Recently, I saw mica tape wrapped around a fan-shaped copper conductor at a cable factory for use in manufacturing fire-resistant cables. This actually does not meet the quality requirements for fire-resistant cables.
In my country, as early as the 1990s, when fire-resistant cables were just starting out, some manufacturers tried using sector-shaped conductors to manufacture fire-resistant cables, but all failed the fire resistance test. Later, other manufacturers continued to produce fire-resistant cables with sector-shaped conductors and mica tape wrapping, but these also failed the fire resistance test. Analysis revealed two main reasons for the failures: first, the surface of the tightly compressed sector-shaped conductor was not smooth, especially the corners of the sector, which had burrs that easily punctured or scratched the mica tape; second, when multiple sector-shaped conductors wrapped with mica tape were cabled, the mica tape cracked and detached. These facts have repeatedly proven that sector-shaped conductors wrapped with mica tape cannot be used to manufacture fire-resistant cables.
The fire-resistant properties of mica tape rely on its mica paper layer. If the mica paper cracks or falls off, the cable loses its fire-resistant function and fails the fire resistance test. Fire-resistant cables generally use round, tightly compressed copper conductors, wrapped with mica tape, and for added reliability, an additional layer of fiberglass tape is wrapped around the outside. The surface of the tightly compressed conductor must be very smooth, without any burrs or other defects to prevent damage to the mica layer.
It has now been discovered that many manufacturers' fire-resistant cables are only wrapped with one layer of phlogopite mica tape or thin-film mica tape, which makes it difficult to say that their quality is up to standard. The traditional fire-resistant cable structure should be: tightly compressed round copper conductor + 2 layers of mica tape + 1 layer of fiberglass tape.
