UNIT I ELECTRICAL AND ELECTRONIC SYSTEMS: ELECTRICALWIRING SYSTEMS 10Laws of electrical circuits: Ohms and Kichoffs LawsBasics of electricity – Single/Three phase supply. Earthing for safety – types of earthing - ISIspecificationsElectrical wiring systems in domestic and commercial buildings. Conduits, Types of wiringDiagram for connection

The Basic Principles of Electricity

Electricity

Electricity, simply put, is the flow of electric current along a conductor. This electric current takes the form of free electrons that transfer from one atom to the next. Thus, the more free electrons a material has, the better it conducts. There are three primary electrical parameters: the volt, the ampere and the ohm.

1. The Volt

The pressure that is put on free electrons that causes them to flow is known as electromotive force (EMF). The volt is the unit of pressure, i.e., the volt is the amount of electromotive force required to push a current of one ampere through a conductor with a resistance of one ohm.

2. The Ampere

The ampere defines the flow rate of electric current. For instance, when one coulomb (or 6 x 1018 electrons) flows past a given point on a conductor in one second, it is defined as a current of one ampere.

3. The Ohm

The ohm is the unit of resistance in a conductor. Three things determine the amount of resistance in a conductor: its size, its material, e.g., copper or aluminum, and its temperature. A conductor’s resistance increases as its length increases or diameter decreases. The more conductive the materials used, the lower the conductor resistance becomes. Conversely, a rise in temperature will generally increase resistance in a conductor.

 

Ohm’s Law

Ohm’s Law defines the correlation between electric current (I), voltage (V), and resistance (R) in a conductor.

Ohm’s Law can be expressed as:

Where: V = volts, I = amps, R = ohms

 

Kirchhoff’s Current Law

Kirchhoff’s current law (KCL) states that the algebraic sum of currents entering a node (or a closed boundary) is zero.

v=i. R

Mathematically,

∑n=1

N

in=0

Kirchhoff’s voltage law

Kirchhoff’s voltage law (KVL) states that the algebraic sum of all voltages around a closed

path (or loop) is zero.

Mathematically,

∑m=1

M

vn=0

Single-phase electric power Single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors. A single-phase supply connected to an alternating current electric motor does not produce a revolving magnetic field; single-phase motors need additional circuits for starting, and such motors are uncommon above 10 or 20 kW in rating.

Standard frequencies of single-phase power systems are either 50 or 60 Hz. Special single-phase traction power networks may operate at 16.67 Hz or other frequencies to power electric railways.

Three-phase electric power Three-phase transformer with four wire output for 208Y/120 volt service: one wire for neutral, others for A, B and C phases Three-phase electric power transmissionThree-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution.It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. It is also used to power large motors and other heavy loads. A three-phase system is usually more economical than an equivalent single-phase or two-phase system at the same voltage because it uses less conductor material to transmit electrical power.

Earthing:

Methods of earthing:

Plate earthing

Wiring:

Cleath batten

Metal sheath casing/ capping

conduit