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# Describe the features of three-phase, AC magnetic motor starters The fundamental purpose of any motor starter is to safely start and stop the motor, and to provide running (overload) protection for the motor. They may be simple manual devices, or more complex automatic ones. A motor starter is a c...

# Describe the features of three-phase, AC magnetic motor starters The fundamental purpose of any motor starter is to safely start and stop the motor, and to provide running (overload) protection for the motor. They may be simple manual devices, or more complex automatic ones. A motor starter is a controller - a term that implies more operating functions than simply starting and stopping the motor. A controller may also allow for: * Reversing operation * Reduced voltage starting * Speed control * Sequencing control * Remote control operation * Operator safety ## The across-the-line magnetic starter One of the most common controllers for three-phase motors is the across-the-line magnetic starter. Magnetic in this context means that an electromagnet is used to operate a set of contacts for making and breaking the electric circuit to the motor. Across-the-line means that the motor is started with full line voltage. ## Basic construction A basic magnetic starter has two fundamental parts: a contactor and an overload relay. The contactor starts and stops the motor and the overload relay provides running protection for the motor. ## Contactor Figure 1 shows the construction of two types of contactor - the clapper type and the vertical lift type. The stationary contact terminals are connected in series with the line to the motor. By energizing and de-energizing the electromagnetic coil, the start-stop action of the motor is controlled in the following way: * When it is energized, the coil attracts a movable iron piece called the armature. * The movement of the armature closes a set of normally open contacts (by pushing a set of movable contacts against stationary ones). * When the coil is de-energized, the armature is released, opening the contacts again.