFNG And OFCG? Understanding Fiber Optic Cable Fire Ratings

Just like copper cables, NEC (National Electrical Code) requires indoor fiber optic cables be marked with their fire and smoking ratings. NEC requires all indoor fiber cables be marked correctly and installed properly for its intended use.

According to NEC, a building's inside area is divided into three types of sections: plenums, risers and general purpose areas.

:: What is a Plenum area?

A Plenum area is a building space used for air flow or air distribution system. In most buildings, the area above a drop ceiling or under a raised floor is used as the air return (source of air) for the air conditioning. Those drop ceiling and raised floors are also where fiber cables are often installed. If those cables were burning, they would give off toxic fumes and the fumes would be fed to the rest of the building by the air conditioner. As a result, people could be injured even though they are a long way from the fire.

:: What is a Riser area?

A Riser area is a floor opening, shaft or duct that runs vertically through one or more floors

:: What is General Purpose area?

All other area that is not plenum or riser and on the same floor is a general purpose area.

:: Fiber Optic Cable Fire and Smoking Rating Markings

OFNP Cables:

OFNP stands for Optical Fiber Nonconductive Plenum. OFNP cables have fire-resistance and low smoke production characteristics. They can be installed in ducts, plenums and other spaces used for building airflow. This is the highest fire rating fiber cable and no other cable types can be used as substitutes.

OFCP Cables:

OFCP stands for Optical Fiber Conductive Plenum. OFCP cables have the same fire and smoking rating as OFNP cables but they have a conducting armor or central strength member which is usually steel. OFCP cables must be properly grounded at both ends. As a result, OFCP cables can not be installed in the same cable tray or conduit as power cables.

OFNR Cables:

OFNR stands for Optical Fiber Nonconductive Riser. OFNR cables are used in Riser areas which are building vertical shafts or runs from one floor to another floor. OFNR cables can not be installed in plenum areas since they do not have the required fire and smoking rating as Plenum rated cables. OFNP plenum cables can be used as substitutes for OFNR cables.

OFCR Cables:

OFCR stands for Optical Fiber Conductive Riser. OFCR cables have the same fire rating characteristics as OFNR cables but they have conducting armor or central strength member which is usually steel. OFCR cables should also be properly grounded at both ends. OFCP cables can be used as substitutes for OFCR cables. OFCR cables can not be installed in the same cable trays or conduits as power cables.

OFNG Cables:

OFNG stands for Optical Fiber Nonconductive General-Purpose. They are typically used in horizontal cabling, single floor applications. OFNG cables can not be used in plenums or risers. OFNP and OFNR cables both can be used as substitutes for OFNG cables.

OFCG Cables:

OFCG stands for Optical Fiber Conductive General-Purpose. They have the same fire characteristics as OFNG cables but they have conducting armor or central strength members which is typically steel. OFCG cables should be properly grounded at both ends. They should not be installed in the same cable tray or conduits as power cables.