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Motors FAQ

  • How do I get my motor investigated?

    First, you need to decide what coverage you need. If the motor has inherent thermal protection such as Impedance Protection or a built-in thermal protector, have it investigated as a Thermally Protected Motor. UL 1004-2, the Standard for Safety of Impedance Protected Motors or UL 1004-3, the Standard for Safety of Thermally Protected Motors as appropriate, also requires the motor comply with UL 1004-1, the Standard for Safety of Rotating Electric Machines. If the motor is not thermally protected, UL 1004-1 will be the Standard used. UL 1004-1 covers the construction and normal operation of the motor or generator.

  • What type of protection do I need for my motor: running overload, running fan duty, intermittent duty or locked-rotor protection only?

    There are several types of protection:

    • Running overload is for applications where the failure of motor bearings could cause overheating. In this case, UL investigates the motor to make sure it complies if it experiences an overload condition. (Note: This applies to both fan and non-fan-duty motors).
    • A running fan duty heating test is for applications where the motor would only be driving a fan. Here, UL tests to see the effects on the motor if the fan were to come off the motor.
    • The intermittent duty running heating tests are for applications where the motor is only intended to run for short time periods but is still under a load.
    • Some product requirements do not require the motor to have any type of running heating protection in the motor itself. In these cases, locked-rotor protection only will apply.
  • What programs does UL offer for ordinary location (non-hazardous) motors?

    There are several types of programs:

    • Construction evaluation -- this program evaluates the construction and normal operation of electric motor(s). The Standard used is UL 1004-1, the Standard for Safety of Rotating Electric machines.
    • Thermally Protected -- this program covers thermal protectors for direct current, single phase and three phase motors. When applied, it protects the motor against overheating due to overload or failure to start. Testing is required. The Standard used for this type of evaluation is UL 1004-3, the Standard for Safety of Thermally Protected Motors.
    • Impedance Protected -- this program covers motors that do not employ any protective device other than the impedance of the winding to limit motor temperatures. There is testing required. The Standard used to evaluate these motors is UL 1004-2.
  • What is UL1004-1?

    UL 1004-1 is the Standard for Safety of Rotating Electric Machines. This Standard evaluates ordinary location motors and generators for materials, spacings, normal operation and construction. In addition, we look at the insulation system, plastic parts and components of the motor such as capacitors, start switches, relays, and terminal blocks.

  • Are any tests required in UL1004-1?

    Yes, nonmetallic functional parts internal to the motor are required to have a mold stress test.

    If the motor employs a start switch, there are tests to evaluate that component.

    A motor that employs a power supply cord with strain relief would require a 35lb pull strain relief test.

    If the leads are interconnecting, then a 20lb pull is required for each lead. If the leads are not exposed in the end application, then the testing is not required.

    Additional testing may be required or conducted depending on the specific construction or end use application. It is best to supply us with information on its intended end use if possible.

  • When does my insulation system need to be UL Recognized?

    When it is an epoxy or integral ground insulation or if the class of insulation is rated higher than class A.

  • What are the advantages of getting my motor Recognized or Listed to the UL 1004 series?

    If the motor is intended to be used in an end use piece of equipment that is currently or going to be UL Listed, it will help your customer since they will not have to have a full evaluation on the motor. By investigating your motor to UL 1004-1, we have checked materials, spacings, and normal operation. Additionally, we will list major points in the report under engineering considerations that the end-use engineer needs to be concerned with.

  • What are UL 1004-2, and UL 1004-3?

    These are Standards for thermally protected motors and are used to investigate motor-protector combinations (where the protector is inherent to the motor) and impedance protected motors.

  • What is an impedance protected motor?

    A motor that relies solely upon the impedance of the windings to prevent overheating.

    Tests for an impedance protected motor include winding resistance, input (no-load and locked rotor), 72 hour locked rotor temperature test, dielectric, 15 day locked rotor endurance test and dielectric. Three samples of each motor are required for testing.

  • What is a thermally protected motor?

    A motor that relies upon a protector to prevent overheating.

    Tests for thermally protected motors:

    Running heating

    • Direct drive fan (no-load) -- when motor is directly coupled to a fan or blower assembly
    • Intermittent duty -- not intended to be run continuously
    • Continuous duty -- intended to run at rated nameplate indefinitely

    Locked rotor

    • Auto reset - 72 hours
    • Manual reset -- 10 cycles
    • Thermal cutoff -- one time device (we require a minimum of three samples, if multi speed -- three samples for each speed)


    • Locked rotor endurance
    • 15 day for an automatic reset protector
    • 50 cycles for a manual reset device
  • How do I begin a motor investigation?


    There are three easy steps to beginning an investigation:

    1. Decide what coverage is best for your motor. Additionally, ask your customer what is required for their end product.

    2. Click on one of the product information forms (noted below). The form needs to be filled out completely. You may include additional drawings, schematics and parts list if necessary.

    Product information form for thermally protected motors (pdf)
    Product information form for impedance protected motors (pdf)
    Product information form for electric motors and generators (pdf)

    3. Provide a letter indicating information about your motor i.e. model number, complete electrical ratings, etc. Indicate applicant's (owner) complete company name, address, contact person, phone and fax number. Indicate manufacturers name, address, contact person at that facility, phone number and/or fax number.

  • Where can I purchase a Standard?