The Importance of Motor Enclosure Type

There are several specific types of electric motor enclosures available on the market, and they can be broken down into two basic types: “totally enclosed” and “open.” I would like to take one step further and say “expensive” and “cheap.”

The Totally Enclosed Fan Cooled (TEFC) motors (photo above) are designed to operate with minimal impact from the ambient environment. Ambient temperature and the external cleanliness of the motor are the only operational concerns. In addition to routine maintenance, keep these motors clean and within the design temperature parameters and they can last 20 years or more. This is also why I refer to them as expensive. Enclosures aren’t cheap, but they can pay for themselves over the lifetime of the motor.

Open Drip Proof (ODP) motors (photo above) are usually much cheaper than TEFC motors, but are highly susceptible to whatever contaminants are present in the ambient environment. Anything and everything in the air surrounding the motor is pulled through and around the interior of the motor. When we add some humidity to the mix it means a hot motor in the process of cooling off is not only pulling in air, it’s pulling in moisture too. This condensation coupled with dust and particulate from the manufacturing process attaches to the insulation. This in turn can make the motor run hotter than it should.

In order to attain full longevity on a motor, the most important thing is to keep the operating temperature of the motor within the design parameters of the insulation class. Any motor exceeding that temperature leads to motor failure. To put it bluntly, installing an ODP motor outside, or inside in a moderately dirty environment is a substantial waste of money. When they are not running, insects and critters seem to use these motors for nests. These motors last a fraction of the time that TEFC motor does. These motors are fine when installed in clean climate controlled environments.

Make sure that when you procure motors, you choose the right type of motor for the ambient environment it is designed to operate in. This might prove to be more expensive initially, but will save considerably over the life of the motor.

Types of Enclosures

The main function of an enclosure is to provide protection not only to the working personnel but also to the motor itself against the harmful ingress of dirt, abrasive dust, vapours and liquids and solid foreign bodies such as a spanner or screw driver etc. At the same time, it should not adversely affect the proper cooling of the motor.

Hence, different types of enclosures are used for different motors depending upon the environmental conditions. Some of the commonly used motor enclosures are as under :

1. Open Type:

In this case, the machine is open at both ends with its rotor being supported on pedestal bearings or end brackets. There is free ventilation since the stator and rotor ends are in free contact with the surrounding air. Such, machines are housed in a separate neat and clean room. This type of enclosure is used for large machines such as d.c. motors and generators.

2. Screen Protected Type:

In this case, the enclosure has large openings for free ventilation.However, these openings are fitted with screen covers which safeguard against accidental contacts and rats entering the machine but afford no protection from dirt, dust and falling water. Screen protected type motors are installed where dry and neat conditions prevail without any gases or fumes.

3. Drip Proof Type:

This enclosure is used in very damp conditions. i.e. for pumping sets. Since motor openings are protected by over-hanging cowls, vertically falling water and dust are not able to enter the machine.

4. Splash-proof Type:

In such machines, the ventilating openings are so designed that liquid or dust particles at an angle between vertical and 100° from it cannot enter the machine. Such type of motors can be safely used in rain.

5. Totally Enclosed (TE) Type:

In this case, the motor is completely enclosed and no openings are left for ventilation. All the heat generated due to losses is dissipated from the outer surface which is finned to increase the cooling area. Such motors are used for dusty atmosphere i.e. sawmills, coal-handling plants and stone-crushing quarries etc.

6. Totally-enclosed Fan-cooled (TEFC) Type:

In this case, a fan is mounted on the shaft external to the totally enclosed casing and air is blown over the ribbed outer surfaces of the stator and endshields. Such motors are commonly used in flour mills, cement works and sawmills etc. They require little maintenance apart from lubrication and are capable of giving years of useful service without any interruption of production.

7. Pipe-ventilated Type:

Such an enclosure is used for very dusty surroundings.The motor is totally enclosed but is cooled by neat and clean air brought through a separate pipe from outside the dust-laden area. The extra cost of the piping is offset by the use of a smaller size motor on account of better cooling.

8. Flame-proof (FLP) Type:

Such motors are employed in atmospheres which contain inflammable gases and vapours i.e. in coal mines and chemical plants. They are totally enclosed but their enclosures are so constructed that any explosion within the motor due to any spark does not ignite the gases outside. The maximum operating temperature at the surface of the motor is much less than the ignition temperature of the surrounding gases.