OFNP vs LSZH: Plenum Listing and Low-Smoke Material Are Not the Same Thing

Quick answer: OFNP and LSZH answer two different questions and are not interchangeable. OFNP is a US listing (NEC Article 770) proving an optical fiber cable passed the NFPA 262 plenum burn test — it regulates where the cable may be installed. LSZH is a material class — jacket compounds that emit minimal smoke and no halogen acids when burned, verified under IEC 60332/60754/61034 — it regulates what the cable gives off in a fire. A cable can be OFNP without being LSZH (most US plenum cable is fluoropolymer or low-smoke PVC based), and LSZH without being OFNP. Global projects frequently need to satisfy both.

This confusion lands in our inbox from two directions. Cable plant engineers quoting a US data-center job ask whether their LSZH jacket “counts as OFNP.” US integrators bidding Middle East or European projects ask whether their OFNP-listed cable “is LSZH.” Both questions assume the two labels sit on one scale, one stricter than the other. They don’t — they belong to two different regulatory philosophies, and knowing which philosophy governs your install site is the whole game.

OFNP: A Location Permission, Written by the NEC

Q: What does OFNP stand for? Optical Fiber, Nonconductive, Plenum — the top flame rating for all-dielectric fiber cable under NEC Article 770.

The US National Electrical Code sorts communications cable by where it may legally run, and the plenum — the air-handling space above dropped ceilings — is the most demanding location, because HVAC airflow would pump smoke from a burning cable through an entire building. To earn OFNP, a cable passes NFPA 262 (the Steiner-tunnel-derived plenum test): flame spread and, critically, optical smoke density limits under forced airflow. The hierarchy stacks downward:

Note what OFNP does not test: halogen content and acid gas. US plenum cable historically earns its low smoke with FEP (a fluoropolymer — halogenated by definition) or specialised low-smoke PVC. Perfectly legal, OFNP-listed — and disqualified from any halogen-free specification on the planet.

LSZH: A Material Promise, Written by IEC

Q: What does an LSZH rating actually verify? Three material behaviours, each with its own IEC standard: the cable resists flame propagation (IEC 60332), emits near-zero halogen acid gas when burned (IEC 60754, <0.5% HCl equivalent), and produces little smoke (IEC 61034, light transmittance ≥60% in the 3-metre cube).

LSZH grew from the opposite worry: not where fire spreads, but what the fire does to people and equipment in enclosed spaces — tunnels, ships, trains, data halls. Burning PVC releases dense smoke and hydrochloric acid that blinds escape routes and corrodes electronics; LSZH compounds replace the halogen chemistry entirely, using polyolefin jackets loaded 50–65% with mineral hydroxides. The full material argument — including where PVC remains the rational choice — is in our LSZH vs PVC comparison, and the compound side lives on our flame retardant cable compounds page.

The crucial asymmetry: LSZH is defined by emissions chemistry, so a standard LSZH jacket does not automatically survive the NFPA 262 plenum burn — forced-airflow flame spread is a harder aerodynamic problem than the IEC vertical tests. Compounders have closed the gap with high-performance LSZH plenum grades, but it took formulation work, not relabelling.

So Which One Does Your Project Need?

1. US commercial building, cable in air-handling spaces → OFNP is legally mandatory; LSZH is optional. The AHJ checks the listing printed on the jacket, full stop.
2. European/IEC-jurisdiction building → no OFNP concept; CPR Euroclasses (B2ca/Cca/Dca) plus LSZH requirements govern. An OFNP listing impresses nobody.
3. Global data-center operators → increasingly demand both: NEC listing for the US sites, LSZH emissions behaviour as corporate policy everywhere (smoke corrosivity is an equipment-protection issue, not just life safety). This dual-spec cable — halogen-free plenum — is the hardest compound in the fiber world and the fastest-growing ask we see.
4. Ships, rail, tunnels, defense → LSZH by sector standards; NEC categories don’t apply.

One real-world note from a cable customer of ours exporting to both markets: they run one LSZH jacket compound engineered to pass NFPA 262, rather than two inventories (FEP-based for US, LSZH for export). Their per-metre compound cost is higher than commodity LSZH, but they eliminated dual tooling, dual stock and mislabelling risk. Whether that trade wins depends on your volume split — but it is only possible when the compound’s mineral system is engineered for forced-airflow flame spread from day one, which in practice means high-purity, surface-treated magnesium hydroxide flame retardant systems pushed to loadings where dispersion quality decides pass or fail.

For the fiber-specific picture — how OFNP, OFNR and LSZH interact with tube materials, strength members and riser/plenum architecture — our article on flame retardant fiber optic cable completes this one. And if you are on the compound side of the problem — building an LSZH jacket that has to clear IEC 61034 smoke or chasing a halogen-free plenum grade — that is exactly our lab’s home ground: send the target spec and we’ll propose a mineral system and loading with screening data.

FAQ

Is OFNP better than LSZH?

Neither is “better” — they measure different things. OFNP certifies plenum-grade flame and smoke behaviour for US code compliance; LSZH certifies low smoke and zero halogen acid emissions. The strictest modern specification is the combination: an LSZH-material cable that also holds an OFNP listing.

Can an LSZH cable be used in a US plenum?

Only if that specific cable carries an OFNP (or CMP, for copper) listing. The LSZH label alone has no standing under the NEC — the AHJ needs the listed marking, which means the cable passed NFPA 262 regardless of its jacket chemistry.

Is OFNP cable halogen-free?

Usually not. Most OFNP cable achieves its plenum rating with FEP or low-smoke PVC, both halogenated. If your specification says halogen-free, you must ask for it explicitly — “plenum-rated” does not imply it.

What is the difference between OFNP and CMP?

Same plenum test, different cable family: OFNP covers nonconductive optical fiber cable (NEC 770), CMP covers communications/copper cable (NEC 800). A hybrid cable containing both fiber and conductors falls under the conductive/communications listings, not OFNP.

—— Rectivas Materials 团队 老陈