Electrical Distribution Systems
MOTOR CONTROLLERS
Figure 10 Typical Three-Phase Magnetic Controller
A magnetic contactor (Figure 11) is a device operated by an electromagnet.
The magnetic contactor consists of an electromagnet and a movable iron armature on which
movable and stationary contacts are mounted. When there is no current flow through the
electromagnetic coil, the armature is held away by a spring. When the coil is energized, the
electromagnet attracts the armature and closes the electrical contacts.
Overload devices are incorporated into magnetic controllers. These overload devices protect the
motor from overcurrent conditions that would be extremely harmful. There are many types and
forms of overload devices. The following types of overload devices are commonly used in
motor-control equipment.
Fuses
Thermal overloads
Magnetic overloads
The thermal overload device is shown in Figure 10.
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