What is a LSZH Cable
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What is a LSZH Cable? This article will be a ultimate guide to LSZH cables(Low Smoke Zero Halogen Cables) It will tells everything including the past and present of LSZH (Low Smoke Zero Halogen) cables.
1. Preface
Currently, the outer jackets of cables on the market are primarily made from two materials: low smoke zero halogen (LSZH) and PVC. Engineering professionals in the structured cabling industry are well aware of LSZH cables, but they know little about their origins, uses, and advantages and disadvantages.
LSZH cables are more expensive to produce than those made from PVC or other halogen materials. Due to our lack of understanding and their high cost, many non-standard manufacturers take advantage of this by using inferior materials and misleading consumers, causing many problems and unnecessary losses. Next, we will delve into the details of LSZH cables.
2. The Application of PVC Materials
Self-extinguishing Polyvinyl Chloride
We know that in 1886, Bell invented twisted pair cables alongside the telephone to transmit analog signals. At that time, chemical material engineers compared several materials and chose self-extinguishing polyvinyl chloride (PVC) as the cable jacket. PVC cables can to some extent prevent flames from spreading. Therefore, PVC materials were used as the protective jackets for communication and power cables in subsequent buildings.
3. The reason why LSZH Become Widespreading
3.1 The King's Cross Underground Fire Incident
In the 1970s, with the globalization of technology, these PVC-jacketed cables were introduced to Europe from the United States. Early in Europe, PVC-jacketed cables were used as communication and power media. These self-extinguishing cables were highly regarded.
However, everything changed in 1987 with the tragic King's Cross Underground fire. That year, the King's Cross Underground fire in London killed more than 30 people and injured over 100. Investigation revealed that a match in the elevator caused the fire.
One of the reasons for the numerous casualties was that the subway used PVC-jacketed wires and cables, which produced a large amount of black smoke and toxic gases like chlorine during combustion. These not only obstructed the vision of escaping people but also caused many to die from burns due to poisoning.
The PVC cables used at that time were far less safe and environmentally friendly compared to today's standards. Modern PVC materials can produce only a small amount of white smoke and release less chlorine when burned. We know that cable flame-resistance does not mean non-combustibility; under suitable conditions and continuous flame supply, it can burn. Therefore, in a fire, it can continue to burn, which is why black smoke and toxic gases were released in the King's Cross Underground fire.
King's Cross Station Fire Scene
3.2 RoHS Directive and REACH Regulation
After this incident, the UK began to require the use of LSZH cables, a decision quickly followed by other EU countries. Later, a consensus was reached in meetings that cables entering the EU market must use LSZH materials for their jackets, leading to the establishment of the current RoHS directive and REACH regulation.
3.3 Over Centuries of Improvement, PVC Safety Has Increased Significantly
Although the EU requires the use of LSZH cables, other regions outside the EU still use PVC-jacketed cables. This is because, after centuries of improvement, the safety of modern PVC cables has significantly increased.
3.4 Composition of Low Smoke Zero Halogen Materials
LSZH materials are primarily composed of thermoplastic polyolefins, which are a class of polymers. Polyolefins typically refer to thermoplastic resins obtained from the homopolymerization or copolymerization of α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, and certain cycloolefins. These materials contain only carbon and hydrogen elements.
Ethylene Propylene 1-Butene 1-Octene 1-Hexene 1-Pentene
3.5 LSZH Cables are Classified by Flame-Resistant Levels
Due to their special atomic structure, they produce little or no smoke and no toxic gases when burned. However, polyolefins themselves are not flame-resistant; they need to be mixed with anhydrous minerals like magnesium hydroxide and aluminum hydroxide as flame retardants to achieve flame-resistance. Here, engineering professionals need to understand that LSZH cables are not inherently flame-resistant. Only LSZH cables with flame-resistant levels can truly be flame-resistant.
4. Application Environments of PVC and LSZH
4.1 PVC Cables
For PVC cables, UL has established the UL1581 series standards, which classify flame-resistant levels as CMX, CM/CMG, CMR, and CMP. The applications of these flame-resistant level cables are shown in Table (1):
Application Scenarios for PVC Network Cables with Different Flame Retardant Ratings
Currently, the widely used level in horizontal links is the CM level.
4.2 LSZH Cables
LSZH cables also have flame-resistant level requirements. IEC has established three standards for LSZH cables through the IEC 60332 series, namely IEC60332-1, IEC60332-2, and IEC60332-3. Common LSZH cables can also be non-flame-resistant, with four types: IEC 60332-1, IEC 60332-2, IEC60332-3. The applications of these level cables are shown in Table (2):
Since IEC does not permit combustion tests under ventilated conditions, there is no level equivalent to CMP, meaning LSZH cables are not allowed to be used under ventilated conditions.
5. Widely Used Locations
LSZH cables are widely used in Class A office buildings, large shopping malls, hospitals, subway stations, train stations, and airport terminals in densely populated indoor areas due to their low smoke (producing little or no smoke when burned) and zero halogen (not releasing toxic gases) advantages. Additionally, they are used in crowded, confined areas of vehicles such as trains, subways, high-speed trains, airplanes, and cruise ships.
Widely used applications of LSZH cables
However, since LSZH does not have flame-resistant tests and material applications under ventilated conditions, once a high-speed vehicle catches fire, the fire can burn through an entire carriage in minutes. Even using IEC 60332-3 level cables will burn, so the primary purpose of using LSZH cables in vehicles is to create low smoke and non-toxic conditions for escape during a fire.
Therefore, both LSZH and PVC cables are fundamentally flame-resistant, but they serve different purposes. For small and medium-sized projects without special conditions, eco-friendly flame-resistant PVC cables that meet the requirements can be chosen. For the scenarios listed above, flame-resistant LSZH cables should be used.
