Chapter 3: AC and DC Motors - AC Motors: Enclosure Types and Cooling

Enclosure Types and Cooling
Motors are often exposed to damaging atmospheres such as excessive moisture, steam, salt air, abrasive or conducting dust, lint, chemical fumes, and combustible or explosive dust or gases. To protect motors, a certain enclosure or encapsulated windings and special bearing protection may be required.

Motors exposed to the following conditions may require special mountings or protection: damaging mechanical or electrical loading such as unbalanced voltage conditions, abnormal shock or vibration, torsional impact loads, excessive thrust, or overhung loads.

Many types of enclosures are available. A few of the most common types are listed here, many of which are the same designations as for DC motors. It is strongly recommended that personnel actively involved with applying induction motors be familiar with, and adhere to, the contents of NEMA MG2 ("Safety Standard for Construction and Guide for Selection, Installation and Use of Electric motors and Generators").

Open Motor
The open motor enclosure type has ventilation openings that permit passage of external cooling air over and around the windings.

Open Drip-proof Motor
The open drip-proof (ODP) enclosure type is constructed so that drops of liquid or solids falling on the machine from a vertical direction cannot enter the machine. (This vertical direction is not at an angle greater than 15°.)

Guarded Motor
(This could be abbreviated DPFG drip-proof fully guarded.) The guarded enclosure type has all ventilation openings limited to specified sizes and shapes. This enclosure prevents insertion of fingers or rods and limits accidental contact with rotating or electrical parts.

Splash-proof Motor
The splash-proof enclosure type is so constructed that drops of liquid or solid particles falling on the motor cannot enter. (These liquid or solid particles can be in a straight line or at any angle not greater than 100° from the vertical.)

Totally Enclosed Motor
The totally enclosed enclosure type prevents the free exchange of air between the inside and outside of the case, but is not airtight.

Totally Enclosed Non-Ventilated (TENV) Motor
The totally enclosed non-ventilated enclosure type is not equipped for cooling by external devices.

Totally Enclosed Fan-Cooled (TEFC) Motor
The totally enclosed fan-cooled enclosure type has a shaft-mounted fan to blow cooling air across the external frame. It is a popular motor for use in dusty, dirty, and corrosive atmospheres.

Totally Enclosed Blower-Cooled (TEBC) Motor
The totally enclosed blower-cooled enclosure type is totally enclosed and is equipped with an independently powered fan to blow cooling air across the external frame. A TEBC motor is commonly used in constant torque, variable-speed applications.

Encapsulated Motor
The encapsulated enclosure has windings that are covered with a heavy coating of material to protect them from moisture, dirt, abrasion, etc. Some encapsulated motors have only the coil noses coated. In motors with pressure-embedded windings, the encapsulation material impregnates the windings, even in the coil slots. With this complete protection, the motors can often be used in applications that demand totally enclosed motors.

Explosion-Proof (TEXP) Motor
The explosion-proof enclosure is totally enclosed and built to withstand an explosion of gas or vapor within it. It also prevents ignition of gas or vapor surrounding the machine by sparks, flashes, or explosions that may occur within the machine casing.

Enclosure Types and Cooling
Motors are often exposed to damaging atmospheres such as excessive moisture, steam, salt air, abrasive or conducting dust, lint, chemical fumes, and combustible or explosive dust or gases. To protect motors, a certain enclosure or encapsulated windings and special bearing protection may be required.

Motors exposed to the following conditions may require special mountings or protection: damaging mechanical or electrical loading such as unbalanced voltage conditions, abnormal shock or vibration, torsional impact loads, excessive thrust, or overhung loads.

Many types of enclosures are available. A few of the most common types are listed here, many of which are the same designations as for DC motors. It is strongly recommended that personnel actively involved with applying induction motors be familiar with, and adhere to, the contents of NEMA MG2 ("Safety Standard for Construction and Guide for Selection, Installation and Use of Electric motors and Generators").

Open Motor
The open motor enclosure type has ventilation openings that permit passage of external cooling air over and around the windings.

Open Drip-proof Motor
The open drip-proof (ODP) enclosure type is constructed so that drops of liquid or solids falling on the machine from a vertical...