Disadvantages of YTTW Flexible Fireproof Cable
1. YTTW cable utilizes a copper sheath, which significantly increases production costs due to the increased copper usage.
2. Cables with larger cross-sections are still relatively rigid and lack flexibility, so larger cross-sections (greater than 630mm²) cannot be produced yet and cannot meet the high current requirements of the system. Furthermore, the copper sheath of cables with larger cross-sections is prone to cracking, as will be explained later.
3. According to the testing requirements specified by the British Metro, during testing, YTTW cable samples were subjected to two stages of combustion and spray testing. When bent 180° at the impact point, the copper sheath of the inorganic mineral insulated cable (YTTW) cracked along the weld at the bend. The crack was over 10 cm long, and the mica tape was visible, having been burned into a black powder. Subsequent impact testing was continued at the bend point, with impacts occurring every 30 seconds for 15 minutes. The crack in the YTTW copper sheath at the bend was even larger, and the mica at the crack had significantly fallen off. The insulation test showed 0 MΩ. After the impact, the sample was immersed in water and a voltage of 750V was applied. The YTTW sample failed the test due to cracks on the sheath surface and a short circuit.
Observations of the samples during the test and the final test results indicate that, under conditions of sustained high-temperature combustion, the mica, which provides insulation and fire resistance, in inorganic mineral insulated cables (i.e., flexible fire-resistant cables), will shed as powder, and the glass fiber cloth will become hard and brittle. Due to its structural characteristics, there are considerable gaps between the sheath and the insulation layer, providing space for the shed mica powder, making it very easy for external impact to cause an electrical short circuit. Furthermore, the insulation layer of this type of cable lacks the dense aluminum sheath of BTLY cables, resulting in poor explosion-proof performance. Combustible gases, gasoline, and steam can spread through the gaps between the cable sheath and the insulation layer to connected electrical equipment or other areas requiring explosion-proof protection. Therefore, caution should be exercised when selecting this cable for use in critical locations, such as fire protection systems.
4. According to cable withstand voltage test regulations, the voltage should not break down when increased to 2500V at a rate of 150V/s for 15 minutes. However, some YTTW cables broke down when the voltage was increased to 1300V. Three hours later, when the voltage was reapplied and increased to 2000V, the cables broke down again. This test demonstrates that after a breakdown, YTTW cables cannot recover their electrical performance and must be scrapped.
