LSZH: Understand When and Where to Use These Cables


Communication cable terms such as CM, LSZH, and PVC are pretty standard in the cable industry. However, the trend of using LSZH, or low-smoke zero-halogen electrical cables, is increasing. With the several advantages of LSZH cables, it might look logical that engineers must use these cables only. However, before selecting these cables for a particular application, electrical engineers need to understand them in detail.

Table of Contents

Communication Cable Types

  • CM: it indicates that a cable is compliant with standards like NFPA70 and NEC. You can use CM-designated cables for low voltage communications confined to the floor.
  • CMR: You can use riser-rated cables in vertical installation between floors. These cables help to prevent the spread of fire in vertical structures.
  • CMP: Plenum-rated cables stop the propagation of flames to five or less than five feet and limit the amount of smoke in the case of a fire. Use them in suspended ceilings to allow air to pass.
  • PVC: PVC stands for Polyvinyl chloride and is closely related to CM and various CMR-rated cables.
  • FEP: FEP is related to the CMP cable. This cable may have an outer jacket of low smoke Poly Vinyl Chloride.
  • LSZH, LSOH, LSNH: Letters like ZH, NC, HF, OH, and NH indicate that the cables are halogen-free. Here, “LS” means low smoke, which means that these cables use materials that emit low smoke. Sometimes, you may get confused between LSF and LSHF cable and consider them the same. However, LSZH has a more stringent classification. Thus, engineers must always know what they choose, what they want, and what they pay.
  • FRLS: Here, FS stands for flame retardant, which means cable material has improved reaction to the fire. These low smoke, zero halogen, and low fire cables must follow IEC standards.
LSZH Cables

The rise of LSZH Cables

Most network cables like Cat5 and Cat 6 use polyvinyl chloride, polyethylene, or thermoplastic urethane insulation. In the case of fire, these halogens containing insulation release hydrogen chloride (HCl), a poisonous gas. This HCL forms hydrochloric acid when it comes in contact with water.

However, LSZH or LSOH cables use low-smoke zero-halogen plastic for cable jacketing. Such jacketed cables use compound materials that release minimal smoke and no corrosive gases in case of fire. As a result of this feature, LSZH cables are suitable for plenum areas with deficient ventilation. These areas are plenum, aircraft, tunnels, rail cars, etc., where smoke accumulates and can harm people.

Further, LSZH cable material complies with the European Union’s Restriction of Hazardous Substances (RoHS) directive and similar safety standards to North American safety and environmental standards.

Where LSZH cables make sense

With so many standards and housing codes, it is difficult to determine the use of LSZH cable. However, in general, you can use them in confined places where cables are very near each other, ventilation is poor, high voltage is high, and less evacuation space. Some examples are surface ships, submarines, commercial aircraft, tunnels, theatres, nightclubs, some areas of airports, and nuclear facilities where smoke and toxic gases can prove to be terrible.

Recently, data centers started using LSZH cables as these areas have bunches of cables and massive cooling infrastructure. Such infrastructure can lead to the rapid spread of fire.

LSZH cables

LSZH cables are not for every application

Although these cables are quite advantageous, it is impossible to use them in every application. They cannot always replace halogenated cables due to several reasons:

  • Firstly, the PVC and FEP cables are fire resistant, and thus their contribution to fire becomes less prominent.
  • Secondly,  FEP and PVC cables cost less than LSZH cables 
  • Thirdly, they deliver superior electrical performance. 
  • Also, these cables are suitable for wet and dry conditions. 
  • They are flexible, temperature resistant, chemical resistant, and very rugged. 

So, conclusively, you can use LSZH cables where standard cables can be harmful, but you cannot replace PVC and FEP cables with LSZH cables.

Confusing requirements about LSZH cable

Several acronyms are used for cables that offer protection from fire, and they are:

  • FRLS: Fire-resistant, low smoke cables
  • FRNC: Fire retardant, non-corrosive cables
  • HFFR: Halogen-free flame retardant cables
  • LC: Low corrosivity cables
  • LH: Low halogen cables
  • LS: Low smoke cables
  • LSF: Low smoke and fume cables
  • LSHF: Low smoke, halogen-free cables
  • LSNH: Low smoke, no halogen cables

“Low” halogen refers to less than 0.2% halogen content by weight. The department of defense has mentioned halogen content in MIL-C-24643. On the contrary, some other standards consider low halogen based on the amount of acid gas produced but not on halogen levels.

According to the National Electric Code, the cables for plenum spaces must have a “low smoke” rating. Some people debated that plenum spaces have less fuel load and fewer sources for ignition, so there is no requirement for low smoke cables in the plenum. However, the National Fire Protection Association (NFPA) keeps the NFPA-262 standards for plenum cables.

Underwriters Laboratories offer certification programs for LSZH and Halogen-free cables based on IEC 62821 and IEC 60754 standards. IEC 62821 defines low-smoke, halogen-free thermoplastic insulation requirements and sheathing with 750 volts. Now, wires and cables use UL’s LSZH and HF marking on different cables, including appliance wiring, fiber optic, power and control tray cable, and flexible cords.

The UL-certified cables also meet other general UL standards. The Underwriters Laboratories have also extended their component recognition program under UL 2885, which includes the evaluation of halogens. All this will help insulation and jacket, compound manufacturers.

LSZH cables

Performance and cost of LSZH cables

The manufacturers have been working on improving LSZH cables, and today, these cables have superior fire-retardant properties and provide excellent electrical performance. However, LSZH cables are costlier than traditional ones due to the additional steps and time required for manufacturing. However, you can expect a lower cost in the coming times when demand for LSZH cables will increase in the market. Earlier, LSZH cables were not suitable for use at low temperatures, but now, with proprietary techniques, this problem has been reduced in modern LSZH cables.


Due to several rules, regulations, codes, and standards, it is becoming difficult for cable manufacturers to define cables as LSZH. Some manufacturers release data sheets that only mention the primary jacket of the cables leaving dielectric material. Some other manufacturers say LSZH characteristics in their datasheets, while others hide them. If you need a cable and are doubtful about its fire-related characteristics, it is better to contact the manufacturer. At Bloom, we manufacture custom-made cables with some attributed fire performance and help choose the type of cable that satisfies your fire performance requirements.