Enclosures for Motors Below 500 Horsepower

Choosing a motor enclosure can be complicated. National Electrical Manufacturers Association (NEMA) and, in some cases, internal protection (IP) ratings for motor and cabinet enclosures need to be considered. But there are two primary factors to consider when selecting a motor enclosure: the environment in which the motor will be operating and the level of protection the enclosure is required to provide personnel working around the motor. In areas where people interact with motors, fully protected enclosures are normally chosen for worker safety. The primary concern in choosing an enclosure, therefore, typically involves the harshness of conditions in the operating environment. Enclosure choice should be based on the environment and conditions in which it will be installed. Environments can vary dramatically. Some environments are so dangerous that they require hazardous or explosion-proof enclosures. The focus is typically on commercial and industrial environments, such as: Commercial buildings may include a variety of environments where motors are present. Fire pump motors, for example, are often housed in cleaner environments. Booster pumps and other heating/cooling system pump motors are in service spaces where the air is usually not conditioned. Pump motors for cooling towers are typically found outdoors. Wastewater treatment is performed in severe environments. Most motors located in close proximity to toxic wastewater and treatment activities, including the motors used to operate aerators, require extremely severe duty motors and enclosures. Mining industry pump applications can place a motor in contact with everything from relatively clean water to extremely caustic or acidic liquids. For the sake of consistency and safety, many end users choose standard severe duty enclosures for all installations. Agriculture irrigation pumps are located outdoors and require enclosures that protect them from the elements. When used in coastal or high humidity environments, these motors also typically require enclosures that provide abrasion resistance and capability to withstand higher ambients. Food industry motors are often subjected to washdown, chemicals, humidity and other severe environmental conditions, and require enclosures that accommodate them.

When selecting an enclosure for your application, there are many types to choose from. Some are better suited for some applications than others, including:

1. Drip-Proof/Open Drip-Proof (DP/ODP)—Designed for use on horizontal motors, such as fire pump motors, these prevent drops of liquid or solid particles from entering ventilating openings in the enclosure at any angle from 0 to 15 degrees downward from the vertical. Typical rating: IP21, IP22 or IP23.
2. Totally Enclosed Fan Cooled (TEFC)—These enclosures are often used in environments that are not air-conditioned. They do not allow the free exchange of air, but are designed to control air flow. A fan attached to the shaft pushes air over the frame during operation to support the cooling process. TEFC motors can be constructed to offer varying levels of protection, making them suitable from general purpose duty (IP44), industrial duty (IP54) and very harsh severe duty (IP55) applications. TEFC enclosures, for example, are commonly used for booster pumps and other heating and cooling system pump motors found in service spaces and tend to be IP44 or better. The outdoor pump motors used for cooling towers typically use IP54 or better enclosures. Severe wastewater treatment environments also predominately call for TEFC enclosure construction, with pumps located near the wastewater typically specified as IP55. Aerator duty usually calls for severe duty motor with an enclosure rated IP55 or IP56. Mining industry applications typically specify an all cast iron IP55-rated enclosure.
3. Washdown Duty—Designed for the food processing industry and other applications that are routinely exposed to washdown, chemicals, humidity and other severe environments, these enclosures are typically rated IP55 to IP56.
4. Weather Protected I (WPI)—Designed for vertical or large horizontal machines found in agriculture applications, these enclosures have ventilating passages that minimize the entrance of rain, snow and airborne particles and prevent passage of a 0.75 inch diameter cylindrical rod. An IP23 rating is typical.
5. Weather Protected II (WPII)—Very common in water and large vertical wastewater applications, these enclosures offer the protection of a WP1. The normal path of ventilating air is arranged to offer at least three 90-degree or more abrupt changes in direction. Typical rating: IP25 or IP26.

Making Sense of Enclosure Ratings

Enclosures are described and rated in multiple ways. NEMA differentiates between cabinet enclosures and electric motor enclosures. It further distinguishes motor enclosures two ways. NEMA’s traditional terminology describes motor enclosures as ODP, Weather Protected 1 (WP1), Weather Protected 2 (WP2) and TEFC. To minimize confusion, it now also recognizes International Electrotechnical Commission (IEC) IP ratings for motor enclosures, which refers to the degree of protection an enclosure offers. NEMA describes cabinet enclosures differently. These enclosures are used with nonrotating equipment. They are defined by type, based on the degree of protection they offer. Type 1 enclosures, for example, are designed for use in indoor, relatively clean environments. At the other end of the spectrum is Type 13, which is designed for use in environments where spraying water and oil are present. Cabinet ratings are comprised of a number. If the letter X is added to the number, it indicates the enclosure’s ability to guard against a potential chemical in the environment.