What Motor Do I Need?

The Electric Motor Buyer's Guide

There are many variables to consider when purchasing or replacing electric motors. If an existing motor is being replaced it would have been supplied with a manufacter's nameplate offering all the details about the original motor necessary for offering a replacement. Starting with the original nameplate information is the best way to obtain a new one, even if the exisiting motor is obsolete. Should a nameplate not exist or it be a new application then the following information is necessary for replacement.

Electric Motor Identification

Each motor includes a metal nameplate which identifies the following motor characteristics:

  • Model number or Catalog number
  • Serial number
  • Horsepower (HP) / Kilowatt (Kw)
  • Speed in RPM
  • Frame Size
  • Voltage
  • Frequency
  • 3 phase, 1 phase or DC
(Enclosures do not appear on the nameplate and are dictated by the environment where the motor will operate.)

Electric Motor Horsepower & Speed Rating

It is important that any that any motor application matches load requirements or duplicates the OEM specifications. Electric motor horsepower ratings are generally divided into three categories: fractional motors (1/20th HP to 1 HP), integral horsepower motors (1 HP to 400 HP), and large motors (100 HP to 50,000 HP).

Motor rotating speed (RPM) should also match load requirements or the OEM equipment. Common RPM ratings are 3600 RPM (2 pole), 1800 RPM (4 pole), and 1200 RPM (6 pole).

Electric Motor Frame

North American Standards for motors follow NEMA dimensional designs signified by frame sizes. Fractional motors are generally NEMA 48 or 56 frame. Integral horepower motors also have frame numbers, followed by the letter T. NEMA T-Frame motors range from 143T through 449T. The appropriate frame is dictated by Horsepower, speed (RPM) and enclosure.

International standards for frame size follow IEC classifications. As with NEMA motors, Horsepower, RPM and enclosure dictate frame sizes. IEC frame sizes are numerical and range from 56 through 355 and larger.

Voltage Requirements

The location where the motor is used dictates the voltage and frequency requirments. In North America it is common to to have 3-phase motors built in dual voltage ratings of 230/460 volts, 60 hertz. Often in Canada 575 volts, 60 hertz is the standard. Some motors will also offer 208 volts or custom motors are available in 200 volts.

Outside of North America voltages and frequencies vary from country to country. It is common in Europe for a motor to be built at 220/380 volts, 3-phase, 50 hertz. Any 50 hertz motor would operate at 5/6 design speed at 60 hertz (eg. an 1800 RPM motor becomes a 1500 RPM motor).

Enclosures & Mounting Positions

Electric motors can be divided into two types: open and enclosed. The majority of open motors are designated as dripproof, meaning that most contaminant particles can not fall directly into the motor from a 15 degree angle above the motor. Enclosed motors are considered totaly enclosed in order to prevent particles from entering the cavity of the body of the motor.

Enclosed motor types include totally enclosed, non-ventilated (TENV), totally enclosed, fan-cooled (TEFC). Greater degrees of totally enclosed protection appear below.

To review available mounting position for motors and the degree of protection provided by various enclosures, download the pdf's below. 

NEMA Motors Mounting Configurations
IEC Mounting Enclosures
IEC Flange Mounting Options


Severe duty and IEEE 841 Motors

Severe duty motors have special designs to prevent contaminants from entering the motor and they have protective treatments, both internal and external, to create longer life in harsh environments. Severe duty motors are commonly found in foundries, pulp & paper, chemical plants, petro-chemical, mining, waste management, and chemical plants.

IEEE 841motors meet even higher severe duty standards. These motors were designed to comply with a IEEE 841 directive that motors meet premium efficiency levels and unique construction features for extreme duty. These motors are provided with inpro seals, final test and vibration reports and are built to single voltage design.

Washdown Motors

Washdown motors have been constructed to withstand high pressure washdowns required in food processing, pharmaceuticals, and packaging applications. There are two types of exteriors on washdown motors: painted and stainless steel. Painted washdown motors use electrically-charged epoxy paint that is highly resistant to corrosion and chipping. 

Hazardous Duty Motors

Hazardous duty motors are used in areas where the potential for igniting the environment is a consideration. They are commonly referred to as Explosion Proof since their design will contain any internal failure within the body of the motor, preventing the environment from being ignited. To learn more visit the Hazardous Duty Motor page.

High Performance Vector and Inverter Duty Motors

When operating conditions require variable speed motors, inverter duty motors are built to provide constant torque over wide speed ranges. They incorporate winding and insulation materials to withstand the demands of operating on variable frequency drive power. When high performance or tight speed regulations are required, a vector duty motor may be chosen to achieve more rigorous performance levels. Vector duty motors often can include a feedback device to further achieve tight speed regulation demands.

Industries such as printing, web handling and packaging, are common examples where a vector duty motor may be called for in a closed or open loop feedback system. 

With over 50 years of UL approved AC/DC motor repair, we can also help you determine if a motor repair is a more cost-effective alternative than outright replacement. Learn more about our motor repair, rebuild, recondition, and overhaul services. We'll gladly perform a cost-analysis to determine the best option.