LEESON Electric Corporation  

FAQ's - Motors

Space Heaters
What is the importance of a space heater and what affect does it have on warranty?

Electric motors frequently have space heaters installed, at the customer’s request, to prevent moisture condensation in the motor when it is not running. In applications where the possibility of condensation is not a factor, or where continuous operation of the motor prevents the formation of condensation, space heaters are not necessary. See and/or refer to LEESON's current terms & conditions of sale.

LEESON Electric's warranty policy covers manufacturing defects, and allows for repair or replacement to remedy any situations which may arise within the warrantable period. The failure of a motor due to condensation does not fall into this category, and is therefore not considered for warranty coverage. If the project plans and specifications do not require space heaters, then the space heaters present in the unit may be left unconnected and the space heater warranty nameplate may be removed. However, as previously stated, motor failure due to condensation is not warrantable.
Trickle Voltage Heating vs. Space Heaters
What are the advantages and disadvantages when employing the use of trickle voltage heating rather than conventional space heaters?

Yes, trickle voltage heating has some distinct advantages, especially when applied in the field after the motor is built. Compared to space heaters this device compares favorably in cost and provides improved heat distribution throughout the winding. Specifications for adding trickle voltage heating are available from your LEESON Rep.

Motor Inspection Procedure after Storage
After storing my motor for an extended period of time, I am now ready to install it. Is there any specific inspection procedure that must be followed?
Yes. Following storage, an extensive inspection must be performed on a motor by one of LEESON Electric’s authorized service stations. See and/or refer to LEESON Electric's Warranty section in this website.
This inspection must include the following elements:
  • Render an external inspection of the motor to assure the unit is clean, ventilation openings are free of obstructions, and no damage has occurred.
  • Perform a megger test of motor windings to insure satisfactory insulation resistance.
  • Rotate the shaft to check for roughness in bearings or interference between rotating and stationary parts.
  • Perform a bench test on the unit to check for excessive amp. draw, noise, or vibration.
  • Re-grease the motor bearings (as applicable) in accordance with the unit’s operating instruction folder.
  • LEESON Electric’s authorized service station must install a plate/tag indicating the date of inspection. This tag will be considered a new factory date code for warranty purposes.
  • Make any corrections which inspection shows to be needed.
Part Winding Start of a 12 Lead Y-Delta Motor

My motor has a connection plate which says Dual Voltage, Wye Start, Delta Run with PWS (Part Winding Start) on the Low Voltage. How should I hook it up?

This motor has very good versatility and may be used in several power supply applications. It is a dual voltage machine and may be used on either voltage as defined on the connection plate. It is designed for use on a Wye Start, Delta Run starter. This is a special motor contactor which starts the motor on its Wye connection to limit the inrush and then switches to Delta for running. The motor must not be run on the Wye connection for more than 30 seconds as severe winding damage may occur. This motor may also be started across the line and run on the Delta connection. In addition, the motor may be used on the low voltage connection as a part-winding start motor, also to limit the inrush required. After a brief period, it is switched to the full winding.

Motor Life

What is the typical life expectancy of an AC Motor ?

Engineers are occasionally asked to predict average motor life or mean time between failures for a given three-phase induction motor. A reasonable answer can be obtained if the numerous variables that affect motor life are quantified, such as:

 1. Supply voltage and frequency: Although NEMA MG1-12.44.1 stipulates that motors must tolerate +-10% voltage variation and +-5% frequency variation; the motor should be operated at nameplate voltage and frequency for optimum life.

 2. Supply source: Supply voltage waveforms should be sinusoidal, balanced within 1%, per NEMA MG1-12.45, with rise times greater than 2 milliseconds and contain less than 2% total harmonic voltage distortion (typical of ‘clean’ utility power).  This reduces turn-to-turn, coil-to-coil, and phase-to-ground voltage stress and prolongs motor insulation life.  Hard-switching solid-state inverters must be equipped with output-side inductive filters with >5% impedance to provide a comparable waveform

. 3. Motor environment: The motor must be installed in an environment that is appropriate for the motor enclosure.  Ambient temperature should remain between (0 and 40)°C and elevation at 3300 ft or less.  Motor ventilation must not be obstructed and mechanical shock and vibration must be held to a minimal level. 

4. Bearing maintenance: Motor bearings must be properly lubricated per IOM published guidelines, with water and contaminants kept to a minimum.  Bearing loads should be controlled to provide a minimum B-10 life of 25,000 hours and bearings must be replaced periodically to prevent permanent motor damage.  Shaft voltages (caused by unbalanced line voltage or operation from inverter power) must be limited to 0.5 volts peak. 

5. Motor Starting: Across-the-line starts should be kept to a minimum and not exceed NEMA MG1-12.54 guidelines, since the life of a motor is affected by the number of across-the-line starts.   When the above conditions are met, the insulation life of the motor can be estimated with reasonable accuracy.  In 1980 the US Department of Energy published report DOE / CS-0147 to define the average expected life of electric motors, which is summarized in the table below.

HP Range         Average Motor Life (years)               Life Range (years)                                                           <1                                   12.9                                              10 – 15                                                                                      1 - 5                                 17.1                                              13 – 19                                                                                    5.1 - 20                             19.4                                               16 - 20                                                                                  21 - 50                               21.8                                              18 – 26                                                                                51 - 125                             28.5                                              24 – 33                                                                                  > 125                                 29.3                                              25 – 38

                                                             Ave. life of all ratings = 13.27 yrs


Lubrication Instructions
How can motors in service be relubricated? Refer to the LEESON Electric IOM Manual.
Units are prelubricated at the factory and do not require initial lubrication. Relubricating interval depends upon speed, type of bearing and service. Refer to the tables in the Operating and Instruction Manual* provided with motor for suggested regreasing intervals and recommended greases. Operating conditions may dictate more frequent lubrication. Motor must be at rest and electrical controls should be locked open to prevent energizing while motor is being serviced (refer to O&M manual's section on Safety). If motor is being taken out of storage, refer to storage procedures.

To relubricate bearings, remove the drain plug. Inspect grease drain and remove any blockage with a mechanical probe taking care not to damage bearing. Under no circumstances should a mechanical probe be used while the motor is in operation. Remove any and all dirt and debris from grease inlet and add new grease at the grease inlet. New grease must be compatible with grease already in the motor. Refer to the IOM for the grease. Run the motor for 15 to 30 minutes with the drain plug removed to allow purging of any excess grease. Shut off unit and replace the drain plug. Return motor to service. Typical standard grease is Exxon Polyrex EM which is a polyurea type grease. Contact your LEESON Rep for more information if necessary.



Overgreasing can cause excessive bearing temperatures, premature lubricant breakdown and bearing failure. Care should be exercised against overgreasing.

Greases of different bases (lithium, polyurea, clay, etc.) may not be compatible when mixed. Mixing such greases can result in reduced lubricant life and premature bearing failure. Prevent such intermixing by disassembling the motor, removing all old grease from bearings and housings (including all grease fill and drain holes). Inspect and replace damaged bearings. Fill bearing housings and bearing approximately 30% full of new grease. Remove any excess grease extending beyond the edges of the bearing races and retainers. Refer to O&M Table 2 for recommended greases.