Introduction: LSZH and PVC in UTP Sheath
UTP twisted pair for office and home networks is sold in 305 m coils with different sheaths. The two main materials are polyvinyl chloride (PVC) and a halogen‑free LSZH compound (Low Smoke Zero Halogen, sometimes LSOH). The choice between them determines whether the cable route will pass a fire inspection in a public building and how safe evacuation will be in the event of a fire.
UTP with a PVC sheath is cheap and flexible, but when burning it emits thick black smoke and corrosive hydrogen chloride. The LSZH sheath is halogen‑free, produces tens of times less smoke and toxic gases, which is why it is valued in schools, hospitals, shopping centres. Both types are produced for Cat5e and Cat6 categories, with 4 pairs of 24AWG conductors, both in unshielded U/UTP and shielded F/UTP versions. A detailed review of the twisted pair design and its categories is given in the article about UTP cable.
Comparative Table of LSZH and PVC Sheaths
| Parameter | LSZH | PVC |
| Decoding | Low Smoke Zero Halogen — low smoke emission, halogen‑free | Polyvinyl chloride (PVC) — contains chlorine |
| Smoke emission during combustion | Very low, the smoke is almost transparent, visibility is preserved | High, thick black smoke sharply reduces visibility |
| Toxicity of combustion products | Minimal, HCl and other halogen‑containing gases are absent | High, hydrogen chloride and other toxic substances are released |
| Fire safety according to GOST R 53246‑2008 | Complies with requirements for installation in buildings with mass occupancy, including ng(A)‑LS | Limited: allowed in technical rooms, in concealed wiring with low requirements |
| Resistance to ultraviolet | Low, not designed for direct sunlight | Low, as with LSZH; for outdoors, PE polyethylene is required |
| Operating temperature range | From –20 to +60 °C | From –20 to +60 °C |
| Flexibility and installation | Slightly stiffer, but the bending radius is the same — 4 diameters | More flexible, easier to place in ducts and corrugated conduit |
| Cost (305 m coil) | 10–25 % higher | Lower |
| Compatibility with RJ‑45 connectors | Full | Full |
| Chemical resistance | Good, resistant to oils and weak acids | Good, but some oils may cause swelling |
| Service life indoors | 25 years and more | 20–25 years (plasticizers migrate over time, the sheath becomes brittle) |
| Main application | Public buildings, schools, hospitals, offices, escape routes, all places with smoke emission requirements | Technical floors, warehouses, cable ducts with low fire‑safety requirements, temporary networks |
Fire Safety, Smoke and Toxicity
The key difference between UTP LSZH and PVC manifests itself during a fire. PVC contains up to 50 % chlorine by mass. Under the action of flame it decomposes, releasing HCl — hydrogen chloride. Combining with air moisture, HCl forms hydrochloric acid, which corrodes metal and concrete, and also causes burns of the respiratory tract. The black smoke of PVC sharply reduces visibility, hindering the evacuation of people and the work of firefighters. According to SP 256.1325800.2016, in buildings with mass occupancy, cables that release toxic gases during combustion in excess of the established norms are prohibited on escape routes.
The LSZH compound does not contain halogens. When burning, it releases tens of times less smoke, and this smoke is light, non‑toxic. According to the fire hazard classification, such cables correspond to the ng(A)‑LS index — they do not propagate combustion in bundled installation and have reduced smoke and gas emission. Manufacturers often mark them as LSZH HF — Halogen Free. Therefore, for hospitals, schools, cinemas, railway stations and open‑plan offices, designers specify precisely LSZH. The differences between shielded and unshielded versions are described in the comparison FTP or UTP.
Mechanical Properties and Operating Conditions
From the installation point of view, PVC is slightly softer and easier to lay in narrow ducts. However, at low temperatures, PVC becomes brittle: installation at –5 °C already requires caution. LSZH retains elasticity down to –20 °C, which makes it more convenient in unheated rooms during the cold season.
Both sheath types are not intended for outdoor use without protection. Neither PVC nor LSZH is resistant to ultraviolet radiation. For outdoor installation, a cable with a polyethylene PE sheath is used, sometimes in combination with LSZH for the internal section. Inside a building, the choice between LSZH and PVC is dictated only by fire regulations. With correct installation according to TIA/EIA‑568, the service life of LSZH reaches 25 years and more, whereas PVC loses plasticizers over time and can crack after 15–20 years. Installation rules taking into account bending radii and termination are set out in the guide UTP installation.
When to Choose UTP with LSZH Sheath
- Public buildings with mass occupancy: shopping centres, airports, railway stations, stadiums. Smoke emission requirements are strict, PVC is prohibited.
- Educational and medical institutions: schools, kindergartens, hospitals, polyclinics. Evacuation of children and patients requires a minimum of smoke and toxins.
- Office centres with open spaces where raised floors and suspended ceilings are used. When concealed, LSZH ensures safety.
- Server rooms and data centres, where in addition to fire safety, chemical neutrality is important: PVC when smouldering releases acid that is harmful to electronics.
- Residential buildings in common areas: corridors, staircases, lift halls. SP 256.1325800.2016 requires cables with the LS index to be laid on escape routes.
When PVC Sheath Is Acceptable
- Technical rooms without permanent human occupancy: boiler rooms, pump rooms, ventilation chambers, basements with a separate entrance. Smoke emission requirements are reduced.
- Open installation in production workshops where forced ventilation is laid and the fire load is controlled by other means.
- Temporary networks on construction sites, exhibition stands, where the cable is used for a few weeks and dismantled.
- Home networks with a small number of subscribers, if the owner consciously saves money and the inspection authorities do not impose requirements. A PVC sheath is cheaper, but in living rooms, LSZH is still preferable from the point of view of personal safety.
- Cables for video surveillance systems laid in separate ducts outside escape routes, in the absence of regulatory restrictions.
Typical Mistakes When Choosing a Sheath
- Buying PVC for an office building being commissioned. The fire inspectorate will not accept the facility — it will prescribe to replace the cable with LSZH.
- Laying LSZH outdoors without protection. The material is not resistant to ultraviolet radiation; after 1–2 seasons the sheath will crack. For outdoors, PE is needed, not LSZH.
- Confusion of indices: LSZH does not mean “for outdoors”. LSZH — fire safety indoors, PE — weather resistance. Sometimes a combined indoor/outdoor cable with an LSZH sheath and UV protection is found, but it is rare.
- Using PVC in a kindergarten or hospital. During an inspection, a violation of No. 123‑FZ and SP 256 will be revealed, which will entail administrative liability.
- Expecting that PVC will serve for 25 years in a hot room. At temperatures above 40 °C, the migration of plasticizers accelerates, the sheath cracks, and the cable requires replacement already after 10–12 years.
- Choosing LSZH and saving on SCS elements — patch cords, sockets, patch panels must also be of LSZH category to preserve the fire certification of the entire system.
Frequently Asked Questions
How are LSZH and PVC deciphered?
LSZH — Low Smoke Zero Halogen, a halogen‑free sheath with low smoke emission. PVC — polyvinyl chloride, contains chlorine, when burning releases toxic smoke.
What is the difference between UTP LSZH and UTP PVC?
In behaviour during a fire. LSZH almost does not smoke and does not emit poisonous gases, PVC produces thick black smoke and HCl. Mechanically, LSZH is slightly stiffer, PVC is more flexible and cheaper.
Can a PVC cable be used in an apartment?
From the point of view of personal safety, LSZH is better. The legislation does not prohibit PVC in apartments, but during a fire, the combustion products of PVC pose a serious threat. In new buildings, LSZH is often used at the initiative of the developer.
What to choose for an office: UTP PVC or LSZH?
For an office with more than 10 workplaces, especially with an open layout, LSZH is required by fire safety standards. Designers specify the ng(A)‑LS index, which implies an LSZH sheath.
Does the sheath type affect the data transmission speed?
No. The speed and frequency characteristics depend on the category — Cat5e or Cat6. The sheath material does not affect the electrical parameters. More about the categories — in the article Cat 5e or Cat6.
Is there an LSZH cable for outdoors?
Usually not. LSZH itself is not resistant to ultraviolet radiation. Outdoor cables are made of polyethylene PE, and LSZH is used indoors. There are combined “indoor/outdoor” solutions with an LSZH sheath and UV stabilisers, but their application is limited.
Conclusion
The choice between UTP with an LSZH sheath and PVC comes down to fire safety requirements and the type of facility. LSZH is mandatory in public buildings, on escape routes and wherever human lives are valued. PVC remains a budget solution for technical rooms and temporary networks. Saving on the sheath in an inappropriate place threatens not only fines but also real danger during a fire. Both sheath types are available for all common categories and designs — from U/UTP Cat5e to SF/UTP Cat6, with 24AWG copper conductors. You can view the models in the catalogue UTP PVC cable and LSZH.
