Current, Electric 1
Current, Electric 1 : Electrical current is of two kinds; direct (DC) and alternating (AC). Direct current is a continuous flow in the same direction, as in batteries; alternating current creates a flow which is periodically reversed and creates a system of waves. The number of cycles is the number of waves per second. As a rule, alternating current circuits are in single or three-phases. Single-phase is carried by a two-wire circuit although a third or neutral wire is often used which does not alter the principle. In a threephase, three-wire, balanced (delta) circuit, the current flow in each conductor leads or lags the current in the other two conductors and the algebraic sum of the three is zero. Any of the two wires of a three-phase circuit is much greater than that required to operate it once it is in motion or at normal speed. The common voltages are 120/208 and 277/480. (Ref. National Electrical Codes) The flow of electric current creates magnetic force and a change in magnetic field surrounding a system of wires. This produces an electric voltage which, in turn, creates current flow. These facts are the basis of the generator and the electric motor. Voltage is produced in the windings of the motors and generators. In a motor, voltage created by the rotor is known as back electromotive force. To some extent this restricts the flow of current through the motor. The current required to start a motor is much greater than that required to operate it once it is in motion or at normal speed
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