TEFC VS. ODP MOTORS
Irrigation pump motors typically have two types of enclosures: Open Drip Proof (ODP), and Totally Enclosed Fan Cooled (TEFC). These two names refer to the method used to cool the motor windings and describe the type of motor enclosure and internal construction.
Electricity flowing through motor windings develops heat due to the resistance of the windings. This heat is developed continuously and therefore the heat must also be removed continuously or the temperature of the windings would rise until the winding insulation burned out. ODP and TEFC motors use different methods to remove heat from the windings.
ODP motors have an internally mounted fan pulling outside air from intake vents in one end of the motor, through the windings, then out of the other end of the motor enclosure through exhaust vents. These vents are placed to prevent falling rain from directly entering the motor enclosure. Even a slight angle on the rain drops, as seen when driven by a moderate wind, causes the rain drops to enter into many ODP motors.
ODP motors have THREE ADVANTAGES: low price, easily available, and they are more resistant to runaway heating. ODP motors have FOUR DISADVANTAGES. First, air is moved directly through the windings which leaves deposits on the windings from air borne contaminants such as dust, aerosols, and moisture. Secondly, splash and wind driven rain can enter the motor. Thirdly, insects and vermin easily enter the motor. Fourth, single phase ODP motors contaminate the starting switch mechanism (see third paragraph down).
“TEFC” motors have an externally mounted fan covered by a shroud blowing air across the surface of the motor enclosure. Heat developed in the windings moves by convection outward through the motor case then into the air moving along the surface of the motor case. The motor case is a heat sink drawing heat from the motor interior to the outside. TEFC motors may have fins on the motor case enhancing this heat transfer into the air.
TEFC motors have FOUR ADVANTAGES. First, air is not drawn into the motor for cooling and therefore the windings stay clean and dry. Two, the windings are protected against direct entry of wind driven rain, directed spray, and splash from the ground. Three, insects and other vermin cannot enter the motor. And four, TEFC motors protect the single phase switch keeping it clean and dry. TEFC motors have THREE DISADVANTAGES: they cost more, they are not as easily available, and TEFC motors are more vulnerable to runaway heating when used improperly.
Most single phase motors (except submersibles) have a switch mechanism located next to the windings which operates the start capacitors and windings. This switch is easily affected by dust, sand, dirt, and corrosion, and this switch may be the largest cause of problems on single phase motors. ODP motors constantly pull contaminated air over this switch causing problems. TEFC motors keep the single phase switch clean and dry, and therefore single phase TEFC motors have fewer problems than single phase ODP motors. Field experience shows that this single phase switch on ODP motors is a frequent source of trouble, especially when ODP motors are located outdoors, even if the motor is covered.
Convection through a motor enclosure (TEFC) is less efficient than directly cooling the windings with air (ODP). This makes TEFC motors more expensive to build. Some of the construction differences that make TEFC motors more expensive are: TEFC motor cases are often longer and thinner than ODP motors, finned motor cases cost more, the fan shroud, and a higher grade winding insulation is used to withstand higher temperatures.
It is important to note that TEFC motors should never be thought of as "sealed" or "wash down" duty motors, which they are not. TEFC motors are resistant to directed spray, but TEFC motors are definitely not intended to withstand directed sprays or washing. Air that is heavily laden with caustic or oxidizing vapors can enter a TEFC motor, but more slowly than an ODP motor.
Irrigation Craft Policy
TEFC and ODP Motors
Irrigation Craft uses only TEFC motors on all products. Some think that an ODP motor can be used if the motor is located inside a building, or if a rain shroud is put over the motor to protect the motor from rain and splash. These ideas sound good but there are still problems.
ODP motors will always have the problem that air is pulled into the motor and through the windings. This air may have high humidity, contain dust, and chemical aerosols such as insecticides, fertilizers, solvents, chlorine from pools, and other contaminants harmful to winding insulation and single phase switches. Furthermore vermin such as ants can and do easily enter ODP motors. Some ODP motors have screens over their vents, but these screens do not have small enough openings that will stop small insects. The screens also may become clogged and cause motor overheating.
ODP motors are not to be thought of as cheap or poor quality motors because they are not. ODP motors are correct for many applications. But Irrigation Craft believes that ODP motors should not be used for irrigation applications in general because irrigation pumps are usually not located in clean dry environments. Irrigation pumps are found in the worst environments including buildings containing pool treatment chemicals.
TEFC motors are more vulnerable to runaway heating due to overloading, low voltage, unbalanced voltage, and high flow rates. However all Irrigation Craft pump motor combinations are totally non-overloading and the motor service factor is never used at any point on the pump curve. This safety margin makes Irrigation Craft pumps run cooler which makes them last longer. High flow problems can never cause the pump motor to overload, and non-overloading pumps are more resistant low voltage and voltage unbalance.
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