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Cables

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A cable is either a stranded conductor ( single-conductor cable) or a combination of conductors insulated from one another. The term cable is a general one and in practice it is usually applied only to the larger sizes of conductors. A small cable is more often called a stranded wire or cord. Cables may be bare or insulated. The insulated cables may be covered with lead, or protective armor.

Types of Cables

Cables can be classified according to various factors given below:

1) According to insulation:

a. Cotton covered Cable. b. Silk coated Cable. c. Asbestos covered Cable. d. Rubber coated Cable. e. PVC coated Cable.

2) According to conductors material:

a. Copper. b. Aluminium.

3) According to their shapes:

a. Round shape. b. Flat shape.

4) According to cores:

a. Two core. b. Three core. c. Three and half core.

5) According to mechanical protection:

a. Unarmored. b. Armored.

6) According to voltage grade:

a. Low voltage grade. b. High voltage grade.

Uses of cables:

1. Small industries. 2. Big industries and factories. 3. Distribution lines. 4. Transmission lines (High voltage cable). 5. Low voltage cables are used in domestic wiring for appliances.

Current carrying capacity of wire or cable

It is a maximum safe value of current in amperes which can pass through a cable without generating heat above room temperature. Any excess current flowing above safe value will result in heating of cable in a very short duration which will damage the insulation and if persists for a long period will result in short circuit. Any insulation will always have a short time over current capability but it’s not recommended to use this capability under normal operating conditions.

Conductor splices and terminal connections

Conductor splices and connections are an essential part of any electric circuit. When conductors join each other, or connect to a load, splices or terminals must be used. It is important that they be properly made splice or connection both mechanically and electrically as strong as the conductor or device with which it is used.

Striping the Insulation

The first step in making a splice is preparing the wires or conductor. Insulation must be removed from the end of the conductor and the exposed metal cleaned. In removing the insulation from the wire, a sharp knife is used in much the same manner as in sharpening a pencil. That is, the knife blade is moved at a small angle with the wire to avoid “nicking” the wire. This produces a taper on the cut insulation, as. The insulation may also be removed by using a pliers like hand operated wire stripper. After the insulation is removed, the bare wire ends should then be scraped bright with the back of a knife blade or rubbed clean with fine sand paper, when you removing insulation you should be take care of do not cut insulation near at right angle this will be very bad practice. Probably it causes nicking of insulation and conductor. A nicked conductor became so weak, after be in bend a few times, it will almost certainly break.

Terminating

The entry of a cable end into a accessory is known as a termination. In the case of a stranded conductor, the strands should be twisted together with pliers before terminating. Care must be taken not to damage the wires.

Types of terminal

There is a wide variety of conductor terminations. Typical methods of securing conductors in accessories are pillar terminals, screwheads and nuts, washers. A pillar terminal has a hole through its side into which the conductor is inserted and then secured by a set screw. If the conductor is small in relation to the hole, it should be doubled back when two or more conductors are to go into the same terminal, they should first be tightly twisted together. In the case of flexible cord terminations, the strands must be twisted up (and then bent back if room permits) before being entered into the terminal. When fastening conductors under screwheads or nuts, it is best to form the conductor end into an eye by means of the roundnosed pliers. The eye should be slightly larger than the screw shank, but smaller than the outside diameter of the screwhead, nut or washers. The eye should be placed in such a way that rotation of the screwhead or nut tends to close the joint in the eye. If the eye is put the opposite way round the motion of the screw or nut will tend to untwist the eye, and will probably result in inperfect contact.

What you have learnt

In this lesson we read conductors and insulators as well as wire and cable. Now we have known the types of conductors and can classify them and also use them. Wires and cables are being used in house wiring, home appliances, and in electrical Instuements, apperatus etc in our daily life. Since we are living in Modern era or Science’s era So Eleetricity and its appliances play an important role in our life.

Terminal Question

1) Describe the uses of following materials

a) Conductor b) Cable c) Standard Wire Gauge

Answer to InText Questions

Fill in the blanks i) Good conductor ii) Bad Conductor Match the pair i) b ii) d iii) c iv) a

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