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## Learning Task 2: Describe the operation of across-the-line magnetic motor starters An across-the-line magnetic motor starter uses full-line voltage to start the motor. Most AC magnetic starters are considered as across-the-line (or full voltage) types. The three-phase AC magnetic starter consis...

## Learning Task 2: Describe the operation of across-the-line magnetic motor starters An across-the-line magnetic motor starter uses full-line voltage to start the motor. Most AC magnetic starters are considered as across-the-line (or full voltage) types. The three-phase AC magnetic starter consists of two circuits: the power circuit and the control circuit. ### Power Circuit The power circuit of a magnetic motor starter usually consists of a: * Disconnect switch * Overcurrent protection * HP-rated contacts * OLR heaters of the magnetic starter * Motor **Figure 1** is a schematic diagram of the power circuit of a three-phase, across-the-line, magnetic starter. Note that all devices are normally shown in the de-energized state. **Figure 1** - Power circuit schematic for a three-phase motor starter When the power for the control circuits is derived from the three-phase supply to the motor as shown in Figure 1: * Two of the three phase line conductors supply single-phase power to the control circuit. These are taken from the line side of the motor circuit. * When the disconnect switch is closed and the control circuit for the magnetic starter is activated, the power circuit to the motor is complete. * When the disconnect switch is open, both the motor circuit and control circuit are deenergized. This is typical of most, but not all, motor control circuits. Power circuits are the same for most three-phase motor starters, so it is usual not to refer to them in schematic drawings. This is why it is extremely important to understand their component structure and to be aware of their existence.