An electrical contractor - from Wikipedia
An electrical contractor is a business person or firm that performs specialized construction work related to the design, installation, and maintenance of electrical systems?a $130 billion industry in the United States.1
An electrical contractor is different from an electrician; an electrician is an individual tradesman and an electrical contractor is a business person or company that employs electricians. Both usually hold licenses and insurances to properly and safely operate a business, protecting the employees and home owners/business owners from insurance liabilities. These requirements vary from state to state. Electricians may work for an electrical contractor, or directly for individuals or companies.
How alone lay the electrical system?
Although many people isolated attempts to control the domestic installations, usually professional help is highly desirable especially in more complex cases. As far as changing a light bulb or perform other similar tasks require more visits electrician so much already in the case of laying wires or installation of distribution are more complicated. Isolated executed electrical installations can make later, at the stage of operational problems arise, for example, through the inclusion of too many devices to the power supply circuit may occur. So let's take care of it, to the more complex work carried out specialist, because working with electricity can be dangerous for inexperienced employee.
Definition of AC Power
Power in an electric circuit is the rate of flow of energy past a given point of the circuit. In alternating current circuits, energy storage elements such as inductors and capacitors may result in periodic reversals of the direction of energy flow. The portion of power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as active power (sometimes also called real power). The portion of power due to stored energy, which returns to the source in each cycle, is known as reactive power.