A fiber cable’s printed designation is eight letters long at most, and most of them describe the cable’s fire and smoke behavior. Two of them describe something else entirely, and those two decide a question the fire rating cannot answer: whether this cable may sit in the same tray or raceway as power conductors.
The mark is OFNP, OFNR, OFNG, OFN, OFCP, OFCR, OFCG or OFC. Read it as two facts stacked on top of each other rather than as one code.
The mark carries two independent facts
The first fact is whether the cable contains a metallic member. The second is where it is permitted to be installed. The code spells both out in its marking table.
Mark | What the code says it is |
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OFNP | Nonconductive optical fiber plenum cable |
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OFCP | Conductive optical fiber plenum cable |
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OFNR | Nonconductive optical fiber riser cable |
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OFCR | Conductive optical fiber riser cable |
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OFNG | Nonconductive optical fiber general-purpose cable |
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OFCG | Conductive optical fiber general-purpose cable |
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OFN | Nonconductive optical fiber general-purpose cable |
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OFC | Conductive optical fiber general-purpose cable |
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The letters parse in a fixed order. OF is optical fiber in every case. The next letter is N or C: nonconductive or conductive, meaning the cable either does or does not contain a metallic member. The final letter, where there is one, is P for plenum, R for riser or G for general purpose. So OFCR is a conductive optical fiber riser cable, and its C and its R answer two unrelated questions.
One detail in that table is worth noting. In the edition consulted, OFN and OFC carry the same "general-purpose" description as OFNG and OFCG, and the substitution table groups each pair into a single row. The two sets behave as one class there, so a jacket marked without the G sits in the same row as one marked with it.
What the code does not cover
The article says so on its first page, and it is the most useful sentence in it for anyone comparing a designation against a datasheet. The provisions apply to optical fiber cables and raceways, and then: this article does not cover the construction of optical fiber cables and raceways.
A mark of OFNR therefore tells you nothing about fiber count, mode, core and cladding dimensions, buffer type, jacket material, tensile rating or attenuation. Those are properties of the cable, described in different documents. The mark describes the cable’s fire and smoke performance and its conductive status, and that is all. Where construction is concerned, the guide to loose tube versus tight buffer construction is the right place to look.
The code does define a few terms that bear on the mark. A cable sheath is a covering over the optical fiber assembly that includes one or more jackets and may include one or more metallic members or strength members — which is how a conductive cable comes to be conductive. And a composite optical fiber cable, one containing optical fibers and current-carrying electrical conductors, is classified as an electrical cable in accordance with the type of its electrical conductors, and must be constructed, listed and marked under the article for that type. A fiber-plus-copper composite is not a fiber cable with copper in it. It is an electrical cable.
The one case where the N and the C change the answer
The installation article deals with mixing fiber with other conductors in three separate paragraphs, and the N or C matters in exactly one of them.
Mixed with | In what | Nonconductive (N) | Conductive (C) |
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Electric light, power, Class 1, non-power-limited fire alarm, or medium-power network-powered broadband circuits at 600 volts or less | The same cable tray or raceway | Permitted | Not permitted |
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The same circuits | An enclosure housing the electrical terminations of that circuit | Not permitted, subject to five listed exceptions | Not addressed by this provision |
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Communications circuits, community antenna television and radio distribution, and low-power network-powered broadband circuits | The same cable tray, enclosure, raceway or cable routing assembly | Permitted | Permitted |
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Class 2 and Class 3 remote-control, signaling and power-limited circuits, and power-limited fire alarm systems | The same cable tray, enclosure or raceway | Permitted | Permitted |
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Where the N or the C actually changes the answer
Read the first row and the last two rows together and the pattern is clear. A nonconductive fiber cable may share a tray or raceway with power conductors rated 600 volts or less. A conductive one may not, and the paragraph says so directly rather than by implication. But when the other conductors are communications, or CATV, or Class 2 and Class 3, or power-limited fire alarm, both kinds of fiber cable are permitted together with them and the distinction disappears.
The second row is a different rule wearing similar words. The prohibition there is on enclosures that house the electrical terminations of a power circuit, and the exceptions include a fiber cable functionally associated with the circuit, factory- or field-assembled control centers, and installations in industrial establishments where only qualified persons service the work. The distinction between a tray or raceway and an enclosure holding terminations is easy to lose, and it changes which rule applies.
The same letter decides substitutions, and only in one direction
The listing article gives a substitution table, and reading its direction is more informative than reading its rows.
Cable type marked | Permitted substitutions |
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OFNP | None |
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OFCP | OFNP |
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OFNR | OFNP |
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OFCR | OFNP, OFCP, OFNR |
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OFNG, OFN | OFNP, OFNR |
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OFCG, OFC | OFNP, OFCP, OFNR, OFCR, OFNG, OFN |
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The column heading is the giveaway: these are the types that may be used in place of the cable marked in the first column. So an OFNP cable may be installed where an OFCP cable was specified, and an OFCP cable may not be installed where an OFNP was specified.
Sort the whole table by that direction and a single rule covers every row. A nonconductive cable may substitute for a conductive one, and a conductive cable never substitutes for a nonconductive one. OFNP has no permitted substitution at all, which makes it the top of the hierarchy in both senses: it is the fire and smoke rating that satisfies every location, and being nonconductive it can also stand in for the conductive types. OFCG and OFC accept six substitutions none of which is conductive except through the generic list.
That is the same direction as the admixing rule above, arrived at from a different part of the code. Nonconductive is the safer direction in both: a decision that moves toward fewer metallic members is the safe move, and one that moves toward more has to be justified.
The substitution hierarchy runs one way
The P, the R and the G are fire and smoke, and each one is tested
The remaining letter describes where the cable may be installed, and each level is backed by a test.
Mark | Listed for | The test the code names |
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OFNP, OFCP | Ducts, plenums and other spaces used for environmental air, with adequate fire-resistant and low smoke producing characteristics | Peak optical density of 0.5 or less, average optical density of 0.15 or less, and maximum flame spread distance of 1.52 m (5 ft) or less, where tested to NFPA 262 |
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OFNR, OFCR | A vertical run in a shaft or from floor to floor, with fire-resistant characteristics capable of preventing the carrying of fire from floor to floor | ANSI/UL 1666 |
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OFNG, OFCG | General-purpose use, with the exception of risers and plenums, and resistant to the spread of fire | Char length not exceeding 1.5 m (4 ft 11 in.) in the CSA vertical flame test for cables in cable trays |
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The installation article then applies these levels to locations rather than describing them again. In fabricated ducts used for environmental air, up to 1.22 m (4 ft) of Types OFNP and OFCP cable is permitted where it is directly associated with the air distribution system, and the full set of types is permitted where it is installed in a raceway. In other spaces used for environmental air — plenums — OFNP and OFCP cable and plenum raceways are the permitted materials, and any of the eight types may be used where it is installed in a raceway. And in vertical runs penetrating one or more floors, or in a shaft, the permitted cables are OFNP, OFCP, OFNR and OFCR, together with plenum and riser raceways and riser routing assemblies.
The eight designations on two axes
Installation rules that catch people
Several provisions have nothing to do with the mark and everything to do with the site.
Provision | Requirement |
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Listing | Optical fiber cables, raceways and cable routing assemblies installed in buildings must be listed. Cables installed under the outside-plant allowance are excepted |
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Support | Optical fiber cables must not be strapped, taped or attached by any means to the exterior of a conduit or raceway as a means of support. Overhead aerial spans may be attached to a raceway-type mast intended for that purpose |
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Securing | Cables installed exposed on ceilings and sidewalls must be supported by the building structure so that normal building use cannot damage them, and secured with hardware designed and installed so as not to damage the cable |
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Abandoned cable | The accessible portion of abandoned optical fiber cable must be removed. Where a cable is tagged for future use, the tag must withstand the environment |
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Access | Access to electrical equipment must not be denied by an accumulation of fiber cables that prevents removal of panels, including suspended ceiling panels |
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Penetrations | Openings around penetrations of fire-rated walls, partitions, floors and ceilings must be firestopped using approved methods so that the rating is maintained |
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In a Chapter 3 raceway | Listed plenum, riser or general-purpose optical fiber raceway may be installed as innerduct inside any listed raceway permitted in Chapter 3 |
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The firestopping informational note carries a number that is easy to miss and applies generally: a 600 mm (24 in.) minimum horizontal separation usually applies between boxes installed on opposite sides of a fire-resistance-rated wall assembly. The detail of sealing a penetration is covered in cable penetration firestopping.
When there is a metallic member, someone has to ground it
A conductive cable carries a non-current-carrying metallic member, and where that cable is exposed to contact with electric light or power conductors the code requires the member to be dealt with in one of two ways. It may be grounded, or it may be interrupted by an insulating joint or equivalent device. Either way the grounding or the interruption must be as close as practicable to the point of entrance where the cable enters a building, or to the point of termination where the cable terminates on the outside of one.
Where the member is grounded, the conductor doing it is specified rather than left to the installer. It must be listed and may be insulated, covered or bare; it must be copper or another corrosion-resistant conductive material, stranded or solid; it must not be smaller than 14 AWG and its current-carrying capacity must be at least that of the metallic member it grounds, though it is not required to exceed 6 AWG; it must run in as straight a line as practicable; and where it runs in a metal raceway, both ends of that raceway must be bonded. Within a building, non-current-carrying conductive members are bonded to a grounded equipment rack or enclosure or grounded by the same method.
There is also an allowance for outside plant cable that is not listed. Unlisted conductive and nonconductive outside plant cable may be installed inside a building where the length within the building, measured from the point of entrance, does not exceed 15 m (50 ft) and the cable enters from outside and terminates in an enclosure. Unlisted nonconductive outside plant cable may also run in intermediate metal conduit, rigid metal conduit, rigid PVC conduit or electrical metallic tubing.
FAQ
What is the difference between OFNP and OFCP?
The P means the same thing in both: plenum-rated, suitable for ducts, plenums and other spaces used for environmental air. The letter before it is the difference. OFNP is a nonconductive cable with no metallic member, and OFCP is a conductive cable with one. The conductive version may not share a cable tray or raceway with power conductors rated 600 volts or less, where the nonconductive version may.
Does a fiber cable marking tell me anything about the fiber?
No. The article that governs the markings states that it does not cover the construction of optical fiber cables and raceways. Fiber count, mode, dimensions, buffer type, jacket material and attenuation are described in other documents, and a composite cable containing current-carrying conductors is classified and marked as an electrical cable rather than as a fiber cable.
Conclusion
A fiber cable mark carries two unrelated facts in one short string. The trailing letter describes fire and smoke performance and is backed by a named test. The letter before it says whether the cable contains a metallic member, and that one fact decides whether it may share a tray or raceway with power, and which way it may substitute. Both rules point the same way: nonconductive is the safe direction, and a decision that adds metallic members is the one that has to be argued.
Fiber the mark does not describe
ZONG Cable supplies fiber optic cable and can print the mark and the construction detail on the same jacket, so that the designation and the datasheet can be checked against each other. Tell us the location the cable has to serve and whether it will share a pathway with power, and we will confirm which marking the construction carries. The range sits under fiber optic cable, the copper version of the same letter system is set out in the guide to CM, CMR and CMP cable, what makes a space a plenum is covered in plenum space cable requirements, and private-label construction for a specified project is handled under OEM support.
Sources
- NFPA 70, National Electrical Code, 2011 edition, Article 770, Optical Fiber Cables and Raceways. Read directly for this article: 770.1 Scope and its statement that the article does not cover the construction of optical fiber cables and raceways; 770.2 Definitions, including the definitions of abandoned optical fiber cable, cable sheath, composite optical fiber cable, exposed to accidental contact, and point of entrance; 770.3 and its paragraph on composite cables being classified as electrical cables; 770.12 Innerduct for Optical Fiber Cables; 770.21 Access to Electrical Equipment Behind Panels Designed to Allow Access; 770.24 Mechanical Execution of Work including both informational notes; 770.25 Abandoned Cables; 770.26 Spread of Fire or Products of Combustion including its informational note on separation between boxes on opposite sides of a wall; 770.48 Unlisted Cables and Raceways Entering Buildings paragraphs (A) and (B); 770.93 Grounding or Interruption of Non-Current-Carrying Metallic Members paragraphs (A) and (B); 770.100 Entrance Cable Bonding and Grounding paragraph (A) subparagraphs (1) through (5); 770.106; 770.110 Raceways for Optical Fiber Cables paragraphs (A) and (B); 770.113 Installation of Optical Fiber Cables and Raceways and Cable Routing Assemblies paragraphs (A), (B), (C) and (D); 770.114 Grounding; 770.133 Installation of Optical Fibers and Electrical Conductors paragraphs (A), (B) and (C) including all five exceptions in (A); 770.154 paragraphs (b) and (D) and Table 770.154(b) Cable Substitutions and its accompanying figure caption; and 770.179 Optical Fiber Cables paragraphs (A), (B) and (C) and Table 770.179 Cable Markings together with the informational notes citing NFPA 262-2007, ANSI/UL 1666-2002 and CSA C22.2 No. 0.3-M-2001. Source text read from a full-text copy of the 2011 edition.
- ZONG Cable fiber optic cable range. https://zh-zong.com/fiber-optic-cable/
