Application Exploration of Extruded Fireproof Mud Structure in Non-armored B₁-Class Flame-Retardant Multi-core Low-Voltage Cables

To address the urgent market demand for B₁ Class and low-cost power cables, this paper proposes a novel structural solution involving the continuous extrusion fireproof paste between the stranded conductor and outer sheath, replacing the complex traditional designs reliant on high-quantity oxygen-blocking materials or multi-layer flame-retardant wrapping/armoring. Based on this approach, a 0.6/1 kV WDZB1-YJY-0.6/1 kV 5×6 copper core cross-linked polyethylene insulated halogen-free low-smoke polyolefin sheathed flame-retardant B1 class power cable was successfully trial-produced. Systematic comparisons of the flame propagation performance of the new structure against two conventional cable designs revealed: the new cable achieved a char height of only 0.34 m, reduced by 0.25 m compared to the optimal conventional design; the maximum temperature inside the combustion chamber dropped from 62°C to 43°C, a decrease of 19°C; and the combustion duration was significantly shortened from 8 minutes and 42 seconds to 3 minutes and 43 seconds. Structurally, the new cable eliminates core filling, simplifies the wrapping layer design, and establishes an integrated flame-retardant barrier through the extruded fireproof paste layer, achieving a 5.88% reduction in material costs while significantly enhancing flame retardancy. XRD and FTIR analyses identified the main phases of the ceramic hard shell as silicates and oxides, with an endothermic capacity of approximately 850 J/g, further elucidating its thermal insulation and oxygen barrier mechanisms. This study validates the effectiveness of the "extruded fireproof paste" structure in improving cable flame retardancy levels, suppressing flame spread, and reducing combustion temperatures, providing a feasible technical pathway and practical engineering reference for developing new flame-retardant cables with both superior fire resistance and cost efficiency.