Wire and cable testing items and testing methods

As people's living standards improve, their expectations for quality of life continue to grow. Wires and cables, which are essential components in human production and daily activities, have become increasingly important for ensuring safety. Consequently, the state’s oversight of wire and cable quality has intensified. Below, we’ll delve deeper into several key areas, including DC resistance, insulation resistance, electrical conductivity, voltage, and the physical dimensions and appearance of the wires and cables.

(1) DC Resistance Testing of Wire and Cable

When testing the DC resistance of wires and cables, the focus is primarily on verifying the actual conductivity. The DC resistance data directly reflects the quality of the materials used and the efficiency of the conductor. During the test, when the cross-sectional area of the wires and cables is consistent, a higher resistance suggests poorer current flow, while lower resistance indicates better performance. Additionally, within equal current conditions, better electrical conductivity means superior material quality. According to national standards, the maximum allowable resistance at 20 degrees Celsius serves as a benchmark. If the measured resistance at the same temperature is closer to this standard value, the sample is considered more qualified; otherwise, it may be deemed不合格(unqualified).

In terms of testing methods, two primary approaches are commonly used: the bridge method and the current method. The bridge method includes the single-arm bridge and double-arm bridge techniques. For resistances above one ohm, the single-arm bridge is typically employed, while resistances below one ohm require the double-arm bridge method. Another method is the current method, or micro-ohm method, which predicts the appropriate current based on the resistance value. This approach offers a broader measurement range compared to the bridge method. To minimize errors and enhance accuracy, a four-terminal measurement device can be utilized, providing both credible and authentic results.

(2) Insulation Resistance Testing of Wire and Cable

The insulation resistance test focuses on assessing the effectiveness of the wire and cable's insulation properties. These properties play a crucial role in reducing risks like electrical leakage, short circuits, and open circuits during practical usage. Proper insulation ensures that any electrical issues are automatically blocked, preventing harm to people and property. During testing, the quality of the wire and cable can be gauged by examining the resistance values. Generally, the insulation resistance decreases as the length of the wire increases, meaning longer cables have higher resistance, while shorter ones have lower resistance. To calculate the resistance value, the measured resistance can be multiplied by the cable length, yielding the overall resistance of the wire and cable.

In practice, the high-resistance meter method, also known as the voltage-current method, is predominantly used. This method is particularly suitable for testing the insulation resistance of metallic and multicore cables. After immersing the cable in water, the insulation resistance of single-core cables in multicore cables can be tested. For multicore cables, the remaining cores must also be connected to water. Throughout the measurement process, the water temperature should remain constant to ensure consistency in the results, making the experiment more accurate and reliable.

(3) Performance Testing of Wire and Cable

When evaluating the performance of wires and cables, it’s essential to assess not only their electrical conductivity but also their fire resistance, toxicity, flame retardancy, and density. In testing electrical conductivity, the strength of the wire and cable is directly proportional to its performance when the temperature and current are constant. Additionally, the toxicity test requires a rigorous experiment using mice. Gas released from the wire and cable is analyzed under high temperatures and sufficient heat. If the generated gas contains harmful substances exceeding the limit, the product is deemed unqualified. Conversely, if it meets the criteria, it passes the test. Fire resistance testing involves burning the sample under specified conditions. If the product sustains burning for a set period, it fails the test. On the other hand, flame-retardant cables cannot be used post-fire but can delay the spread of flames and provide valuable time for rescue efforts. In contrast, fire-resistant cables remain operational after a fire, offering practical benefits during emergencies.

(4) Dimensional and Appearance Testing of Wire and Cable

Assessing the dimensions and appearance of wires and cables is equally critical. The exterior appearance forms the initial impression of the product, influencing perceptions about its quality. Detailed inspections are necessary to identify and rectify defects such as cracks or oil stains that could impact usability. Additionally, the dimensions of the sample must align with the inspection standards, ensuring proper thickness, height, and density. Any deviations from these criteria indicate an unqualified product.