Given that a very high percentage of the electrical loads in the world are electric motors, this chapter pays specific attention to design of electrical systems for these very important loads. While there are many unique specific-duty motors, the alternating-current (ac) squirrel-cage three-phase induction motor is the primary "workhorse" of the industry.

The rotor of an ac squirrel-cage induction motor consists of a structure of steel laminations mounted on a shaft. Embedded in the rotor is the rotor winding, which is a series of copper or aluminum bars that are all short-circuited at each end by a metallic end ring. The stator consists of steel laminations mounted in a frame containing slots that hold stator windings. These stator windings can be either copper or aluminum wire coils or bars connected to the motor t-leads that are brought out to the motor junction box. Energizing the stator coils with an ac supply voltage causes current to flow in the coils. The current produces an electromagnetic field that creates magnetic fields within the stator. The magnetic fields vary in intensity, location, and polarity as the ac voltage varies, thus creating a rotating flux within the stator. The rotor conductors "cut" the stator flux, inducing current flow (and its own magnetic field) within the rotor. The magnetic field of the stator and the magnetic field of the rotor interact, causing rotation of the rotor and motor shaft. This action causes several motor characteristics, such as rotating speed (given in revolutions per minute), motor...