In our daily life, we often see various kinds of wires and cables. What is the difference between them? Today, ZMS cable editor introduces low-voltage cables.
A cable is a conductor used to transmit electric or signal current and signal voltage. It consists of an insulation layer, a protective layer, a shield layer, etc.
The voltage can be divided into high-voltage cables and low-voltage cables.
Low-voltage cable lines and low-voltage overhead lines, low-voltage overhead insulated lines compared to the higher cost, are more difficult to lay and maintain. However, it is widely used in low-voltage distribution systems because it has the characteristics of reliable operation, no pole, and does not occupy the ground.
What is a Low-Voltage Cable?
Low-voltage cable is composed of three parts: core, insulation, and protection layer.
The core is used to conduct current and is generally made of multi-stranded copper or multi-stranded aluminum wire stranded together.
Low voltage cables are single-core, double-core, three-core, four-core, and so on. Double-core cables are used for single-phase lines, while three-core and four-core cables are used for three-phase three-wire lines and three-phase four-wire lines, respectively.
Single-core cables can be used in single-phase lines or three-phase lines as needed.
Structure of low-voltage cables
1 Insulation Layer
The insulation layer is the insulation material in the cable with a specific function to withstand the voltage.
It is divided into two types: core insulation and tape insulation.
- The insulation wrapped around the line core is called core insulation.
- Multi-core cable insulation core together and then add the insulation is called with insulation.
The insulation layer is usually made of oil-impregnated paper, plastic, rubber, etc.
1.1 Plastic cable
An insulation layer is made of thermoplastic extrusion cross-linked cable.
Plastic cables can be divided into three types: PVC cables, polyethylene cables, and cross-linked polyethylene cables.
1.2 Rubber cable
An insulation layer is made of natural butyl rubber, butyl rubber, ethylene propylene rubber, and other materials.
A voltage level of 1 kV for low-voltage cable can be used for paper insulated cable and plastic cable, more plastic cable; a voltage level of 0.5 kV for low-voltage cable, and more rubber cable.
2 Protective Layer
The protective layer is a layer or layers of metal or non-metallic material covering the outside of the cable.
It is used to protect the insulation layer in the transportation, laying, and use process, from external damage and moisture intrusion.
2.1 Paper insulation cable protection layer
The protective layer of paper-insulated cable is divided into two parts: the inner sheath and the outer sheath.
The inner sheath is directly extruded on the insulation layer, in addition to protecting the insulation from moisture.
There is also the role of preventing the outflow of insulation oil, which has a certain mechanical strength. The inner sheath has the lead package, aluminum package, and polyvinyl chloride package three.
The outer sheath is to protect the inner sheath, to increase the ability of the cable to withstand mechanical external forces and corrosion prevention.
The outer sheath includes the inner liner layer, metal armor layer, and outer being layered.
2.2 Plastic cable protection layer
Usually, polyvinyl chloride sheath is used outside the plastic insulation.
2.3 Rubber cable protective layer
The protective layer of rubber cable is divided into inner and outer sheaths.
The inner sheath has a PVC sheath, neoprene sheath, and lead package.
The outer sheath is divided into three kinds of steel belt armor, rubber sheath, and plastic sheath.
The line of low-voltage cable
Low-voltage lines using cables.
There are many types of cables, and low-voltage cable lines are mainly used for low-voltage power cables.
The type of low-voltage power cable is mainly selected according to the environmental conditions of use and laying method.
Low-voltage cable lines are mainly used for high-reliability requirements for power supply. There are corrosive gases and flammable, explosive, and other places where it is not appropriate to erect low-voltage overhead lines or low-voltage overhead insulated lines.
Select the Cable Path
1 Avoid mechanical external forces, overheating, corrosion, and other hazards to the cable.
2 The cable laying path should be as short as possible.
3 Easy to construct and maintain.
4 Avoid places where construction is needed in the planning.
5 Try not to cross with other pipelines.
Low-voltage cable laying method
When laying the cable, first choose the cable laying path, and then consider the laying mode and laying requirements.
When using cable trench or cable tunnel laying, also consider fire.
Low-voltage Cable Laying Method
1 Direct Buried Laying
The number of cables laid along the same path is not more than 8, should try to use direct burial laying.
The net distance between the directly buried cables and the various facilities parallel or crossed should not be less than the value in Table 1.
Cable through buildings, railroads, roads and other sections should be protected by the pipe.
Directly buried laying, construction is convenient, cost-saving, and has good heat dissipation.
The disadvantage is that cable maintenance is not convenient, cannot reliably prevent external mechanical damage, and is susceptible to corrosion.
Direct buried laying is suitable for the occasion that the number of cables is not many, and the laying path is long.
2 Cable Trench Laying
The cable trench is divided into an indoor cable trench and low-voltage distribution device cable trench and a general outdoor cable trench.
The cover of the indoor cable trench is paved with the ground.
The cover of the cable trench in the outdoor distribution device should be higher than the ground, which is also used as an operating walkway.
General outdoor cable trench, in order not to hinder drainage, its cover should generally be 0.3 m lower than the ground, and sand or crushed soil should be laid on it.
Cable trench laying investment than cable tunnels, pipe laying, etc. to less. And the maintenance and replacement of cables are more convenient and cover an area of small, easy alignment.
When the cable trench and the underground pipe network intersection is not much, the number of cables in the same path is not more than 18, it is generally appropriate to use cable trench laying.
Selection of Low-Voltage Cables
The choice of cable mainly includes the choice of cable type and cable cross-section.
Low-voltage Cable Type Selection
This should be based on environmental conditions, laying methods, power equipment, and other factors to determine.
1 in the general environment and places should use aluminum core cable.
However, in intense vibration and special buildings and places with special requirements, copper-core cables should be used.
2 buried cable, generally using the armored cable with the outer sheath.
In places where no mechanical damage is possible, plastic-sheathed cables and lead or aluminum-clad cables with an outer sheath can also be used.
3 in the chemical corrosion or stray current corrosion of the soil, should try not to use buried laying cable.
If you have to lay buried should be used when anti-corrosion type cable.
4 laid in the tube or row of cable, generally using the plastic-sheathed cable, can also use bare armored cable.
Low-Voltage Cable Cross-Section Selection
This should be selected according to the following four conditions
1 heat generation conditions
2 Allowable voltage loss
3 mechanical strength conditions selection
4 with line protection device equipment
The above is the introduction of low-voltage cables. The selection of cables with the help of some information will help you choose more accurately and faster. ZMS cable company is committed to providing a variety of high-quality cables, for the product has a strict manual qualification audit. High professionalism in cable manufacturing and trustworthy products.
