Cross linked polyethylene YJV power cables or PVC BV wires can be used for ordinary load cables concealed in public areas of multi-storey residential buildings and high-rise residential buildings; However, the cables for common loads laid in public areas of high-rise residential buildings are likely to be delayed in case of fire. In order to reduce the harm to people in the building, halogen-free low smoke flame retardant WDZ-BYJ/YJY cables and wires should be used for power supply; The indoor lines of residential buildings are now laid in a concealed manner through pipes. Even in case of fire, the possibility of all wires burning in a short time is small, and the content of halides generated by burning and the scope of influence are limited, so BV wires can be laid in a concealed manner through pipes. Among them, open laying methods include direct laying of cables, laying of cables in ladders and laying of wires through protective conduits. If cables are laid in trough type bridges and installed outside the protective body of effective structures (such as laying in the ceiling), they are considered as open laying. If cables are laid in electrical shafts, they are not open laying. Wires can be used for pipe laying. ② Wires and cables for fire load Wires and cables for fire load shall be of different types for fire power supply trunk, emergency lighting and automatic fire alarm lines.