AutomationDirect AC Motor Selection Guide

Understanding Motor Efficiency Standards

EPAct (1992)

The Energy Policy Act of 1992 established minimum efficiency requirements for general-purpose Design A & B motors in the U.S. Since 1997, two-, four-, and six-pole motors have been required to meet these guidelines.

Premium Efficiency (EISA 2007)

The Energy Independence and Security Act of 2007 (EISA 2007), effective December 2010, mandated a higher level of energy efficiency for AC industrial motors, commonly referred to as NEMA Premium®. Motors manufactured or imported into the U.S. after December 2010 must meet these stricter guidelines.

Motors Covered Under EISA 2007 (Premium Efficiency Mandate)

This mandate applies to industrial AC electric squirrel-cage general-purpose motors that are single speed, polyphase, 1–200 hp with 3-digit frame sizes, 2, 4, & 6 poles (3600, 1800, & 1200 rpm), NEMA design A & B, and continuous rated.

Motors not included in Premium Efficiency standards but still required to meet EPAct standards include JM, JP, round body (footless), 201-500 hp, fire pump, U-frame, Design C, and 8-pole motors. Certain motors like Inverter/Vector Duty and NEMA design D are not covered by EISA 2007.

For the full text of the act, visit www.energy.senate.gov and search for the "ENERGY INDEPENDENCE & SECURITY ACT OF 2007".

Nominal Full-Load Efficiency Standards Comparisons (%)

General-Purpose vs. Inverter-Duty Motors & VFD Compatibility

Choosing the Right Motor

General-purpose motors are the standard workhorses across industries. Many AutomationDirect (ADC) general-purpose 3-phase motors are inverter-rated, meaning they can handle the higher voltage spikes produced by Variable Frequency Drives (VFDs).

For applications requiring precise speed control or sustained high loads at lower speeds, high-performance inverter-duty motors are recommended. These motors are designed to run at very slow speeds without overheating, though they are typically more expensive.

AC Drive (VFD) Motor Control

VFDs allow for variable speed control of AC motors by converting incoming AC power to DC, then "chopping" this DC voltage to simulate a sine wave at a desired frequency and voltage.

Traditional Across-the-Line Control: Applies full voltage at startup, leading to high inrush current (5-6 times normal), fixed speed operation, potential inefficiency for flow control, and increased maintenance due to arcing.

VFD Control Advantages: Lower inrush current, adjustable motor speed, and improved efficiency, especially for fan and pump applications where flow can be controlled by motor speed, eliminating the need for valves or dampers. VFDs offer solid-state power delivery with minimal maintenance.

Note: VFD control is applicable only for 3-phase AC motors.

Key Considerations for VFD Applications

1. Heat Considerations

General-purpose motors rely on shaft-mounted fans for cooling. At lower speeds, fan cooling is reduced, potentially leading to motor overheating and reduced insulation life. Minimum continuous speed requirements are crucial.

• Constant Torque (CT) Applications: (e.g., conveyors, machine tools) require motors to maintain torque regardless of speed.
  • EPAct Motors: Minimum continuous speed is 2:1 (1/2 rated speed).
  • Premium Efficiency (PE) Motors: Minimum continuous speed is 4:1 (1/4 rated speed).
• Variable Torque (VT) Applications: (e.g., fans, centrifugal pumps) require less torque at lower speeds.
  • EPAct Motors: Minimum continuous speed is 5:1 (1/5 rated speed).
  • Premium Efficiency (PE) Motors: Minimum continuous speed is 10:1 (1/10 rated speed).

For applications needing to run at speeds below these limits, Marathon high-performance inverter-duty motors are recommended.

2. Voltage Spike Considerations

VFDs generate high-voltage spikes. Long cable lengths between the drive and motor, and high carrier frequencies, can cause reflected waves that effectively double the voltage, potentially damaging motor insulation. Line reactors can mitigate these spikes.

For applications requiring longer cable runs, Marathon high-performance inverter-duty motors are advised.

3. Carrier Frequency Limitation

The AC Drive carrier frequency should be set to 6kHz or less for optimal performance and motor longevity.

Diagram Descriptions:

• Figure 1: Illustrates how a VFD converts incoming AC power to DC and then "chopping" it to create a simulated sine wave for motor control, varying voltage and frequency to adjust speed.
• Figure 2: Shows a typical setup with an AC drive, a line reactor connected between the drive and the motor, representing a method to reduce voltage spikes.

Motor Series Overview

IronHorse General Purpose AC Motors

IronHorse motors offer a range of general-purpose AC induction motors designed for various industrial applications. Key specifications vary by frame type and enclosure:

For detailed specifications on other IronHorse models, consult the full product documentation.

Regal AC Motors (Marathon & Leeson)

AutomationDirect also offers motors from Regal, including Marathon and Leeson brands, which provide a variety of specialized and general-purpose AC motors:

• Marathon Motors: Feature general-purpose, NEMA Premium XRI®, 4-in-1 XRI®, and high-performance inverter-duty series (Micro MAX™, MAX+, Black Max®, Blue Max®, Symax PMAC). These cater to a wide range of applications, including demanding VFD use and specific performance requirements.
• Leeson Motors: Offer general-purpose, washdown-specific (Washguard®), and other industrial motor types. The Washguard® series is designed for environments requiring resistance to moisture and chemicals.

Detailed selection tables for these series are available in the original document.

Leeson Washguard Motors Chemical Resistance Comparison

The following table compares the chemical resistance of Leeson Washguard® motors with Stainless Steel and White Epoxy finishes.