Fiber Cable Jackets: OFNP vs OFNR vs LSZH Explained
OFNP, OFNR and LSZH describe how a fiber cable's jacket behaves in a fire. OFNP (plenum) and OFNR (riser) are North American listings under NEC Article 770: OFNP passes the strictest flame and smoke test (NFPA 262) for air-handling spaces, and OFNR passes a vertical-shaft test (UL 1666) for runs between floors. LSZH (low smoke zero halogen) is a material property tested to IEC standards: the jacket gives off little smoke and no corrosive halogen gas. LSZH is not a plenum rating. In the EU, cables are classified under the Construction Products Regulation (CPR) with Euroclasses such as Cca or Dca.
The jacket does not change the optical performance of a cable; the glass and connectors do that. But the jacket decides where you are allowed to install the cable, and the wrong one can fail an inspection. This guide explains each rating, the test behind it, the substitution rules and how to choose for data centers in North America, Europe and elsewhere.
Why the Jacket Rating Matters
In a fire, cables can carry flame along a building and produce smoke and toxic or corrosive gas. Building codes control which cables may go where:
- Plenum spaces (above suspended ceilings or below raised floors used for return air) move air around the building, so smoke there spreads fast.
- Risers (vertical shafts between floors) can act like chimneys.
- General areas (inside a room, in a rack or cable tray on one floor) have lower requirements.
The authority having jurisdiction (AHJ), usually the local building or fire inspector, enforces the rule on site. The cable must carry the right marking printed on its jacket.
North America: NEC Article 770 Listings
The US National Electrical Code (NFPA 70) Article 770 covers optical fiber cable. The type names follow a pattern:
- OF = optical fiber
- N = nonconductive (no metal) or C = conductive (with a metallic member)
- P = plenum, R = riser, G or blank = general purpose
| Listing | Location | Fire test | What the test checks |
|---|---|---|---|
| OFNP / OFCP | Plenum (air-handling) spaces | NFPA 262 (formerly UL 910), horizontal Steiner tunnel | Flame travel ≤ 5 ft (1.5 m), peak smoke density ≤ 0.50, average ≤ 0.15 |
| OFNR / OFCR | Risers between floors | UL 1666, vertical shaft | Flame height ≤ 12 ft (3.66 m), temperature limit |
| OFNG / OFN / OFCG / OFC | General purpose, one floor | UL 1685, vertical tray | Limited flame spread; no smoke limit |
Most data center fiber, including MPO trunks and patch cords, is nonconductive, so the relevant listings are OFNP, OFNR and OFN.
Substitution runs upward only
Under NEC Table 770.154(b), a higher-rated cable may always replace a lower one, never the reverse:
| Required | Permitted substitutes |
|---|---|
| OFNP | none (highest) |
| OFNR | OFNP |
| OFNG / OFN | OFNP, OFNR |
So OFNP can go anywhere in the building. That is why many data centers simply standardize on plenum-rated fiber, even where riser or general purpose would be allowed.
LSZH: Low Smoke Zero Halogen
LSZH (also written LS0H, LSFH or LSHF) describes the jacket compound, not an installation listing. A jacket is LSZH when it passes:
- IEC 61034 – smoke density: little visible smoke, so people can see exits.
- IEC 60754-1 and -2 – halogen acid gas and corrosivity: no significant hydrochloric or similar acid gas, which harms people and corrodes electronics.
Flame spread is tested separately, typically to IEC 60332-1 (single cable) or IEC 60332-3 (bunched cables).
Two common misunderstandings:
- LSZH is not "better than plenum" or "equal to plenum". They are different tests. A cable is only plenum-rated if it is listed OFNP. Some cables are both OFNP and LSZH, but one does not imply the other.
- PVC is not LSZH. Many standard riser and general-purpose jackets are PVC-based, which contains halogen. Plenum jackets often use fluoropolymer or special low-smoke PVC compounds.
LSZH is widely required in Europe, the Middle East and Asia, and in enclosed spaces with people or sensitive equipment: data centers, transport tunnels, ships, hospitals and public buildings.
Europe: CPR Euroclasses
In the EU, cables permanently installed in buildings fall under the Construction Products Regulation (EU) No 305/2011, with the harmonized standard EN 50575. Cables are tested and given a reaction-to-fire class:
| Euroclass | Fire performance |
|---|---|
| Aca | Non-combustible (in practice mineral cables) |
| B1ca, B2ca | Very limited fire contribution |
| Cca | Limited fire contribution |
| Dca | Medium fire contribution |
| Eca | Basic flame spread performance |
| Fca | No performance declared |
Additional classes describe smoke (s1, s2, s3), flaming droplets (d0, d1, d2) and acidity (a1, a2, a3). For example, B2ca-s1a,d1,a1 is a high class with low smoke and low acidity, while Dca-s2,d2,a2 is a common minimum for data centers in some countries.
National rules decide which class is required where; the CPR itself only sets the classification. Cables must carry CE marking and a Declaration of Performance (DoP). Ask your supplier for the DoP when you specify a CPR class.
An LSZH cable will often reach a good smoke (s) and acidity (a) class, but the Euroclass still has to be tested and declared.
OFNP vs OFNR vs LSZH at a Glance
| OFNP | OFNR | LSZH | |
|---|---|---|---|
| Type | NEC listing | NEC listing | Material property (IEC tests) |
| Region | North America | North America | Global, especially EU, Middle East, Asia |
| Main test | NFPA 262 | UL 1666 | IEC 61034, IEC 60754 (+ IEC 60332 for flame) |
| Where | Plenum, riser, general | Riser, general | Where low smoke and no halogen is required |
| Smoke limit | Yes | No smoke limit in UL 1666 | Yes (IEC 61034) |
| Halogen-free | Not necessarily | Usually not (PVC) | Yes |
How to Choose a Jacket
- Find the code that applies. NEC in the US, CEC in Canada, CPR plus national rules in the EU, local codes elsewhere.
- Identify every space the cable crosses. If any section passes through a plenum, the whole run must be plenum-rated (or in a rated raceway).
- Check the end-user specification. Many data center operators require LSZH, OFNP or a minimum Euroclass regardless of the code.
- Consider the environment. LSZH jackets can be stiffer and less resistant to oil or abrasion than some PVC jackets; outdoor runs need outdoor-rated cable.
- Specify it on the order. State the rating, and ask for the print legend and documents (listing or DoP) you need for inspection.
For a mixed route, it is usually simpler to choose the highest rating needed anywhere on the route for every cable.
Jackets and Cable Assemblies
For pre-terminated MPO trunk cables, the jacket covers the main cable and usually the breakout legs. Patch cords and harnesses have their own jackets. All parts in a regulated space must meet the requirement, including the short cords in an enclosure if that enclosure sits in a plenum.
Jacket colour is a separate convention: aqua for OM3/OM4, violet or erika violet for OM4 in some regions, lime green for OM5, and yellow for OS2. See OS2 vs OM3 vs OM4 vs OM5 and MTP/MPO trunk vs patch cables.
Huawellux Jacket Options
Huawellux MTP® and MPO trunk cables are offered with OFNP or LSZH jackets. Our listed operating temperature for trunks is −20 to 60 °C; storage temperature is −40 to 80 °C for OFNP and −20 to 70 °C for LSZH. Breakout harness cables are specified with an OFNP reference jacket, and patch cables and cords are configured with a jacket to suit your link. Tell us the rating and documentation your project requires when you request a quote.
Huawellux's specification for MPO and MTP® assemblies (identical for both) is insertion loss ≤0.35 dB for single-mode and multimode, with return loss ≥60 dB APC; single-mode UPC ≥55 dB (MTP/MPO) or ≥50 dB (LC/SC); multimode >30 dB. LC and SC patch cords are listed at insertion loss ≤0.35 dB and return loss ≥50 dB (single-mode UPC), ≥60 dB (single-mode APC) and >30 dB (multimode). Every Huawellux product receives end-face visual inspection under a 400x video microscope and is tested for insertion loss (IL) and return loss (RL) before it ships. Interferometric end-face geometry (fiber height, coplanarity, end-face angle and radius) is sample-checked in production; a geometry report is supplied only if you specify it. Dust caps are fitted on every connector, and an IL/RL test report ships with every order.
Between buildings: indoor ratings do not cover outdoor runs; see OS2 trunks for DCI and campus links for outdoor cable and building entry.
Frequently Asked Questions
What is the difference between OFNP and LSZH?
OFNP is a North American plenum listing under NEC Article 770, based on the NFPA 262 flame and smoke test. LSZH is a jacket material property tested to IEC standards for low smoke and no halogen acid gas. A cable can be one, the other or both.
Can I use LSZH cable in a plenum space?
Only if it is also listed OFNP (or installed in a plenum-rated raceway, where the code allows). LSZH alone is not a plenum rating.
Can OFNP cable replace OFNR?
Yes. Under NEC substitution rules, OFNP can replace OFNR and OFN. OFNR can replace OFN, but never OFNP.
What does CPR class Cca or Dca mean?
They are EU reaction-to-fire Euroclasses under the Construction Products Regulation and EN 50575. Cca means limited fire contribution and Dca medium; extra codes describe smoke (s), droplets (d) and acidity (a). National rules decide which class is required.
Does the jacket affect fiber performance?
No. Insertion and return loss depend on the fiber and connectors. The jacket decides fire performance, flexibility and where the cable may be installed.
Specify the Right Jacket with Huawellux
Huawellux manufactures MPO and MTP® assemblies at our factory in Shenzhen, with genuine US Conec MTP® or standard MPO connectors, in OS2, OM3, OM4 and OM5. We supply MTP/MPO trunk cables, MPO patch cables, breakout harness cables, standard fiber patch cords and fiber management enclosures.
Huawellux replies to inquiries within 24 hours. Estimated preparation for all orders, including custom orders, is 1–5 business days after payment confirmation. Standard listed patch cords have no formal MOQ.
- Estimate lengths and quantities: Visual Cable Quote
- Send your jacket rating and route: Request a Quote
This guide is general information, not legal or code advice; always confirm requirements with the authority having jurisdiction. MTP® is a registered trademark of US Conec Ltd.