The People's Republic of China Industry Standard Electr […]
The People's Republic of China Industry Standard Electric Industry Safety Work Regulations DL 408-91: 1.4 Electrical equipment is divided into high voltage and low voltage: high voltage: equipment with a ground voltage of 250V or more; low voltage: equipment with a ground voltage of 250V and below.
How to distinguish the voltages of high-voltage cables and low-voltage cables:
1. Know the voltage level. In my country's power industry, common voltage levels are 220 volts, 380 volts, 10,000 volts, 35,000 volts, 110,000 volts, 220,000 volts, and 500,000 volts. Under normal circumstances, 220 volts and 380 volts are considered low voltages, mainly for household electricity; 35,000 volts and above are high voltages, mainly used for power transmission. The one in between is medium pressure. It must be pointed out that touching high-voltage wires or carrying out live work under the wires is extremely dangerous.
2. Know the types of poles and towers. Towers are facilities used to support electric wires, and we see them almost every day in our lives. The most common are cement poles, steel poles and iron towers.
3. Identify low-voltage lines. Outdoor low-voltage lines have several obvious characteristics:
Cement poles are basically used for support, and the cement poles are relatively short, generally no more than 5 meters.
The thickness of the wires is the same, and the number of wires is a multiple of 4. This is because low-voltage wires generally use a three-phase four-wire system. If you have these characteristics, you can determine that the line voltage of the wire is 380 volts, and the phase voltage is 220 volts. (The phase voltage is the line-to-ground voltage, and the line voltage is the voltage between the two lines)
Selection principle of low voltage cable
General principles for selecting cable cross section
In order to achieve safe, reliable, economical and technically reasonable power supply, the wire cross section should be determined according to the following principles:
1. Select the wire cross-section according to the allowable load current for the duration. Make the wire work for a long time under the maximum compliance without overheating, that is, it does not exceed its long-term allowable temperature.
2. Select the wire section according to the allowable voltage loss. Make the receiving end have enough voltage to ensure the quality of power supply.
3. Select the wire cross section according to the economic flow density. Make the annual operating cost of the transmission line the lowest and achieve the purpose of economic power supply.
4. Select the wire section according to the mechanical strength. Avoid disconnection during operation or installation, or damage due to smashing pressure, to ensure the safe operation of power supply.
5. Select the wire section according to the thermal stability conditions during short-circuit. The short-term allowable temperature of the wire shall not be exceeded when passing the short-circuit current.www.yatongcable.com