Single phase alternating current is most often used in homes, small businesses and on farms. In large commercial buildings and industrial locations where large motors are used, single phase power is not usually adequate. Single-phase power requires fewer wires on both the electrical distribution system and the customer's system than three-phase electric service, resulting in lower installed costs.

Rotating Bar Magnet Graphic The production of single-phase alternating current is best described by thinking of the generator as a simple bar magnet rotating inside a single coil-shaped loop of wire. When the magnet rotates, the magnetic lines of force cut through the coiled wires. The strength of the field created depends the number of these lines that are cut each second. At a constant speed, more coils of wire will be cut per second as the loop approaches the one-fourth revolution point and the generated voltage reaches a maximum at this point. As the north pole moves from the one-fourth revolution point to the one-half revolution point, fewer wire coils are being cut per second. The voltage decreases and goes to zero at the one-half revolution point where the magnetic field is parallel to the coils of wire.

Rotating Bar Magnet Graphic 2 As the magnet continues to rotate, the South pole's magnetic field cuts the coiled wires in the opposite direction, producing an opposing voltage which again builds up to a maximum at the three-fourths revolution point. As the north pole moves from three-fourths turn to one full revolution, the voltage then decreases to zero.

One complete revolution of the magnetic field is called a cycle. If there was only one coil of wire in the outer portion of the generator this would be a single phase device. By adding two additional coils of wire to the generator, we could then generate current in three individual coils or phases, or three-phase power.

The word phase is often abbreviated using the Greek letter"phi" and is written as a zero with a slash mark through it.