01 Common types of power cables
In current building electrical design, commonly used cables can be divided into the following categories: ordinary cables, flame-retardant cables, fire-resistant cables, halogen-free low smoke cables, and mineral insulated cables. Corresponding to the various types of cables mentioned above, different manufacturers have different products, but the basic requirements and definitions are consistent.
① Ordinary cable
Mainly refers to PVC insulated wire BV line and cross-linked polyethylene insulated PVC sheathed power cable YJV.
② Flame retardant cable
Wires and cables that are difficult to ignite and have the ability to prevent or delay the spread of flames. This cable usually refers to wires and cables that can pass the GB/T18380.3 (equivalent to IEC60332-3) test. Including flame retardant PVC insulated wire ZRBV wire and flame retardant cross-linked polyethylene insulated PVC sheathed insulated power cable ZRYJV
③ Fire resistant cables
A wire and cable that can maintain the integrity of the circuit even under the specified temperature and time of flame combustion. Usually refers to wires and cables that have passed the GB/T12666.6 (equivalent to IEC60331) test. Including fire-resistant polyvinyl chloride insulated wire NHBV line and fire-resistant cross-linked polyethylene insulated polyvinyl chloride sheathed insulated power cable NHYJV
④ Halogen free low smoke cable
Halogen free low smoke flame-retardant cable WDZ-BYJ/YJY: The material does not contain halogens, produces less smoke and dust during combustion, and has the ability to prevent or delay the spread of flames. Generally, wires and cables that can pass the three standard tests of GB/T 17650.2 (equivalent to IEC60754-2), GB/T17651.2 (equivalent to IEC61034-2), and GB/T18380.3 (equivalent to IEC60332-3) are called halogen-free low smoke flame-retardant wires and cables.
WDZN-BYJ/YJY: A halogen-free, low smoke, flame-retardant and fire-resistant cable made from materials that do not contain halogens, produce less smoke and dust during combustion, and have the ability to prevent or delay flame spread while maintaining the integrity of the circuit. Generally, wires and cables that can pass the four standard tests of GB/T17650.2 (equivalent to IEC 60754-2), CB/T 17651.2 (equivalent to IEC61034-2), GB/T 18380.3 (equivalent to IEC 60332-3), and GB/T12666.6 (equivalent to IEC60331) are referred to as halogen-free low smoke flame-retardant and fire-resistant wires and cables.
⑤ Mineral insulated cable
Cables using minerals (such as magnesium oxide) as insulation materials. Usually composed of copper conductors, mineral insulation, and copper sheaths, without organic materials; And it has non combustible, smokeless, non-toxic, and fire-resistant characteristics.
02 Selection and laying requirements for wires and cables in residential buildings
The selection of wires and cables in residential buildings mainly refers to the provisions of the "Code for Electrical Design of Residential Buildings" and the "Code for Electrical Design of Civil Buildings".
① Ordinary load wires and cables
According to regulations, ordinary load cables concealed in public areas in multi story and high-rise residential buildings can all use cross-linked polyethylene YJV power cables or polyvinyl chloride BV wires; The ordinary load cables laid in public areas of high-rise residential buildings are more likely to be delayed in fire. To reduce the harm to personnel inside the building, halogen-free low smoke flame-retardant WDZ-BYJ/YJY cables and wires should be used for power supply; The indoor wiring in residential areas is now concealed through conduit. Even in the event of a fire, the likelihood of all wires burning in a short period of time is low, and the halide content and impact range generated by combustion are limited. Therefore, BV wires can be concealed through conduit.
Among them, the exposed laying methods include direct cable laying, cable laying in ladders, and wire laying through protective conduits. If the cable is laid in a trough type cable tray and installed outside the effective structural protective body (such as in a suspended ceiling), it is considered exposed laying. Cable laying in an electrical shaft is not considered exposed laying. When laying through pipes, wires can be used.
② Fire load wires and cables
Different types of cables should be selected for the fire power supply main line, emergency lighting, and fire automatic alarm line for fire load wires and cables.
03 Selection and laying requirements for wires and cables in other civil buildings
① Ordinary load wires and cables
In general engineering, cross-linked polyethylene insulated YJV cables and polyvinyl chloride BV wires are selected. For high-rise buildings and important public places with high fire safety requirements, halogen-free low smoke flame-retardant WDZ-BYJ/YJY cables should be used.
The Fire Protection Design Regulations for Civil Building Wire and Cable further classify various locations to clarify the wire and cable that should be selected for each location.
Based on this, cables used for ordinary load power supply, directly buried and concealed through pipes can use ordinary cable YJV. In addition, wires and cables used for special and first level locations should use halogen-free low smoke type WDZ-BYJ/YJY, and wires and cables used for second level locations should use halogen-free low smoke type WDZ-BYJ/YJY. Wires used for ordinary equipment lines can use ordinary wire BV when threading through pipes
When wires and cables are laid in bundles, to avoid cable ignition in case of fire, flame-retardant wire and cable ZRBV/YJV should be used; In places where it is necessary to maintain the integrity of the power line and maintain power supply under external fire, fire-resistant wire and cable NHBV/YJV or mineral insulated cable BTTZ should be used for the power supply main line used for particularly important loads in special and first level places. Mineral insulated cable BTTZ should be used for the power supply main line used in important wooden public buildings.
② Fire load wires and cables
The wires and cables used for fire protection loads mainly refer to the provisions of the "Code for Electrical Design of Civil Buildings", "Code for Fire Protection Design of Wire and Cable in Civil Buildings", and the new version of the "Code for Fire Protection Design of Buildings".
The power supply trunk of fire protection facilities in special grade locations shown in Table 4.0.1 of the specification adopts mineral insulated cable BTTZ; Emergency lighting adopts halogen-free low smoke flame-retardant and fire-resistant WDZN-BYJ/YJY cables; The automatic fire alarm circuit adopts halogen-free low smoke flame-retardant and fire-resistant WDZN-BYJ/YJY cables.
The power supply trunk of fire protection facilities in first level places should use mineral insulated cable BTTZ, and can use halogen-free, low smoke, flame retardant, and fire-resistant WDZN-BYJ/YJY cables; Emergency lighting adopts halogen-free low smoke flame-retardant and fire-resistant WDZN-BYJ/YJY cables; The automatic fire alarm circuit adopts halogen-free low smoke flame-retardant and fire-resistant WDZN-BYJ/YJY cables. The concealed part can use flame-retardant and fire-resistant ZNBV/YJV cables.
The power supply trunk of fire protection facilities in secondary and tertiary places adopts ordinary flame-retardant and fire-resistant ZNBV/YJV cables; Emergency lighting adopts ordinary fire-resistant NHBV/YJV cables; The automatic fire alarm circuit adopts ordinary fire-resistant NHBV/YJV cables.
04 Requirements for laying distribution lines
The selection of cable laying methods should be based on factors such as engineering conditions, environmental characteristics, cable types and quantities, as well as the principles of reliable operation, easy maintenance, and technical and economic rationality.
① Requirements for laying fire power distribution lines
The laying requirements for fire protection distribution lines should meet the need for continuous power supply in the event of a fire, and their laying should comply with the following regulations:
When laying in the open (including in the suspended ceiling), metal conduits or enclosed metal trough boxes should be used for protection. Fire protection measures should be taken for metal conduits or enclosed metal trough boxes; When using flame-retardant or fire-resistant cables and laying them in cable wells or trenches, metal conduits may not be threaded or enclosed metal trough boxes may be used for protection; When mineral insulated non combustible cables are used, they can be directly laid in the open;
When concealed, pipes should be threaded and laid within non combustible structures, with a protective layer thickness of no less than 30mm;
Fire power distribution lines should be laid separately from other distribution lines in different cable wells and trenches; When it is indeed difficult to lay in the same cable well or trench, it should be arranged separately on both sides of the cable well or trench, and the fire power distribution line should use mineral insulated non combustible cables.
② Fire prevention measures for cable laying
In addition to ensuring the normal operation of the equipment, the cable itself also needs to take fire prevention measures. Therefore, the laying method also has the following requirements:
1) When laying wires and cables, effective fire sealing or separation measures should be taken for cable trays and cable shafts.
2) Power cables and non power cables should be laid separately. If it is necessary to lay them in the same cable tray, isolation measures should be taken.
3) When the non-metallic material capacity of cables laid in the same cable tray is greater than 14L/m, isolation measures should be taken.
4) When laying wires openly, metal pipes or metal wire ducts should be used for laying in special and first level locations, and metal pipes or metal wire ducts should be used for laying in second level locations.
5) When wires are concealed, it is advisable to use metal pipes or flame-retardant hard plastic pipes for laying, and they should be laid inside non combustible structures. When the fire equipment wiring is concealed, the requirement that the thickness of its protective layer should not be less than 30mm should also be met.
6) Mineral insulated cables can be laid on brackets or exposed along walls.
③ There are several points about cable laying that are not clearly specified in the specifications, but they are still worth studying
1) For first level loads, powered by dual power sources, low-voltage cables are led from transformers with different high voltages. The cables are usually fire-resistant and flame-retardant, but there is no regulation for the high-voltage incoming cables of the transformers. At present, there are many projects where substations do not rely on external walls, and high-voltage incoming cables may be laid in the cable tray for a section before entering the substation. In this case, if a fire occurs, the high-voltage cable does not have the fire-resistant ability, and the operation of the low-voltage fire-fighting equipment cannot be guaranteed. Therefore, the author believes that in this case, high-voltage incoming cables should use fire-resistant and flame-retardant cables.
2) Similarly, if the busbar from a diesel generator to a substation is laid in an unprotected section, at least fire-resistant busbar or mineral insulated cable should be used.
