The design and construction of building decoration engineering is a new profession. Therefore, with the development of market economy, the number of building decoration engineering is increasing day by day. The electrical design, construction and installation is an important part of Building Decoration Engineering, which accounts for a large proportion of decoration engineering. The quality of electrical design and construction has a direct impact on the quality of Building Decoration Engineering, directly related to the safety of Building Decoration Engineering and the quality of fire prevention.
Electrical fire prevention of building decoration includes fire prevention of power distribution equipment, electrical circuit, electrical equipment and grounding system.
Grounding form of low voltage power grid
TN-S system shall be selected for high-rise buildings with substation. The TN-C-S system is applied to the building decoration project powered by the low-voltage line of the urban public transformer or the building decoration project powered by the low-voltage line of the unit transformer. TN-S or TN-C-S system meets the protection requirements of preventing indirect electric shock, line damage and electrical fire.
Fire protection of electrical circuit
Good copper core cable or copper core insulated wire shall be used for power line, distribution main line and branch of building decoration works, and the cable or wire below 25 mm2 shall be used. The cable or wire with equal cross section shall be used in low voltage 380 / 220 V three-phase four wire system. Because the electrical circuit is an important part of the electrical system.
The fire caused by electrical circuit is caused by electric spark and arc caused by electric circuit leakage, short circuit, overload, over-voltage, too large contact resistance and damage or breakdown of conductor insulation. For example, if the electrical circuit is short circuited, in a very short period of time, a lot of heat will be generated, so that the melting of the metal wire will also produce electric sparks and arcs, which will ignite the surrounding combustibles while the insulation layer of the wire burns, thus causing a fire. At present, most of the building decoration materials are combustible, so in the building decoration engineering, all electrical lines must be protected by pipes. If the line overload also exceeds the maximum allowable working temperature of the conductor, the aging of the insulation layer will be accelerated. Serious overload will cause the combustibles in the insulation layer of the conductor to burn, which will ignite the nearby combustibles and cause a fire. If the contact resistance is too large, it means that the connection between the wire and the wire is not firm, and the wire and the wiring nose cannot be put through and pressed, resulting in the contact resistance is too large. When the large current flows through the contact resistance part, it will generate high heat in this part. The contact point of the metal wire is hot, and the electric spark and arc will flash at the moment of burning off, burning the insulation layer of the electrical circuit, and igniting the combustible nearby It's a fire.
The voltage of low-voltage power grid fluctuates greatly in the daytime and at night, with the voltage as high as 270 V and as low as 170 v. therefore, some lamps and electrical equipment are in over-voltage operation at night, resulting in the explosion of lighting bulbs and the burning of electrical equipment. If you don't pay attention to it, it will also cause fire, so the fire caused by over-voltage is also common. But as long as the cross-section of cable and conductor is selected strictly according to the design requirements and the construction is carried out according to the regulations, the fire of the line can be prevented.
Fire protection of distribution box
It is strictly prohibited to install air switch, fuse and other electrical equipment directly on board, wooden keel and decorative board in the building decoration project. The switch, fuse and other electrical equipment must be installed on the iron distribution board in the iron distribution box. The distribution box made of iron shall be sealed with sheet iron to prevent fire caused by combustible decorative fiber entering the distribution box. It is also not allowed to cover the distribution box with decorative plate, and the distribution box must be exposed for heat dissipation. The iron distribution box, metal shell, metal pipe rack and iron plate surface shall be well grounded, and the grounding resistance shall not be greater than 4 ohm.
The air switch and electrical equipment of the distribution box shall not be faked or imitated. They must be selected according to the design requirements, otherwise the switch itself will ignite in case of short circuit and cause fire. The fuse melt of the setting value of the automatic air switch shall be selected and equipped according to the design requirements, and the switch and the insulated wire shall be matched. It is suggested that the automatic air switch with short-circuit and overload protection and the automatic voltage protector with self-protection should be selected first in the building decoration works to prevent the fire caused by the short-circuit, overload and over-voltage of the distribution box and lines.
Fire protection of lighting and lamps
Improper installation and use of lighting lamps will also cause fire. Different lighting, lamps and light sources shall be selected for building decoration works according to different functions, uses and environments. The commonly used lamps include incandescent lamp, fluorescent lamp, iodine tungsten lamp, high pressure mercury lamp, low pressure halogen lamp, neon lamp, neon tube lamp, etc. incandescent lamp will emit a lot of heat when it is working. When installing the lamps and lanterns, the location is improper. The distance between the lamps and combustibles is too close or the combustible dust and fiber fall on the lamps and lanterns, the lamps will also burn. When the incandescent lamp is connected to the power supply, the filament can reach 2000-3000 ℃. The surface temperature of the incandescent lamp glass is very high, and if you don't pay attention to it, the surrounding combustible materials will be ignited. Ceiling lamp, embedded lamp and lamp slot shall be insulated with non combustible asbestos board. Fluorescent ballasts, especially inductive ballasts, shall be installed on non combustible materials with good ventilation. The shell of electronic ballasts shall be made of flame-retardant materials, and shall not be installed on combustible materials such as wood boards and wooden keel.