Types of Motor Enclosures for your Centrifugal Air Compressor

Careful selection of the proper motor enclosure will help ensure longer and more reliable motor life and increased customer satisfaction. A basic understanding of various motor enclosures will enable you to select a motor that will perform best for your customer, meet various sound level specifications, and identify the most cost effective design. Here’s some information to help with this process.

There are essentially five different motor enclosures that are supplied with Centacs. These are shown as follows with the equivalent IEC codes for enclosures only.

Please note that IEC motors are much different than NEMA motors.
    1) Open Drip Proof (ODP) or (IP23)
    2) Weather Protected Type II (WPII) or (IPW24)
    3) Totally Enclosed Water to Air Cooled (TEWAC) or (IP54)
    4) Totally Enclosed Air to Air Cooled ( TEAAC), or (IPW54)
    5) Totally Enclosed Fan Cooled (TEFC) or (IPW54)

OPEN DRIP PROOF
This is the standard motor enclosure provided with fully packaged Centacs, and is suitable for most indoor industrial applications. Cooling air will enter through louvered openings, pass over the rotor and stator, and exit through the openings in the sides of the frame. This open enclosure design should not be selected for outdoor installations, washdown areas, and dirty environments where cotton fibers and high dust levels cannot be kept away from the motor. Centac’s motor specification requires that this motor meet an 85 DBA sound level requirement.

WEATHER PROTECTED TYPE II
This enclosure is designed for use outdoors in adverse conditions. The air intake is in the top half of the motor to minimize entrance of ground level dirt, rain or snow. For certain models, this enclosure can be modified to include filters for extremely dirty conditions - however this will often result in frequent filter replacement. The air passage includes three abrupt 90 degree changes in direction plus an area of reduced velocity to allow solid particles or moisture to drop out before the ventilating air contacts active parts of the motor. All particulates but super fine dust (cement and coal) and foreign material (cotton fibers, etc.) are virtually eliminated. In addition, WPII motors include anti-corrosion treatment on both internal and external components, a weather proof conduit box, waterproof insulation, and space heaters to keep the motor dry during periods of non use. WPII motors are typically 2-3 DBA quieter than ODP motors, but when faced with sound restrictions, you should always ask to be sure.

TOTALLY ENCLOSED WATER-TO-AIR COOLED
This enclosure isolates all critical motor components from the surroundings. It can be used indoor or outdoors in clean and dirty environments. TEWAC enclosures include a water cooled heat exchanger mounted in the top portion of the motor for cooling the recirculated ventilating air. Motor heat is conducted away by circulating water and not by discharged air. Key advantages of TEWAC motors over other totally enclosed motors include better efficiencies, shorter frames, lower cost ,and much lower sound levels. TEWAC motors are the quietest of all available enclosures, and are the best choice when quoting a Centac Process Package because a stub shaft for the shaft driven main oil pump can easily be added. TEWAC motors should also be considered in high altitude applications where air cooling is less efficient. TEWAC frames can be sized much smaller than air cooled frames.

TOTALLY ENCLOSED AIR-TO-AIR COOLED
This enclosure will also isolate critical motor components from the surroundings. In contrast to the TEWAC, the TEAAC enclosure discharges heat in the immediate area of the motor. The construction of this enclosure utilizes a top mounted air-to-air heat exchanger. External air is drawn in by a shaft mounted fan enclosed in a housing opposite the drive. The air is forced through the cooling tubes at high velocity to promote efficient cooling and cleaning of the tubes. A TEAAC motor will be noisier than an ODP, WPII, or TEWAC motor. Typical sound levels are around 90DBA, so if there are sound restrictions, please ask for a lower sound design.

TOTALLY ENCLOSED FAN COOLED
This enclosure is often supplied on smaller motors for Centacs where isolation of critical motor components from the surroundings is required. Most of these designs use a round cast-iron ribbed construction design, where the cooling air is pulled through the grill of the external shaft mounted fan and is directed by the frame fins by the fan hood. As mentioned earlier, TEFC motors are often less expensive than WPII at smaller sizes. However, be careful when specifying TEFC motors when there are sound restrictions, as due to the cooling fan, sound levels are often at 90DBA unless you specify lower levels are needed.

In summary, suggestions for you to consider include:

    1. Never specify ODP motors for an outdoor application.
    2. If cotton fibers or other fine dust cannot be kept away from the motor, an enclosed motor should be considered.
    3. Sound levels are additive. If a motor is rated at 85DBA, the overall compressor package will be at least 3DBA higher.
    4. TEWAC motor enclosures offer big advantages over TEAAC and TEFC.