Branch cable distribution system technology advanced, can be said to be a branch cable is a modern building tailor-made, professional products, with the best applicability and technical economy, but in the engineering design, we need to pay attention to one point - that is the branch line protection problem.
Due to the feeder sections are generally smaller than main line, therefore, when the feeder had cut or short circuit, main protection system will not happen on its effect, must set the protector in the distribution box feeder, protector and branch connector is generally not more than 3 m, such as more than, branch line do lay in the pipe or tank of non-combustible, and when this single phase or two phase short circuit, main protection should be able to disconnect.
Attention should be paid to this.
As a new type of building distribution cable imported from abroad, branch cable has been popularized and applied in many domestic projects, and has been recognized and used by the majority of designers.
The purpose of this paper is to show that the branch cable distribution is consistent with the existing building electrical related codes, and can better reflect the guidelines of the code, which is an advanced and economic distribution mode that can meet the existing codes.
Nylon sheathed wire
China's building indoor power cord wiring has been using PVC insulated BV cloth wire.
In the rapid development of economic construction and the quality of life of urban and rural residents to improve today, family life electrification, modernization of the step is coming rapidly, not only the number of household appliances is increasing, and the capacity of all kinds of home appliances is also on the rise, thus putting forward new requirements for indoor power circuit design.
For a long time, China's building indoor power cord wiring has been using PVC insulated BV cloth wire.
In the rapid development of economic construction and the quality of life of urban and rural residents to improve today, family life electrification, modernization of the step is coming rapidly, not only the number of household appliances is increasing, and the capacity of all kinds of home appliances is also on the rise, thus putting forward new requirements for indoor power circuit design.
Not only the quantity of the circuit is required, but also the quality of the circuit, especially the safety of the wiring as the circuit in the prevention of electric shock and short circuit fire accidents put forward higher requirements.
According to the national public security department, in recent years, in large and small alarming fire accidents, 30 percent are due to electrical fires.
This makes the prevention of electric wire short circuit accident become the design, construction and decoration of the first problem to be solved.
According to the analysis, the short circuit of the building wire is nothing more than the following reasons, namely, the aging of the wire, the wire in the pipe in the insulation scratch, the formation of potential short circuit hidden danger, the line overload operation, the temperature exceeds the prescribed range and burned out the insulation, a number of disastrous fire accidents have caused great concern of the whole society.
Since 2001, in the column of "Building Conductor Promotion Project" of "International Copper Industry Association (Beijing)", experts have continuously carried out extensive and in-depth discussions on residential electrical design issues.
With great attention paid to preventing fire accidents, it is expected that experts will look for a new product with superior performance to replace indoor power wiring.
This not only increases the level of electrification of urban and rural households, but more importantly reflects the country's high attention to the improvement of people's quality of life and the value of human life.
In 1997, China's wire and cable industry and Shanghai Cable Research Institute introduced American technology, researched and developed PVC insulated and nylon sheathed wire and cable with rated voltage up to and including 450/750V.
A few domestic savvy faster enterprises to promote use.
In May 2001, China Machinery Industry Federation approved and issued JB/T20261-2001 "PVC insulated nylon sheathed wire and cable with rated voltage up to and including 450/750V".
This can be said to be the BVN type wire stage in China's three steps.
What BVN type wiring will be BV wiring alternatives, we from the half a century of usage can be seen at home and abroad, the United States is a highly developed capitalist country, science and technology has been in the international leading level, in the early 50 s BVN type wire cloth is widely into all kinds of construction of family homes, to make still enduring.
In some countries in the 1970s, BVN type wire is only used in some aviation aircraft, automobile, power system and control system, which shows that BVN type wire than BV type wire has a unique superiority.
Advantages of BVN type wire
For BVN wire, experts have summarized the following seven advantages after repeated trials and long-term practice:
1. Convenient pipe piercing.
The diameter of wire is fine, and the friction coefficient is obviously reduced when the pipe is penetrated.
2. Increase the threading capacity of the wire conduit.
The diameter of the wire is small, and the same size of the conduit can be penetrated into more wires or carry more flow.
3. Excellent resistance to reduce the damage to insulation when wire is threaded and laid.
This point is very important, can effectively reduce the potential short circuit accident.
4, excellent hydrocarbon resistance performance, good chemical stability, that is, excellent oil resistance, liquid gas and gas corrosion performance, effectively improve the reliability and service life of the wire (aging performance test proves that the service life of BNV wire than the original BV wire at least doubled that is 40 years or more).
5, high safety performance.
The BVN type wire has good thermal stability and thermal shrinkage resistance.
This will help to avoid the possibility of short-circuit failure due to overheating of the connection point, which may cause the wire insulation to shrink and expose the copper wire.
6, have the ability to withstand a considerable short circuit current, 5 seconds short circuit temperature is higher than the ordinary BV type.
This is because of the nylon sheath, and nylon has a melting point of 2150C.
7. It has the same flame retardant performance as PVC insulation.
According to the relevant expert test, the toxicity released by its combustion is far less than PE.
8. Manufacturer name, product model, voltage grade and other signs are printed between PVC insulation and nylon sheath, with clear signs and abrase-resistant.
Comparison of material structure between BVN type wire and BV type wire
BVN refers to China's mechanical standard JB/T10260-2001, namely "rated voltage 450/750V and up to PVC insulation layer dragon sheathed wire and cable".
The BV refers to the national standard GB5023, that is, "rated voltage 450/750V and the following PVC insulated cable", here we might as well take out to do a comparison, (specific can see the standard, omitted here).
The structure shows that the material cost of BVN is slightly higher than that of BV wire, and the processing is slightly more complex, so the price of BVN is slightly higher than that of BV wire.
It can be expected that this new type of product will soon be accepted by users.
At present in Beijing, Shanghai and other big cities part of the large buildings (such as the Olympic Games venues) has been required to use BVN type wire cloth.
Widely used in Europe, the United States, Canada and the Middle East, this kind of nylon sheath BVN wire occupies more than 95% of the market of cloth wire in foreign markets.
Although China has just started, but has bred a huge market.