The difference between wires and cables
A wire is composed of one or several flexible wires, wrapped in a light and soft protective layer; A cable is composed of one or several insulated wires wrapped in a tough outer layer of metal or rubber.
Cables and wires are generally composed of three components: core wire, insulation sheath, and protective sheath.
The characteristics of commonly used cables are as follows:
CEF – Ethylene propylene rubber insulation chloroprene rubber sheath, marine flame-retardant power cable. CVV – PVC insulated and PVC sheathed flame-retardant power cables for ships. The BV, bx, rv, and rvv series wires are often used for oxygen cabin wires, among which:
BV – Copper core PVC insulated wire, with a long-term allowable temperature of 65 ℃, a minimum temperature of -15 ℃, and a working voltage of 500V AC and 1000V DC. It can be fixed indoors or outdoors and can be laid in an open or concealed manner.
Bx – Copper core rubber insulated wire, with a maximum operating temperature of 65 ℃, applied indoors.
Rv – PVC insulated single core flexible wire, with a maximum operating temperature of 65 ℃ and a minimum operating temperature of -15 ℃. The working voltage is 250V AC and 500V DC, used for internal wiring of instruments and equipment.
RVV – Copper core PVC insulated and sheathed flexible wire, allowing long-term working temperature of 105 ℃, working voltage of 500V AC and 1000V DC, used in damp, high mechanical protection requirements, frequent movement and bending situations.
In fact, there is no strict boundary between “wires” and “cables”. Products with fewer cores, smaller product diameters, and simpler structures are usually referred to as wires, those without insulation are referred to as bare wires, and others are referred to as cables; The conductor with a large cross-sectional area (more than 6 square millimetre) is called a large wire, the smaller one (less than or equal to 6 square millimetre) is called a small wire, and the insulated wire is also called a wiring wire. This is simple and easy to understand!
Cables generally have more than 2 layers of insulation, most of which are multi-core structures and are wound on cable reels, with a length generally greater than 100 meters. Electric wires are generally single-layer insulated, single core, rolled up to 100 meters in a coil, and wireless. Common cable models:
Vv represents: polyvinyl chloride insulation (first v), polyvinyl chloride sheath (second v)
Yjv22 refers to flame-retardant cables (wires) with cross-linked polyvinyl chloride insulation (YJ), polyvinyl chloride sheath (V), and steel strip Kaizhuang (22) models added with “zr” or “fr”. The model of aluminum wire with “l” is relatively simple:
BVV – PVC insulated and sheathed copper core wire, BVV – PVC insulated copper core wire, BVR – PVC insulated copper core flexible wire, bx – rubber insulated copper core wire, rhf – chloroprene rubber sheathed copper core flexible wire.
2、 Conditions for selecting the cross-section of wires and cables
In order to ensure the safe, reliable, high-quality, and economical operation of power supply and distribution lines, the selection of wire and cable sections must meet the following conditions:
The heating temperature generated by wires and cables when passing through the normal maximum load current (i.e. the calculated current of the line) should not exceed the maximum allowable temperature during normal operation.
Voltage loss conditions: The voltage loss generated by wires and cables when passing through the normal maximum load current should not exceed the allowable voltage loss during normal operation.
For lines with an economic current density of 35KV and above, and lines with a high current below 35KV, the conductor and cable cross-section should be selected according to the economic current density to minimize the annual cost expenditure of the line. Users usually do not select lines of 10KV and below based on economic current density.
