Cables and Wires: Usage and Protective Measures
Cables are typically made by twisting several strands or groups of conductors (with each group consisting of at least two wires) into a rope-like structure. Each group of conductors is insulated from one another and is usually twisted around a central core. The entire assembly is then covered with a highly insulating sheath. Cables are often installed overhead, underground, or underwater and are used for telecommunication or power transmission. Based on their applications, cables can be categorized into power cables, communication cables, control cables, and so on.
There are numerous types of electrical cables and wires available in the market, with varying quality levels. The quality of these cables directly affects the construction quality and the safety of consumers' lives and property.
So, are there safety requirements for the use of cables? What are the protective measures? And how should they be stored?
I. Safety Requirements
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When cables cross each other, high-voltage cables should be positioned below low-voltage cables. If one of the cables is protected by a conduit or separated by a partition within a range of 1 meter before and after the crossing point, the minimum allowable distance is 0.25 meters.
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When cables are near or cross thermal pipelines, with proper thermal insulation measures in place, the minimum distances for parallel and crossing should be 0.5 meters and 0.25 meters, respectively.
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When cables cross railways or roads, they should be protected by conduits, which should extend at least 2 meters beyond the tracks or road surface.
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The distance between cables and building foundations should ensure that the cables are buried outside the building's drainage area. When cables enter a building, they should be protected by conduits, which should also extend beyond the building's drainage area.
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Directly buried cables should be spaced 0.25 to 0.5 meters away from general grounding devices. The burial depth of directly buried cables should generally be no less than 0.7 meters and should be below the frost line.
II. Protective Measures
With the rapid development of underground cable installation projects, higher demands have been placed on cable protection. Cable protection tubes are made from polyethylene (PE) and high-quality steel pipes through processes such as sandblasting, pre-treatment, plastic coating or painting, and heat curing.
These are the most commonly used electrical insulation tubes for protecting wires and cables. They are widely used because of their excellent insulation properties, high chemical stability, rust resistance, non-aging characteristics, and ability to withstand harsh environments.
Using cable protection tubes can provide the following advantages:
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Good corrosion resistance and long service life, suitable for use in damp and saline-alkali areas.
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Flame retardancy and excellent heat resistance, capable of long-term use at high temperatures up to 130 degrees Celsius without deformation and non-combustible in fire.
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High strength and rigidity. When buried directly under traffic lanes, no additional concrete protective layer is required, which can accelerate the progress of cable engineering projects.
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Both the cable protection tubes and fittings have a certain degree of flexibility, which can resist destruction caused by external pressure and foundation settlement.
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Good resistance to external signal interference.
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Smooth inner walls that do not scratch the cables. The design uses a plug-in connection method for easy installation and connection. Rubber seals are added at the joints to adapt to thermal expansion and contraction and to prevent the ingress of mud and sand.
III. Storage Methods
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Under eaves. Cables can be used as long as they are not directly exposed to sunlight or extremely high temperatures. Standard LAN cables are recommended, and the use of conduits is suggested.
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On exterior walls. Avoid direct sunlight exposure and human-induced damage.
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Inside conduits (plastic or metal). If in conduits, pay attention to the damage of plastic conduits and the heat conduction of metal conduits.
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Suspended applications/overhead cables. Consider the sag and tension of the cables, the method of bundling, and whether the cables are directly exposed to sunlight.
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Directly laid in underground cable trenches. This environment is the least controllable. Regular checks for dryness or moisture levels in the cable trench installation are necessary.
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Underground conduits. To facilitate future upgrades, cable replacement, and isolation from surface pressure and the surrounding environment, laying cables in separate conduits is a good method. However, do not expect the conduits to remain dry forever, which will affect the selection of cable types.
IV. Additional Notes
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For long-term storage of cables, contact with acids, alkalis, and mineral oils must be avoided.
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Harmful gases that can damage cables (such as those containing tin-plated copper wire or bare copper wire) should not be present in the storage warehouse.
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Cables should be stored systematically, according to specifications and manufacturing dates, to ensure proper and safe storage. Cables should be used within one and a half years from the manufacturing date; if this is not possible, they should not be stored for more than two years.
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Due to the varying degrees of compression over time and the different hardness levels of the protective sheaths, cables may be affected during storage. Therefore, they should be rolled periodically (every three months in summer, and the frequency can be adjusted in other seasons). During rolling, to avoid moisture, the cable reels should be rolled with the bottom edge facing up. After rolling, the integrity of the cables must be checked.
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The transportation of cables is also a key aspect of cable storage protection. During transportation, it is strictly forbidden to throw cable reels from a height, as this can cause the insulation and sheath to crack.
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Cables should never be stored flat, as this can cause certain degrees of wear on the insulation layer or protective sheath. The damage to bare stranded wires would be even more severe. Moreover, if cables are stored flat and become disordered, it will inevitably affect the quality of the wires.
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