Description of electric wires
Reliability, durability and safety of wiring in many respects is defined by the right choice of the conductor.
Let's begin with simpler – parch cords which in the electrician are applied everywhere.
The range of cords which is available now, wires and cables is rather various. All these products differ by several criteria:
- Transverse section of veins (from 0,75 to 800 mm).
- Cover cover (metal, rubber, plastic).
- Material of conducting veins (aluminum, алюмомедь, copper).
- Number of veins (single-core and multicore, from 1 to 37 veins).
- Isolation (rubber, paper, yarn, plastic, etc.).
Each cord, wire and cable has the operating (rated) and test voltage. These sizes for wires and cables characterize breakdown strength of their isolation.
This tension defines the stock of breakdown strength of the applied isolation. It is always higher than the worker.
This largest mains voltage at which the cord, the wire and the cable can be operated.
It is known that all wires have to correspond to the connected loading. For example, for same brands and sections of the wire are allowed loadings, different in size, which in many respects depend on conditions of laying and the possibility of cooling of conductors. Any conductors which are laid openly are cooled better than that which are laid in electroadjusting products or are hidden under the plaster coat.
Section of conducting veins is chosen usually, making a start from maximum permissible heating of veins at which isolation of wires is not damaged. The allowable load with increase in section increases not in proportion to section, and much more slowly (whereas all other conditions are equal). At the arrangement of several wires in the electroadjusting product of the condition of their cooling considerably worsen, they also heat up from each other, and for this reason the permissible current for them has to be reduced by 10-20%.
Working temperature of conductors in molded insulation should not exceed +70 °C, in rubber +65 °C. From here it is possible to draw the conclusion that at the room temperature of +25 °C admissible overheating should not exceed +40-45 °C.
All wires are made with the isolation expected tension 380, 600, 3000 alternating-current V (what is alternating current, you already know), cables are expected all tension. As a rule, at the insulated conductor the conducting vein is covered with the isolating cover.
For protection from various mechanical damages and environmental activities isolation of some brands of wires is covered outside with the cotton braid and impregnated with special solution (it becomes in some cases to prevent isolation rotting). Isolation of the wires intended for laying in places where there is the increased danger of damage mechanically is protected always by the additional braid (so-called armor).
One of the main characteristics of the vein is sectional area. All producers of conductors always and everywhere specify it, but there are such cases that there is the need to check the sectional area. It is possible to make it by means of the caliper (best of all electronic will be suitable for this purpose). Having measured core diameter, it is possible rather just to calculate its area on the well-known formula S = πr2 where S – the sectional area (circle), number π = 3,141, and r – radius. Section of the wire is always measured in square millimeters.
With the multi-wire vein it is a little more difficult, but also it is possible to determine the area of its section. For this purpose you should just reel up, for example, 15 rounds of the vein cleaned from isolation on the screw-driver, very densely to squeeze them and to measure spiral length the ordinary ruler. Core diameter will be equal to this length separated into quantity of rounds. Other way – measure the separate delay, and increase the received number by their quantity further. Vein section is measured in its diameter on the formula S = 0,785d ² where d – core diameter.
Precisely the section of wires and cables up to 1000 V is determined by means of two conditions.
- On the heating condition long design current.
- On the condition of compliance of section of the wire to the protection class.
To approach the solution of the question of the choice of the conductor for the electrical wiring, it is necessary to remember (at least approximately) the range of standard sections lived. He is rather great: from 0,03 to 1000 mm. But will be to remember sections from 0,35 enough (this minimum section for connection of electrical household appliances) to 16 mm ². Sections of veins change on standard ranks: 0,35; 0,5; 0,75; 1,0; 1,2 (these are only copper); 1,5; 2,0; 2,5; 3,0; 4,0; 5,0; 6,0; 8,0; 10,0; 16,0 mm ² (copper, alyumomedny and aluminum veins).
At rather small values of current the section of veins is defined by the mechanical durability of the conductor. Especially it concerns screw terminal clamps. From this it follows that the section of the copper vein should not be less value 1 mm ², and for the aluminum vein – 2 mm ².
There will be appropriate one council. Be always vigilant, do not buy the cable and the wire from little-known producers and suppliers whatever tempting was economy upon purchase. Remember that at the price of your avarice or economy there can be human life. Even if it turned out to buy the conductor with the underestimated section what effects of such purchase can be? The answer is rather simple. Heat generated on the conducting vein when passing of current on it is directly proportional to resistance. Means, big heating of the vein will lead to isolation melting, the short circuit and further – to ignition.
In the form of the application several useful tables:
To use the table rather easily. For example, you have the conductor with values 3×1,5 of mm ². It means that in the conductor 3 veins with the rated section of S=1,5 of mm ². Means, each vein has to have diameter of 1,38 mm (the copper wire).
Cord – two or more isolated flexible or especially flexible veins with a section up to 1,5 mm twisted or laid in parallel over which, depending on operating conditions, the nonmetallic cover and protecting covers can be imposed.
Cords are intended for connection of household appliances to the network circuit. But they can be used also in house wiring (at the same time remembering load of this site). Lived always and it is surely applied multi-wire, in addition veins are connected among themselves by twist or the general braid.
Two-core cords apply if the body of the device does not demand protective grounding. If grounding is required, it is better to use the three-core cord. Section (at the choice of the cord) always depends at most current of the attached device. That is the device is more powerful, the section of veins of the cord is more.
The number of tables which to you will help not to make the wrong choice of the cord.