In recent years, reports of counterfeit and substandard low-voltage cables have been rampant. Many unscrupulous manufacturers in the cable industry sacrifice product quality in pursuit of profit, resulting in a market filled with inferior products and making it difficult for consumers to choose. Quality and length compliance are even more challenging for consumers. Recently, several substandard cables were exposed, serving as a wake-up call for the cable industry: improving quality and increasing efficiency is a long and arduous task. This article, along with industry colleagues, discusses how to distinguish the quality of wires and cables. There are two main ways to identify wire and cable quality: inspection and testing.
Inspection involves checking for quality system certification; confirming compliance with the certificate; verifying the manufacturer's name, address, inspection stamp, and production date; and verifying the printed trademark, specifications, and voltage information on the wires and cables. The main methods are:
1. Identify the Certificate of Conformity
When purchasing, be sure to check the certificate for the "3C" certification mark, and ensure that the model, specifications, rated voltage, length, manufacturing date, certification number, inspection, implementation standards, manufacturer name, and address are clearly marked.
2. Pay attention to the packaging
When purchasing, look for attractive packaging with clear printing, and complete information about the model, specifications, manufacturer name, and address. Counterfeit and substandard wires and cables are often "three-no" products, yet may have ambiguous origin markings such as "Made in China" or "Made in a certain province or city in China," effectively omitting the origin.
3. Check the Appearance
When purchasing, check for a smooth, rounded surface, uniform color, and pleasant feel. For rubber-type wires and cables, the sheath and insulation should be able to withstand a cigarette burn and remain intact.
4. Check the Conductor
The conductor should have a certain gloss and be moderately flexible, and its dimensions should meet national standards. A cross-section of the copper core of a wire or cable indicates that high-quality copper should be bright and soft in color; otherwise, it is considered inferior.
5. Check the length
When purchasing, avoid being tempted by the price and purchasing cables that are only 90m or 80m long, or even without length markings. The length must meet the standard requirement of 100m (+/-) 0.5m.
6. Check the PVC sheath
If you can see regular "roughness" on the surface of the compressed inner braid, this indicates good craftsmanship and no relative slippage, indicating a good cable. If the appearance is smooth, with no visible unevenness from the compressed braid, and the sheath feels loose when squeezed, it indicates a poor quality cable.
7. Check the shield braid
Check the number of braids to ensure the copper braid is sufficient. Check for solderability. Scrape the tinned copper wire to see if it is copper underneath. Aluminum-magnesium alloy wire is significantly harder than copper wire. If the braid is sparse, unevenly distributed, or loosely wrapped around the insulation, it indicates a poor quality cable.
8. Check the core wire
Diameter: SYV cable has a core diameter of 0.78-0.8mm, while SYWV cable has a core diameter of 1.0mm. Recently, a SYV75-5 cable with a core diameter of 1.0mm has appeared. The characteristic impedance of this cable is definitely not 75 ohms and should not be used in 75 ohm transmission systems.
What is the second test? It involves repeatedly bending a piece of wire or cable by hand. Cables that feel soft, have good fatigue resistance, have a high elasticity to the plastic or rubber, and have no cracks in the insulation are considered high-quality. The main methods are:
1. Weighing
High-quality wires and cables generally fall within the specified weight range. For example, a commonly used 1.5 mm² plastic-insulated single-strand copper core wire weighs 1.8-1.9 kg per 100 m; a 2.5 mm² plastic-insulated single-strand copper core wire weighs 2.8-3.0 kg per 100 m; and a 4.0 mm² plastic-insulated single-strand copper core wire weighs 4.1-4.2 kg per 100 m. Poor-quality wires and cables are underweight, either because they are insufficiently long or because the copper core contains excessive impurities.
2. Test the toughness
Qualified copper core wires and cables should have a lustrous, purple-red color and a soft feel. Substandard copper core wires, on the other hand, have a purple-black, yellowish, or whitish color, are high in impurities, have poor mechanical strength, and are prone to breaking with even the slightest force. They often experience broken wires. To inspect, simply strip 2 cm from one end of the wire or cable. Then, gently rub a piece of white paper against the copper core. If black material appears on the paper, it indicates a high level of impurities in the copper core. Furthermore, while the insulation of counterfeit wire and cable may appear thick, it is often made of recycled plastic, which has poor toughness and resistance to damage, and is prone to peeling and cracking. Over time, the insulation degrades, leading to leakage and potentially causing safety hazards.
3. Checking the Bonding Strength between the Core Wire and the Insulation
Cut the insulation layer diagonally and pull the core wire apart in the direction of stripping to verify adhesion between the core wire and the insulation. Good cables have strong adhesion, while poor cables have no adhesion.
4. Longitudinal Tensile Test
Take a one-meter cable and strip the core wire, insulation layer, shielding layer, and outer sheath, leaving 10 cm of each. The method is to hold two adjacent layers of the cable with one hand and pull in opposite directions. A good cable will generally be difficult to pull, while a poor cable can be easily pulled without much force. This is particularly important for elevator cables, as many so-called "elevator-specific cables" suffer from this issue.
5. Fire Test
As the saying goes, true gold fears no fire. Genuine copper wire, such as SYV and RVV, can also be tested with fire. First, peel back a section of the wire to expose a section of copper and spread it thinner (this works better). Generally, a windproof lighter will reveal the copper. Genuine copper wire is very heat-resistant and will withstand temperatures exceeding one minute; at most, it will change color slightly. Copper-clad aluminum or copper-clad aluminum-magnesium alloy will quickly bend. Copper-clad steel or copper-clad iron will reveal its shape after being burned with a knife.
Finally, it’s time to talk about price. Since the production cost of counterfeit and shoddy wires and cables is low, vendors often sell them at low prices under the guise of good quality and low prices, thus deceiving people.
