Branched cable distribution system has advanced technology. It can be said that branch cable is a professional product tailored for modern architecture and tailored. It has the best and applicability and technology economy. But in engineering design, we should pay attention to the protection of branch line. Since the section of branch line is generally smaller than that of main line, the main line protection system will not affect the branch line when it is cut off or short circuited. The protector must be set in the distribution box of branch line, and the distance between the protector and branch joint shall not exceed 3M. If it exceeds 3M, the branch line shall be laid in non combustible pipe or trough, and when single-phase or two-phase short circuited occurs in this section, the main line protection shall be able to Enough to disconnect. Attention should be paid to this.
As a new type of building distribution cable introduced from abroad, branch cable has been widely used in many domestic projects, and has been recognized and used by the majority of designers. The purpose of this paper is to show the consistency of branch cable distribution with the existing building electrical related specifications, and to better reflect the guiding ideology of the specifications. It is an advanced and economic distribution mode that can meet the existing specifications.
Nylon sheathed wire
In China, PVC insulated bv type wiring has been used for indoor power line wiring. Today, with the rapid development of economic construction and the urgent need to improve the quality of life of urban and rural residents, the electrification and modernization of family life is coming rapidly. Not only the number of household appliances is increasing, but also the capacity of various household appliances is rising, which puts forward new requirements for indoor power circuit design.
For a long time, PVC insulated bv type wiring has been used for indoor power wiring in China. Today, with the rapid development of economic construction and the urgent need to improve the quality of life of urban and rural residents, the electrification and modernization of family life is coming rapidly. Not only the number of household appliances is increasing, but also the capacity of various household appliances is rising, which puts forward new requirements for indoor power circuit design. It not only requires a large number of circuits, but also puts forward higher requirements for the quality of circuits and the safety of wiring as circuits in preventing electric shock and short circuit fire accidents. According to the information issued by the state public security department, in recent years, 30% of the shocking fire accidents, large and small, are caused by electrical fires. This makes the prevention of wire short circuit accident become the primary problem to be solved in design, construction and decoration. According to the analysis, there are no more than the following reasons for the short circuit of building wiring, that is, the aging of the wiring, the scratch of the insulation in the pipe, the formation of potential short-circuit hazards, the overload operation of the line, the temperature exceeding the specified range and the burning of the insulation, and many serious fire accidents have aroused great concern of the whole society. Since 2001, in the column of "building conductor promotion project" of "International Copper Association (Beijing)", experts have continuously carried out extensive and in-depth discussion on residential electrical design.
With people's great attention to the prevention of fire accidents, it can be expected that for indoor power wiring, experts will seek a new product with superior performance to replace it. This not only increases the level of household electrification of urban and rural residents, but also reflects the country's high attention to the improvement of people's quality of life and the value of human life. In 1997, China wire and cable industry and Shanghai Cable Research Institute introduced American technology, researched and developed PVC insulated nylon sheathed wire and cable with rated voltage of 450 / 750V and below. Some domestic savvy enterprises will promote the use. In May 2001, China Federation of machinery industry approved and issued JB / t20261-2001 PVC insulated nylon sheathed wires and cables with rated voltage of 450 / 750V and below. This can be said to be the three steps of bvn type wiring in China.
What kind of bvn wiring will become the alternative product of BV wiring? We can see from the use of bvn wiring at home and abroad in the past half century that the United States is a highly developed capitalist country, and its science and technology has been at the international leading level. As early as the 1950s, bvn wiring has been widely used in all kinds of residential buildings, and it is still enduring. In some countries, in the 1970s, bvn type wires were only used in some aircraft, automobiles, power systems and control systems, which shows that bvn type wires have unique advantages over bv type wires.
Advantages of bvn wire
After repeated tests and long-term practice, experts have summed up the following seven advantages of bvn wire
1. It is convenient to put through the tube. The diameter of the wire is small, and the friction coefficient decreases obviously when the wire passes through the pipe.
2. The threading capacity of wire conduit is increased. The diameter of the wire is small, and for the same size conduit, more wires can be penetrated or the current carrying capacity is large.
3. Excellent durability reduces the damage to insulation when wires are laid in pipes. This is very important, which can effectively reduce the potential short circuit accident.
4. Excellent hydrocarbon resistance, good chemical stability, that is, excellent oil resistance, resistance to liquefied gas and gas corrosion performance, effectively improve the reliability and service life of wiring (aging performance test shows that the service life of BNV type wire is at least twice as long as the original bv type wire, that is, 40 years or more).
5. High safety performance. The test results show that bvn type wire has good thermal stability and heat shrinkage resistance. This will help to avoid the possibility of short-circuit fault caused by overheating of grounding point and shrinkage of wire insulation to expose copper wire.
6. It has the ability to withstand considerable short-circuit current, and the short-circuit withstand temperature for 5 seconds is higher than that of ordinary bv type. This is because of the nylon sheath, and the melting point of nylon is 2150c.
7. It has the same flame retardant property as PVC insulation. According to the test of relevant experts, the toxicity released by its combustion is far less than that of PE.
8. The manufacturer's name, product model, voltage grade and other marks are printed between PVC insulation and nylon sheath, and the marks are clear and scratch resistant.
Comparison of material structure between bvn type wire and bv type wire
Bvn refers to Chinese mechanical standard JB / t10260-2001, i.e. PVC insulated and sheathed wires and cables with rated voltage of 450 / 750V and below. Bv refers to the national standard GB 5023, i.e. PVC insulated cables with rated voltage of 450 / 750V and below. Here we can make a comparison (see the standard for details, which is omitted here). The structure shows that the material cost of bvn is slightly higher than that of BV wire, and the processing is slightly complex, so the price of bvn is slightly higher than that of BV wire.
It can be expected that this kind of new products will soon be accepted by users. At present, in Beijing, Shanghai and other big cities, some large buildings (such as Olympic venues) have required the use of bvn type wiring. It is widely used in Europe, the United States, Canada and the Middle East. In the foreign market, this kind of bvn wire with nylon sheath occupies more than 95% of the market. Although China has just started, it has bred a huge market.