These application tips and suggestions will help extend motor life in these hostile environments.

If you have a motor application that involves operation in a wet or damp environment, you should know the proper choice of motor enclosure, the correct location of weep holes, and, in some cases, the use of an auxiliary heating device or system to warm the motor during nonoperating times. Let's take a look at the various motor designs available today and pick up on these application suggestions and tips.

Open-type motors

Generally speaking, most commonly used open-type motors are not suitable for wet environments.

But, you say, you have a piece of equipment specifically meant to be installed in a wet or damp environment, and it has an open-type motor. What happened here? The answer is that the original equipment manufacturer used an open-type motor because of its lower first cost. So, what do you do now?

By following the suggestions listed below, you may be able to extend the life of that motor.

Shielding. First, the motor should be shielded or sheltered from the direct impact of rain, sleet, snow, hosing-down, etc. But, you have to be careful. You don't want to restrict air flow to and around the motor. The installation of a shelter over a motor is effective as long as the shelter is well ventilated, or louvered, so that any hot air is not trapped inside. The hotter the air inside the shelter, the shorter the motor life.

Motor orientation. Next, you must understand that open-type motors are built to be mounted with a certain orientation. For example, many such motors have "Venetian blind" type louvers in their end housings so that water falling from above will be deflected away from the inside of the motor. This works fine except where the motor is mounted to a wall (vertical), or with feet up (ceiling mounted).

In the case of a ceiling mounted motor, unless the position of the end housing is changed relative to the motor's base, the louvers will have a funnel effect, directing rain, snow and other debris into the windings and shortening the motor's life. Thus, the end housing should be rotated so that the louvers will be in the proper position to fend off rain, rather than funneling it inside.

When your open-type motor does fail in this wet or damp environment, take this opportunity to replace it with a motor having an enclosure more suitable for the application.

TEFC motors

A totally enclosed, fan-cooled (TEFC) motor is much more adaptable to outdoor locations and high moisture areas. With a bit of care, you can expect this type of motor to work well and have a long life. However, there are some suggestions that will ensure the expected longevity of this motor.

Motor orientation. A TEFC motor has weep holes at the bottom of its end housing; they're put there to allow for the draining of condensation and/or other accumulations of moisture. When you're going to use this type motor in a different position, you must reposition its end housing so that the weep holes are at the lowest point of the motor. For example, a TEFC motor may be mounted in an unusual position, with its shaft still horizontal but its base mounted to a vertical wall. Now, the weep holes are out of position by 90 [degrees], and the only time they can do their job is when the motor is half full of water. This, of course, is totally unacceptable and must be remedied.

The correct weep hole orientation is especially important in applications such as brush drives in car washes and similar situations where water is apt to be falling on the motor continuously.

When a TEFC motor is mounted at an odd angle, where the weep holes can't be properly repositioned to the lowest point, you can remedy the problem by carefully drilling a small hole at the motor's lowest point. Special note: Make sure the motor is deenergized and locked-out and be careful not to touch or damage the windings or bearings with the drill bit.

Sealed motors

Motors such as those designated "Wash Down," "Severe Duty," or "Mill and Chemical" are designed so that they are sealed to prevent the entrance of moisture. However, no matter how well constructed and sealed, it's nearly impossible to keep all water out. Thus, it's very important that weep holes be positioned so that any water entering the motor (either by direct impingement or by exchange of air saturated with moisture) can drain away freely, rather than accumulating within the motor's housing.


Another source of water accumulation within a motor is condensation, which can occur with repeated motor heating and cooling cycles. For example, when a motor gets hot, the air within it expands and pushes out. Later, when the motor cools, fresh, moisture-laden air will be drawn in as the air within it contracts.

As this cycle repeats again and again, substantial quantities of water can accumulate and, if left unchecked, will eventually lead to motor insulation failure. Once again, this points out the importance of having weep holes properly positioned so that condensate water can drain before it accumulates in sufficient quantities to cause damage.

Methods to keep motor dry

When a motor runs continuously, the heat generated by it in its normal operation will keep its windings dry. However, infrequent use of the motor may cause wide fluctuations in motor temperature, possibly creating condensation. Here are two methods you can use to reduce motor susceptibility to failure caused by accumulated moisture.

Heaters. The first and most popular method is the use of heaters installed within the motor. Cartridge or strip heaters are placed within the motor and are turned on during nonoperating periods. The object of this is to maintain the temperature inside the motor 5 [degrees] to 10 [degrees] warmer than the surrounding air. When this is done, condensation within the motor is prevented, and it will stay dry. The heater method is quite similar to the way light bulbs are used in closets where the climate is humid to prevent mildew on clothing and leather goods.

When internal heaters are used, they usually are interlocked with the motor starter so that they are energized when the motor is not running and deenergized when it's running.

Trickle heating. This second method accomplishes the same result as the first method: Preventing condensation in motors that are at rest. In this case, however, low-voltage, single-phase power is applied to the 3-phase motor windings while the motor is at rest. This application of power results in a low-energy, single-phasing condition that provides heat in the windings, rotor, and, indirectly, the bearing of the motor.

Trickle heating is a particularly good method for groups of identical motors, such as those used on aerators in pollution control lagoons.