Other Motors Topics
Motor Enclosures
NEMA standards MG1-1.25, 1- 1.26, and 1-1.27 define more than 20 types of enclosures
under the categories of open machines, totally enclosed machines, and machines with
encapsulated or sealed windings.
Open machines — Very few open machines are made today.
Most standard motors are drip-proof and guarded, Figure 15, or at least semiguarded.
To improve the protection offered by drip-proof enclosures, some manufacturers offer
special processes or treatments to protect the windings and bearings.
Totally enclosed machines — Most totally enclosed machines are fan-cooled,
Figure 16. However, some models in fhp ratings are totally enclosed and nonventilated.
Totally enclosed motors are more expensive, but offer better protection.
Outside ventilating air and contaminants are excluded from interior parts of a totally
enclosed motor. The motor is not airtight, but usual entrances to the interior,
such as the conduit box, are gasketed. Clearances like those around shafts are kept
as small as possible.
 Figure 18 - In a frameless motor, the casing around the stator windings provides mechanical stability for the windings and a path for transmitting winding heat to the cooling medium — typically a liquid that circulates through the finned structure. |
 Figure 19 - A complete frameless motor assembly includes a rotor, stator, and feedback sensor supplied by the motor manufacturer. The machine manufacturer provides the bearings, shaft, housing, and cooling medium. |
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