Understanding the Design Inputs Required to Select a Motor Control Solution

Stay Informed

Professionals in the electrical industry often wonder about the top questions to ask when dealing with motor control. Although there are probably eight or ten questions that need to be answered sometime during the life of the order, it's more economical (both dollars and lead-time) to answer them from the beginning.

To quickly understand the design inputs required for selecting a motor control solution, let’s take a closer look at three steps: motor nameplate data, starter design, and enclosure.

1. Motor Nameplate Data

Motor nameplate data can check multiple boxes, as you will have the motor voltage, full load amps, frequency, horsepower/kilowatt, speed, and service factor. Because not all motors are created equal, the voltage and the current are the most important. A motor’s performance may be affected if used at a different voltage than indicated on the nameplate.

2. Starter Design

The electrical industry has many acronyms, but starter design can be broken down into three categories:

Across the line or full voltage starter

In its purest form, this solution consists of a contactor and a type of thermal overload protection. The operation is either ON or OFF by energizing the contactor coil. When the contactor is closed, this will apply full line voltage to the motor terminals and run the motor at its rated speed. This can be further divided into The National Electrical Manufacturers Association (NEMA) or The International Electrotechnical Commission (IEC) contactors, and the overload can be either bi-metallic or electronic.

Reduced voltage or soft-starter (RVSS)

Current technology can achieve this using a solid-state starter, enabling the user to program an acceleration and deceleration ramp time. When a start command is applied, this approach will lead to a gradual ramp-up to full speed, and a progressive ramp down when a stop command is used. Today's RVSS is commonly equipped with an internal contactor which closes when the motor is up to speed. The associated energy savings are a result of not having the same inrush currents as the across the line approach.

Variable frequency drive (VFD)

This solution offers the most significant energy savings as the motor can be operated at any given speed. The essential items to remember is that the VFD requires a form of speed reference in addition to run command. Speed reference can be manually entered via the keypad, but more dynamic options are achieved by an analog signal (0-10V, 4-20mA) or communicated over a Fieldbus.

3. Enclosure

This category can have multiple inputs – the most obvious will be the installation environment. Several standard organizations describe the environmental performance ratings for enclosures, but it comes down to the degree of protection against solids and liquids. It's critical to understand where the enclosure will be installed because the construction and cost will differ for a solution installed in a dirty or dusty underground application (ex. mine) versus a washdown area (ex. food and beverage).

A distributed solution should also be considered, which would consist of starters installed individually in standalone enclosures, generally located closer to the motor. Another option would be to choose a consolidated solution which groups all the starters in an assembly with compartments such as a motor control center. It is also important that the pilot devices used for cover control, such as pushbuttons, selector switches, and pilot lights, are incorporated onto the door.

Selecting the Right Motor Control Solution

Now you understand the basic information required to engage in a constructive conversation about motor control. This dialog will help a customer envision what is being quoted, but more importantly, it will give the customer a sense of confidence that they chose the correct partner and solution to rely on.

With locations coast to coast, Eaton is available to help with standard and custom applications. Eaton’s packaged industrial control and power management technologies are reliable, efficient, and safe. Are you ready to get started?

Eaton's Industry-Leading Motor Control Solutions are Safe and Cost-Effective

The opinions expressed in this piece are solely Eaton's. They do not necessarily represent WESCO’s views.