1, Check the certification mark. Products that have obtained mandatory certification through the purchase of qualified THHN wire methods and techniques should have the certification mark, also known as the "UL" mark, prominently displayed on the product. Otherwise, it is considered an unlicensed product.
2, Refer to the inspection report. As a product that affects personal and property safety, it has always been listed as a key focus of government supervision and inspection, and regular manufacturers are subject to periodic inspections by supervisory departments. Therefore, the seller should be able to provide inspection reports from the quality inspection department, otherwise, the quality of THHN cable will lack basis.
3, Check the insulation and sheath of THHN wire. The thickness of insulation and sheath should be uniform without deviation, and there should be obvious tension and elongation when touched. At the same time, the insulation and sheath surfaces should have continuous printed markings of the manufacturer's name and product model, with a spacing of no more than 200mm for insulation and 500mm for sheath.
4, Observe the smoothness and color of the wire THHN body. THHN wire copper conductor is annealed copper wire, aluminum conductor is aluminum or aluminum alloy wire, with a smooth surface. Copper conductor is light purple, and aluminum conductor is silver white. Otherwise, the conductor may be doped with other impurities, causing a decrease in conductivity.
5, Measure DC resistance. To ensure the quality of the purchased product is qualified, 3-5 meters can be cut from the THHN cable to be purchased and sent to the inspection agency for DC resistance measurement.
6, Measure the length. The national standard has clear regulations on the delivery length of THHN wire. The length of the coil should be 100m, and the length of the coil should be greater than 100m. Consumers can measure according to the length indicated on the label. The standard stipulates that the length error should not exceed 0.5% of the total length. If it does not meet the lower limit specified in the standard, it is considered unqualified.
