FAQ

In the design of fireproof cables, in addition to the requirements of fireproof and flame retardant, we often see

tests that require low smoke and halogen-free. Here we share the concept and test requirements of low smoke

and halogen-free cables.

Low smoke refers to the smoke released by the combustion of non-metallic materials during the combustion of

the cable, and the light transmittance is used to measure whether the test has passed. The international

standard IEC 61034 is usually applied. The light transmittance of LSZH cables is generally required to be greater

than 60%. Some standards have higher requirements for light transmittance, greater than 70%, such as rolling

stock cables.

Halogens are non-metallic elements, including fluorine, chlorine, bromine, iodine, and astatine. The halogens we

often refer to are fluorine, chlorine, bromine, and iodine. Halogen-free does not mean zero halogen. Halides will

also decompose denser halogenated gases during combustion to produce a covering effect, thereby isolating or

diluting the air, and ultimately achieving the purpose of flame retardancy and fire extinguishing. The

international standards commonly used in testing are IEC 60754-1 and IEC 60754-2, which are determined by

acid gas content, pH value and conductivity.

IEC 60754-1 tests the content of halogen acid gas, and generally requires a maximum of no more than 0.5%.

IEC 60754-2 measures the pH value of halogen compounds (i.e. halogen acids) and the conductivity of their

solutions, with the requirements of pH value not less than 4.3 and conductivity not exceeding 10μS/mm.

The ways in which they obtain halogen acids are different. Their heating methods are similar. However, the

halogen acid of IEC 60754-2 is obtained by dissolving halogen compound gas in pure water or deionized water.

The halogen acid of IEC 60754-1 is obtained by dissolving halogen compound gas in sodium hydroxide solvent.

The higher the pH, the lower the halogen acid content, which indirectly reflects the halogen content.