Knowledge of basic electricity !!

Electricity is the flow of electrons from the one place to another. Electrons can flow through any materials, but does so more easily in some than in others. How easily it flows is called resistance. The resistance of a material is measured in Ohms.

Matter can be broken down into:

Conductors: electrons flow easily. (Low resistance)Semi-conductors: electron can be made to flow under certain circumstances. (Variable resistance according to formulation and circuit condition.)Insulator: electrons flow with great difficulty. (High resistance) 

Since electrons are very small, as a practical matter they are usually measured in very large numbers. A Coulomb is 6.24 x 10¹⁸ electrons. However, electricians are mostly interested in electrons in motion. The flow of electrons is called current, and is measured in Amps. One amp is equal to a flow of one coulomb per second through a wire.

Making electrons flow through a resistance requires an attractive force to pull them. This force, called Electro-Motive Force or EMF, is measured in volts. A volt is the force required to push 1 Amp through 1 Ohm of resistance.

As electrons flow through a resistance, it performs a certain amount of work. It may be in the form of heat or magnetic field or motion, but it does something. This work is called Power and is measured in Watts. One Watt is equal to the work performed by 1 Amp pushed by 1 Volt through a resistance.

Remember this:

Amps is amount of electricity.
Volts is the push, not the amount.
Ohms slows the flow.
Watts is how much gets done.

There are two standard formula that describe these relationship:

Ohm's Law:

R = Resistance (Ohms)
E = Electro-motive Force (Volts)
I = Intensity of Current (Amps)

R = E/I

To express work done: Power formula (PIE Law):

P = Power (Watts)
I = Intensity of Current (Amps)
E = Electro-motive Force (Volts)

P = IE

This law is often restated in the units of measure as the West Virginia Law.

W = VA

Watts = Volts x Amps

All this is important because all electrical equipment has a limit to how much electricity it can handle safely, and you must keep track of load and capacities to prevent failure, damage or a fire. For example, a lamp is rated at 1000 W 120 V. That means that at 120 volts it will use.

1000 W / 120 V = 8.33 A

A common shortcut is to use 100 V instead of 120. This makes calculating easier and builds in some head-space. So:

1000 W / 100 V = Approx. 10 A

A Simple Circuit:

The simplest circuit has a power source, like a battery or outlet, a wire running from the hot side to a load then a wire from the load back to the power source. There is also usually a switch to open or close the circuit. The load will function only when the circuit is closed or complete.

In more complex circuits where more than one load is connected, they may be either in series or in parallel. In a series, current must pass through one to get to the next. Voltage is divided between them. If one goes out, they all go out.

Look at the series circuit diagram:

In a parallel circuit, each load is electrically connected to the source at the same point, each gets the full voltage simultaneously. If one goes out, the rest stay lit.

Parallel circuit Diagram:

Most circuits are combinations of the two types. Circuit breakers and fuses are in series with the load, but multiple loads on a circuit are paralleled. Circuit breakers and fuses can be placed in the supply circuit before the plug, as in lighting circuits or between the plug and the load internally, as in most sound equipment or both.

Cable, Connectors and Circuits are all rated in amps according to the size.