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Tuesday, September 21, 2010



            To study the basic electrical accessories, materials and tools used in wiring.

Electrical Wiring:

Electrical wiring in general refers to insulated conductors used to carry electricity. Materials for wiring interior electrical systems in buildings vary depending on:
  • Intended use and amount of power needed of the circuit
  • Type of occupancy and size of the building
  • National and local regulations
  • Environment in which the wiring must operate.
Wiring systems in a single family home or duplex, for example, are simple, with relatively low power requirements, infrequent changes to the building structure and layout, usually with dry, moderate temperature, and non corrosive environmental conditions. In a light commercial environment, more frequent wiring changes can be expected, large apparatus may be installed, and special conditions of heat or moisture may apply.

Types of wiring systems:
1.      Cleat wiring
2.      Casing capping wiring
3.      Metal sheathed wiring
4.      Conduit wiring

Rules for Electric Wiring:
As per I.S.I. rules the following point to be noted:
1. A.C. and D.C. circuit should be separated. 3 phases should be indicated with Red, Yellow and Blue colour and the neutral should be indicated with Black colour. In D.C. we should be indicate +ve with Red, -ve with Blue and neutral with black.     
2. If the voltage exceeds 250 volt, the Distribution Board and main switches should be provided with danger board symbol.
3. Number of points should not be more than ten and total load in a circuit should not exceed more than 800 watt.
4. Correct size of the conductor should be used, such that the voltage drop should not increase more than 3% of the connected voltage when full load current is following.
5. All distribution boards should be marked as PDB (power distribution board) or LDB (light distribution board).
6. All the accessories should be fixed on the round blocks or board with screws.
7. In the domestic wiring 3-pin plug should be used.
8. All the iron clad appliances, switches, etc., should be earthed
9. All the switches should be connected through live wire.
10. All switchboards should be fixed at a height of 1.l5 meters.
11. All the boards and switches should be fixed on left hand side of the entrance.

The Three Conductors:

In most countries, household power is single-phase electric power, in which a single live conductor brings alternating current into a house, and a neutral returns it to the power supply. Many plugs and sockets include a third contact used for a protective earth ground, which only carries current in case of a fault in the connected equipment.

·         Live or Phase

The live conductor (also known as phase, hot or active) carries alternating current from the power source to the equipment.

·         Neutral

The neutral conductor returns current from the equipment back to the power source or distribution panel. It is in most (but not all) cases referenced to the earth. Except under fault conditions it does not pose a danger because the voltage between the neutral contact and the earth is close to zero, but is nevertheless treated as live in most installation practices because it can develop a high voltage under fault conditions.
The main danger posed by the neutral is the voltage can rise as high as the voltage on the live conductor if a broken neutral cable in the wiring disconnects the neutral but leaves the live conductor connected.

·         Earth/Ground

The earth contact (known as ground in American English) is only intended to carry electric current when connected to equipment that has developed an insulation fault. The earth connection was added to modern plugs because, if a live wire or other component in a device touches the metal casing, anybody touching the device may receive a dangerous electric shock. In many countries devices with metal cases must have the case connected to the earth contact. This reduces but does not eliminate the possibility of the case developing a high voltage relative to the earth and grounded metalwork.
It is a common misconception that the purpose of the earth connection is to take fault currents safely to earth. The primary purpose of the earthing system is to cause a fuse to blow or a breaker to trip to automatically disconnect the power supply to any device or cable which develops a wiring fault. The secondary purpose is to hold all touchable metal in a house to the same voltage to prevent electrical shocks when touching two metal objects at the same time. In addition, some equipment such as surge protectors required an earth connection to function properly because they operate by shorting the excess current to the earth.
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