What does LSZH stand for?
LSZH stands for Low-Smoke Zero-Halogen, which means that the cable emits little to no toxic halogens and minimal smoke when in contact with fire. LSZH wire and cable are also called: low smoke non-halogen (LSNH), low-smoke halogen-free (LSHF), and low-smoke zero-halogen (LS0H).
What are halogens?
Halogens are non-metallic elements found in the periodic table. The five halogens are fluorine, chlorine, bromine, iodine, and astatine. They are present in PVC insulation and jacketing, and are highly flame retardant. However, when they are burned, halogens emit thick toxic smoke and become corrosive which can cause damage to equipment and pose a safety concern.
Why consider Halogen-Free Cable and where can it be used?
Halogen-free cables are used when fire safety, fire damage prevention, and environmental issues are a concern. Halogen-free cables help eliminate the use of environmentally sensitive materials.
The halogen-free cable is intended for use in applications in which insulation with low toxicity, low smoke generation, and low corrosiveness is needed. Examples include rapid transit, industrial, shipboard, aerospace, and commercial applications where human safety and protection of equipment is a concern.
Does the NEC allow Low-Smoke Halogen-Free Cable in all applications?
The NEC (National Electrical Code) doesn't prohibit halogen-free cable or wire installation in any application. The NEC does require low smoke cables for plenum spaces.
Is there a difference between low-smoke and zero-halogen?
Low smoke cable emits a thinner and clearer smoke when burning, making possible evacuation and firefighting efforts easier and safer. A cable may be low smoke and still contain toxic halogens.
Zero halogen means that the cable does not contain fluorine, chlorine, bromine, iodine, or astatine. Zero halogen cable may still emit thick smoke when burned. Both properties are not always needed for all cables. Check specifications to be sure that the cable meets both requirements if necessary for your application.
Are there any disadvantages to using Low-Smoke Zero-Halogen cables?
Low smoke zero halogen cables provide a lot of great safety advantages, but there can be an electrical and mechanical trade-off.
In order to be low-smoke zero-halogen, the cable jacket must incorporate a high percentage of filler material. This increase in filler material could make the jacket less chemical and water-resistant and could provide poorer mechanical and electrical properties than a non-LSZH counterpart. LSZH jackets are also more likely to experience jacket cracking during installation, so special lubricants may be necessary to avoid damage, especially in cold environments.
Because of the limited flexibility of LSZH, it is not recommended in robotic or continuous flex applications. As a result, LSZH cable is commonly chosen for applications where fire safety is more of a concern than the cable’s specific electrical and mechanical properties. Advances in compound materials and processing have decreased some of these issues.
Can LSZH cables pass a flame test?
Yes. LSZH may pass a standard flame test. To determine how an LSZH cable will react in a fire, the following five criteria are considered:
- How easily the cable will catch fire?
- How quickly the fire will spread along the cable?
- How much smoke is produced upon combustion?
- How toxic are the byproducts?
- How corrosive are the byproducts?
Some test standards related to this type of cable are plenum-rated, LS rated, S1 rated, and ASTM D5424.
What should be considered when choosing LSZH cables?
When choosing LSZH products, factors such as the environment and price should be considered. The temperature of the application’s environment can affect the flexibility of the cable. Low smoke zero halogen cable also tends to cost more due to its special properties.