Get Control of Your AC Motors

Control. Without it, anarchy? That perhaps is a bit melodramatic, but in the realm of electric motors, control means an increase of efficiency, saving expenses, and saving your motor.

There are several ways of controlling an AC Motor. This post from the Electrical Energy blog breaks down several of them.

Power distribution systems used in large commercial and industrial applications can be complex. Power may be distributed through switchgear, switchboards, transformers, and panel boards  Power distributed throughout a commercial or industrial application is used for a variety of applications such as heating, cooling, lighting, and motor-driven machinery. Unlike other types of power distribution equipment, which are used with a variety of load types, motor control centers primarily control the distribution of power to electric motors.

Wherever motors are used, they must be controlled. In Basics of Control Components you learned how various control products are used to control the operation of motors. The most basic type of AC motor control, for example, involves turning the motor on and off. This is often accomplished using a motor starter made up of a contactor and an overload relay. The contactor’s contacts are closed to start the motor and opened to stop the motor. This is accomplished electromechanically using start and stop push buttons or other pilot devices wired to control the contactor. The overload relay protects the motor by disconnecting power to the motor when an overload condition exists. Although the overload relay provides protection from overloads, it does not provide short-circuit protection for the wiring supplying power to the motor. For this reason, a circuit breaker or fuses are also used.

Typically one motor starter controls one motor. When only a few geographically dispersed AC motors are used, the circuit protection and control components may be in a panel near the motor.

Motor Control Center (MCC)

In many commercial and industrial applications, quite a few electric motors are required, and it is often desirable to control some or all of the motors from a central location. The apparatus designed for this function is the motor control center (MCC). Motor control centers are simply physical groupings of combination starters in one assembly. A combination starter is a single enclosure containing the motor starter, fuses or circuit breaker, and a device for disconnecting power. Other devices associated with the motor, such as push buttons and indicator lights, may also be included.


Tiastar (pronounced tie-star) is the trade name for Siemens Motor Control Centers Some of the advantages of using Tiastar motor control centers are:

  • Ruggedness and reliability
  • Reduced time needed for installation and start-up
  • Space saving design
  • Excellent component selection
  • Simplicity in adding special components
  • Ease of future modifications.


The TIA portion of the tiastar name stands for Totally Integrated Automation. TIA is more than a concept. It is a strategy developed by Siemens that emphasizes the seamless integration of automation, networking, drive, and control products. The TIA strategy has been the cornerstone of development for a wide variety of Siemens products. TIA is important not just because it simplifies the engineering, start-up  and maintenance of systems developed using Siemens products, but also because it lowers the life-cycle costs for systems incorporating these products. Additionally, by reducing engineering and start-up of systems, TIA helps customers reduce time to market and improve overall financial performance.


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