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How to buy wires and cables?

2022-09-29

Fire-resistant cables are designed to maintain safe operation for a specified period even when exposed to flames. According to China's national industry standard GB12666.6 (equivalent to IEC 331), fire-resistance tests are categorized into two levels: Class A and Class B. Class A involves flames at temperatures ranging from 950°C to 1000°C, with continuous fire exposure lasting 90 minutes, while Class B uses flames at temperatures between 750°C and 800°C, also under continuous fire conditions for 90 minutes. Throughout the entire test duration, the cable samples must carry the rated current value as specified by the product’s technical requirements.

　How about discussing how to buy wires and cables?

　　Fire-resistant cables are designed to maintain safe operation for a specified period even when exposed to flames. According to China's national industry standard GB12666.6 (equivalent to IEC 331), fire-resistance tests are classified into two levels: Class A and Class B. Class A cables withstand flames at temperatures ranging from 950°C to 1000°C, with continuous fire exposure lasting up to 90 minutes. Meanwhile, Class B cables endure flames at temperatures between 750°C and 800°C, also under continuous fire conditions for 90 minutes. Throughout the entire test duration, the cable samples must carry the rated current value as specified by the product’s technical requirements.

　　Fire-resistant cables are widely used in multi-story buildings, subways, underground shopping malls, large and medium-sized power plants, and other critical industrial and mining facilities—areas essential for fire safety and emergency rescue operations. For instance, they serve as the power supply lines and control circuits for vital emergency equipment, such as firefighting tools and emergency lighting systems.

　　1. The insulation layer of the cable protection sleeve (typically exceeding 100 MΩ) and its dielectric strength (above 500 V but below 1500 V).

　　2. Line resistance (must not exceed a certain resistor value under given cable diameter, conductivity, and length).

　　3. Under continuous high-temperature shock of 140°C, the wire must not exhibit cracking or other damage at ultra-low temperatures as low as -30°C.

　　4. The design must comply with standards; the cables must include certification marks, the manufacturer’s name, cable diameter information, and the grounding wire should feature a light-green cable jacket.

　　Are there any things to keep in mind when storing cables?

　　1. Cables should be regularly rotated during storage (every 3 months in summer; during other seasons, the interval can be adjusted accordingly).

　　2. When unrolling the cable reel and laying it down, be sure to avoid exposing the bottom layer to moisture and cold. Also, during storage, make sure the cable ends remain intact and undamaged.

　　3. The storage period for cables should be limited to the production time of new products, not exceeding one and a half years—and in no case longer than two years.

　　4. Cables or cable trays must not be stored in high-altitude areas, especially under relatively low ambient temperatures (typically below 5°C).

　　5. When lifting, never attempt to hoist multiple thick steel plates simultaneously. Ensure that vehicles, ships, and other transport vehicles securely hold the cable tray in place as much as possible to prevent impacts or tipping, thereby avoiding any mechanical damage to the cables.

　　How to tell genuine from counterfeit high-temperature wires and cables

　　1. The resistance of the electrical conductor exceeds the standard. Copper wires used in wires and cables should ideally be made from high-purity electrolytic nickel, as this raw material produces uniformly drawn, lustrous strands. However, some manufacturers in the recycled copper industry prioritize profit by cutting corners—either by using inferior materials or reducing the actual copper content—which leads to significantly higher-than-allowed conductor resistance.

　　2. The raw materials used for insulation layers and protective sheaths should meet appropriate physical performance standards (tensile strength, elongation at break). For wires and cables where these indicators fail to meet the required specifications, plastic recycled materials should be selected, as their tensile strength and elongation at break do not satisfy the application requirements. Additionally, the cable’s highly susceptible structural design can lead to cracking under mechanical stress, potentially causing short circuits, electrical leakage, and even dangerous charge-discharge phenomena.

　　3. The new project for thermal expansion of high-voltage cable insulation has failed to meet standards. Some of the new products experienced melting and breakage in their insulated layers under thermal expansion, making them prone to short-circuit failures and safety hazards at elevated temperatures.

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