Whether the motor environment is indoors or outdoors, your motor may be exposed to moisture, dirt, and dust. The right electric motor enclosure will massively reduce maintenance costs and extend your motor's service life and benefit your company’s bottom line. There are a variety of different types of enclosures, classified according to two different rating standards. At first glance, it may not be obvious what the strengths and weaknesses of each one are. This article will give you a clear perspective on what electric motor enclosures are commonly found in different types of applications and how choosing the right one can enable you to reduce the total cost of ownership of your electric motor.

Enclosure Ratings

Enclosure ratings provide precise information about the type of protection that an enclosure design offers. In North America, the National Electrical Manufacturers Association (NEMA) provides a standard rating system for electrical enclosures in industrial applications. Each NEMA classification describes the protection provided by an enclosure against a different type of environmental hazard in different environmental conditions.

At the international level, the International Electrotechnical Commission (IEC) provides the IP (Ingress Protection) classification system, also known as the IEC standard 60529, to describe the protection that electrical enclosures provide the operator and the motor. The first digit in the IP classification describes the protection against accidental contact with electrical parts by the operator and the intrusion of solid objects into the motor. The second digit describes the protection against liquid ingress into the motor.

NEMA standards are more descriptive, whereas the IP standards are more technical and precise. Visit the NEMA and IEC websites for a full list of ratings and detailed information.

Now let’s look at some of the common types of electric motor enclosures and examine their strengths and weaknesses.

Open Drip Proof (ODP)

The Open Drip Proof (ODP) enclosure protects against falling drops of liquid entering the motor from angles of up to 15 degrees from the vertical. A shaft-mounted fan pulls air directly from the environment through open vents in the motor's body, circulating it around the inside of the motor and over the stator and rotor windings for cooling.

While relatively cheap, ODP enclosures offer very little protection against airborne dust, moisture and contamination. Operating them outdoors or in contaminated environments will quickly build corrosion and dirt inside the motor, reducing cooling efficiency and shortening the motor's lifespan. They are only suitable for clean, dry, indoor environments, such as equipment manufacturing.

If your ODP has been damaged from the outdoors, consider replacing the motor with a more suitable TEFC.

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Totally Enclosed Fan-Cooled (TEFC)

With a Totally Enclosed Fan Cooled (TEFC) enclosure, seals and gaskets prevent air from freely moving between the interior of the motor and the surrounding environment – although this does not necessarily mean that the motor is completely airtight or watertight. An external shaft-mounted fan at the rear of the motor blows air over the body to cool it.

TEFC enclosures are very common in industrial environments, especially outdoors, and are becoming even more widely adopted as industry practices lean toward low maintenance washdown environments. They are more expensive than ODP enclosures but provide a much higher level of protection, and when properly maintained, ensure that the motor remains in peak condition for a long time. However, one drawback of this design is that the cooling performance of the shaft-mounted fan depends on the motor speed, and they are not suitable for applications where the motor regularly operates with high torque at low speeds.

TEFC enclosures require a small amount of routine maintenance that includes keeping the motor body clean to minimize heat transfer and ensuring that the internal temperature of the motor always remains higher than the surrounding environment to prevent condensation from forming inside the motor and corroding the windings. Drain plugs are often used to allow moisture to escape from the motor, and an internal heater may be used to prevent condensation altogether and keep the internals of the motor dry.

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Totally Enclosed Non-Ventilated (TENV)

Totally Enclosed Non-Ventilated (TENV) motors are very similar to TEFC motors, except that they have no fan cooling system, relying on passive cooling with the surrounding air to keep the motor temperature under control. They have much the same strengths and weaknesses as TEFC enclosures. Still, more care must be taken to operate the motor so that the internal temperature stays within the manufacturer’s ratings, including avoiding frequent stops and starts that build heat inside the motor windings.

Because of the reduced cooling performance of the TENV enclosure, it is more often found on smaller motors, and it usually features relatively large and numerous cooling fins to maximize heat transfer out of the motor. When the temperature is managed correctly, TENV enclosures also provide good protection in harsh conditions involving moisture, dust and other forms of contamination.

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Totally Enclosed Blower-Cooled (TEBC)

Totally Enclosed Blower-Cooled (TEBC) motors are similar to TEFC motors, except that instead of a shaft-mounted fan that provides cooling when the motor is operating at high speed, the motor body is cooled by a separate ‘blower’ fan that is mounted on the body. This retains the benefits of a fully-enclosed body, keeping contaminants and moisture away from the windings while enabling the motor to be fully cooled while operating at any speed.

TEBC motors are generally more expensive than TEFC motors. However, because of the separate cooling system, TEBC motors can achieve full torque at 10% or less of base speed without overheating. This makes them especially suitable for variable speed applications or those which involve frequent stops and starts.

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Explosion Proof (XP or XPFC)

Explosion Proof enclosures are designed to maximize operator and infrastructure safety by containing an explosion of a specified hazardous substance inside the motor without igniting flammable gases or particles surrounding the motor. When operating motors with explosion-proof enclosures, care must be taken to ensure that the motor temperature never approaches the ignition temperature of contaminants in the vicinity.

Explosion-proof motors are often used in hazardous applications such as in the petroleum and gas industry. They are classified according to the characteristics of the contaminant that they protect against. Their design is closely regulated according to the standards of various agencies, including the National Electrical Code and the Underwriters Laboratories. Before purchasing an explosion-proof motor, first, confirm the classification.

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By understanding the NEMA and IP ratings and the key electric motor enclosure designs on the market today, you'll have a better understanding of how to choose an enclosure for your application that ensures a long and trouble-free service life for your motor.

eMotors Direct provides a wide range of high-quality industrial motors with enclosures designed for all types of industrial applications and environmental conditions, ensuring maximum uptime for your operation.