Monday 24 August, 2020 | RSS Feed

LSZH vs. PVC - What cable jacket should I prefer?

by www.fiber-mart.com

In the present era of rapid technology growth and the constant rush for high quality products, we can easily forget about the safety regulations and the various dangers that surround us. This is an extremely important part of the network infrastructure for the IT managers to concentrate on. The large number of networking equipment, together with the cables and possible power weak links, make the Datacenter buildings vulnerable to fire and other possible catastrophes. When designing a network infrastructure, it is important to follow the latest regulations and to follow the various safety tips, no matter the cost, because following them could eventually save a lot of lives.
When it comes to fiber optic cables, the cable jacket is a lot more important part of the network as some may think. The European market is demanding that all cables which would be used in Wide Area Networks (WAN), Local Area Networks (LAN), Storage Area Networks (SAN) etc., meet the latest requirements governed by the IEC 60332-1 which is the standard for Flame Retardant Grade specification. These requirements are met by the Low Emitting Zero Halogen or LSZH cables, and they are not met by the (PVC) polyvinyl chloride cables. Today almost every large installation in Europe must meet this specification. Latest trends show that IT managers even started following the more advanced IEC 60332-3 specification which is a more demanding flammability specification for LSZH cables.
However, the standards in Europe and North America are not the same. While the European standards tend to focus on low-smoke with zero-halogen cables, North American standards mainly focus on a combination of the fire resistance and specific electrical performance, with emphasis on wet electrical qualifications. This is why the North American markets have a tendency of slowly adopting the LSZH products.
The quality of these cables is tested with a variety of tests. They are tested for their electrical performance, flame propagation, halogen content measurement and smoke measurement. The electrical performance test is the most valuable test that separates the insulation material from the jacket material. The most known tests of this kind are the long-term insulation testing in water and the capacitance and relative permittivity tests.
The long-term insulation testing in water measures the resistance of the insulating material and its capability to resist the flow of electrons and current. This test is called long-term because it’s conducted over a period of 12 to 36 weeks. The test is done by immersing the insulated conductor in water at the temperature of the specific cable (generally 90 degrees Celsius) while an AC voltage is applied through it. The AC voltage applied must be equal to the voltage rating of the specific cable. The insulation value of the cable is measured on a weekly basis. If the resistance has not decreased by a large value over a period of 12 weeks, than the cable is considered to be safely used in wet and dry applications at the rated temperature.
The capacitance and relative permittivity test measures the capacitance and permittivity level of wet-rated conductors. The relative permittivity measures the ratio of the amount of electrical energy stored in the material by an applied voltage and the capacitance is the ability of the material to store charge. The test involves submerging the wire into water and after 24 hours the capacitance and permittivity would be measured. The capacitance is also measured after 7 and after 14 days. The acceptable value for the relative permittivity is 6.0 or less, while for capacitance the requirement is to keep the capacitance value from increasing more than a specified percentage at the given intervals.
The second test is the test of flame propagation. These tests are conducted by stringing together a specified number of eight foot cables samples in a vertical tray and placed in a flame chamber. In the chamber, a flame is applied at the bottom of the cables for 20 minutes. After the flame application, the flame source is removed, and the cables are left to self-extinguish. The test would be acceptable if the measured char at the bottom of the cable is below the prescribed limit of the standard.
The smoke measurement test is conducted at the same time with the flame propagation test. While the cables are burning in the flame chamber a system of complex sensors measure the amount of smoke and peak smoke released. If the total smoke released is less than 150 m2 and the total peak smoke release value is less than 0.40 m2/s the test is passed.
The halogen content measurement is done via an X-ray fluorescence test. The test is passed if the material has less than 0.2% of halogens by weight.
The key difference between PVC and LSZH cables is the amount of dangerous, toxic gases emitted in case of fire. The reduction of the emission of these gases is way bigger with LSZH cables compared to PVC cables. This is mainly because of the compound used in LSZH cables. Even though PVC cables also meet the various requirements of UL 1581, UL 1666 and UL910, they still emit a large amount of toxic and deadly gases. What is interesting about the UL specifications is the fact that those are specifications that specify that the fire can eventually be extinguished faster, but they don’t specify the amount of deadly gases emitted in case of fire.
When comparing these two cables, physically they are very different. You can distinguish one from another just by touching them. PVC cables are softer to a touch because of the material they are made of. On the other hand, due to the rigidness of the flame resistant material needed to manufacture LSZH cable, these cables are rougher and more rigid when compared to PVC cables. Because of the same reason they are also less flexible than PVC cables.  
In case of fire PVC cables would emit a thick, black smoke containing toxic gasses like hydrochloric acids. Low Smoke Zero Halogen cables have a fire resistant jacket which emits no toxic fumes. Because of these safety mechanisms, which could save countless lives, LSZH cables are a bit more expensive than PVC cables. According to the latest Cenelec standards EN50167, 50168 and 50169, the LSZH cables must also be halogen free. The main concern in a fire with PVC cables is the “fire leaping”. This term describes the process of the fire traveling along the cable, leaping from one room to another just by burning along the cables.  
Another key difference is the PVC’s vulnerability to corrosion over time due to various conditions. For example one of the corrosive substances is oil. Because PVC is a material based on petroleum, they can easily dissolve when coated with oil. This won’t be a problem if oil wasn’t widely used in large factories and industries. PVC cables are also vulnerable to UV exposure. Cables that would be exposed to the sun for long periods of time would need to be replaced more often.

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